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?

 

[Guest111]

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?

As others have said,when filling in a cert you need a value of each individual circuit.

 

[HandySparks]

As others have said,when filling in a cert you need a value of each individual circuit.

Guidance Note 3, Inspection & Testing, Sixth edition, page 40, Section 2.7.7 Initial testing, Insulation Resistance:

"Simple installations that contain no distribution circuits should preferably be tested as a whole..."

"To perform the test in a complex installation it may need to be subdivided into its component parts."

 

[Engineer54]

Guidance Note 3, Inspection & Testing, Sixth edition, page 40, Section 2.7.7 Initial testing, Insulation Resistance:

"Simple installations that contain no distribution circuits should preferably be tested as a whole..."

"To perform the test in a complex installation it may need to be subdivided into its component parts."

The whole idea behind reporting/recording IR values on initial certificates and subsequent electrical reports is to monitor any detrimental trend changes. How are you going to know what circuit, in a 10 circuit installation has a downward trend?? To be honest i would not classify a domestic installation with 10 circuits as a ''Simple installation'', that would be reserved for CU's with ''4'' circuits. It's pure laziness not to measure IR values for each circuit, and as far as i'm concerned it would be a viewed as a pretty much worthless piece of paper....

 

[R G]

The only thing I can think off that you can apply it to is maybe a switch fuse supplying a single circuit , i.e. a radial circuit ,that you could apply it too as final results maybe

 

[HandySparks]

The whole idea behind reporting/recording IR values on initial certificates and subsequent electrical reports is to monitor any detrimental trend changes. How are you going to know what circuit, in a 10 circuit installation has a downward trend?? To be honest i would not classify a domestic installation with 10 circuits as a ''Simple installation'', that would be reserved for CU's with ''4'' circuits. It's pure laziness not to measure IR values for each circuit, and as far as i'm concerned it would be a viewed as a pretty much worthless piece of paper....

OK, I'm not saying that IR testing of individual final circuits is wrong. In fact, more often than not, I end up testing individually because of a poor global IR and the need to identify the offending circuit. (And, on a new installation or replacement CU, where individual testing is easy, I'll do it anyway.)

As far as comparison with previous results goes, since you mention domestic work, how often do you think that the previous results are made available? In my experience, it's once in a blue moon.

 

[Engineer54]

OK, I'm not saying that IR testing of individual final circuits is wrong. In fact, more often than not, I end up testing individually because of a poor global IR and the need to identify the offending circuit. (And, on a new installation or replacement CU, where individual testing is easy, I'll do it anyway.)

As far as comparison with previous results goes, since you mention domestic work, how often do you think that the previous results are made available? In my experience, it's once in a blue moon.

That is not a reason for NOT conducting circuit by circuit IR testing, at least YOUR test report will available for comparison with any future test reports being conducted at the property....

The ease of testing a circuit, should not form the basis of whether or not tests are correctly conducted or not!!

 

[GLENNSPARK]

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

thats why you IR at 250V first....

once its clearness has been verified...then you zap it at 500V...

 

[GLENNSPARK]

OK, I'm not saying that IR testing of individual final circuits is wrong. In fact, more often than not, I end up testing individually because of a poor global IR and the need to identify the offending circuit. (And, on a new installation or replacement CU, where individual testing is easy, I'll do it anyway.)

As far as comparison with previous results goes, since you mention domestic work, how often do you think that the previous results are made available? In my experience, it's once in a blue moon.

or parrallel paths...

 

[HandySparks]

or parrallel paths...

Care to explain?

 

[R G]

thats why you IR at 250V first....

once its clearness has been verified...then you zap it at 500V...

I do that anyway , but still a bit wary of anything not isolated , (old habits)