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

 

[Nickj]

Hi Guys,

Attached are my forms. Would appreciate it if you could check to see if I've ticked the correct boxes and my results look ok.

One other cause for concern is item 7.7 on the schedule of inspections.

The earthing conductor present before the board change was 6mm and so it needed to be upgraded to at least 10mm (tails are 16mm). I upgraded to 16mm.

I did not realise at the time that the tails and earthing conductor were 3 core.

It was not possible for me to bring the new earthing conductor along the same path as the 3 core cable without a lot of chasing.

I opted to bring the new earthing conductor into the house by a different route aided with trunking and fire clips where needed.

All circuits and tails were chased when installed (some 40 years ago) and entered the old fuse board through the back. I have brought all those cables through the back of the new consumer unit however I could not (without chasing and running the risk of damaging the already installed cabling) bring the new earthing conductor in through the rear.

I have read varying opinions on this with some saying it is ok for the earthing conductor to enter through a separate hole of the consumer unit (with some saying niceic advise that it doesnt apply to meter tails and earthign conductor so long as meter tails L & N enter same hole) and some saying it's not ok and should be noted as a deviation from the regs.

What would you guys do for assessment purposes? Would you enter it as a deviation? Would an assessor accept a deviation like this?

Sincere thanks to you all for the help so far

 

[NDG Elecs]

Hi Nick,

I would not list the main earth coming into the CU by itself as a deviation. I have never heard anyone ever say that it would be. Nor do I understand why it would be. Meter tails should be brought through together on metal enclosures due to possible eddy currents. That is what item 7.7 refers to.

Had a quick look through your cert. Couple of bits I noticed; on schedule of test results polarity is to be ticked. Think you have mistakenly put a megohm figure in mate. Also, as it's all RCBO protected I would expect different values for x1 & x5 tests. Seems to be a lot of 28.8 across the various RCBOs. Also you have not put anything in the "description of installation" box on the first page...I would put new consumer unit and upgrade to main earth and bonding in that box. I would also mention that you carried out remedial works to the RFC CPC due to the end to end value you got.

What are the IR readings? Does that say >2 ?? My test meters highest reading is >299Mohms @500V, which is the value I write down.
And why were some Zs' calculated?

Other than the niggly bits I mention it looks OK with a quick scan.

 

[Nickj]

Hi ndg,

Thanks for scanning over the forms. I too was surprised at all the 28.8s across 3 of the rcbos but they were all tested individually. For lights and heating they were tested at board and for cooker and sockets they were tested at the sockets.

I did indeed miss polarity box, I hope I wouldn't have when I wrote it out as a final copy!

Yes all irs are >2

I picked up on this forum about the main earth needing to come in with the meter tails. regulation 521.5.1. Some say that it doesn't apply to tails, with some saying niceic don't consider the tails with this regulation. quite confused by it all as it's new to me.

 

[NDG Elecs]

OK, fair play re the x1 x5, but test the cooker and sockets at the board to.

Does your meter not go higher than >2Mohms... They normally do.

Maybe I am wrong re the main earth. I thought it was just live conductors only that had to be together or the board slotted. If I am wrong, thankfully I have used the tail glands on all my metal CUs!

 

[NDG Elecs]

Item 7.2 tick! A 60947-3 is a linked switch.

 

[Wilko]

Hi Nick, A few thoughts in addition to NDGs good points.
Meter tails item 7.7 - reg 521.5.1 says (in last part) 'does not preclude the use of an additional protective conductor ... to enter enclosure individually'. To me, the expected method is for line, neutral and protective conductor to enter together. IMHO what you have is functionally safe due to current levels, but may well be questioned. So have a close read of 521.5.1 and be ready to discuss.
Also, I think you might be questioned about IR > 2meg results. It is expected that this be the actual result you measured. A result near 2meg would be widely viewed as needing further investigation. Just saying.
A couple of others to confirm :
Max demand is 35A ?
Metal partitions are ticked in 8.14 ?
Adequacy of working space is blank in 9.4 ?
Hope that helps

 

[Pat H]

IR is normally recorded as the reading your test kit shows not that its above the required resistance.

