2 Questions

[iamgary25]

Hi all

I'm using a fluke multimeter and when i test insulation resistance i get a reading of about 300Mohms on a cooker circuit but if i disconnect the cooker switch and link the cable straight to the cable going to the cooker connection unit (no cooker connect) i get >500Mohms. so is it ok that the switch lowers my reading?
BTW this is a new circuit. Also on the ring finals the tester goes from 350ish to >500... whats that all about?

Next question...

I have a metal CU and SWA going to an outbuilding with a metal CU but i'm going to TT the building. Which means there will be a parallel earth i guess this is perfectly acceptable?

Thanks in advance

 

[davesparks]

How long did you apply the IR test for?

As for the second part, guessing isn't really a good way to do an electrical design, try referencing some regulations instead. But if you are going to guess I'd say you should guess again!

 

[iamgary25]

5 to 10 seconds or so...

and yer thanks for the help...

 

[tomspark93]

1. I wouldn't be reading in to it too much 350M ohms is still a very high reading and would be no cause for concern even on a new build. Think about resistors in parallel, that's all it may be.

2. If your TT'ing the sub main then I would consider earthing the armour solely from the TN end where it will be supplied from and then either installing an insulated consumer unit in the outbuilding and not using a fly lead at that end OR glanding in to an adaptable box first and then feeding in to your metal CU from there. How come you are favouring a TT Earth for the outbuilding anyway?

 

[Deleted member 26818]

Not sure what you mean by parallel earth?

 

[Simonslimline]

Hi all

I'm using a fluke multimeter and when i test insulation resistance i get a reading of about 300Mohms on a cooker circuit but if i disconnect the cooker switch and link the cable straight to the cable going to the cooker connection unit (no cooker connect) i get >500Mohms. so is it ok that the switch lowers my reading?
BTW this is a new circuit. Also on the ring finals the tester goes from 350ish to >500... whats that all about?

Next question...

I have a metal CU and SWA going to an outbuilding with a metal CU but i'm going to TT the building. Which means there will be a parallel earth i guess this is perfectly acceptable?

Thanks in advance

Plenty of older threads on this subject. Have a search.

 

[iamgary25]

The steel on the SWA i mean... i know you shouldn't connect the CPC conductor at both ends but i've been told by some people to bond at both ends and just one end by others which means it shouldn't matter if the CU is metal or not? i'm just asking for more advice. And the outbuilding is about 70 something meters away. Hope this clears up my question

 

[Simonslimline]

The steel on the SWA i mean... i know you shouldn't connect the CPC conductor at both ends but i've been told by some people to bond at both ends and just one end by others which means it shouldn't matter if the CU is metal or not? i'm just asking for more advice. And the outbuilding is about 70 something meters away. Hope this clears up my question

Maybe get an electrician in if your not sure.

 

[iamgary25]

Plenty of older threads on this subject. Have a search.

I did, didn't find anything, so posted a new thread, i don't post oftern... oh and thanks for your help

 

[iamgary25]

Maybe get an electrician in if your not sure.

Ah i see what you did there

 

[Deleted member 26818]

When you TT the outbuilding, neither the CPC or the armour should be connected at the outbuilding end.

 

[iamgary25]

When you TT the outbuilding, neither the CPC or the armour should be connected at the outbuilding end.

ok, i agree with this... but it will be glanded into a metal CU will this matter? or as tomspark93 said, i should connect it into an adatable box?

thanks

 

[Leesparkykent]

ok, i agree with this... but it will be glanded into a metal CU will this matter? or as tomspark93 said, i should connect it into an adatable box?

thanks

what do you think? Are you an electrician?

 

[Simonslimline]

Have a look at this.




http://www.cmp-products.com/uploads/documents/768da3b3b0734472a7ed7c0ae57301f9-1591.pdf

 

[Deleted member 26818]

You can connect into a plastic adaptable box, use an insulating (plastic) gland into the CU, or I have seen the gland made off into a kind of bracket with just the Line and Neutral then taken to the CU.