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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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 11 May 2018 08:54 AM
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LACarbon

Posts: 3
Joined: 15 March 2018

I have been asked when carrying out EICRs on properties that if there is a shower present to provide both r1+r2 and r1+m, any one enlighten me on what this actually is?

Thanks

Carbon
 11 May 2018 09:07 AM
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leckie

Posts: 4649
Joined: 21 November 2008

r1 is the resistance of the line conductor
r2 is the resistance of the circuit protective conductor

I would think "m" is a typo or a misread and actually means "n", properly referred to as rn. rn looks like m! So that's the resistance of the neutral conductor.
 11 May 2018 09:11 AM
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dustydazzler

Posts: 1970
Joined: 19 January 2016

As above

I'm almost certain m is a typo and it should be n
 11 May 2018 09:20 AM
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mapj1

Posts: 10430
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I.e. to verify the continuity and record the resistance of all 3 cores of the cable, L, N, E from the shower back to the board, but in a way that does not need an unreasonably long meter lead, by first placing a temporary shorting link L-N at one end and measuring the resistance round that loop from the other, and then move the temporary short to be L-E and repeating. (and then removing both short and meter before re-energising, or it can become a bit more expensive)

I presume there have been problems with poor joints in the neutral being missed on a basic inspection, that would probably not include a neutral test and then overheating in use.

The text book convention is that
r1 is the resistane of the live core between the load and the board,
r2 is the resistance of the earthing
rn (see how r n can look like an 'm') is the resistance of the neutral.

-------------------------
regards Mike
 11 May 2018 11:45 AM
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LACarbon

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Thanks guys, clearly I have misread and its not some new test 'fandangled' test method I have missed out on. r n and not m

Mike, we carry out a large number of EICRs and this one particular client has asked for this reading on all shower circuits recorded

Thanks again chaps

Carbon
 11 May 2018 01:05 PM
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geoffsd

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That's why they have Bum's night in Scotland.
 11 May 2018 04:17 PM
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alanblaby

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Originally posted by: mapj1
The text book convention is that

r1 is the resistane of the live core between the load and the board,

r2 is the resistance of the earthing

rn (see how r n can look like an 'm') is the resistance of the neutral.


Surely that should be R1, R2 and Rn?
It's a shower circuit, so a radial, not a ring.
 12 May 2018 01:46 PM
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Zoomup

Posts: 3964
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Blinkin ek, that would mean taking the cover off the electric shower risking losing the small screws down the drain hole if you forget to cover the drain hole. Also, why do makers put the info. label at the base of electric showers so that it is nearly impossible to read. And isn't the print so small on the info labels?



Z.
 12 May 2018 07:21 PM
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Jaymack

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Originally posted by: Zoomup
Also, why do makers put the info. label at the base of electric showers so that it is nearly impossible to read. And isn't the print so small on the info labels?

Not a problem, if you have a camera on a smart phone!

Regards
 13 May 2018 12:40 AM
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Legh

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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?

Legh

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

http://www.leghrichardson.co.uk

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 13 May 2018 08:21 AM
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lyledunn

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Voltage drop check?

-------------------------
Regards,

Lyle Dunn
 13 May 2018 10:19 AM
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Weirdbeard2

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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.
 13 May 2018 10:29 AM
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Weirdbeard2

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Originally posted by: LACarbon

I have been asked when carrying out EICRs on properties that if there is a shower present to provide both r1+r2 and r1+m, any one enlighten me on what this actually is?



So it's been established that rn is most likely the resistance of the neutral and r1, are you doing dead tests for the r1+r2 and connecting in temporary links or subtracting Ze from measured earth loop tests?
 13 May 2018 10:39 AM
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sparkingchip

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Checking there is short circuit protection in a TT earthed installation?
 13 May 2018 10:50 AM
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Weirdbeard2

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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?
 13 May 2018 12:23 PM
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Legh

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Originally posted by: lyledunn

Voltage drop check?


That would give you the off load volt drop, probably better to measure the voltage when the shower is turned on....... rubber gloves and boots maybe required.....

Legh

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

http://www.leghrichardson.co.uk

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 13 May 2018 12:26 PM
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Legh

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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......

Legh

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

http://www.leghrichardson.co.uk

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 13 May 2018 12:43 PM
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Zoomup

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Also make sure that the shower is not connected like this..............http://www.youtube.com/watch?v=XoihIp9veSs

Z.
 13 May 2018 12:44 PM
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Weirdbeard2

Posts: 297
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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?
 14 May 2018 12:23 AM
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mapj1

Posts: 10430
Joined: 22 July 2004

But to measure an R2 (sorry not an r2.. ) you still have to connect and disconnect your temporary link. I suspect as others have noted the reason this test may well appear to reduce failures, is least partly that it obliges folk to take the covers off, and at that point some one says 'ooh that looks a bit blue' and an expensive failure is nipped in the bud, rather than waiting for the magic smoke to curl out from the enclosure. The numerical value read on the meter is not so important comared to the fact that it has been looked at more closely.
Years ago I worked on a job where some delicate electronics had a push-fit screening can, that was to be pressed into place. In reality this meant it was fitted by bored people on a production line, who by mid-shift were not pressing it fully into place, the result being that by delivery some of the finished articles were arriving with a bit of cunningly folded tinplate rattling around loose in the box.
Stern talking to had only partly achieved the desired effect, nor did a few other ideas.
The successful fix was a further production step, after passing an extra box with a green light on the top, to apply a 'test pass' sticker to the centre of the offending metal push-fit lid. The act of pressing the sticker driving the can lid home onto its mount.
The 'test pass' label itself was a red herring, as no-one would ever see it, and it may as well have read "Killroy was 'ere" for all the use the words were. But the wider purpose of improving production yield was achieved.
How things will work out with human behaviour is not always initially clear.

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

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