High Loop Impedance reading

[asalcedo]

A washing machine engineer has refused to work on my faulty washing
machine because he carried out an earth fault loop impedance test and
found a high reading, I believe it was 3 ohms.

He requires the circuit to be made safe before doing any work on the
washing machine.

A PAT test has been done and confirms that the appliance earthing
insulation and earth leakage were ok

I have been told by the PAT engineer that I need a niceic electrical
contractor to test the wiring

Is this the only avenue to address this problem?


How do I correct a high loop impedance reading?

Thanks,

Antonio




--
asalcedo

[Bob Minchin]

You need to find out where the earth problem lies by tracing where the
earth in your property comes from and then onto the ring mains.
It is just possible the earth supplied by your supply is faulty but that
is pretty unlikely.

3 ohms is very high and needs sorting out pronto

[A.Lee]

Bob Minchin <bob.minc...@YOURHATntlworld.com> wrote:

> asalcedo wrote:
> > A washing machine engineer has refused to work on my faulty washing
> > machine because he carried out an earth fault loop impedance test and
> > found a high reading, I believe it was 3 ohms.
> >
> > He requires the circuit to be made safe before doing any work on the
> > washing machine.

Is it protected by a RCD? If so, it is likely to be 'safe'.

> You need to find out where the earth problem lies by tracing where the
> earth in your property comes from and then onto the ring mains.
> It is just possible the earth supplied by your supply is faulty but that
> is pretty unlikely.
>
> 3 ohms is very high and needs sorting out pronto

I'd be asking what the supply characteristics are.
If it is a TT supply, 3 Ohms is very low, and quite acceptable.
To the OP, if you have that circuit protected by a RCD, then you can
probably have an earth fault loop impedance of up to 1667 Ohms, and
still be compliant.
Of course, it isnt ideal, as you want it as low as possible, presumably
this is a 32A ring final circuit, so ideally you want it below 1.4 Ohms,
but it all depends on the supply.

More information required before any good advice can be given.
--
To reply by e-mail, change the ' + ' to 'plus'.

[meow...@care2.com]

Common TT installs normally have > 3ohm earth impedannce. If it has an RCD or ELCB thats ok. If it has neither, 3ohm's too high.

If its the ring cct thats >3ohms, as it sounds like, best check your socket earth screws are done up tight.

I dont know why a wm repair guy would be testing your earth impedance, or why he didnt plug it in elsewhere.


NT

[Dave Plowman (News)]

In article <asalcedo...@diybanter.com>,

asalcedo <asalcedo...@diybanter.com> wrote:
> A washing machine engineer has refused to work on my faulty washing
> machine because he carried out an earth fault loop impedance test and
> found a high reading, I believe it was 3 ohms.

I'd first ask for proof he was qualified to carry out such a test - and
also ask to see the certification for the instrument he used. Before
telling him to f*** off, and getting in someone else.

--
*I never drink water because of the disgusting things that fish do in it..

Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.

[John Rumm]

On 23/05/2013 20:51, asalcedo wrote:

> A washing machine engineer has refused to work on my faulty washing
> machine because he carried out an earth fault loop impedance test and
> found a high reading, I believe it was 3 ohms.
>
> He requires the circuit to be made safe before doing any work on the
> washing machine.
>
> A PAT test has been done and confirms that the appliance earthing
> insulation and earth leakage were ok
>
> I have been told by the PAT engineer that I need a niceic electrical
> contractor to test the wiring
>
> Is this the only avenue to address this problem?

First you need to establish if it is a problem. That will depend on the
type of earthing you have.

There are three common ways that the earth in a property is supplied.
These are explained in detail here, along with pictures etc so you can
figure out which you have:

http://wiki.diyfaq.org.uk/index.php?title=Earthing_Types

In summary, if it turns out your earthing is TN-S or TN-C-S (common in
towns) then, yes it sounds like there is a problem.

If you have TT, then in fact your earth is remarkably good.

FYI:

http://wiki.diyfaq.org.uk/index.php?title=TT_Earthing

> How do I correct a high loop impedance reading?

Assuming it is a fault, and assuming the earth impedance is ok at the
main earth terminal, then it would indicate a fault in circuit feeding
the socket where he carried out the test. If could be damage to the
cables, or a lose connection at any socket between that point and the
consumer unit.

Finding it is not too difficult if you have some basic test equipment
like a multimeter, and are confident enough to carry out some tests.
Post back here for more information.


