Various electrial questions
Piers Finlayson
- I'll be using SWA to feed the CU some distance from the incoming
supply. I've read the excellent terminating SWA article on the wiki,
but it is unclear about exactly what size SWA can be cut using bolt
croppers. I'll probably be using 10mm2 or 16mm2 SWA - is it reasonable
to expect bolt croppers to be fine for cutting these sizes?
- Is my supply TN-S or TN-C-S?
While I have seperate PE and N entering my building, the PE and N are
connect together on my property. I have two wires (11kV?) coming onto
my property, which terminate on a larger transformer on a telegraph
pole. I can see the PE is provided from underground at the pole, and
is connected to the N supply from the transformer. So my thinking is
that I'm TN-S if the transformer is considered the power source, but
TN-C-S otherwise. Thoughts?
(Yes, I have asked my electricity supplier, but they have suggested
that I contact the DNO. I haven't yet summoned up the energy to do
this.)
- I'm considering using a metal CU. From doing a bit of research
online it may be a requirement that the supply to this CU is protected
by a 100mA time delayed RCD. However, I'm unclear as to whether this
is only a requirement for TT systems or whether it's applicable to my
scenario. I'll be digging out my 17th ed regs later, but can anyone
let me know whether the RCD is a requirement here?
- I'm considering a three phase CU, and using this as a single phase
CU. I'm unfamiliar with the internal construction of these CUs - is
there generally any problems with using a TP CU as a single phase one?
(The main obvious issue I've seen is that for the model I'm looking at
a DP incoming switch is not available - so I'd have to use a TP one and
leave one pole unused.
- Finally, any recommendations or brands to steer clear of? I've been
looking at the Hager Invicta 3.
Thanks,
Piers
John Rumm
> I'm contemplating a serious rewire/CU replacement and had a few questions:
>
>
> - I'll be using SWA to feed the CU some distance from the incoming
> supply. I've read the excellent terminating SWA article on the wiki,
> but it is unclear about exactly what size SWA can be cut using bolt
> croppers. I'll probably be using 10mm2 or 16mm2 SWA - is it reasonable
> to expect bolt croppers to be fine for cutting these sizes?
Yup they should hack it - you may need to "nibble" at it and take a
couple of bites. If not then a hacksaw is your friend (at least to get
you started).
> - Is my supply TN-S or TN-C-S?
>
> While I have seperate PE and N entering my building, the PE and N are
> connect together on my property. I have two wires (11kV?) coming onto
> my property, which terminate on a larger transformer on a telegraph
> pole. I can see the PE is provided from underground at the pole, and is
> connected to the N supply from the transformer. So my thinking is that
> I'm TN-S if the transformer is considered the power source, but TN-C-S
> otherwise. Thoughts?
Its not uncommon for TN-C-S to be provided on overhead supplies these
days. The fact that there is a join inside your property would suggest
TN-C-S. Are there no PME stickers on your head end gear?
> (Yes, I have asked my electricity supplier, but they have suggested that
> I contact the DNO. I haven't yet summoned up the energy to do this.)
> - I'm considering using a metal CU. From doing a bit of research
> online it may be a requirement that the supply to this CU is protected
> by a 100mA time delayed RCD. However, I'm unclear as to whether this is
> only a requirement for TT systems or whether it's applicable to my
> scenario. I'll be digging out my 17th ed regs later, but can anyone let
> me know whether the RCD is a requirement here?
The RCD protection of all circuits is nominally only for TT type systems
(although the 17th edition nudges you closer to that anyway for all systems)
The fundamental question to answer is your earth loop impedance at the
supply adequate to clear a line to earth fault in the CU. If it is then
a metal CU is fine, and TT style protection is not required.
> - I'm considering a three phase CU, and using this as a single phase
> CU. I'm unfamiliar with the internal construction of these CUs - is
> there generally any problems with using a TP CU as a single phase one?
They tend to be of higher quality construction than the domestic ones.
