INSULATION RESISTANCE - WHO DOES?

[ebee]

Good Egg.
it`s the only way

 

[TeesdaleSpark]

don't understand why you can't calculate R1+R2 in instances when Zs and Ze have been measured. I know its not allowed, but don't know why.

You don't need to calculate R1+R2 for a PIR.

If you look in the Onsite Guide it shows an example of a correctly filled in PIR in the R1+R2 column there are ticks to indicate that the Zs measurement has confirmed this.

However I think the quickest method is to turn everything off do R1 and R2 on everyhting and then calculate Zs. If you do R1+R2 on your socket outlets is easy to find where the spurs are. When doing a Zs the readings arent as accurate. I always test ring continuity as many properties fail this.

The idea of shorting live and neutral together on the insulation test is that when you apply your test voltage they are at the same potential which means your electronic devices don't get damaged. I would never not do this on a PIR as you never know what's hidden away somewhere.

I'd recommend getting a copy of Guidance Note 3 and reading the section on PIRs. You will save a lot of time and stress. Once you get into the swing of things you will be able to do things a lot faster. You won't get one house done in one hour though.

 

[plugwash]

In maths the Ze + R1 + R2 = Zs is OK and then it would follow that Zs - Ze = R1 + R2.

the trouble is Ze + R1 + R2 = Zs is NOT true, what is true is Ze + R1 + R2 >= Zs

the reason its not a strict equals is twofold

1: paralell paths
2: Ze is not nessacerally purely resistive.

 

[ebee]

What your saying is , do the full ins res on your new bit but then when you connect to existing just do Lives to E to avoid any hidden easily destructable existing bits. Yes very sensible approach.
Yet me old home made megger thingy (23uA measured) never blew owt up and gave pretty accurate results

 

[ebee]

In maths the Ze + R1 + R2 = Zs is OK and then it would follow that Zs - Ze = R1 + R2.

the trouble is Ze + R1 + R2 = Zs is NOT true, what is true is Ze + R1 + R2 >= Zs

the reason its not a strict equals is twofold

1: paralell paths
2: Ze is not nessacerally purely resistive.

Yes

Ze measured and Zs measured are done under different conditions (Bonds coinnected/not)

 

[ambrougham]

Hi All, I know I will get slated for this question, but gonna ask anyway. The firm I work for expect 6 test and inspects (including certs) in as many hours. In an attempt to get this achieved, nobody bothers with I.R tests,myself included, though I hate signing to say its been done.

I'm not an electrician (but am qualified electrical/electronic engineer) and even on DIY electrics I would most definitely NOT skip what I consider to be essential safety tests and never have done even when there wasn't really a specific requirement to do them. However, I'm not in the least bit surprised that this kinda p*ss poor practice goes on which is why various (so-called) qualified tradesmen and electricians in particular are most certainly not welcome in my house

As I commented in a previous post regarding testing installations (in a Part P discussion somewhere on here) two words spring to mind and BOTH of them affect YOU directly (IMHO) regardless of what your employer may or may not have said: (1) Negligence and (2) Fraud. YOU are potentially open to being sued for negligence should there be a problem in the future and YOU are completing test records fraudulently. The way I would see it is that unless you have documentary evidence to prove that your employer has instructed you to do this then it is your neck on the block and not theirs. Sure doesn't sound like a good situation to be in to me. I seriously suggest that you at least seek some profesional advice if you don't feel able to do something about the situation yourself. I'm not exactly a fan of Trade Unions or similar organisations but if you belong to something along those lines then that would perhaps be a good starting point.

I know it isn't exactly easy to handle things like this because I've sort of been put in a similar situation myself but for your own sake not to mentions others you really need to do something. I was fed with large ammounts of mis-information (aka blatant lies) by more senior management as well as deliberately being kept totally in the dark over some falsified records (failed test(s) officially documented as passed) by so-called colleagues who were told verbally to do it but keep it quiet and then I was asked to sign the job off i.e. certify that everything was totally OK prior to dispatch. Worst-case scenario of the dodgy work concerned: someone dies. It was almost purely by chance that I discovered that I was being seriously conned into putting my name to some well dodgy goings on. Not happy and needless to say I didn't sign the job off and walked pretty soon after. Please do something about this before you either get caught out or something much worse happens. Just remember that the first thing your employer will no doubt do should a problem ever arise is point to YOUR signature on the test records and say "but you signed this ...."

 

[ban-all-sheds]

However you reconnect the bonds before reapplying power to safely measure Zs.

Not everyone agrees with that: http://www.iee.org/forums/forum/messageview.cfm?catid=205&threadid=6173

 

[TraineeSpark]

thanks all 4 replies. Another thing they all seem 2 do at this firm is, if 4 example doing R1+R2 from shower, take reading from isolator switch as opposed to shower unit itself (quicker 2 disconnect). I know its only a couple of meters difference, but not happy with it. Yeah, i do know the answer, but just wanted 2 further point out how they cut corners. In a week or so time, when i got new job, I will name and shame the firm (maybe)

 

[Adam_151]

In the shower switch situation, if you over esitimate the short length of cable from switch to shower, consult tables as regards to the resistance of it and add it onto the Zs value, then I can't see the problem, afterall a similar method is emplyed to deal with temperature factors (the 75%/80% rule of thumb for Zs) and if you have a high impedance connection on your shower, I maintain that you'll have bigger problems than a bad Z's

 

[TeesdaleSpark]

I can't see the problem, afterall a similar method is emplyed to deal with temperature factors (the 75%/80% rule of thumb for Zs) and if you have a high impedance connection on your shower, I maintain that you'll have bigger problems than a bad Z's

R1+R2 measurement is also to check polarity and to confirm that the shower is earthed - if you do it at the isolator you don't know that it OK.

More often than not it's easier to take R1+R2 at the shower than at the isolator. Many showers even only have one screw. Problem I've often come across is the lid fixing is broken and someone has used a wood screw to connect the cover to the base just screwing into the plastic of the base.