Station Earth / RF Earth for shack on 2nd / 3rd floor
Martin
I am in stalling my radio station in to the small "box room" on the 2nd
floor
of the building and I have in the past not worried about a separate earth
for
the station. But as this station is going to be a more permanent arrangement
than my other previous locations I want to make sure that :-
1) the station is safe electrically. (of course the supply earth will be
connected)
2) protected form static (lightening etc).
3) has a good RF performance. (this means low resistance earth connection)
4) is as clear of EMC problems as possible.
So any one got some pointers or helpful hints on installing a separate
station
earth. The ground connection is easy 3 to 6 off 6' long 1" dia copper pipes
driven all the way in to the soil (I know it is a big is job but not
impossible).
The bit I am puzzling over is do I use a heavy copper strap as used on
church
lightening conductors to provide a common earth for every thing or just for
the
static protection and then a separate heavy conductor to provide the shack
equipment earth.
In either case how can I ensure that the earthing does not radiate RF (I
assume
that making sure the aerials are correctly balanced with suitable baluns
fitted is
the answer here.)
I did here about using RG8 type coax and connecting both inner and screen
to the hardware in the ground but only connecting the shack earth buss to
the
inner - any thoughts on this.
Cheers Martin
Martin
"Martin" <Martin@_NOSPAM_g1gyc.demon.co.uk> wrote in message
------><------- snipped
Oops I forgot to add :-
REMOVE _NOSPAM_ to send email back to me or reply to the group.
Thanks Martin
Steve
> Hi, and thank you for reading this.
> I am in stalling my radio station in to the small "box room" on the 2nd
> floor
> of the building and I have in the past not worried about a separate earth
> for
> the station. But as this station is going to be a more permanent
arrangement
> than my other previous locations I want to make sure that :-
> 1) the station is safe electrically. (of course the supply earth will be
> connected)
it's vital that your external earth is connected to the house wiring earth
at the meter panel. I'm sure there will be IEE wiring regs on how this
should be done. You might also try to get your hands on an article called
'The Killing Fields' by Peter Chadwick, G3RZP. It was in RadCom a good many
years ago.
Steve
Brian Reay
news:auiv4t$f10$1$8300...@news.demon.co.uk...
> I am in stalling my radio station in to the small "box room" on the 2nd
> floor
> of the building and I have in the past not worried about a separate earth
> for
> the station. But as this station is going to be a more permanent
arrangement
> than my other previous locations I want to make sure that :-
> 1) the station is safe electrically. (of course the supply earth will be
> connected)
If you have a PME system you also need to ensure the earth bonding point
where the supply enters your house is bonded by 10mm2 wire to your local
earth rod(s). This is especially important if your power comes via overhead
cables. You can usually get to the bonding point next to the power company
fuses.
If not, under certain fault conditions a LOT of currrent can try to pass via
your shack to earth. Not good.
> 2) protected form static (lightening etc).
Static isn't too difficult- use DC grounded antennas on VHF/UHF and provided
a 'bleed path' via a choke or even a resistor for HF antennas.
You can get devices to protect against lightning but having seen the effects
of lightning tests I don't think I would trust a cheap one. I always
disconnect.
> 3) has a good RF performance. (this means low resistance earth connection)
> 4) is as clear of EMC problems as possible.
These often go hand in hand.
For VHF/UHF the problems are generally resolved by using good coax,
connectors, sensible antenna siting, and filtering (as required).
For HF, given the likely problems of a earth lead impedance at HF, I
recommend an external ATU- either a SGC (or similar) automatic beast or a
remotely variable arrangement. The latter need not be overly complex- a
simple LC arrangement, L either switched with relays or a roller coaster
with a small motor (a cheap electric screwdriver is ideal) and a motorised
capacitor(s). I can look out a circuit I did for someone else if you like-
he want something cheap and cheerful and I think the motorisation cost him
about £10! I works very well, if I ever get around to HF myself I may build
one.
To get a good RF earth you can run out radials from the ATU, the more the
better. These should be bonded to an earth rod at the ATU. A buried 'earth
mat' is nice but not always practical.
The above approach tends to keep the RF 'in' via the coax and equipment
casing until it get to the ATU which, as the latter is remote, minimises
coupling to other equipment.
Once the RF gets to the antenna it may still cause EMC problems- but that is
down to the fact it is radiating, which it is meant to do ;-) Then it is
down to filtering to minimise harmonics etc. and coupling into domestic
items.
73
Brian
G8OSN
www.g8osn.org.uk
Anon
PME - I think NOT!
Both Peter Chadwick and I, who've had previous discussions and agreement
on this would profoundly disagree with you!
PME, where the neutral has a disconnection somewhere outside of your
property has likelihood to pass huge amounts of current, and hence a
rise in potential down and to any local earth you might provide or have
in your home. It is a cheap but dangerous way to supposedly provide an
electrical earth.
The answer is to provide yourself with some good quality ELCB's (30ma if
possible) at your shack and home. Provide yourself with a good quality
earthing system which is tested to current standards and when this is
done disconnect the crappy PME system.
And yes I have seen the effects of a disconnected neutral with PME,
which has resulted in persons receiving shocks as well as interference
to electrical equipment
From someone with Experience! Who has his PME disconnected and that's
the way it's staying!
In message <Aujmro$7cdq4$1...@ID-140397.news.dfncis.de>, Brian Reay
<brian...@bigfoot.com> writes
--
Brian Reay
news:aIr2kvBx...@btinternet.com...
> Well is that so? Add yourself a bit of extra earthing and bond it to the
> PME - I think NOT!
>
> Both Peter Chadwick and I, who've had previous discussions and agreement
> on this would profoundly disagree with you!
