Earthing Metal Back Box?

[Damian30]

Hi All,

I had an electrician around last week to do a few jobs, including extending an existing ring into a conservatory. Customer service was pretty low and although had all the badges, there were a few statements which made me a little concerned (e.g. you can't get 10 amp fuses for a spur that needed one).

Anyway, we had previously agreed for an accessible joint where the break into the existing ring would be, covered by a blank plate. I asked whether he would earth the back box and he said that it would affect the reading when he tested the extended ring, so he didn't. I would have thought he might have done it after the testing but as you can see from the picture below, the earth terminal in the box isn't being used. I would have though that a bit of sleeved 2.5mm copper from the box to one of the earth block connectors would be good practice.

Do you agree? I also had a MK Grid switch setup also wired up and this back box also isn't earthed. Wouldn't be a big job for me to correct this but just checking it is the right things to do.

Any thoughts much appreciated.

Many thanks,

Damian

 

[PrenticeBoyofDerry]

Good practice yes, why it would affect tests results I do not know?
And a 10A fuse for what exactly? And why can one not be sourced if needed?

 

[deadshort]

I would earth the box, as it is a joint box and there is no earthing bridge on a blank plate.


DS

 

[sparkwright]

As DS says, the back box for the joint ought to be earthed.

On a socket it's not so vital, as the earth bridge described by DS provides an earth to the box via the fixing screws.

The grid switch doesn't necessarily need it's box earthed, but the metal yokes in which the switch modules are fixed to DO need earthing.

 

[Damian30]

Thanks - absolutely agree chaps, I will get sorted. Shame my electrician didn't think the same!

 

[JohnW2]

The grid switch doesn't necessarily need it's box earthed, but the metal yokes in which the switch modules are fixed to DO need earthing.

I certainly agree with the second bit, but surely a metal back box of a grid switch needs to be earthed just as much as does the metal back box of any other accessory? ... or are you perhaps saying that, although the box needs to be earthed, it doesn't have to be earthed 'directly', since it will get earthed by its connection to the grid plate/yoke?

Kind Regards, John

 

[ban-all-sheds]

Not if fitted by an electrician who doesn't see the need to connect a cpc to any terminals marked with an earth symbol.

Or who thinks he can't because it will affect his test results.

 

[securespark]

I don't see why he didn't use the earth terminal in the back box to join the CPC's

 

[sparkwright]

The grid switch doesn't necessarily need it's box earthed, but the metal yokes in which the switch modules are fixed to DO need earthing.

I certainly agree with the second bit, but surely a metal back box of a grid switch needs to be earthed just as much as does the metal back box of any other accessory? ... or are you perhaps saying that, although the box needs to be earthed, it doesn't have to be earthed 'directly', since it will get earthed by its connection to the grid plate/yoke?

Kind Regards, John

Yes, that's what I'm saying.

Assuming the grid switch has earthed metal yokes, then the back box earthed via the fixing screws.

Exactly the same way as a socket provides earth to the back box.

Obviously a fly-lead between the two is more preferable.

 

[Jackrae]

On the plus side - he did make a neat hole for the box

 

[DaveHerns]

Why are there 5 connectors when you'd expect just 3?

 

[bubachuba]

Why are there 5 connectors when you'd expect just 3?

I was thinking the same Dave. Looks like the CPC's are not connected

 

[OwainDIYer]

Why are there 5 connectors when you'd expect just 3?

because the ring is being extended, not spurred.

L & N ring in
L & N ring out
E

although I think there's a 6th hiding at the top left. possibly the E is separate for In and Out and the electrician thinks that earthing the back box will disrupt his end-to-end tests on the E.

 

[Jackrae]

There's another brown wire hiding somewhere (on the basis that two blues requires two browns)

 

[ban-all-sheds]

Why are there 5 connectors when you'd expect just 3?