--
Cheers,

John.

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| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

[Martin Crossley]

"asalcedo" <asalcedo...@diybanter.com> wrote in message
news:asalcedo...@diybanter.com...

Plug it into an RCD adaptor and throw a couple of (not anti-static) rubber
mats on the floor for him to work on..
That gives him a working environment safer than normal. I'm surprised he
doesn't carry these with him anyway.

[Andy Burns]

meow...@care2.com wrote:

> On Thursday, May 23, 2013 8:51:13 PM UTC+1, asalcedo wrote:
>
>> A washing machine engineer has refused to work on my faulty washing
>> machine because he carried out an earth fault loop impedance test
>

> I dont know why a wm repair guy would be testing your earth
> impedance, or why he didnt plug it in elsewhere.

About 6 years ago a newly purchased washer-dryer developed a fault and
the manufacturer sent a bod round to fix it, the first thing he did was
whip out a PAT tester and check the machine and the socket, presumably
it's their standard "Health and safety + Human Rights Act guv" approach.

[asalcedo]

John Rumm;3067065 Wrote:
> On 23/05/2013 20:51, asalcedo wrote:

> -

> A washing machine engineer has refused to work on my faulty washing
> machine because he carried out an earth fault loop impedance test and
> found a high reading, I believe it was 3 ohms.
>
> He requires the circuit to be made safe before doing any work on the
> washing machine.
>
> A PAT test has been done and confirms that the appliance earthing
> insulation and earth leakage were ok
>
> I have been told by the PAT engineer that I need a niceic electrical
> contractor to test the wiring
>

> Is this the only avenue to address this problem?-

>
> First you need to establish if it is a problem. That will depend on the
> type of earthing you have.
>
> There are three common ways that the earth in a property is supplied.
> These are explained in detail here, along with pictures etc so you can
> figure out which you have:
>

> 'Earthing Types - DIYWiki'
> (http://wiki.diyfaq.org.uk/index.php?title=Earthing_Types)

>
> In summary, if it turns out your earthing is TN-S or TN-C-S (common in
> towns) then, yes it sounds like there is a problem.
>
> If you have TT, then in fact your earth is remarkably good.
>
> FYI:
>

> 'TT Earthing - DIYWiki'
> (http://wiki.diyfaq.org.uk/index.php?title=TT_Earthing)
> -
> How do I correct a high loop impedance reading?-

>
> Assuming it is a fault, and assuming the earth impedance is ok at the
> main earth terminal, then it would indicate a fault in circuit feeding
> the socket where he carried out the test. If could be damage to the
> cables, or a lose connection at any socket between that point and the
> consumer unit.
>
> Finding it is not too difficult if you have some basic test equipment
> like a multimeter, and are confident enough to carry out some tests.
> Post back here for more information.
>
>
> --
> Cheers,
>
> John.
>
> /=================================================================\

> | Internode Ltd - 'Internode Limited - Computer Consultancy
> and Software Development' (http://www.internode.co.uk) |

> |-----------------------------------------------------------------|
> | John Rumm - john(at)internode(dot)co(dot)uk |
> \=================================================================/

Thank you for the links and explanations.

Based on the pictures, I have a TN-S supply.

I do not have RCDs in the house, only MCBs

That particular circuit has a 32A MCB.

The washing machine is connected to that circuit via a spur socket.

The PAT technician has told me that if I install an RCD, or RCBO the
circuit would be made safe. But based on the information provided here
it seems that even with the RCD and given the high impedance the circuit
might not be safe still. Is the PAT technician's advice wrong?


Thanks,

Antonio




--
asalcedo

[Brian Gaff]

Yes that is the case but from the mere working on principal, I'd suggest
that as its unplugged there is no reason why parts cannot be changed if you
know the fault.
Chances are the socket its plugged into was an afterthought so might be
worth checking the resistance elsewhere on the system and hopefully its ok
and its a problem of dodgy connections into the system used in the kitchen
or wherever the machine is. it could be as simple as doing gup some screws.

Brian

--
From the Sofa of Brian Gaff Reply address is active
"Bob Minchin" <bob.minc...@YOURHATntlworld.com> wrote in message
news:knlvoo$r8m$1...@dont-email.me...

[Brian Gaff]

With respect I think he is protecting himself from being sued at leaving the
device in a dangerous condition. You know what folk are like these days.