Well I note you haven't put your name to this claim bit never mind, lets
look at it.
>
> PME, where the neutral has a disconnection somewhere outside of your
> property has likelihood to pass huge amounts of current, and hence a
> rise in potential down and to any local earth you might provide or have
> in your home. It is a cheap but dangerous way to supposedly provide an
> electrical earth.
>
The rise is potential is dependant on the resistance of the bonding lead.
The local electricity company recommend 10mm2 as being adequate for the
job. I assume they would know- the engineer I spoke to knew all about the
problem once I mentioned what I was concerned over.
> The answer is to provide yourself with some good quality ELCB's (30ma if
> possible) at your shack and home. Provide yourself with a good quality
> earthing system which is tested to current standards and when this is
> done disconnect the crappy PME system.
>
The local electricty company advised against this method - especially in
situtions where there was a real risk of the neutral disconnection, eg in an
area supplied by overhead wires. (It is extremely rare with buried supplies
they tell me.) In fact, they advised they would disconnect my supply if I
used it this method.
>
> From someone with Experience! Who has his PME disconnected and that's
> the way it's staying!
>
OK, but if you local supply company don't like it you may well get
disconnected.
Frank Turner-Smith
<snip>
> I did here about using RG8 type coax and connecting both inner and
> screen to the hardware in the ground but only connecting the shack
> earth buss to the
> inner - any thoughts on this.
>
> Cheers Martin
At my last QTH I did exactly as you describe and it worked well for many
years. I also disconnected the earth pin on every mains lead for my rig and
linked all the chassis together with coax braid.
I'm not sure of the legalities of this, but what nobody knows, nobody
worries about. Good luck.
;>)
--
73 de Frank Turner-Smith G3VKI
watch this space - if it moves, see your optician.
r.dring
items of elevated earthing that need to be addressed. Any mains operated RF
equipment must have an efective electrical earth, which is not the same as
an RF earth. Any RF earth lead, dropping from an elevated shack, could be a
significant portion of a wavelength, so you really ought to decide what
bands you are expecting to work. It is not difficult to solve once you know
the pitfalls.
If you are in the UK have a look at your electricity meter instalation, and
see if there is a label marked PME or Protective Multiple Earthing, if you
are in a high rise block you may need to make further inquiries as many were
wired in that way.
Regards Ray G0BXG
"Martin" <Martin@_NOSPAM_g1gyc.demon.co.uk> wrote in message
news:auiv4t$f10$1$8300...@news.demon.co.uk...
Gareth Rowlands
Has anyone ever installed a mains isolating transformer or two
and run the shack items off of that ? The idea being that those
shack items can then have their chassis connected to an 'RF'
garden-style earth rather than the household mains earth - there
being no direct connection between the two earths.
Cheers,
Gareth.
Dan Wood
Gareth Rowlands <gar...@lightfox.demon.co.uk> wrote in message
news:20021229....@lightfox.demon.co.uk...
This can get very dangerous if it is possible to come into contact with the
'mains' earth in the house, and the 'shack' earth simultaneously. Any
difference in potential can be quite uncomfortable, and under certain
conditions might be fatal!
If you go down this road, make absolutely sure that nothing that is earthed
on the house supply, or any metalwork, pipes etc is anywhere near anything
in the shack. Something as innocent as vacuuming out the shack (not that I
ever have) could prove nasty if you have one hand on the vacuum cleaner and
the other touches your radio gear...
I had my earthing checked out after I got a surprise one day while standing
out in the garden and reaching through the kitchen window to turn the
wireless up. Funny buzzing sensation... I measured about 95 volts between
mains earth and a spike stuck in the lawn! Turns out that all my wiring and
earthing is all OK according to qualified people, but personally I'm not
convinced. I just treat 'inside' and 'outside' as two very different places.
I'm not sure how the 95 volt potential is developed as I'm not on PME here,
even though it seems like the kind of thing that happens when PME goes
wrong!
Dan.
Brian Reay
news:20021229....@lightfox.demon.co.uk...
>
> Has anyone ever installed a mains isolating transformer or two
> and run the shack items off of that ? The idea being that those
> shack items can then have their chassis connected to an 'RF'
> garden-style earth rather than the household mains earth - there
> being no direct connection between the two earths.
>
Yes, a local does that. Only potential (no pun intended) problem is ensuring
you can't readily contact anything grounded to the PME - such as the CH
pipes or any equipment in the shack not connected via the isolating
transformer.
73
Brian
Richard Clark
Hi Gareth,
I do this for my battery charger (a laboratory grade linear power
supply) and run off batteries. However, I still connect the two
grounds together, at the ground rod.
I am not particularly bothered with the prospects of lightning, not in
the Pacific Northwest (we have the lowest incidence of lightning
strike in the 48 states). However, I do still maintain lightning safe
practices like a one point entry window for all RF and electronics
which is tied to that same ground rod (less than 10' away).
Having an isolation transformer can be turned into an illusion of
isolation very easily through the casual connection of one piece of
equipment that has a ground path (somewhere). Do you have an outboard
DSP that uses a "brick" power supply? Ground may be busted DC-wise,
and yet it may be a conduit for noise from the Mains. How about a
computer connection for packet? Does the computer have a modem
attached to a phone line? How about one of those premium SWR meters
with backlights and digital displays - again, plugged into some
anonymous wall-wart power supply? The opportunity to violate the
isolation is exceedingly easy to come by and simple to implement.
Another point, the isolation transformer is good at decoupling of RF
and noise, but it is not an RF ground buster. You do not separate the
two grounds, except by the DC and low AC path. At HF, it is a must
that you have two good grounds otherwise the transformer turns into a
very large coupling cap. By the nature of good transformer
construction (which includes a Faraday shield), both grounds are
figuratively strapped together for RF. The greater virtue of an
isolation transformer is it allows you to extend the "balanced"
metaphor where it counts: at the source. It also lets you choose
which ground as being superior for your situation.