The main objections to using one would be cost and size. Do you
anticipate having three phase supplied to it in the future then?
> (The main obvious issue I've seen is that for the model I'm looking at a
> DP incoming switch is not available - so I'd have to use a TP one and
> leave one pole unused.
I would expect the incomer to have 4 poles - one for each phase and
neutral. The CUs would normally supply a good number of single phase
circuits.
> - Finally, any recommendations or brands to steer clear of? I've been
> looking at the Hager Invicta 3.
In my limited experience of the three phase kit, the Memshield II stuff
was nice with a very good range of MCBs (including some high breaking
capacity ones as well (10kA)).
--
Cheers,
John.
/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/
Piers Finlayson
>
>
>> - Is my supply TN-S or TN-C-S?
>>
>> While I have seperate PE and N entering my building, the PE and N are >
>> connect together on my property. I have two wires (11kV?) coming onto
>> > my property, which terminate on a larger transformer on a telegraph >
>> pole. I can see the PE is provided from underground at the pole, and
>> is > connected to the N supply from the transformer. So my thinking is
>> that > I'm TN-S if the transformer is considered the power source, but
>> TN-C-S > otherwise. Thoughts?
>
> Its not uncommon for TN-C-S to be provided on overhead supplies these
> days. The fact that there is a join inside your property would suggest
> TN-C-S. Are there no PME stickers on your head end gear?
Nope.
>
>> (Yes, I have asked my electricity supplier, but they have suggested
>> that > I contact the DNO. I haven't yet summoned up the energy to do
>> this.)
>
>
>> - I'm considering using a metal CU. From doing a bit of research >
>> online it may be a requirement that the supply to this CU is protected
>> > by a 100mA time delayed RCD. However, I'm unclear as to whether this
>> is > only a requirement for TT systems or whether it's applicable to my
>> > scenario. I'll be digging out my 17th ed regs later, but can anyone
>> let > me know whether the RCD is a requirement here?
>
> The RCD protection of all circuits is nominally only for TT type
> systems (although the 17th edition nudges you closer to that anyway for
> all systems)
>
> The fundamental question to answer is your earth loop impedance at the
> supply adequate to clear a line to earth fault in the CU. If it is then
> a metal CU is fine, and TT style protection is not required.
OK, thanks. I'll be asking the DNO for max Ze as well as supply type,
but I'm guessing it's worth me measuring myself as well?
>
>> - I'm considering a three phase CU, and using this as a single phase >
>> CU. I'm unfamiliar with the internal construction of these CUs - is >
>> there generally any problems with using a TP CU as a single phase one?
> They tend to be of higher quality construction than the domestic ones.
> The main objections to using one would be cost and size. Do you
> anticipate having three phase supplied to it in the future then?
I see a number of benefits:
- Better quality construction.
- Better looks - more industrial and less cheap white plastic (the new
CU will be fairly exposed, both due to the convenient location and also
to ensure accessibility).
- More space inside for wiring (I hate fiddling around inside normal CUs).
- Many way - I've identified the need for at least 18 circuits and
want to leave room for expansion. I've got my eyes on either an 8 way
or 12 way TP CU.
>
>> (The main obvious issue I've seen is that for the model I'm looking at
>> a > DP incoming switch is not available - so I'd have to use a TP one
>> and > leave one pole unused.
>
> I would expect the incomer to have 4 poles - one for each phase and
> neutral. The CUs would normally supply a good number of single phase
> circuits.
You're right - most of them are 4 pole (but there are a few 3 pole ones).
>
>> - Finally, any recommendations or brands to steer clear of? I've been
>> > looking at the Hager Invicta 3.
>
> In my limited experience of the three phase kit, the Memshield II stuff
> was nice with a very good range of MCBs (including some high breaking
> capacity ones as well (10kA)).
Thanks - I'll take a look at these.
Dave Osborne
> - I'm considering a three phase CU, and using this as a single phase CU.
