UK First consumer unit change.

[Raptor0014]

Did my first consumer unit change yesterday.
A few dodgy things with the old board as I’m sure most will see.

Owner wanted bringing up to date with individual circuit RCD protection and surge protection.

So fitted a Fusebox 10 way RCBO board. Complete with surge protection.

Also removed the bell transformer that was being fed from a hole directly in the side of the CU and put the cooker cable into some conduit as the owner didn’t want it chasing in. I didn’t think it wise to leave it draping over the top of the CU like it was previously!

Any feedback is welcome as I’m always happy to learn from the more experienced amongst the forum.

Only thing I couldn’t seem to rectify is the slight leaning of the RCBOs/Main switch. No matter what I did as soon as I torqued everything up on the busbar it moved slightly.

One of the RCBO was a tad close on testing as you can see on the pic. But a pass is a pass and I tested that both at the board and at a socket (was on a Ring Final).

Anyhoo here are some pics.

 

[MJPD29]

Good job. Better than many do after 30 years.

 

[Flanders]

Do you mean that, it test the RCD, but does not test the circuit will be protected by the RCD, or am I missing something?

Yes you only need to test the rcd for the rcd results, that way you get a clean result. The circuit is not relevant for the rcd test

 

[Midwest]

I always RCD test at the end of the circuit. Its a live test, and its a safety device that should be tested in full. If I recall there's some manufactures who recommend testing at source, but I would be more confident testing at outlet. Each to their own.

 

[buzzlightyear]

My nicic test engineer says you don't need to test at the end of circuit just test at source.but always will.

 

[loz2754]

The MEM add on RCD pods, MR30s don't like being tested at the board. They refuse to trip when tested. Apart from these, I always test RCDs at the board, preferably with no load connected.
But I also like to do a test at the other end of the circuit for good measure.

 

[Mike Johnson]

It's an interesting point, testing the RCD to ensure it operates is one thing, but in reality it must be tested with the circuit intact to ensure it does its job from the other end, discuss, perhaps we ought to take this to the Arms?

 

[telectrix]

Dare I ask how you managed to fit the new tails, Isolator already there???

i have 2 alternatives.dependent on the condition of the dNO fuse assembly, and presence of seals.

1.Pull fuse . Still need to cut seals on meter or fit Henlys. .
2. Cut meter seals. ensure no load on installation. remove tails from meter (live). This negates the need to touch the DNO fuse. Safer IMHO. it's how we done it back in the 15th. then a tongue in cheek call to the supplier, say i notice your meter seals are missing.or fit non-standard seals courtesy of ebay.

had one t'other week where meter fitter had broke one of the slots in a meter terminal screw. took ages to rag the screw out using sharp precision sidecutters . new slot made with junior hacksaw. good as new.

 

[Soi disant]

[picky]B40 first on the busbar, not last.[/picky]

 

[Raptor0014]

Not sure I would have that 6.0 on a 40A as it is contained in conduit.

It isn't. The cooker is on a 32a. It is in conduit for approx 1.2m then is clipped direct to the skirting board before chased into the wall to the socket (don't ask, I didn't install it! ?) Total length of the cable is approx 2.5m to the switch then approx 1.5m to the cooker terminal.

I worked out the load as it is a 7.43kw cooker.

So taking diversity into account the 6.0 & 32A is more than sufficient as it is 10A +30% of remainder (22.3a) = 16.69a + 5A for the plug socket on the switch = 21.69A.

6mm in conduit is rated to 38A & 34A once in the wall. So it's well within spec.

The 6.0 40A is supplying the garage and that is clipped direct.?

 

[westward10]

[picky]B40 first on the busbar, not last.[/picky]

Can you give a valid reason for this.

 

[westward10]

It isn't. The cooker is on a 32a. It is in conduit for approx 1.2m then is clipped direct to the skirting board before chased into the wall to the socket (don't ask, I didn't install it! ?) Total length of the cable is approx 2.5m to the switch then approx 1.5m to the cooker terminal.

