TT earthing arrangment and CU

[sparky1508]

Hi all,

Would it be possible to get a little advise from the guys.
I have today been to look at a job whereas there is a TT earthing arrangement with no 100ma time delayed RCD on the incoming tails so that is the first thing that needs to be done but the question is, the existing CU has a 30ma main switch RCD. Am I correct to think that this should be changed for a split board with 2 RCD's as well as the installation of the main 100ma RCD. All advice is appreciated.
Cheers

 

[saspm]

Some people replace the consumer main switch with a 100ma RCD the last one I did, I didn't bother and it was used in an assessment visit and they were happy about it. Also speaking to NICEIC help line they also seem to think it is ok without.

 

[Octopus]

Why do you think the CU needs any changes? What are you quoting to do?

 

[sparky1508]

I was asked to take a look as a British Gas engineer had pointed out a couple of issues.
1/ No 100ma RCD before the CU.
2/ does the consumer unit need changing to meet regs

I have been out to the property this evening and I have seen that there is no time delayed RCD and there is only 1 30ma RCD on the whole CU.
I haven't quoted anything yet as I want to make sure that I advise the customer properly so I am not doing work that is unnecessary and also charging the customer for this work also. I'm no cowboy.
So my main concern is that it only has 1 RCD in the CU.
should this have a split board or is the existing board ok as long as I put the 100ma RCD on there.
I suppose I could even swap out the existing main switch and replace it with a double pole RCD.

 

[Leesparkykent]

Why does it need a 100mA time delayed RCD if there is a 30mA already in place?

 

[freddo]

It doesn't sound like anything needs to be done from your description. Section 3 of the on site guide gives suggested consumer unit arrangements. Having one 30mA RCD covering all circuits is not very convenient. But during an inspection I would only note it down as a code 3. I certainly wouldn't be concerned in this scenario. Why is a 100mA RCD required before the 30mA RCD main switch? Is the consumer unit remote from the supply position?

 

[westward10]

Have British Gas done a Periodic on it.

 

[Octopus]

I was asked to take a look as a British Gas engineer had pointed out a couple of issues.
1/ No 100ma RCD before the CU.
2/ does the consumer unit need changing to meet regs

1, So what
2. No

 

[Dave OCD]

BG may have been over cautious here I think.

 

[Octopus]

Have British Gas done a Periodic on it because they are notorious for highlighting issues that don't actually exist or simply incorrectly coding issues

Edited that for you

 

[sparky1508]

Thanks Guys,
Well, maybe the british gas engineer and my understanding of a TT arrangement are misunderstood as I was under the impression that a TT arrangement required a 100ma RCD.

 

[sparky1508]

So, if I can just get this straight. the BG engineer is incorrect and no work is required as the CU is protected by a 30ma RCD.

 

[westward10]

Have British Gas done a Periodic on it

 

[Octopus]

If you are doing a fuseboard change, or a new install then you would adopt, perhaps, a different approach.

Going round advising people to update CU's is simply going to alienate potential customers.

FWIW there are so many homes, on TT supplies, with good old BS3036 CU's...

 

[westward10]

Careful Westward, if BG see that and take exception I'm sure they have fancier lawyers than you, just saying...

Ammended

 

[Dave OCD]

Mine too.

 

[sparky1508]

If you are doing a fuseboard change, or a new install then you would adopt, perhaps, a different approach.

Going round advising people to update CU's is simply going to alienate potential customers.

FWIW there are so many homes, on TT supplies, with good old BS3036 CU's...

I have done work on TT supplies with the good old BS3036 CU's and all have 100ma RCD's installed before the board.
That's the reason I am asking besides the fact that the BG engineer said the same thing.

 

[westward10]

So, if I can just get this straight. the BG engineer is incorrect and no work is required as the CU is protected by a 30ma RCD.

Yes. Before Amm 3 of BS7671 if you used a CU with a metal enclosure on a TT it was frowned upon and a separate rcd could be fitted to provide fault protection to the enclosure.

 

[sparky1508]

Yes. Before Amm 3 of BS7671 if you used a CU with a metal enclosure on a TT it was frowned upon and a separate rcd could be fitted to provide fault protection to the enclosure.

This is a plastic consumer unit, 8 way, 3 spare with 1 30ma main switch RCD.

 

[Octopus]

Why is the BG engineer telling you about this?