Brian

--
From the Sofa of Brian Gaff Reply address is active

"Martin Crossley" <Mar...@g8uwm.NOSPAMabelgratis.net> wrote in message
news:5t2dnZUx5MunKQPM...@brightview.co.uk...

[Fredxx]

How old is your installation?

Are you sure it's TN-S? If so the earth fault loop impedance should be
a fraction of 3 ohms! Yet 3 ohms seems too low for a fault in your
installation.

Generally if you added an RCD or RCBO that would make your installation
safe. If your consumer unit can accept RCBOs, I would add them to your
ring circuits. But first I would get down to the bottom of
understanding the type of earthing you have.

[meow...@care2.com]

On Friday, May 24, 2013 9:56:33 AM UTC+1, asalcedo wrote:

> Thank you for the links and explanations.
> Based on the pictures, I have a TN-S supply.
> I do not have RCDs in the house, only MCBs

Then 3ohms is not safe. Time to check all your earth screws are tight.

> The PAT technician has told me that if I install an RCD, or RCBO the
> circuit would be made safe.

true, if the 3ohms is stable.


NT

[Tim Watts]

On Friday 24 May 2013 11:11 meow...@care2.com wrote in uk.d-i-y:

> On Friday, May 24, 2013 9:56:33 AM UTC+1, asalcedo wrote:
>
>> Thank you for the links and explanations.
>> Based on the pictures, I have a TN-S supply.
>> I do not have RCDs in the house, only MCBs
>
> Then 3ohms is not safe. Time to check all your earth screws are tight.
>

TT Earth?

--
Tim Watts Personal Blog: http://squiddy.blog.dionic.net/

http://www.sensorly.com/ Crowd mapping of 2G/3G/4G mobile signal coverage

Reading this on the web? See:
http://wiki.diyfaq.org.uk/index.php?title=Usenet

[John Rumm]

On 24/05/2013 09:56, asalcedo wrote:

> Thank you for the links and explanations.
> Based on the pictures, I have a TN-S supply.
> I do not have RCDs in the house, only MCBs
> That particular circuit has a 32A MCB.
>
> The washing machine is connected to that circuit via a spur socket.
>
> The PAT technician has told me that if I install an RCD, or RCBO the
> circuit would be made safe. But based on the information provided here
> it seems that even with the RCD and given the high impedance the circuit
> might not be safe still. Is the PAT technician's advice wrong?

No, in principle he is correct. In situations where the earth loop can't
be got low enough (like TT installations) an RCD is relied on the open
the circuit in the event of an earth fault (i.e. a short circuit to earth).

While adding an RCD to the circuit would be advisable anyway, one ought
to find the actual fault as well.

There is a good method for easily finding where the fault is, and its
described here:

http://wiki.diyfaq.org.uk/index.php?title=Testing_a_ring_circuit

You should be able to do it with a reasonable multimeter. However it
does involve taking the cover off the consumer unit, and disconnecting
the circuit wires from the MCB and neutral and earth bus bars. If you
turn off at the main switch, then *most* of the CU will be safe. However
note that the wires into the main switch itself will still be live, so
don't go poking around near its input terminals!

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |

[asalcedo]

'Fredxx[_3_ Wrote:
> ;3067293']On 24/05/2013 09:56, asalcedo wrote:-
> John Rumm;3067065 Wrote:-

> On 23/05/2013 20:51, asalcedo wrote: - A washing machine engineer
> has refused to work on my faulty washing machine because he carried
> out an earth fault loop impedance test and found a high reading, I
> believe it was 3 ohms.
>
> He requires the circuit to be made safe before doing any work on
> the washing machine.
>
> A PAT test has been done and confirms that the appliance earthing
> insulation and earth leakage were ok
>
> I have been told by the PAT engineer that I need a niceic
> electrical contractor to test the wiring
>
> Is this the only avenue to address this problem?-
>
> First you need to establish if it is a problem. That will depend on
> the type of earthing you have.
>
> There are three common ways that the earth in a property is
> supplied. These are explained in detail here, along with pictures
> etc so you can figure out which you have:
>
> 'Earthing Types - DIYWiki'

> ('Earthing Types - DIYWiki'
> (http://wiki.diyfaq.org.uk/index.php?title=Earthing_Types))

>
> In summary, if it turns out your earthing is TN-S or TN-C-S (common
> in towns) then, yes it sounds like there is a problem.
>
> If you have TT, then in fact your earth is remarkably good.
>
> FYI:
>
> 'TT Earthing - DIYWiki'