I worked out the load as it is a 7.43kw cooker.

So taking diversity into account the 6.0 & 32A is more than sufficient as it is 10A +30% of remainder (22.3a) = 16.69a + 5A for the plug socket on the switch = 21.69A.

6mm in conduit is rated to 38A & 34A once in the wall. So it's well within spec.

The 6.0 40A is supplying the garage and that is clipped direct.?

Apologies my error.

 

[Raptor0014]

Very tidy job - well done. BTW looking at first photo of new board did you originally have it too close to the ceiling to get the cover on ;-) Most of us have similar at some point!

I have a Fusebox board sitting here - I'm fitting one tomorrow for the first time.
I'm impressed with it so far. The cover has screw catchers, the knock outs actually knock out, and it feels very solid. It's also a nice size to replace a 6 module rewireable Wylex if space is limited.

I very nearly did. Then luckily had a flash of wisdom.

The board is very nice and good quality. I was impressed with it myself. Just irked my CDO with the slight lean.

 

[Raptor0014]

Dare I ask how you managed to fit the new tails, Isolator already there???

Yes fortunately they had a 100a switched isolator fitted when the DNO fitted a smart meter.

 

[HappyHippyDad]

Very good first CU change @Raptor0014 ! Did you have a moment of worry when you saw hundreds of cables sticking out of the wall, with you the only one responsible for putting it all back together? ? I still remember that feeling from my first CU cjange.

Also very brave to put it online as every minor detail will be examined and criticised, still I guess that is what you want for learning purposes.

@westward does have a good point about the 6mm in conduit though, on a 40A breaker. I'm never too sure which reference method takes preference though when only a very short run is in the more strict reference method.

I will add reg 521.5.1 . I believe the main earth should enter through the same hole into the CU as the line and neutral tails, to negate possible electromagnetic effects. I stand to be corrected though. If I am correct then I will be chuffed that I spotted it before @westward10

 

[Baddegg]

Nice n neat good job ??, with regards the high readings I generally find fusebox pretty consistent with the trip times unless it’s a type A then they get abit close to maximum ?

 

[Raptor0014]

[picky]B40 first on the busbar, not last.[/picky]

That was what I initially intended to do. But the way the cable run had been installed left it with no play and I didn't have time to take the covered walkway panels down, unclip it and see if there was enough play to move the RCBO nearer to the switch.

In reality I doubt the garage would ever pull anywhere near 40A. It's only got sockets and lights at the other end.

 

[telectrix]

Can you give a valid reason for this.

used to be usual to put the highest loads closest to the main switch. the reasoning being that the larger load currents didn't have to travel further along the busbar. no logic behind it, it was realised about 30 yearsa go that the electricity did not leak out proportionaelyt to the length of the busbar and this pracice was stopped along with the old wives tale of "exporting the earth".

 

[Raptor0014]

Nice n neat good job ??, with regards the high readings I generally find fusebox pretty consistent with the trip times unless it’s a type A then they get abit close to maximum ?

They are all type A RCBOs

 

[Baddegg]

They are all type A RCBOs

That’ll do it then....can I ask why type a on lights and cooker etc?

 

[Raptor0014]

Very good first CU change @Raptor0014 !

Also very brave to put it online as every minor detail will be examined and criticised, still I guess that is what you want for learning purposes.

@westward does have a good point about the 6mm in conduit though, on a 40A breaker. I'm never too sure which reference method takes preference though when only a very short run is in the more strict reference method.

I will add reg 521.5.1 . I believe the main earth should enter through the same hole into the CU as the line and neutral tails, to negate possible electromagnetic effects. I stand to be corrected though.

See my other post, it's not in conduit.

Noted ref the earth.

And yes correct, this is why I posted to ensure I continuously improve myself. Nobody is perfect as they say.