73's
Richard Clark, KB7QHC
CW
ELCB.
"Anon" <pa...@anon.com> wrote in message
news:aIr2kvBx...@btinternet.com...
Dan Wood
CW <clinton...@attbi.com> wrote in message
news:FAKP9.496081$%m4.1...@rwcrnsc52.ops.asp.att.net...
> Would somebody please explain what a PME is. While you are at it, define
> ELCB.
>
I can try, but have no expertise in this field at all! I believe the
following to be true...
Back in the good old days, the supply companies provided 3 conductors: Live,
Neutral and Earth.
For some reason (probably cost?) they did away with the need for a separate
Earth conductor by bonding Neutral and Earth together at the substation. The
buried cable used to bring the supply to homes has 'gaps' in the insulation
along its length, effectively connecting Neutral back to 'mother earth' at
these points. Since there are many of these along the length of the cable,
we get the term 'multiple earthing'. Only when the supply reaches your house
does Neutral get split from Earth again....
PME is a problem for radio amateurs because they may connect additional
metalwork in the ground to their Earth systems. (And because of PME they are
effectively connecting it to Neutral too....) If a fault in the buried cable
develops that breaks the outer Neutral/Earth connection, but leaves the live
intact then all the current supplied after the break will have to find
another way back to the substation through the ground... If your earth
system is connected to the (now disconnected) Neutral conductor then hey
presto a fairly low impedance path is available... Your supply (and all your
neighbours downstream of the fault!) can now complete its circuit through
YOUR earth system. That's a heck of a lot of current (= fires and
explosions!)...
Another risk: Your earth has some resistance.... Voltage=Current x
Resistance.... So there will be a rise in potential around your earth
system. In other words it won't be at 'Earth' anymore... Which means that it
is a problem if you are, and you touch it...
So that's PME! It's late and I rambled... I wonder if *anyone* understands
me?
As for ELCB that's a bit easier. "Earth Leakage Circuit Breaker" - a device
that sits on a supply line and monitors the current in the Live and Neutral
lines. In theory these should be equal because all appliances etc. will form
a circuit between Live and Neutral. If the currents are not equal then some
of the live current is flowing elsewhere (to earth probably, hence an 'earth
leakage') - the ELCB detects this difference and shuts off the supply. Most
domestic ones trip at 30mA and reasonably quickly, the idea being that if it
is a person that the current is leaking through, they might live. In large
installations with lots of PC's and stuff the capacitors connected between
the supply and earth in the power supplies can have a cumulative effect,
leaking enough current to trip ELCB's - you can get special ones with a
higher trip rating for these kinds of situations.
Oops, I rambled again...
HTH (a bit!)
Dan.
Dave
"Dan Wood" <mr....@no.spamthanks.bigfoot.com> wrote in message
news:ujLP9.7251$4k6.630242@wards...
I am not that sure that you did :-))
You have come up with the clearest explanation of PME v radio earth that I
have ever read.
I have always wondered why a PME supply could fail so.
Now I know.
Many thanks
DE G6 KHP
Dave
CW
--
CW
KC7NOD
"Dan Wood" <mr....@no.spamthanks.bigfoot.com> wrote in message
news:ujLP9.7251$4k6.630242@wards...
>
Brian Reay
"CW" <clinton...@attbi.com> wrote in message
news:FAKP9.496081$%m4.1...@rwcrnsc52.ops.asp.att.net...
> Would somebody please explain what a PME is. While you are at it, define
> ELCB.
>
PME = Protective Multiple Earth.
At one time the electricity supply companies used to run 3 cables to each
house, L, N & E. About 50 years back (I'm not sure of the exact date) they
reduced this to 2 , L & N.
To provide a local 'earth' facility they bond the N conductor to all the
pipe work (water and gas etc) at the point where the supply enters the
house, in the box that goes from the 1" dia "coaxial style" cable (which is
not coax, just has a similar appearance) to the two 'tails' that go to the
input of the meter.
There should be a notice on such installations.
ELCB = Earth Leakage Circuit Breaker
A device the detects an imbalance between the currents in the L & N and, if
the imbalance exceeds a preset limit, turns off the supply. The limit is
typically 30mA in a domestic environment. About 3x the benchmark lethal
level.
73
Brian
--
Brian Reay
www.g8osn.org.uk
David Honey
> Hello Martin are you in the UK or some other part of the world. There are 3
> items of elevated earthing that need to be addressed. Any mains operated RF
> equipment must have an efective electrical earth, which is not the same as
> an RF earth. Any RF earth lead, dropping from an elevated shack, could be a
> significant portion of a wavelength, so you really ought to decide what
> bands you are expecting to work. It is not difficult to solve once you know
> the pitfalls.
> If you are in the UK have a look at your electricity meter instalation, and
> see if there is a label marked PME or Protective Multiple Earthing, if you
> are in a high rise block you may need to make further inquiries as many were
> wired in that way.
> Regards Ray G0BXG
> "Martin" <Martin@_NOSPAM_g1gyc.demon.co.uk> wrote in message
> news:auiv4t$f10$1$8300...@news.demon.co.uk...
Thanks for bringing that one up - I wondered when someone would.
Even with the shortest path from a shack to a ground point
outside, you would probably have at least 5m of wire.
At 30MHz, this would be half a wavelength and appear to be
an open-circuit at the shack if it was a perfect RF earth
at the other end. I believe that MFJ make a tunable RF earth
but I have no experience of using such a thing.
