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

 

[Risteard]

(associated switch gear covers this possibly?)

Given that an adaptable box and connectors aren't switchgear of any sort they certainly couldn't be a similar switchgear assembly.

 

[Pat H]

Metal not plastic CU I hope.

 

[Nickj]

Hi Pat, Yes it is indeed a metal consumer unit. Is there a need to seal the rear cable entry or is it ok not sealed?

If I need to extend the cabling does the adaptable box need to be metal too?

Can you see any other flaws in my plan of action?

Really nervous about assessment

 

[Pat H]

If the CU is flush with the wall then it should be fine. Regs state the penetration for top sides etc but not back.
If you need a box above then thats not a CCU so not metal but if you have an entry from that to the CCU then a fire in the CCU would spread up and out so I'd look at a seal between them or use a metal box.

 

[Nickj]

Thank you very much, I am sitting here questioning everything, including myself, I hate assessments

 

[westward10]

I personally would extend conductors within the CU to save another enclosure.

 

[7029 dave]

Hopefully, you will have slack to re term, if not as westie said, extend in CU.

 

[Wilko]

Hi Nick,
Honestly I hadn't thought about plastic wall plugs failing in a fire. I'm hoping as they are covered by a non combustible shield (the CU) they will be fine. I am interested to hear other views ...

A few thoughts/reminders, hopefully helpful

All Labels attached
Periodic test (I tend to put 5 yrs), RCD test, circuit ID (ID the fire alarm), Main Switch, Circuit Details, the 2 versions wiring colour warning (if needed) ... could there be more?

Tails
Good neat job, using tails gland (doesn't have to be metal, I reckon) using internal clamp to secure them (if provided) and keep all insulation on right up to iso switch.

Testing
Allow time for testing the installation. The more thorough and complete you can be with your testing and the certificate the more confident you will feel during interview. And the less they can ping you.

Cheers.

 

[westward10]

Plastic wall plugs into believe are fine as the brickwork will act as a heatsink, well that is what I heard.
Me being fussy use 2.0 bore green/sleeving cos it looks much neater and fits all T&E up to 6.0.
Good luck with it all, don't doubt yourself they will not be trying to catch you out.

 

[Nickj]

If I extend within the consumer unit am I ok to use wagos where possible and then terminal blocks for the cooker cable? (wago don't go high enough unless I use their din mounting stuff).

Tails will be coming in through rear of CU as well (as they currently do). Looking at the picture of CU it has one large knockout at the back.

De-rating aside (I assume I'm fine not to consider de-rating as entry is same as current board?) it's ok for all cables, including tails to come through the one provided rear knock out without the use of glands etc? (I'll use a grommet strip to ensure cables can't be da,he'd from metal)

I have all the labels ready to go and I'm not too worried about the testing side of the assessment as so far not struggled with testing. It's the smaller regs stuff that I'm afraid I've missed.

 

[Pat H]

You can't assume the current grouping and derating is compliant.
I'd do some calcs myself. If unsure detate the breakers.

 

[westward10]

Not a lover of Wagos on a board change, crimps much neater but ensure the green/yellow sleeving in entered into the crimp.

 

[Nickj]

Pat, I was under the impression that as long as the circuits test safe they can be re-energised in a new consumer unit. I was under the impression that I needed to make sure that my work (the replacement of CU complied) and that I didn't need to ensure ratings were correct for the pre-existing circuits.

I didn't install the circuits and so it's difficult for me to ascertain how they've been installed...

I'm happy to be proven wrong here however and would like to see what others have to say?

 

[Nickj]

Westward how do you go about crimping solid core? I love crimping but have stopped crimping solid core due to it not being as strong a connection as I once thought :S

 

[Pat H]

I believe thats true. I just prefer to do some rough calcs. Normally possible to get a rough idea of runs and lengths. Zs of cables will give an indication as well.
If that looks ok then fine. I wouldn't sweat too much on the short local group into the CCU

 

[westward10]

Have you previously tested the installation.

 

[HandySparks]

... and then terminal blocks for the cooker cable? (wago don't go high enough unless I use their din mounting stuff).

Wago 773-173 Push Wire Connector 2.5mm - 6.0mm 3 Pole - https://www.tlc-direct.co.uk/Products/WA173.html

De-rating aside (I assume I'm fine not to consider de-rating as entry is same as current board?)

With de-rating due to grouping on domestic, I wouldn't disregard completely. However, generally the typical loading on circuits will be well within the capacity of the cable. Heavy loading, eg showers, will only be of short duration. Two exceptions might be if the place is lit entirely by dozens of 50W GU10s or for storage heaters and immersion heaters, which are pulling full load for an extended period of time.

Another indication is whether the cables show signs of overheating at the grouped location.

It's better to show that you've considered the situation and deem it acceptable, rather than ignored the issue completely.

 

[Pat H]

I'd agree. Do the maths do the visual inspection. Be happy you can show you've considered those elements.

 

[westward10]

Westward how do you go about crimping solid core? I love crimping but have stopped crimping solid core due to it not being as strong a connection as I once thought :S

I use crimps and Wagos, stick with what you are happy with. if you use Wagos tuck them behind the breakers to keep it tidy.