> I'm unfamiliar with the internal construction of these CUs - is there
> generally any problems with using a TP CU as a single phase one? (The
> main obvious issue I've seen is that for the model I'm looking at a DP
> incoming switch is not available - so I'd have to use a TP one and leave
> one pole unused.
>
Assuming you are planning to use a type B distribution board (with two
columns of MCBs mounted vertically) then you will need a piece of MCB
busbar to short out the three phases on the output side of the (4-pole)
incomer. You may be able to buy this as a single pole conversion kit.
>
> - Finally, any recommendations or brands to steer clear of? I've been
> looking at the Hager Invicta 3.
>
>
Hager single phasing kit JK125BSP on page 12 here:
http://download.hager.com/hager.uk/files_download/catalogues/invicta_3_catalogue.pdf
Also, there is a limit on the length of meter tails of 2m and the DNO
will probably insist on 25mm2 meter tails.
If there isn't already one, you will undoubtedly need to install a a
consumer unit within 2m tails-length of the meter and make your SWA a
sub-main. You will probably need to make this sub-main 25mm2 as well to
make the DNO happy (whether you can prove you need it to be 25mm2 or not).
Piers Finlayson
>
>>
>>> (Yes, I have asked my electricity supplier, but they have suggested >>
>>> that > I contact the DNO. I haven't yet summoned up the energy to do
>>> >> this.)
>>
>>
>>> - I'm considering using a metal CU. From doing a bit of research > >>
>>> online it may be a requirement that the supply to this CU is protected
>>> >> > by a 100mA time delayed RCD. However, I'm unclear as to whether
>>> this >> is > only a requirement for TT systems or whether it's
>>> applicable to my >> > scenario. I'll be digging out my 17th ed regs
>>> later, but can anyone >> let > me know whether the RCD is a requirement
>>> here?
>>
>> The RCD protection of all circuits is nominally only for TT type >
>> systems (although the 17th edition nudges you closer to that anyway for
>> > all systems)
>>
>> The fundamental question to answer is your earth loop impedance at the
>> > supply adequate to clear a line to earth fault in the CU. If it is
>> then > a metal CU is fine, and TT style protection is not required.
>
> OK, thanks. I'll be asking the DNO for max Ze as well as supply type,
> but I'm guessing it's worth me measuring myself as well?
Actually, one other complexity here is that I'll be installing a
incoming feed from my generator behind a break before make switch,
before the SWA to the CU. In the event of a power cut I can't rely on
the earth from the supply being present, so I will be providing my own
via earth spike. In this case I'll be TT and Ze will be much larger,
so even if I don't need to protect the mains supply to the metal CU via
an RCD I will need to protect the feed from the genny supply. But
then, I may also need to protect the feed from the genny to the house
anyway (I haven't figured out how I'm going to run this yet).
>>>
John Rumm
> On 2010-02-28 19:25:04 +0000, John Rumm said:
>>
>>
>>> - Is my supply TN-S or TN-C-S?
>>>
>>> While I have seperate PE and N entering my building, the PE and N are
>>> > connect together on my property. I have two wires (11kV?) coming
>>> onto > my property, which terminate on a larger transformer on a
>>> telegraph > pole. I can see the PE is provided from underground at
>>> the pole, and is > connected to the N supply from the transformer.
>>> So my thinking is that > I'm TN-S if the transformer is considered
>>> the power source, but TN-C-S > otherwise. Thoughts?
>>
>> Its not uncommon for TN-C-S to be provided on overhead supplies these
>> days. The fact that there is a join inside your property would suggest
>> TN-C-S. Are there no PME stickers on your head end gear?
>
> Nope.
not uncommon; unless its be upgraded in-situ relatively recently.
>> The RCD protection of all circuits is nominally only for TT type
>> systems (although the 17th edition nudges you closer to that anyway
>> for all systems)
>>
>> The fundamental question to answer is your earth loop impedance at the
>> supply adequate to clear a line to earth fault in the CU. If it is
>> then a metal CU is fine, and TT style protection is not required.