I'm in a similar situation. My shack is upstairs in the house.
Currently, my set-up is that I connect the chassis of equipment
to mains earth as an electrical safety but with cable that is
wound through a ferrite ring to reduce the possibility of
RF getting back into the mains. Secondly, all of my antennas
are balanced and fed via baluns. Also, each feeder has a number
of turns in the loft before it drops down so that it acts as
an RF current choke to try and keep RF out of the shack.
I haven't had any problems with RF in the shack or RF
getting into mains wiring.
I have heard of others that take this further and use an
RF earth to connect to the coax screen at the antenna
end, connecting to the balun close to that point, then use
ladder feed from the balun to the antenna. Obviously, this
means that you have a vertical ladder feed from ground level
upwards and this might be considered an eyesore by the XYL.
Plus you have the issues mentioned by others of disconecting
mains earth in PME situations as mentioned in detail by other
posters. For these reasons, and the fact I haven't had a problem
with RF in the shack, I didn't do that.
If you are using unbalanced antennas such as a vertical or
end-fed, then having a good RF earth close to the antenna is
important. However, most sources suggest that a few copper
rods is not an effective RF earth (unless you're right by the
sea where ground conductivity is very high) and they suggest a
lot of buried radials. Some people even bury chicken-wire mesh under
the lawn so that they have a large surface area to form an
effective ground plane.
Hope that helps,
David.
Jon H
news:auo9bg$948$3...@helle.btinternet.com...
> > neighbours downstream of the fault!) can now complete its circuit
through
> > YOUR earth system. That's a heck of a lot of current (= fires and
> > explosions!)...
Worth fusing the earth connection?
;-)
JH
OC_CAM's Razor
> Even with the shortest path from a shack to a ground point
> outside, you would probably have at least 5m of wire.
> At 30MHz, this would be half a wavelength and appear to be
> an open-circuit at the shack if it was a perfect RF earth
> at the other end.
Seems that 1/2WL would make a perfect ground wire. Seems that
an even multiple of 1/4WL is what you are talking about.
5m of wire on 20m would be a worst case ground.
--
cheers, CAM http://www.qsl.net/w5dxp
-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
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Dan Wood
Jon H <jon.p.harr...@bt.com> wrote in message
news:aupnq7$dfa$1...@pheidippides.axion.bt.co.uk...
difference in potential on each side of it! :)
RVMJ
>Seems that 1/2WL would make a perfect ground wire. Seems that
>an even multiple of 1/4WL is what you are talking about.
>5m of wire on 20m would be a worst case ground.
If you want to get RF out of the shack, use a quarter-wave
counterpoise, adjusted in length for maximum effect.
Half a wavelength will merely keep the volts where they are, just
where you *don't* want them.....
HTH
--
from
RVMJ
Remove Safety-&-Arming before e-mailing
OC_CAM's Razor
> OC_CAM's Razor wrote:
>>Seems that 1/2WL would make a perfect ground wire. Seems that
>>an even multiple of 1/4WL is what you are talking about.
>>5m of wire on 20m would be a worst case ground.
>
> If you want to get RF out of the shack, use a quarter-wave
> counterpoise, adjusted in length for maximum effect.
>
> Half a wavelength will merely keep the volts where they are, just
> where you *don't* want them.....
1/4WL is good if the other end is open-circuited. 1/2WL is good
if the other end is grounded. If the other end is grounded, the
volts will be close to zero with 1/2WL.
John
news:auoujb$919mc$1...@ID-140397.news.dfncis.de...
and an RDC being overlooked in this thread?
ELCB - Earth Leakage Circuit Breaker. As I understand it, this is a device
in which a voltage of the "earth" of the protected zone is compared with the
voltage of a "true" earth (e.g. an earth rod) and a current flowing between
them is used to initiate tripping of a circuit breaker. The ELCB has the
disadvantage that current leaks at points other than the location of the
ELCB are not detected.
RCD - Residual Current Device. A modern replacement for the ELCB. This is
a device designed to help prevent electric shocks etc. and works essentially
by detecting current imbalance in the L and N conductors, such that when
then L-N current imbalance exceeds a pre-defined value (e.g. 30mA) a circuit
breaker trip is initiated. This has the advantage that a current leak
anywhere in the protected zone will initiate tripping.
J.
M0bcg
level to youre shack , just use some rg213/h100 coax with only the centre
conductor connected , and use the outer braid as a screen only , ie not
connected to earth .
if you can find some screened cable instead of coax, you could use this instead
, but needs to be fairly heavy , ie 10mm sq .
there are data cables about which would suit the job if all the inner wires are
linked together and connected to ground , and the screen is left unconnected .
good luck
Reg Edwards
> level to youre shack , just use some rg213/h100 coax with only the centre
> conductor connected , and use the outer braid as a screen only , ie not
> connected to earth .
============================
The foregoing is either utter nonsense or a leg-pull.
r.dring
in to giving up amateur radio.
We need to answer his questions, and to do that we need to define the
problems, as I see it they are
1 Is his supply PME, and if so what is to be done about it, and what is to
be done to separate the RF noise from the mains, and the mains earth.
2 The RF earth lead could be a resonant length on some bands giving high or
low impedances and voltages, what can be done about it, or even does he need
an RF earth connection at all. What can he do to ensure that no high voltage
RF conductors can come into contact with anyone.
3 What can he do about lightening protection.
4 What can he do to ensure he does not create TVI or BCI to his neighbours.
All of the forgoing questions can be answered, but Martin deeds to supply a
few more details about
his home and surroundings.
some of the questions are as follows:
Is he in the UK if not where is he.
What kind of electricity supply does he have, overhead or underground
feeder, is it PME,
Is his building a high rise block, if not what type/height is it.
