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Topic Title: Shower Circuit Testing
Topic Summary: r1+m
Created On: 11 May 2018 08:54 AM
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 14 May 2018 02:18 PM
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sparkingchip

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Originally posted by: Weirdbeard2

Originally posted by: sparkingchip



Checking there is short circuit protection in a TT earthed installation?




Hi Andy, why would a neutral conductor resistance be relevant to a TT earthed installation, and not the neutral conductors of other earthing arrangements?


Ah yes, human behaviour.

We know there's no difference. In reality neutrals continuites are not generally check, it tends to be assumed that if there is a good earth loop reading the MCB or fuse will operate correctly.However there are those who worry a bit if the earth loop is too high and then start muttering about checking the neutrals.

Andy B.
 14 May 2018 03:55 PM
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Legh

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Originally posted by: Weirdbeard2

Originally posted by: Legh

Originally posted by: Weirdbeard2

Originally posted by: Legh

The reason being the possibility of loose neutral connections on the only domestic circuit pulling a continuous 36 -46A - That would indicate previous fires in tenanted properties no doubt?


I'm not sure that an ohm meter resistance test will prove that there is a loose terminal anymore than performing a loop test at the accessory, a look in the shower isolator switch and shower and a tweak of the terminals to check they are tight would be a better check for loose connections.


I'd agree better to check with a screwdriver and a tug, however, when you consider the logistics of connecting and reconnecting the terminations you are likely to be achieving the same result. An overkill in my opinion......


Thanks for the reply legh, but is 'overkill' appropriate when discussing safety checks? and with regards connecting and reconnecting the terminations, what do you mean? There is no need to unconnect an existing connection and reconnect it to establish its safety?


I think so. If you think about the process of removing the outer case of the shower/instantaneous water heater and connect a link between L-PE and L-N, which is likely to mean screwing a linking wire then after testing unscrewing then re-screwing the conductors back into the terminals.
Now attaching an Ohmmeter, turning it on and wiggling the conductors. the variation of reading might indicate a loose connection.
However, Its more likely to be loose at the isolator and far easier to access. I think the less invasive work the less possibility of generating more faults.

Legh

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http://www.leghrichardson.co.uk

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 14 May 2018 04:07 PM
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Legh

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Now this is shoddy, I would say it is dangerous because of negligent behaviour of the installer's lack of action after the damage was done.

rubbish install

It appears that not only was the job done badly but it appears that RCD protection was not added.

Legh

-------------------------

http://www.leghrichardson.co.uk

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 14 May 2018 05:46 PM
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Weirdbeard2

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Originally posted by: Legh

Originally posted by: Weirdbeard2
Originally posted by: Legh
Originally posted by: Weirdbeard2
Originally posted by: Legh
The reason being the possibility of loose neutral connections on the only domestic circuit pulling a continuous 36 -46A - That would indicate previous fires in tenanted properties no doubt?

I'm not sure that an ohm meter resistance test will prove that there is a loose terminal anymore than performing a loop test at the accessory, a look in the shower isolator switch and shower and a tweak of the terminals to check they are tight would be a better check for loose connections.

I'd agree better to check with a screwdriver and a tug, however, when you consider the logistics of connecting and reconnecting the terminations you are likely to be achieving the same result. An overkill in my opinion......



Thanks for the reply legh, but is 'overkill' appropriate when discussing safety checks? and with regards connecting and reconnecting the terminations, what do you mean? There is no need to unconnect an existing connection and reconnect it to establish its safety?


I think so. If you think about the process of removing the outer case of the shower/instantaneous water heater and connect a link between L-PE and L-N, which is likely to mean screwing a linking wire then after testing unscrewing then re-screwing the conductors back into the terminals.
Now attaching an Ohmmeter, turning it on and wiggling the conductors. the variation of reading might indicate a loose connection.

However, Its more likely to be loose at the isolator and far easier to access. I think the less invasive work the less possibility of generating more faults.


Thanks again legh, I wouldn't recommend adding links at the load end because as you say it would mean interfering with the existing terminations invasively rather than just checking they are tight, it's much better to make a link at the consumer unit and take readings at the accessories, how ever the op hasn't responded to my question about dead tests....I believe the most common form of obtaining a R1+R2 result for an EICR box is to subtract the Ze from Zs, so I suppose the most efficient way for the OP to get a similar meaningless result to fill would be do a normal Zs test at the shower, then clip the earth probe of the tester onto the neutral conductor, and subtract from the Zn reading obtained at the consumer unit?
 17 May 2018 08:22 AM
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leckie

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Obtaining the R1+R2 result by subtracting Ze for Zs is not an acceptable method, I am not sure if that is a common method or not.