>
> OK, thanks. I'll be asking the DNO for max Ze as well as supply type,
> but I'm guessing it's worth me measuring myself as well?
Yup. If you do have PME, then it will in effect be the same as your
supply impedance.
>>> - I'm considering a three phase CU, and using this as a single phase
>>> > CU. I'm unfamiliar with the internal construction of these CUs -
>>> is > there generally any problems with using a TP CU as a single
>>> phase one?
>> They tend to be of higher quality construction than the domestic ones.
>> The main objections to using one would be cost and size. Do you
>> anticipate having three phase supplied to it in the future then?
>
> I see a number of benefits:
> - Better quality construction.
> - Better looks - more industrial and less cheap white plastic (the new
Yup, you will certainly get those...
> CU will be fairly exposed, both due to the convenient location and also
> to ensure accessibility).
> - More space inside for wiring (I hate fiddling around inside normal CUs).
Also probably true - although there are some domestic ones that offer
reasonable space. Many of the more recent ranges have been made a bit
bigger to allow easy use of single module RCBOs.
> - Many way - I've identified the need for at least 18 circuits and want
> to leave room for expansion. I've got my eyes on either an 8 way or 12
> way TP CU.
Nothing stopping you having more than one CU either if it makes it
easier neater etc.
Being TT here, I have one small split load CU for all exterior /
outbuilding circuits, and another larger one for stuff in the house.
Time delay RCDs on the main incomers of both.
>>> (The main obvious issue I've seen is that for the model I'm looking
>>> at a > DP incoming switch is not available - so I'd have to use a TP
>>> one and > leave one pole unused.
>>
>> I would expect the incomer to have 4 poles - one for each phase and
>> neutral. The CUs would normally supply a good number of single phase
>> circuits.
>
> You're right - most of them are 4 pole (but there are a few 3 pole ones).
Indeed - but only really suitable for boards feeding proper three phase
loads only I would have though?
Piers Finlayson
>
>
>>
>> - Finally, any recommendations or brands to steer clear of? I've been
>> looking at the Hager Invicta 3.
>>
>>
>
> Hager single phasing kit JK125BSP on page 12 here:
>
> http://download.hager.com/hager.uk/files_download/catalogues/invicta_3_catalogue.pdf
Excellent,
>
thanks - I hadn't spotted this kit.
>
>
> Also, there is a limit on the length of meter tails of 2m and the DNO
> will probably insist on 25mm2 meter tails.
Yes, I was aware of this.
>
> If there isn't already one, you will undoubtedly need to install a a
> consumer unit within 2m tails-length of the meter and make your SWA a
> sub-main. You will probably need to make this sub-main 25mm2 as well to
> make the DNO happy (whether you can prove you need it to be 25mm2 or
> not).
Hmm, I wasn't aware of this :-(.
ARWadsworth
"Piers Finlayson" <ne...@packom.net> wrote in message
news:4b8ac63d$0$2534$da0f...@news.zen.co.uk...
Once the DNO gives you the supply type then the max Ze is defined by type of
supply.
>>
>>> - I'm considering a three phase CU, and using this as a single phase >
>>> CU.
OKAY. That is most unusual but there is nothing wrong with it if you use a
conversion kit. How many circuits do you want or need?
You can buy very good single phase CUs.
Adam
James Salisbury
Hi,
Merlin Gerlin do some big 23 way industrial single phase units
http://tobinternational.co.uk/acatalog/MM.html
Dave Osborne
Well, I'm being pessimistic. It's not something I've personally
experienced, but it's come up before on this n.g.
I guess It largely depends on whether you are going to get the DNO in to
disconnect/reconnect your tails. If you are, then they can refuse to
re-connect if they don't like the look of your arrangement. If you
aren't, then they'll in all likelihood never know.