Where are the antenna's going to be mounted, on his building or on separate
self supporting structures or other buildings.
Are the antenna's and feeders going to be coax, balanced, or end, fed. Are
they resonant, broadband, or tunable.
Can he use an RF earth or counterpoise.
Martin wants the safest, cost affective solutions for his installation. All
of the problems and hazards are curable with a little care, and he will
still have a suitable and sensitive installation.
I recommend he obtains a copy of the RSGB book "HF antenna collection" which
has the Peter Chadwick article "the Killing ground" reproduced in it.
Another version is in the RSGB Book "The radio amateur guide to EMC.
This reply is already too long so I will put more answers regarding ELCB's
and RCCD's and PME in another email.
regards
Ray
Martin" <Martin@_NOSPAM_g1gyc.demon.co.uk> wrote in message
news:auiv4t$f10$1$8300...@news.demon.co.uk...
> I am in stalling my radio station in to the small "box room" on the 2nd
> floor
> of the building and I have in the past not worried about a separate earth
> for
> the station. But as this station is going to be a more permanent
arrangement
> than my other previous locations I want to make sure that :-
> 1) the station is safe electrically. (of course the supply earth will be
> connected)
> 4) is as clear of EMC problems as possible.
>
r.dring
Anon
when as I remember him telling me she told them where to go when they
did try to provide PME at his home.
The Earth at your premises is YOUR responsibility not the Local supply
companies! And they will either refuse to connect on a new installation
- or disconnect on an old installation if it doesn't meet the required
standard.
From someone with the PME disconnected for ever!
AND Someone who knows!!
>
>The local electricty company advised against this method - especially in
>situtions where there was a real risk of the neutral disconnection, eg in an
>area supplied by overhead wires. (It is extremely rare with buried supplies
>they tell me.) In fact, they advised they would disconnect my supply if I
>used it this method.
>
> >
>> From someone with Experience! Who has his PME disconnected and that's
>> the way it's staying!
>>
>
>OK, but if you local supply company don't like it you may well get
>disconnected.
>
>
>
--
Brian Reay
> They have yet to "DO" me and they haven't done Mr Chadwick! Nor his wife
> when as I remember him telling me she told them where to go when they
> did try to provide PME at his home.
>
> The Earth at your premises is YOUR responsibility not the Local supply
> companies! And they will either refuse to connect on a new installation
> - or disconnect on an old installation if it doesn't meet the required
> standard.
>
> From someone with the PME disconnected for ever!
>
> AND Someone who knows!!
>
I shouldn't worry about it, anyone who can get so worked up and excited
about a NG posting is more likely to have a heart attack or stroke than be
electrocuted.
Calm down, Lan.
73
Brian
r.dring
During the post world war 2 building boom there was a need to reduce the
cost of housing construction. PME could help, by allowing a reduction
in the number of cable cores that needed to be run in a domestic electrical
installation. The neutral and earth being the same conductor.
Origionally the only installations allowed (by special permission or the
Secratary of state) were installations that could garrantee, that every
consumer on a supply transformer would be connected in that arrangement.It
still allowed interleaving of premises across 3 phases, using a common
neutral core in the feeder cable.
In practice this meant that the only use was in high rise blocks of flats
(US = appartments), where the cabling was under total control. In fact there
were some installations with mineral insulated cables were only the live
cores were inside the cable, the joint neutral/earth conductor was the bare
copper sheath.
Later as Britains housing stock was being repaired/replaced another problem
came to light.
The copper or lead water main, was used as the main earth electode in a
normal domestic installation.
During this period plastic water mains became the norm, isolating the
protective conducter, and ensuring that if any faulty appliance, where the
case
became live, also made every other earthed appliance live. Not a very good
arrangement.
To combat this ELCB,s (Earth Leakage Circuit Breakers) were developed,
these were voltage operated and thus series connected devices, they were
installed between the earth continuity conductor and the main earth
electrode (A 1 yard long copper rod driven into the ground in place of the
water pipe).
The disadvantage of this system was that it could be bypassed by plumbing,
structural steelwork,
gas pipes, telephone systems, Ham radio RF earths, and many other parallel
conductors.
To solve this, we now us a much more reliable circuit breaker called an
RCCD. This device uses the current balance priciple, what goes down the
live conductor MUST come back via the neutral conductor, any imbalance or
RESIDUAL current MUST be fault current and so trip the circuit breaker.
To stop any confusion the unit has a different name, RCCD, it is a
Residual Current Circuit-breaking Device.
The residual current can be set at very sensitive levels to take account of
different hazards, 100mA with a delay, for some fixed circuits to stop
neusance tripping but give fire protection.
A lower level of 30mA on plug in appliances is the norm, this being below
the minimum current that will cause fibrillation in the heart, and so give
protection against electocution.
NONE of these devices give any protection against overcurrent. That is
provided by the normal fuses or MCB's (Magnetic or Miniture Circuit
Breakers). MCB's are now the prefared protection method, they provide very
accurate overcurrent protection.
Finally a combination device is now on the market which provides
overcurrent, and residual current protection, and that is what I would use
for the shack supply, although they are more expensive.
Returning to PME. Later still PME was allowed to be used in mixed areas with
the hazards as
described by others. If the neutral core in the supply cable is damaged.Your
house wiring can carry the current from other consumers.
The other more serious effect is that the earth conductors in your property
can float up to full mains voltage. you still cannot get an electric shock
because all bonded metal in the property is also at that potential. The
Danger arises when you bring "in" an external 0volt RF earth, putting
yourself between them can result in a fatal electric shock.
Now reverse the operation and take an earthed metal cased appliance,
supplied with the house earth via a three core flex, out into the garden.