This is how the newer Megger testers carry out the assessment of R1+R2 and they confirm that this is not a suitable method and is only an indication of what the R1+R2 test result is likely to be when the test is carried out as described in GN3. I have asked them.
 17 May 2018 08:26 PM
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Weirdbeard2

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Originally posted by: leckie

Obtaining the R1+R2 result by subtracting Ze for Zs is not an acceptable method, I am not sure if that is a common method or not.


Common enough for a well known brand of electrical tester to include this function in their newer testes?


This is how the newer Megger testers carry out the assessment of R1+R2 and they confirm that this is not a suitable method and is only an indication of what the R1+R2 test result is likely to be when the test is carried out as described in GN3. I have asked them.


 18 May 2018 06:15 AM
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leckie

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You have just repeated what I said WB.

If this is a common method then it is wrong. It has been well documented for many years that this is a incorrect method to obtain R1+R2, and when question Megger agree. So the facility on the meter is basically a complete waste of time. IMO it is a marketing ploy and it is misleading.
 20 May 2018 11:50 AM
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Weirdbeard2

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Originally posted by: leckie

You have just repeated what I said WB.



I did add a bit between the quotes where you said you weren't sure if it was common, then went on to describe that some testers can do it automatically.



If this is a common method then it is wrong. It has been well documented for many years that this is a incorrect method to obtain R1+R2, and when question Megger agree. So the facility on the meter is basically a complete waste of time. IMO it is a marketing ploy and it is misleading.


Fair play to them for having a go at marketing a function in 2018 that performs basic subtraction of one reading from another
 20 May 2018 01:32 PM
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mapj1

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OK - apart from small accumulating errors, of a magnitude that won't really matter much on an RCD protected circuit, why is this such a bad method of ensuring that things really are adequately earthed on an EICR ?
Most of the time its going to be either OK, or awful and "GN says so", on its own, is not really reason enough.

-------------------------
regards Mike
 20 May 2018 01:52 PM
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Weirdbeard2

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Originally posted by: mapj1

OK - apart from small accumulating errors, of a magnitude that won't really matter much on an RCD protected circuit, why is this such a bad method of ensuring that things really are adequately earthed on an EICR ?

Most of the time its going to be either OK, or awful and "GN says so", on its own, is not really reason enough.


Hi mike, who's post is this a reply to?
 20 May 2018 08:49 PM
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leckie

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I don't think arriving at the value of adding two measured values, Ze + R1+R2 is an incorrect method of establishing maximum value of Zs. Nor is direct measurement of Zs; to me they are both measured values. But recording a value of R1+R2 by deducting Ze from Zs is not the same thing. Plus if carrying out an EICR, although you would want to establish that the maximum Zs measured is satisfactory, you do not necessarily have to record R1+R2. If you measure it then fine, but don't enter a figure in the box just in order to fill in a box - it's not necessary.
 20 May 2018 09:25 PM
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Alcomax

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If this is a common method then it is wrong. It has been well documented for many years that this is a incorrect method to obtain R1+R2, and when question Megger agree. So the facility on the meter is basically a complete waste of time. IMO it is a marketing ploy and it is misleading.


Completely agree with the above. It really is dumbing down the industry. Made this point a few months ago about this simplistic gimmick by megger that only serves as a quick box filler to give the impression you know what you are doing when it is then quite obvious to those that do, that you have not got a clue!
 20 May 2018 09:32 PM
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mapj1

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Originally posted by: Weirdbeard2

Hi mike, who's post is this a reply to?


sorry if I was not clear - I was querying the reason for not preferring the taking of two or more Zs readings during an EICR versus dismantling to do a DC metered R1+R2.

In the mean time leckie has in effect answered that one.
For what its worth, I'm usually a fan of testing with AC on a system that is already live, so I prefer Zs and similar, in my mind being a test that is nearer the real fault condition we are looking to clear, reserving DC ohm meter type readings for things that either have yet to be energised, or are already switched off and are in bits for fault finding, servicing, or some other reason. The exception being the wander lead earth test (R2 only), because you can do that with any system, "dead or alive" as it were.
But I like to understand the thinking behind other folks approaches - it is always possible I have missed a trick or two along the way, and so I'm normally up for any cunning wheeze that might get me out of a hole in the future, or ideally help me avoid it altogether. And for what it's worth I spend most of my time in the one place these days, so I don't get the same variation of experiences others may

-------------------------
regards Mike
 20 May 2018 09:55 PM
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leckie

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Well I would generally prefer to directly measure Zs, except when its TT.

Imagine you have a Ra /Ze reading of 50 Ohms. Then you go around measuring the Zs at different points and get results such as 50.3, 50.65, 55.8, etc. These measurements might give a result that disconnects the RCD within the required time, but it's not giving you much feedback on the likely condition of the fixed wiring. So in that situation I prefer to check the R1, R2 and the Rn values where possible.
 20 May 2018 09:59 PM
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mapj1

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Ah yes, fair enough - was really only considering the TN - like case.

-------------------------
regards Mike
IET » Wiring and the regulations » Shower Circuit Testing

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