 

[Midwest]

Lets not have the RCBO/RCD must be tested at the CU debate again.

As regards your 'main earth', have a butchers at this thread if you got a spare half hour;

Advice on regulation 521.5.1 - http://www.electriciansforums.co.uk/threads/advice-on-regulation-521-5-1.103579/

Can honestly say, I'm still confused and I read the thread at the time. Think the OP had it right at #105, as in your case, you using this job as your assessment. So ring your scheme and ask, and whatever they advise, do (IMO)

 

[westward10]

I hope you are going to submit nice neat paperwork and that is your trial run. I believe if your paperwork is untidy this gives an immediate poor impression.

 

[Pat H]

As a slight deviation has anyone re-generated these forms to be easier to use?
The actual layout isn't great and many entry locations are just too small to enter details in a legible way.

 

[Midwest]

I hope you are going to submit nice neat paperwork and that is your trial run. I believe if your paperwork is untidy this gives an immediate poor impression.

Think that's his 'working copy', well I hope so. I use to do that, until I lost a page of test results. Now use a desk diary, harder to lose

 

[Midwest]

As a slight deviation has anyone re-generated these forms to be easier to use?
The actual layout isn't great and many entry locations are just too small to enter details in a legible way.

Are you in a scheme?

 

[Nickj]

Thanks for all the input. I recorded ir as >2 as that's what the electrician I used to work for did. I note your points and will re-record the actual measurements tomorrow (they were all greatly in excess of 2 - none were under 600).

I'll call elecsa first thing tomorrow morning and ask their view. If they want it coming through the back then I'll need to scramble in order to get it done tomorrow as assessment is Tuesday!

Those results are indeed just a working copy. I'll use an electronic system after assessment but that system isn't in place yet.

Nightmare scenario!

 

[Nickj]

To pick up on maximum demand question.

I've put 35A. I came up wih that figure by adding all the breakers together and taking 40% of their total as maximum demand.

I see maximum demand done in so many different ways and I see different opinions on it.

Some say add all breakers and put that result regardless of whether it's greater than main fuse (an approach I'm not keen on?)

Some will use osg and put that figure.

Some use the 40% rule.

I have 32a ring (no diversity can be applied)

32a cooker circuit (I think I worked it out at 27a using diversity)

16a heating (no diversity allowed if immersion - unsure if there is one, then unsure how to calc if there isn't one)

6a lights - 8 lights in house, allow 100w per light so 800w, 3.5a.

Adding all that is greater than 60a.

What would you guys put?

 

[Octopus]

Thanks for all the input. I recorded ir as >2 as that's what the electrician I used to work for did. I note your points and will re-record the actual measurements tomorrow (they were all greatly in excess of 2 - none were under 600).

I'll call elecsa first thing tomorrow morning and ask their view. If they want it coming through the back then I'll need to scramble in order to get it done tomorrow as assessment is Tuesday!

Those results are indeed just a working copy. I'll use an electronic system after assessment but that system isn't in place yet.

Nightmare scenario!

IMHO thats a terrible way to do it and train you!

I can only assume that he did a global IR to achieve such numbers but in reality its a very unhelpful way of doing it when doing a CU change and introducing RCD's.

I always test IR before using a global measure (as a check) but then as the new CU takes "shape" I connect ALL the CPC's to the CU and test all the circuits individually L-N, L-E and N-E - that way you will see the "real" situation in the install.

It would seem that many people do the global IR as L&N to earth, which is simply lazy - the only way to check the installation IR properly you need to isolate as many of the appliances as possible......

As an example I did a global IR recently and got really terrible L&N to E readings - so went round unplugging as much as possible and then found it was 1 circuit in particular - further searching revealed a RCD FCU in the back of a cupboard - so this was swapped for a std unit and the readings improved dramatically