The ground you are standing on will be at 0volts but the case of the earthed
applience could be at 240volts!!! again not a good idea.
If anyone wants I can deal with all of the alternative earthing arrangements
suggested in a later email.This one is already far too long.
One final note, some years ago attended an electrical supply training
course, and I raised this with the tuter lecturing on earthing, his answer
was to mount the transmitter and all other shack equipment inside additional
earthed metal boxes that had holes cut in them to allow you to touch the
plastic control knobs only !!!.
Regards
Raid
Ian Pollard
wrote:
>There seems to be some confusion about PME, and circuit breakers. (UK only)
>During the post world war 2 building boom there was a need to reduce the
>cost of housing construction. PME could help, by allowing a reduction
>in the number of cable cores that needed to be run in a domestic electrical
>installation. The neutral and earth being the same conductor.
<SNIP>
I have a similar kind of installation with a few minor differences. My
mains supply is delivered via overhead lines. I get one phase, neutral
and earth delivered in separate single core conductors from the
nearest distribution transformer (about 1km distant). I have concerns
regarding the earth and reckon it is simply a connection to neutral at
the distribution transformer. What should I do about earthing gear in
the shack? I don't have any kind of circuit breaker, just fuses and a
normal mains switch.
Ian
--
Ian Pollard//Wooler//Northumberland//UK
pol...@bigfoot.com
Dick
Without knowing precisely what your installation consists it is dangerous to
give advice. Peter Chadwick G3RZP has written several articles on this matter
including "Mains safety - the killing grounds" which discussed PME and
associated problems and was included in the book HF Antenna Collection by Erwin
David. (RSGB)
I'm surprised that you have an overhead supply and no ELCB or RCCB. Could the
installation be due for a review?
HTH and HNY
Dick G0XAY
Ian Pollard
I live in an old farmhouse that was built around 1800. It originally
had its own generator house and privately generated supply. I think it
was connected to the mains around 1955 and then totally rewired in the
1980s. It is completely wired in PVC with pukka 13 A type sockets and
a continuous earth. If it is necessary to fit a circuit breaker then I
will do it. I don't particularly want a RCCD as they are a pain in the
backside on an overhead iffy supply. I could fit an ELCB if it was
reckoned as necessary. It is presently fitted with a normal mains
switch and very large cartridge fuses.
Ian Walker
<easth...@msn.com> writes
>I don't particularly want a RCCD as they are a pain in the backside on
>an overhead iffy supply.
I do not see how having an overhead supply will cause a current
imbalance between P & N on the supply to the premises.
--
Ian G8ILZ
Ian Pollard
wrote:
We are having elongated discussions with the supplier, NEDL about the
state of our mains supply. They are presently rebuilding the whole
network and it is causing a few problems. They, NEDL have apparently
just been fined by the regulator and are now having to build two
additional sub stations to get around their problems.
J. McLaughlin
Wow. I always thought that the electrical distribution system in UK
was designed with an emphasis on low cost - you have confirmed it. I
shall add to my safety lectures how things are done in UK.
My suspicions were aroused when the purchase of an electrical
appliance in the UK did not include a plug. One went to a separate
store for a plug. I just put it off to heightened liability concerns
with some small justification being more than one set of socket
standards.
The only justification for the existence of a profession is the
protection of the public. I make sure that my students understand the
scheme used in NA for protecting people and property. Contrasting the
requirements of the NEC (not the antenna one) with the scheme you are
subjected to is bound to impress them more then just discussing the NEC.
Thanks for the explanation. Wow!
73 Mac, N8TT
--
J. Mc Laughlin - Michigan USA
Home: J...@Power-Net.Net
Ian Walker
>On Thu, 2 Jan 2003 21:26:46 +0000, Ian Walker <Jun...@127.0.0.1>
>wrote:
>
>>In article <00691v88dei397pkt...@4ax.com>, Ian Pollard
>><easth...@msn.com> writes
>>>I don't particularly want a RCCD as they are a pain in the backside on
>>>an overhead iffy supply.
>>
>>I do not see how having an overhead supply will cause a current
>>imbalance between P & N on the supply to the premises.
>
>We are having elongated discussions with the supplier, NEDL about the
>state of our mains supply. They are presently rebuilding the whole
>network and it is causing a few problems. They, NEDL have apparently
>just been fined by the regulator and are now having to build two
>additional sub stations to get around their problems.
The only way of obtaining a current imbalance between P & N your side of
your RCCD thereby tripping your RCCD is if there is a leakage to earth
from either P or N on your side of the RCCD. Neither voltage, nor
current imbalance on the supplier's side alone of your RCCD will cause
your RCCD trip.
--
Ian G8ILZ
Dave
Ian Pollard <easth...@msn.com> wrote in message
news:00691v88dei397pkt...@4ax.com...
Roger Muggleton
McLaughlin) wrote:
> My suspicions were aroused when the purchase of an electrical
> appliance in the UK did not include a plug. One went to a separate
> store for a plug.
All this changed some years ago. Now appliances are required to come with
a plug moulded (molded) onto the cable.
Roger.
justme
outlets are protected by mccb`s which in turn are fed via a RCD main
switch.Other ccts such as lights,cooker and immersion heater also
protectedby mccb`s but with a conventional mains switch.
Or a seperate radial supply to your radio room with a rcd mounted in
the room feeding a bank of socket outlets for your radio equipment
you can obtain rcd`s with a higher tripping current of 100ma which can
help eleviate nuisance tripping.
Protective multiple earthing is designed so that the resistance of the
earth path is of a value that allows the protective device to operate
with in a given time 0.4s for socket outlets and bathrooms and 5s for
fixed equipment. This is achieved by creating a equipotential zone
where at any given point in the installation the resistance to earth
is of a value that will achieve the times above.
