Consumer Unit Change

[Nickj]

Hi All,

I am tomorrow going to be changing a consumer unit ahead of my Elecsa assessment next week.

Just wanted to check that I'm not missing anything with regards to amendment 3.

I'm going to be using a BG consumer unit supplied with RCBOs.

It has a cut out at back for cable entry and so I am going to pass all cables through that using a grommet strip around the metal edges. Do I need to seal the entry hole? I believe not however I have heard arguments that it needs to be sealed. Passing all cables through the rear entry may require de-rating cables due to grouping however the cables enter the current board (3036's) through the rear. Can i therefore assume ratings are fine?

I am going to attach the consumer unit to the wall using dewalt wall dogs which require no anchor in wall meaning I don't have to worry about plastic wall plugs falling out in the event of a fire.


If the cables are too short (I sincerely hope they won't be) I'll use an adaptable box above the board to mount a din rail to extend wiring. Does this adaptable box need to be non-combustible too? (associated switch gear covers this possibly?)

Thanks in advance

Nick

 

[Pat H]

The argument for the earth being with the live conductors is that in a fault condition current will flow in the earth and if separate eddy currents will flow. However in a fault condition the small time the current flows won't be enough to generate enough heat to be of concern.

 

[Risteard]

Given that the minimum insulation resistance is for the installation I would prefer to measure all circuits in parallel. Also BS7671 DOES require the Earthing conductor to be collectively surrounded with the live conductors where entering a ferromagnetic enclosure.

Recording the individual circuit readings is the best way to go ..... because if you called back later for, say tripping, you can compare readings to see if any have changed.....

There is NO requirement to bring the main earth through the same aperture as the tails..... so don't waste your time making the call. There are special glands that allow you to bring the tails and earth together but that's a "nice to have" .

 

[Nickj]

A global ir with rcbos would be difficult to achieve since the test would pick up the rcbos?

I was always taught to test each circuit separately.

It seems I'm going to have to call elecsa regarding the main earth and it seems highly likely that tomorrow I'm going to have to tear the install apart to route the main earth through the rear entry with the tails.

Not what I wanted to hear, I'm stressed enough as I is without having to tear apart the work I did

 

[Pat H]

You could leave it as it is. Discuss with the assessor and based on his input decide if re-routing the earth is required.
You don't want to do all that work for him (or her) to say it wasn't an issue.

 

[Risteard]

It may be impracticable with RCBOs but then you need to consider the effects of resistances in parallel through calculation to verify compliance.

A global ir with rcbos would be difficult to achieve since the test would pick up the rcbos?

I was always taught to test each circuit separately.

It seems I'm going to have to call elecsa regarding the main earth and it seems highly likely that tomorrow I'm going to have to tear the install apart to route the main earth through the rear entry with the tails.

Not what I wanted to hear, I'm stressed enough as I is without having to tear apart the work I did

 

[Octopus]

It seems I'm going to have to call elecsa regarding the main earth and it seems highly likely that tomorrow I'm going to have to tear the install apart to route the main earth through the rear entry with the tails.

Suggest you read 521.5.1 (BYB) again... first sentence ends "are contained within the same enclosure".... then the 2nd sentence says "where such conductors enter a ferrous enclosure, they shall be arranged such that the conductors are only collectively surrounded by ferromagnetic material"

Which is a loads of gobbledygook!

The muppets who write and update BS 7671 should have reviewed such regs when the AMD3 CU's were introduced.....

IMHO I don't think you should pull anything apart..... before your assessment, if and I say if you get pulled up on this, have your decision making criteria rehearsed. If the assessor disagrees get him to spell it out why he thinks the L, N and E should be together when entering a metal CU. You do get time to correct any issues....

I've said this on many times, BS 7671 should be submitted to the Plain English Society, and be reviewed BEFORE the next amendment as the whole document is littered with such issues.... that's what happens when many people write single documents - for the best example look no further than the Bible.

 

[westward10]

Don't even bring it up, unless the assessor questions it.

 

[Nickj]

Thank you. If I left it as it is and the assessor didn't like it even after a discussion then would that result in a re-assessment or would I be given the time to alter it and submit photographic evidence that it has been altered after which I'd be accepted?

Not entirely sure what to expect. I know it can be an outright fail or there are instances that photographic evidence of corrected non conformance can allow you to be accepted.

 

[Midwest]

If I could rewind a couple of weeks id opt to do a full rewire. So much easier to control every element that way. I have a rewire job lined up for the new year (assuming I can pass Tuesday!).

Murdoch if questioned by an assessor how would you answer 521.5.1 with regard to the main earth entering separately?

You could tell a little white lie, and say you rang Tech support, and was given the answer as in #105 of 'that thread'. When I ring tech support, they never ask for you or company name or EPP number. I could be Mrs Miggans from the pie shop, for all they know (no jokes.... please ).

I agree with Murdoch, 521.5.1, in this context, is not clear. MFI use to write better assembly instructions than BS7671 submissions. You could ring tomorrow, if you have time to change it, if tech support rules in favour of the red corner. But don't if its going to take some time. The day would be better spent, making sure you have everything in places, and just get all the basics set up in your head, for the questions you'll get asked.

Think you need to put that to one side for now. Worst case scenario, is your have to have the inspector back for tea & biscuits.

Good luck, and go and have a beer. Resolves most things in my personal experience.

 

[Midwest]

Thank you. If I left it as it is and the assessor didn't like it even after a discussion then would that result in a re-assessment or would I be given the time to alter it and submit photographic evidence that it has been altered after which I'd be accepted?

Not entirely sure what to expect. I know it can be an outright fail or there are instances that photographic evidence of corrected non conformance can allow you to be accepted.

It's difficult to tell from here sat looking at screen, but it appears your approach is quite professional, which I expect would be reflected in your work. Which is the main thing they are after. Doubt if there is anyone on this forum that does everything explicitly as BS7671 says (if you can understand everything it says!).

 

[westward10]

I know it is a bit late but did you try to see if you could pull another earthing conductor through using the old one to pull it through.

 

[Nickj]

That was my original plan of action westward however the old 6mm earthing conductor was packaged with the tails in the form of 2 core and earth.

I then tried to follow the same route as the tails thinking it would be easiest however my rods couldn't get through so I took a different route and used trunking along with fire clips where needed.

Knowing what I know now I could have chased out the final approach and entered through the rear with the rest of cables.

If I redid it that's exactly what I'd do. whether it is worth redoing tomorrow with assessment on Tuesday is quite the dilemma. I could end up with a less neat install due to the constrains than I have now.

I'd like to avoid a reassessment at all costs due to it meaning another 6 week wait for appointment etc.

Damned if I do damned if I don't

 

[Richard Burns]

From the point of view of the assessor, if he asks about this, you have cogent and reasoned statements indicating that you had considered the issues and decided that the situation was safe and compliant with BS7671 as far as you understand it.
If you can state this with the assessor at the time and therefore show that you are competent then this should be acceptable.
If the assessor still decides that rectification is necessary then, because you are already demonstrating competence, a simple photographic resolution should be sufficient.

 

[Pat H]

I agree in the unlikely event the assessor feels the earth needs re-routing and you agree to that change a simple photo by email should be enough. They maynot even need that.

 

[Nickj]

That's a relief. I'll leave it as is and argue my case if it comes up.

Now to find all my paperwork...