Insulation Resistance Testing at a Socket Outlet

[kme]

O/P : apart from the other tangential points raised - you do an ins. test on a PME between N-E; you`re not going to get a reading. Further, a global ins. will be a problem if ANY loads are connected anywhere.

As for "where to test"? Wherever is safest and easiest to do so. DB, point, whatever.

"Pulling main fuse" - I`m quite sure no-one on the forum is going to condone such an action - being illegal and all. I fully agree with the live terminals issue; and, on bigger boards, the hazards on trying to disconnect the appropriate neutral for the circuit you want to test - especially if the board contains critical circuits, which, if interrupted, would create a more serious hazard than live working!

If we ALL phoned our DNO for disconnections, the law would soon be changed; because they don`t have the resources or manpower to meet their obligations. The status quo will continue because, like every other "stand" the British make...we fully agree and support it, until it directly affects US - then we don`t like it anymore (fuel protests, anyone?). We`re all as much to blame as anyone else, IMHO

KME

 

[davetheglitz]

O/P : apart from the other tangential points raised - you do an ins. test on a PME between N-E; you`re not going to get a reading. Further, a global ins. will be a problem if ANY loads are connected anywhere

. The OP did state with the main switch off - so neutral and earth are not connected at the MET unless there is a neutral/earth fault. As stated - the global insulation will be degraded by parallel paths - but if it is within the regs - where is the problem

 

[Doc Hudson]

Good point Doc - do you feel lucky! Perhaps it would be best to check before changing the fitting - then you could advise that the fault needs to be located before proceeding. To be honest I tend to do an IR check at a socket when customers ask me to quote for a CU change as a quick and dirty check that I won't have too many problems. With lights on - assuming halogen or filament types - L and N are effectively joined so it's a reasonable measure.

A CU change you will ultimately be taking all circuits off anyway so complications can be identified later, but with an additional socket minor works, you could do a quick preliminary check before committing to the work and this could actually open another can of worms with regard to what is the customer paying for? what work do you do? do you walk away and charge nothing if the circuit fails your prelim check? I could imaging a scenario of a prelim check shows 0.75Mohms, you tell the customer it doesn't comply and needs additional exploratory work to establish the exact cause but they say well all my sockets are working OK at the moment why cant you just put another one on in the kitchen?

Doc H.

 

[freedomrun]

Many thanks everyone for taking the time to post on this - my first posting here - whilst the Thread has gone a little off the track of my original post question, it does seem that i am correct in my initial thoughts regarding the testing of IR in this manner. I was not looking at obtaining Zs by this means, but the earlier post about breaking the Ring Final and doing tests there - this is where i was coming from about testing at a socket outlet if access to the CU is limited or dangerous - I always have in my mind the Electricity at Work Regs, stating that all electrical work and testing on an installation should be done if at all possible in the safest way and with no exposure to the electrical supply, if the CU is rammed or hard to get to, then there is always a risk of injury.

I very much agree with the (davetheglitz) posting, as all i need to do is a quick test to indicate the whole install is good to go before i add or alter the install with what the customer requests - i have also found in the short time i have been working in domestic properties, that most customers (even after explainations) just cannot understand why the CU needs to be opened up and when told faults are present, think you are just trying to rack up more work - a quick simple test they are OK with and does not cause concern with them (others just like the fact that i'm being thorogh).

My question also relates only to Minor Works and NOT EIC or PIR - also, can someone let me know how split boards and / or RCD's present in the CU or lighting transformers, Fluorescent fittings, Immersion heaters - would alter my IR results by testing IR at a socket outlet - anything else i should keep in mind about this, i understand this will not give an accurate IR reading, but if the IR test result for the whole install is within the regs, then the IR of any single cct must compy.

 

[Nicky Tesla]

Ive tested IR at a socket many times on periodics and yes it is quick n easy. First do your continuity tests then at the same time joining a L&N temporarily in a terminal you can do your test, then swap around and do your ring circuit checks and max R1+R2 test (which on a ring doesnot require you to connect at the board)....All done at the same time.....Why is that not quick and easy?

The cpc is connected to the earthing terminal bar

The neutral is connected to the neutral bar , and the

Live is connected to the live busbar through the mcb

Some people just dont think "outside the box" if you pardon the pun

(what about RCBOs? yes i know.............also i have seen this done in a book)

 

[SPECIAL LOCATION]

..... First do your continuity tests then at the same time joining a L&N temporarily in a terminal you can do your test, then swap around and do your ring circuit checks and max R1+R2 test (which on a ring doesnot require you to connect at the board)....All done at the same time.....Why is that not quick and easy?The cpc is connected to the earthing terminal bar

The neutral is connected to the neutral bar , and the

Live is connected to the live busbar through the mcb

A possible problem if trying to read your CPC ring continuity (e.g. for an R1+R2/4 calc)...

at a socket is you have got to verify no earth bonding parallel paths IMHO!

If the ring also happens to supply a boiler..

and the CPC to the boiler then has continuity down via the metal pipework, back via the 10mm gas and/or water bonds to the CU..

It rather messes up the ring CPC (Rn) value?

Or same problem if the upstairs ring has a spur off it to a bathroom fan heater, and the bathroom fan heater is cross bonded to other bathroom metal work & electrics.. it could a have another path back to the earth bar at the CU..

IF the two ring CPC ends are disconnected at the CU then NO path exists.

Guinness

 

[steptoe]

I would have thought the very obvious issue that arises from testing at a point other than the CU is how do you confirm that the cables and terminations are properly identified?

typical 5WW stuff this is.

the regs have no special conditions for basic installs, terminals still need to be identified.

 

[SPECIAL LOCATION]

The CU is packed and quite hard to access in the cupboard it's been boxed in to.

Is this a physiological problem with some electricians that if the most critical safety part of an electrical installation is inaccessible then for some strange reason.....

We make no endeavor to get it improved so that it can be worked on!!!!!!

Whatever happened to 131.8

NO addition alteration temporary or permanent shall be made to an existing installation.....

blah.. blah..

The rating AND THE CONDITION of any existing equipment is adequate.. blah... blah...

And

132.12

Accessibility of electrical equipment ????

Sufficient space for installation... and later replacement... accessibility for operation inspection fault detection, maintenance.. repair....

are they being dropped??? ?:|

Both of those.. and few others are highlighted in my regs book...

anytime I come across work that I don

 

[Doc Hudson]

From Mr Freedomrun's own admission his question has been answered. Even though it had gone slightly off topic, with some healthy debate by various members putting their case for different methods of testing and/or trying to look at various ways to resolve real world problems encountered on site. However Some members now want to debate (argue) a different question, about if or how you should apply exact wordings of guidance rather than resolving on site problems by interpreting the context of what the guidance is saying. These arguments do not have a lot of constructive value to the forum or its broad spectrum of members. So, rather than drag down a good thread with mindless arguments, I have now closed this thread at what appears a natural conclusion and moved the less constructive parts to a separate thread here:-

http://www.talk.electricianforum.co.uk/inspection-testing/17554-ir-testing-global-partial.html

I would remind all members hi-jacking others threads for your own arguments is not acceptable practice on the forum.

Doc H.