The addition of a shack earth which is often a rod and is often ouside
the equipotential zone ( shed or out building) can create a shorter
path to earth in resistance terms which would not present an earth
fault at the protective device to enable it to operatewithin the
given times .
The answer for outbuilings and sheds is to take a supply to the
building from the existing distribution board (pme installation only)
not connecting the earth at the distribution board.
Install rcd protectect fuse board in the outbuilding and then wire sub
ccts from this for lighting and power.
Earthing of this type of installtion is then achieved by installing
and earth stake or stakes. The resistance of this earth path then has
to be measured and of the top of my head i cannot remember what the
maximum resistance should be but it could be 100ohms.
Well thats a long enough waffle from me.
cheers
steve
r.dring
there is a
notice identifying it as PME first. Also examine your installation and try
and identify
the main earthing arangement.
Another person who has had a disagreement with the electricity supply
company over
PME was "Professor Peter Felgett" one of the co-inventers of the Amisonic
surround sound system.
The row was detailed in the New Scientist magazine last year.news:9bl61vkusoaj7gn9b...@4ax.com...
Frank Turner-Smith
news:memo.2003010...@hzk.compulink.co.uk...
Several years ago I recall a demand from the Europrats that we should change
all our 13 Amp plugs and sockets to crappy Euro plugs, (at our expense, of
course.) This was required to save Euro manufacturers money by not having to
make two different mains leads.
Fortunately, this demand was treated with the contempt it deserved.
--
73 de Frank Turner-Smith G3VKI
watch this space - if it moves, see your optician.
Dave
<luc...@eternal-flames.gov> wrote in message
news:mo4g1v4j2ss9q17hv...@4ax.com...
> On Sun, 5 Jan 2003 10:31:15 -0000, "Frank Turner-Smith"
> <g3...@ntlworld.nospam.com> wrote:
>
>
> >Fortunately, this demand was treated with the contempt it deserved.
>
> No doubt if the Europrats proposed the idea again, now, Tony would
> fall in with it.... You have to remember his ambition to one day be
> Euro-president.
>
> Hopefully. If that ever happens, it will only be for one day.
Why, what have you got planned for him :-)
In hope. (please, please, please).
DE G6 KHP
Dave
r.dring
wire on the earth bar in your consumer unit after you have replaced it with
a standard earth arrangement.
If you still have fuses you can usually find a direct plug in miniature
circuit breaker for each fuse that will tighten up the overcurrent
protection. You can run you own earth continuity conductor from your earth
bar in the consumer unit to a new earth electrode. I should not have to tell
you how to get a good low resistance earth electrode connection. Don't
forget to label it "Main Earth connection do not remove". If you can it
would be a good idea to install a suitably rated 30mA instantaneous RCCD in
any circuits that feed sockets, with a 100mA 1second delay RCCD
on the main feeder to the consumer unit. Again rated for the full load of
the consumer unit, If you only can install one on the feeder make it a 30mA
instantaneous RCCD,They give you protection against electric shock but you
can get some nuisance tripping. Current IEE regulations are all about
sizing cable and earth conductors, to ensure in a fault situation,
sufficient current flows to trip the safety devices Evershed and Vignoles
(Megger) do a very good pocket guide book to electricity testing. Finally
many electrical wholesalers in the UK will hire out the line earth loop
impedance testers
that you need to ensure the line earth and neutral earth loops have a
sufficiently low impedance.
You may also be able to hire a 4 contact earth electrode impedance tester.
RayD
r.dring
r.dring
RayD
"J. McLaughlin" <J...@Power-Net.Net> wrote in message
news:v19rp18...@corp.supernews.com...
tweeky
news:_eFS9.1$hB2....@newsfep2-win.server.ntli.net...
"r.dring" <r.d...@ntlworld.com> wrote in message
news:_eFS9.1$hB2....@newsfep2-win.server.ntli.net...
Ray
A very good post indeed, if I may say so. I offer the following additional
comments. [I use "required" in quotes...given the legal status of the
"Wiring Regs"]. Sorry if this is deviating from the topic.
>>Ian if you want to do away with PME you can disconnect the PME earth wire
on the earth bar in
>>your consumer unit after you have replaced it with a standard earth
arrangement."
^^^^
Ray, this is where I disagree with you.... The PME link would need to be
disconnected during testing of the (new) installation to enable proper
measurements of earth loop impedence etc., not afterwards. Given that the
work you suggest involves disconnecting the earth to the installation, a
note of warning: the appropriate percautions must be taken!!
(a) My understanding of the wiring regulations is that where you install
your own earth, the installation of an RCCD is now "required", and is much
more than just "a good idea". Earthing must be such that the RCCD trips
before the potential of "earthed" metalwork can exceed 50V and within 400ms,
as far as I recall
(b) I agree... replacing fuses with MCBs is a good idea, since they can
afford superior protection from over-currents. Must not forget the need for
discrimination and to ensure that an MCB rating is appropriate for the
conductors used in the circuit.
(c) Yes, RCCD discrimination is advantageous. Perhaps a 100mA RCCD on
the main supply and 30mA for sockets into which portable (e.g. garden power
tools) might be plugged. I think that a 30mA RCCD is "required" for any
"external" equipment and out-buildings.
(d) The earth electrode must be connected properly with the right size of
cable and the resistance must be measured to check that it is acceptable. I
have not found where to hire an earth loop impedence tester in East
Anglia... any suggestions, please, Ray (since they are rather expensive to
buy and the "TT" supply could do with checking....)
(e) RCCDs should be tested to ensure that they trip as rated and within
the required time period.