> ('TT Earthing - DIYWiki'
> (http://wiki.diyfaq.org.uk/index.php?title=TT_Earthing)) - How do I

> correct a high loop impedance reading?-
>
> Assuming it is a fault, and assuming the earth impedance is ok at
> the main earth terminal, then it would indicate a fault in circuit
> feeding the socket where he carried out the test. If could be
> damage to the cables, or a lose connection at any socket between
> that point and the consumer unit.
>
> Finding it is not too difficult if you have some basic test
> equipment like a multimeter, and are confident enough to carry out
> some tests. Post back here for more information.
>
>
> -- Cheers,
>
> John.
>
> /=================================================================\
>

> --
> | Internode Ltd - 'Internode Limited - Computer Consultancy--
> and Software Development' ('Internode Limited - Computer Consultancy
> and Software Development' (http://www.internode.co.uk))
> |
> |-----------------------------------------------------------------|
>
> --
> | John Rumm - john(at)internode(dot)co(dot)uk |--
> \=================================================================/-
> -
> -

> Thank you for the links and explanations.
>
> Based on the pictures, I have a TN-S supply.
>
> I do not have RCDs in the house, only MCBs
>
> That particular circuit has a 32A MCB.
>
> The washing machine is connected to that circuit via a spur socket.
>
> The PAT technician has told me that if I install an RCD, or RCBO the
> circuit would be made safe. But based on the information provided
> here it seems that even with the RCD and given the high impedance the
> circuit might not be safe still. Is the PAT technician's advice
> wrong?

> -

>
> How old is your installation?
>
> Are you sure it's TN-S? If so the earth fault loop impedance should be
> a fraction of 3 ohms! Yet 3 ohms seems too low for a fault in your
> installation.
>
> Generally if you added an RCD or RCBO that would make your installation
> safe. If your consumer unit can accept RCBOs, I would add them to your
> ring circuits. But first I would get down to the bottom of
> understanding the type of earthing you have.

Please see picture attached, is this TN-S?


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|Filename: VG5V0290es.jpg |
|Download: http://www.diybanter.com/attachment.php?attachmentid=6869|
+-------------------------------------------------------------------+



--
asalcedo

[John Rumm]

On 24/05/2013 15:01, asalcedo wrote:

> 'Fredxx[_3_ Wrote:

>> How old is your installation?
>>
>> Are you sure it's TN-S? If so the earth fault loop impedance should be
>> a fraction of 3 ohms! Yet 3 ohms seems too low for a fault in your
>> installation.
>>
>> Generally if you added an RCD or RCBO that would make your installation
>> safe. If your consumer unit can accept RCBOs, I would add them to your
>> ring circuits. But first I would get down to the bottom of
>> understanding the type of earthing you have.
>
> Please see picture attached, is this TN-S?
>
>
> +-------------------------------------------------------------------+
> |Filename: VG5V0290es.jpg |
> |Download: http://www.diybanter.com/attachment.php?attachmentid=6869|
> +-------------------------------------------------------------------+

Looks very much like it yes[1]. I take it there is a terminal block just
out of site in the photo to the right of the meter where all those earth
wires join?

[1] The metal boxed CU is another clue its not TT - you would typically
use a plastic one for those installs.

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |

[Fredxx]

On 24/05/2013 15:01, asalcedo wrote:

Looks TN-S to me. 3 ohms is worryingly high and needs further
investigation.

A simple and perhaps unsafe method of to place an 2kW electric fire
between live and earth at the offending socket and measure the voltage
between neutral and earth at the offending socket and at the consumer
unit. A resistance of 3 ohms should give you nominally 27V. If the
voltage is the same in both locations I would be tempted to phone the
supply company for their advice. If the voltage at your consumer unit
is near 0V the high resistance must lie in your circuit.

[Tim Watts]

On Friday 24 May 2013 16:38 Fredxx wrote in uk.d-i-y:

> Looks TN-S to me. 3 ohms is worryingly high and needs further
> investigation.

If it is TN-S, agreed - 3 ohms is well out of the safety zone (0.8 Ohms is
the max permitted).

There's a bad connection somewhere. Or a very loose terminal.

[Andy Wade]

On 24/05/2013 09:56, asalcedo wrote:

> The PAT technician has told me that if I install an RCD, or RCBO the
> circuit would be made safe. But based on the information provided here
> it seems that even with the RCD and given the high impedance the circuit
> might not be safe still. Is the PAT technician's advice wrong?

