GN 3 Queery....

[PEG]

Bit sad but i was just reading through my recently purchased latest edition GN 3 and on page 41,Figure 2.4b,it shows an example of an insulation resistance test of a final circuit. It states "main switch off","circuit breakers on" which means its still testing the "whole consumer unit" as shown in previous diagram 2.4a. They use a very similar set of diagrams in the OSG,but do show the circuit breakers as "off" even though they swop terminology as in ON/CLOSED and OFF/OPEN. I'm fully ready for "you've got it upside down,dipstick!" but it was an expensive journal and i feel used...mg_smile:

 

[SJD]

Both diagrams show the small representations of the circuit breakers as ON / CLOSED, I guess it is just a correction in terminology to use on/off consistently. However, the GN3 text says that this is an example of testing a single final circuit, but in fact it is testing them all. Looking at my older GN3 (2008 version), the circuit breakers are all off, i.e. tested singly. Looks like they decided to recommend testing all together but forgot to change the main text?

I have to say it is disappointing to see these sort of errors (there are others) and it is hard to believe just how long it took to update the document to 2011 with not many changes.

 

[SirKit Breaker]

Typical IET terminology, you only need to glance over the regs, and they are just as bad, if not worse! Some of the clangers in the regs would be good enough to go in the top tips in VIZ!:biggrin5:

Cheers..............Howard

 

[terminator]

Yes, it's open to confusion! In the GN3 they do mention (under Note 1) that 'the test should be initially carried out on the complete installation', but show the example 2.4b as 'insulation test of a final circuit' - which as you note, is actually testing all circuits. I wonder who proof read these books - there is no room for mistakes or ambiguity.

Personally I prefer the use of Off instead of Open and ON instead of Closed. I have had apprentices confuse that because of the common practise of expaining electrical theory with the analogy of water and plumbing systems. Whereby Open in plumbing means flowing and Closed means isolated.