I'm pretty sure they won't like it if you don't have a CU of some sort
at the point of supply. As a minimum, you should have a 1-way metalclad
CU like this:
http://download.hager.com/hager.uk/files_download/hager_catalogue/01_consumer_units.pdf
Page 1.23 (page 29 in pdf reader)
IU4-16 or
IU44-11 or
IU44-18 as appropriate.
As to whether you need 25mm2 SWA for your sub-main, I couldn't say, but
be aware that it *might* be a problem.
Andrew Gabriel
"ARWadsworth" <adamwa...@blueyonder.co.uk> writes:
>
> "Piers Finlayson" <ne...@packom.net> wrote in message
>>>> CU.
>
>
> OKAY. That is most unusual but there is nothing wrong with it if you use a
> conversion kit. How many circuits do you want or need?
There is one gotcha which catches out electricians with this...
If it's rated at, say, 3 x 100A, then as a single phase CU, it's
going to be 1 x 100A, and not 1 x 300A. This is because the
neutral bus bar will only be rated for 100A.
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
John Rumm
Ah, that changes things somewhat! If you do have PME, then you can add
your own local earth provision to it anyway (yours just becomes one of
the "multiple"). Your genny feed would need to include suitable RCD
protection to cope with the local Ze ignoring whatever you are getting
via the supply (which as you say, can't be relied on in the event of an
interruption).
Alternatively you could make the the whole install TT...
John Rumm
>> If there isn't already one, you will undoubtedly need to install a a
>> consumer unit within 2m tails-length of the meter and make your SWA a
>> sub-main. You will probably need to make this sub-main 25mm2 as well
>> to make the DNO happy (whether you can prove you need it to be 25mm2
>> or not).
>
> Hmm, I wasn't aware of this :-(.
A switchfuse would be ok rather than a CU as such:
http://www.tlc-direct.co.uk/Main_Index/Distribution_and_Switchgear_Index/CMD_Switch_Main/CMD_Switchfuse/index.html
http://www.tlc-direct.co.uk/Main_Index/Distribution_and_Switchgear_Index/Switchfuse_TP_and_N/index.html
(can't say I like the look of the price of the mem ones though! ;-)
Andy Wade
> A switchfuse would be ok rather than a CU as such:
> [...]
> (can't say I like the look of the price of the mem ones though! ;-)
For single-phase the Wylex 110M (or 108 / 108M if 60 A is enough) is OK
and won't break the bank:
http://www.tlc-direct.co.uk/Main_Index/Distribution_and_Switchgear_Index/Switchfuse_SP_and_N/index.html
http://www.tlc-direct.co.uk/Main_Index/Distribution_and_Switchgear_Index/Hager_SP_1/index.html
--
Andy
Piers Finlayson
>
>>>
>>>> - I'm considering a three phase CU, and using this as a single phase > >>> CU.
>
>
> OKAY. That is most unusual but there is nothing wrong with it if you
> use a conversion kit. How many circuits do you want or need?
>
> You can buy very good single phase CUs.
I've identified the need for 18 circuits, but want room for expansion -
so at least an additional 5 circuits.
Piers Finlayson
> In article <02Ain.45887$Ym4....@text.news.virginmedia.com>,
> "ARWadsworth" <adamwa...@blueyonder.co.uk> writes:
>>
>> "Piers Finlayson" <ne...@packom.net> wrote in message
>>>>> - I'm considering a three phase CU, and using this as a single phase >
>>>>> CU.
>>
>>
>> OKAY. That is most unusual but there is nothing wrong with it if you use a
>> conversion kit. How many circuits do you want or need?
>
> There is one gotcha which catches out electricians with this...
> If it's rated at, say, 3 x 100A, then as a single phase CU, it's
> going to be 1 x 100A, and not 1 x 300A. This is because the
> neutral bus bar will only be rated for 100A.
Thanks for pointing that out - but that's fine because I won't be
needing more than 100A.
Piers Finlayson
>
>
> I'm pretty sure they won't like it if you don't have a CU of some sort
> at the point of supply. As a minimum, you should have a 1-way metalclad
> CU like this:
Why metal? (I don't have any requirement for it to look good in this
location, and this may require an RCD depending on my earth type/Ze.)
I actually already have a Proteus (nasty stuff) 1-way CU with a 63A
fuse which will be surplus to requirements and I can reuse.
mick
<snip>
>
> Actually, one other complexity here is that I'll be installing a
> incoming feed from my generator behind a break before make switch,
> before the SWA to the CU.
<snip>
Remember that your generator switch has to have a suitable load-make
rating unless there is some other method of protecting the operator (like
a suitable contactor circuit) if it is closed onto full load. It will
also have to switch Neutral so that you can work on the genny with the
mains live (unless you have a separate means of isolation). Ideally (and
*always* on 3-phase systems) the Neutral pole should make first, break
last.
--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.
ARWadsworth
There is a 28 way A board on the Hager webside.
Adam
Dave Osborne
> On 2010-02-28 20:46:41 +0000, Dave Osborne said:
>>
>>
>> I'm pretty sure they won't like it if you don't have a CU of some sort
>> at the point of supply. As a minimum, you should have a 1-way
>> metalclad CU like this:
>
> Why metal?
Only because you can make off the swa directly to it. Saves time, which
may not be an issue for you ;-)
John Rumm
Still surprisingly expensive for something that can be assembled with a
DIN enclosure and off the shelf parts. Still I suppose you do get plenty
of wiring room in the pre built versions.
ARWadsworth
"John Rumm" <see.my.s...@nowhere.null> wrote in message
news:ma2dnY7daL0xJxbW...@brightview.co.uk...
> Andy Wade wrote:
>> John Rumm wrote:
>>
>>> A switchfuse would be ok rather than a CU as such:
>>> [...]
>>> (can't say I like the look of the price of the mem ones though! ;-)
>>
>> For single-phase the Wylex 110M (or 108 / 108M if 60 A is enough) is OK
>> and won't break the bank:
>>
>> http://www.tlc-direct.co.uk/Main_Index/Distribution_and_Switchgear_Index/Switchfuse_SP_and_N/index.html
>> http://www.tlc-direct.co.uk/Main_Index/Distribution_and_Switchgear_Index/Hager_SP_1/index.html
>
> Still surprisingly expensive for something that can be assembled with a
> DIN enclosure and off the shelf parts. Still I suppose you do get plenty
> of wiring room in the pre built versions.
>
> --
> Cheers,
>
> John.
I have been fitting these
when needed. I pay around £20 from my wholesalers inc VAT. The 25mm tails go
straight into the terminals with no bending required. I have found on line
suppliers wanting £50+ for the same item.
Adam
Piers Finlayson
Ah, OK. The SWA will be after the break before make switch for the
genny, which in turn will be after this CU.
John Rumm
What sort of fuse do they take? Are the boxes available in other ratings?
ARWadsworth
"John Rumm" <see.my.s...@nowhere.null> wrote in message
It comes with a HRC fuse. They do a 100A switch but it comes with an 80A
fuse! I assume that it is to allow some diversity against a 100A supply
fuse.
See page 4 of
http://www.scolmore.com/documents/circuit_protection.pdf
Cheers
Adam
ARWadsworth
"ARWadsworth" <adamwa...@blueyonder.co.uk> wrote in message
news:ak4jn.46391$Ym4....@text.news.virginmedia.com...
>
>
> It comes with a HRC fuse. They do a 100A switch but it comes with an 80A
> fuse! I assume that it is to allow some diversity against a 100A supply
> fuse.
>
> See page 4 of
>
> http://www.scolmore.com/documents/circuit_protection.pdf
>
> Cheers
>
> Adam
Additional info
It uses these fuses
http://www.gil-lec.co.uk/products/2262066219
Adam