It's incomplete and misguided, rather than wrong. An RCD on the final
circuit(s) in question would restore effective automatic disconnection
in the event of an earth fault (i.e. an L-E short). But protecting all
circuits would require multiple RCDs, since fitting a whole-house RCD is
no longer considered acceptable. In practical terms you'd end up having
to fit a new consumer unit, and to certificate that the underlying
earthing problem would still need to be sorted!

You need to get a qualified electrician, not a PAT-tester. Explain that
a high Zs reading has been found on one circuit and ask him/her to
confirm and investigate. They should start by checking continuity of
the main earthing conductor and taking a Ze reading - that part of the
earth-fault-loop-impedance external to your house wiring. If
significantly higher than 0.8 ohm the problem lies in the DNO's supply
network and the local DNO will need to be called out urgently.

If the Ze is OK the electrician will then check individual circuit R1+R2
(line+CPC resistance) readings with a low-ohms meter, or the overall Zs
with a loop tester. The location of any high readings can then be found
using normal fault-finding techniques, and fixed. It might be something
as simple as a loose earth terminal screw somewhere, or it might not...

--
Andy

[asalcedo]

John Rumm;3067460 Wrote:
> On 24/05/2013 15:01, asalcedo wrote:

> -
> 'Fredxx[_3_ Wrote:-
> --

> How old is your installation?
>
> Are you sure it's TN-S? If so the earth fault loop impedance should
> be
> a fraction of 3 ohms! Yet 3 ohms seems too low for a fault in your
> installation.
>
> Generally if you added an RCD or RCBO that would make your
> installation
> safe. If your consumer unit can accept RCBOs, I would add them to
> your
> ring circuits. But first I would get down to the bottom of

> understanding the type of earthing you have.-

>
> Please see picture attached, is this TN-S?
>
>
> +-------------------------------------------------------------------+
> |Filename: VG5V0290es.jpg |
> |Download: http://www.diybanter.com/attachment.php?attachmentid=6869|

> +-------------------------------------------------------------------+-

>
> Looks very much like it yes[1]. I take it there is a terminal block just
>
> out of site in the photo to the right of the meter where all those earth
>
> wires join?
>
> [1] The metal boxed CU is another clue its not TT - you would typically
>
> use a plastic one for those installs.
>
> --
> Cheers,
>
> John.
>
> /=================================================================\

> | Internode Ltd - 'Internode Limited - Computer Consultancy

> and Software Development' (http://www.internode.co.uk) |

> |-----------------------------------------------------------------|
> | John Rumm - john(at)internode(dot)co(dot)uk |
> \=================================================================/

Hi John,

Yes, there is that terminal block as seen in the attached picture.

It is then TN-S and I am in conversations with a qualified electrician
to come and test the wiring. I am not at the property these days.
Otherwise I would try to find the fault myself. With all the good
information here I think I would likely be able to do it.

Many thanks.

Antonio


+-------------------------------------------------------------------+
|Filename: VG5V0292es.jpg |
|Download: http://www.diybanter.com/attachment.php?attachmentid=6870|
+-------------------------------------------------------------------+



--
asalcedo

[John Rumm]

On 25/05/2013 08:24, asalcedo wrote:

>> +-------------------------------------------------------------------+
>> |Filename: VG5V0290es.jpg |
>> |Download: http://www.diybanter.com/attachment.php?attachmentid=6869|
>> +-------------------------------------------------------------------+-
>>
>> Looks very much like it yes[1]. I take it there is a terminal block just
>> out of site in the photo to the right of the meter where all those earth
>> wires join?
>>
>> [1] The metal boxed CU is another clue its not TT - you would typically
>> use a plastic one for those installs.

> Hi John,
>
> Yes, there is that terminal block as seen in the attached picture.
> It is then TN-S and I am in conversations with a qualified electrician
> to come and test the wiring. I am not at the property these days.
> Otherwise I would try to find the fault myself. With all the good
> information here I think I would likely be able to do it.

Sounds like a plan... he can test the loop impedance at the head end -
if that is high then the supplier should fix that free of charge. If
that is ok, then its likely to be a fault in your circuit or possibly a
faulty socket.

> Many thanks.
>
> Antonio
>
>
> +-------------------------------------------------------------------+
> |Filename: VG5V0292es.jpg |
> |Download: http://www.diybanter.com/attachment.php?attachmentid=6870|
> +-------------------------------------------------------------------+



--

Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |