IR Testing - Whole Consumer Unit....?

[Jamie]

Hi,

It says in BS7671:2008(2011) Page 95 10.3.3 ii that "When testing simple installations, i.e. those consisting of one consumer unit only, the installation could be tested as a whole with all fuses in place, switches and circuit beakers closed, lamps removed and other current-using equipment disconnected"

So this means there is no maximum to how many circuits are in this "consumer unit" and no limit to how many can be tested at one point??

This means I could go into a house for example, with one consumer unit and test this way, because to me a domestic 10 way board is a "simple installation"...right?

What's the maximum amount of ways in a C/U before sparky's start to class it as not a simple installation??!?!

(I test each circuit individually, but I would like to know this as it is very grey area and doesn't make a lot of sense, why test each circuit when it says this!)

Thanks
Jamie

 

[Octopus]

I wouldn't go doing global IR's on boards with RCD's or RCBO's

 

[Plonker 3]

No such thing as a "simple installation". You could only do a global IR test on a new install where you knew every electrical point on it as any other install could have sensitive equipment or other appliances still connected that you are unaware of.

 

[HandySparks]

if you do a global IR on a board and get a reading of, say, 100Mohm, you know that each final circuit will be better than this and testing individually won't really give you any worthwhile additional information. Obviously, if you do a global test and the result is, say, 2Mohm, you might want to investigate further to identify the poor circuit(s).

 

[R G]

Global IR testing is fine for preliminary testing such as fault finding or reassurance if needed , but deffo not with RCDs on the board and care has to be taken with any equipment still connected to the circuits , remember this is only for initial verification purposes, you would still need to test individual circuits as per the test schedule either for installation certs or EICR

 

[7029 dave]

Global testing has its place, as Ray described,all as above.

 

[Engineer54]

if you do a global IR on a board and get a reading of, say, 100Mohm, you know that each final circuit will be better than this and testing individually won't really give you any worthwhile additional information. Obviously, if you do a global test and the result is, say, 2Mohm, you might want to investigate further to identify the poor circuit(s).

You couldn't be more WRONG!!

 

[HandySparks]

You couldn't be more WRONG!!

OK, on a 230V installation. I do a global IR on 10 circuits and get 100 Mohm. Then I do individual IR testing and get a range of values from 120 Mohm to 450 Mohm. What action would you take as a result of obtaining the additional figures?

 

[Guest111]

OK, on a 230V installation. I do a global IR on 10 circuits and get 100 Mohm. Then I do individual IR testing and get a range of values from 120 Mohm to 450 Mohm. What action would you take as a result of obtaining the additional figures?

think resistances in parallel,that's why you'd get a difference between a global IR test and individual circuits,thats why it's best just to do a global for initial checks and fault finding.

 

[HandySparks]

think resistances in parallel,that's why you'd get a difference between a global IR test and individual circuits,thats why it's best just to do a global for initial checks and fault finding.

Resistances in parallel, OK, I understand that. But if you've already determined that all final circuits have an IR of at least 50 times the required value, what is the merit in proving that some of them are actually, say, 100 times the required value?