(f) The IEE's "On Site Guide" is about £14 and provides lots of
information re installation and testing and is well worth the money in my
view for anyone contemplating electrical installations/tests
(g) The thread heading includes "ELCB". Note that this is generally
taken to imply a **voltage operated** device. I think that these are not
longer mentioned in the latest Regs (but don't have a copy here) and I doubt
that they are readily available these days.
(h) Remember that "domestic" electrical installations should be inspected
/ tested every 10 years at most
(i) When in any doubt whatsoever, employ the services of a competent
person !!
NNNN
Brian Reay
topic with regard to removing the PME and adding your own Earth, is that you
don't really isolated the Earth and Neutral as would first appear due to the
minor problems there being other consumers with PME on your phase. This is
especially a problem if your local supply is buried near you but on 'low'
overheads before that- as in my case and is common on other private roads in
the area. This was the concern of my local supplier who recommend bonding
the PME to 'your' earth.
The message is, check with the local supply company first. In my case, their
default was that bonding PME to local Earth was always safe but other
solutions may be OK, if the supply arrangements are known (apparantly this
is not always so!). I acknowldge their standpoint is safety and not EMI
issues but even the RSGB recommendation on their EMI/EMC site is PME to
Earth bonding.
73
Brian
Gareth Rowlands
"r.dring" wrote:
> Finally many electrical wholesalers in the UK will hire out the line
> earth loop impedance testers that you need to ensure the line earth
> and neutral earth loops have a sufficiently low impedance.
One little point for anyone contemplating - if you have an RCD in the
mains supply, and you are hiring or buying one of these devices, do make
sure it is of the variety built to work without tripping any RCD in
circuit when testing.
The type of earth loop impedance tester that shorts half-a-cycle of
mains from live to earth is pretty good at testing for the presence
of RCDs, and if one is in circuit, not a lot else.
Does anyone know what the status is of having lighting circuits fed
through a 'main' RCD ? There was a period in time when this was felt
to not be a quite a good idea to have a home plunged in to darkness
when a pinhole appeared in the kettle element.
There is an interesting item on earthing power conditioners which may
be of relevance - and which includes having a 'clean earth' at:
http://www.advance-galatrek.co.uk/lowlevel/hb/hb022.htm
73, G.
justme
It is not a good idea to disconnect the P.M.E. of any installation and
probaly against the law as the head unit and earth terminal belong to
the electricity supply company.
In answer to the question on lighting circuits on rcd`s there has been
available for a while now a split distribution board one half fitted
with an rcd main switch feeding power circuits via mccb`s and the
other half fitted with a conventional mains switch feeding the
lighting ccts and so called leaky items like immersion heaters
,kettles and cookers.
doc
justme
Gareth Rowlands
"justme" wrote:
> Protective multiple earthing is designed so that the resistance of the
> earth path is of a value that allows the protective device to operate
> with in a given time 0.4s for socket outlets and bathrooms and 5s for
> fixed equipment.
I thought that the idea was that in any installation, should a short
circuit occur, then the live-earth impedance was such that at least
three times the fusing current should flow, leadsing to a pretty near
instantaneous blowing of the wired fuse
> This is achieved by creating a equipotential zone where at any given
> point in the installation the resistance to earth is of a value that
> will achieve the times above.
If I've got it right, "equipotential zones" are more to do with having
less of a chance of someone developing an electric potential across
parts of their body.
A good example is when lightning stikes earth, and at a given point
say, sets up an equipotential zone of 300 volts per metre.
A human with two feet a foot apart might get a jolt of 100 volts(ish)
between both feet across a rather tender part of the anatomy, but a
cow with 5' between the front and back legs might get 500 volts(ish)
belt.
In the same way, should the casing of an immersion heater go live
because of a fault, equipotenial bonding seeks - via lots of thick
copper wire - to keep the volts (wrt earth) on the hot tap of the
bath the same as the volts (wrt earth) on the cold tap.
Cheers,
Gareth.
justme
Rowlands) wrote:
>In article <58ip1vsl53egaoktl...@4ax.com>,
> "justme" wrote:
>
>> Protective multiple earthing is designed so that the resistance of the
>> earth path is of a value that allows the protective device to operate
>> with in a given time 0.4s for socket outlets and bathrooms and 5s for
>> fixed equipment.
>
>I thought that the idea was that in any installation, should a short
>circuit occur, then the live-earth impedance was such that at least
>three times the fusing current should flow, leadsing to a pretty near
>instantaneous blowing of the wired fuse
You are correct but we are talking about a pme system and speaking
from an electrcians point of view i have several times cut through
live cables protected by wired fuses and they have not blown
>
>> This is achieved by creating a equipotential zone where at any given
>> point in the installation the resistance to earth is of a value that
>> will achieve the times above.
>
>If I've got it right, "equipotential zones" are more to do with having
>less of a chance of someone developing an electric potential across
>parts of their body.
Again from electricians point of view the impedence of the earth
equipotential zones have to be of the correct resistance to ensure the
above does not happen
>
>A good example is when lightning stikes earth, and at a given point
>say, sets up an equipotential zone of 300 volts per metre.
>
>A human with two feet a foot apart might get a jolt of 100 volts(ish)
>between both feet across a rather tender part of the anatomy, but a
>cow with 5' between the front and back legs might get 500 volts(ish)
>belt.
no comment
>
>In the same way, should the casing of an immersion heater go live
>because of a fault, equipotenial bonding seeks - via lots of thick
>copper wire - to keep the volts (wrt earth) on the hot tap of the
>bath the same as the volts (wrt earth) on the cold tap.
The amount of water in the tank acts as an insulation and the element
can rupture and the filement came into contact with the water and
continue to remain live
>
>Cheers,
>
>Gareth.