leccy shower earthing.

[nickso]

whats the standard size of earthing for the isolation switch (its got its own rcd) of an electric shower?

the one coming out of the rcd and attaching to the main cable earth post is pitfully small in my house.

 

[JohnD]

If you mean the RCD has a thin white earth wire, it is only to operate the RCD in certain kinds of fault detection. Otherwise, RCDs do not have an earth, so the earth wire should bridge past them.

If you don't mean that, where does the earth wire you mean, go from and to?

 

[GaryMo]

Is this a separate 1 way RCD protected consumer unit? Are you talking about the size of the main earthing conductor which feeds this 1 way consumer unit?

Can you give us any more information, maybe a picture?

 

[nickso]

i can certainly get a picture of the offending earth wire. ill take one tomorrow.

basically i have an electric shower. it has its own isolation/rcd/mcb ( sorry im not clued up on leccy terms). there is an earth wire that runs from this seperate isolation back to an earth post that then terminates at the mechanical protection for the main cable coming into the house. this earth wire is very small....approx 1/1.5mm sq.

ill post up a piccy tomorrow.

 

[nickso]

the offending wire is the smallest green/yellow wire you can see in the pic. it seems to be the only earth for that isolation switch. is that right?

 

[RF Lighting]

All the earth wires in your photo look too small TBH.

There should be a 16.0mm² earth from the supply head to the MET (main earthing terminal) and then a 16.0mm² to each CU.

There should also be a 10.0mm² from the MET to each incomming service to your property (such as gas and water supplies), which I am not sure if they are present.

The current earth supplying your shower CU appers to be 1.5mm² which is woefully undersized. I also notice your shower does not have RCD protection, which whilst it is not a regulation to have, it ceartaint really is a good idea, and vitually all electricians install it as standard.

 

[nickso]

All the earth wires in your photo look too small TBH.

There should be a 16.0mm² earth from the supply head to the MET (main earthing terminal) and then a 16.0mm² to each CU.

There should also be a 10.0mm² from the MET to each incomming service to your property (such as gas and water supplies), which I am not sure if they are present.

The current earth supplying your shower CU appers to be 1.5mm² which is woefully undersized. I also notice your shower does not have RCD protection, which whilst it is not a regulation to have, it ceartaint really is a good idea, and vitually all electricians install it as standard.

i was thinking of getting a sparky to upgrade the whole sheebang soon as the house is a 1960's effort and all the wiring is original.

a few q's if you will (please excuse my ignorance):

1) whats a CU?
2)is the MET the metal earth posts that are clearly visible?
3)whats a supply head?
4)i thought the red switchy thing was an rcd for the shower? the black switchy thing on the same isolator looks like an mcb too...je suis tres confused

i installed the central heating myself and all the pipework is bonded bar the gas pipe which is long overdue to be bonded back to the shiny earth post that you see in the piccy. i put the shiny one on last week which is why i noticed the undersized wire in the first place. what size is normal for a shower earth back to the main earth?

 

[Adam_151]

1) whats a CU?

CU= Consumer Unit, or distribution board, board, or fusebox if you prefer

2)is the MET the metal earth posts that are clearly visible?

Yes, MET = Main Earthing Terminal, it would be preferable to just have the one, 8 way ones are abaleable

3)whats a supply head?

The big black thing that has the suppliers incomming cable going into it and contains the main fuse, it is the property of the supplier

4)i thought the red switchy thing was an rcd for the shower? the black switchy thing on the same isolator looks like an mcb too...je suis tres confused

The red switchy thing is indeed just that, a red isolator switch, it could easily be swapped out for an RCD though, the black thing next to it is indeed an MCB

EDIT: hole on the top of the shower CU: someone hasn't even tried, it should be closed up to IP4X (Protection from entry by tools, wires, etc., with a diameter of thickness greater than 1.0mm. )


Should have 16mm² from MET to each CU, and 10mm² main bonds

 

[nickso]

so if i were to replace all of the existing bonds to 16mm for the two CU's and 10mm for the pipe bonding to the gas/water supplies everyone would be happy? and of course change the MET's for a larger single one.

 

[briwire]

To cover all regulations, just fit 10mm earth wire from your MET to each consumer unit.

It's all about the speed at which an earth fault will trip the protective device, fuse, MCB RCD. A small cable will have a higher resistance than a larger cable so may take longer to trip if a fault occurs.

A fuse and MCB will trip if its currnet rating is exceeded, The more it is exceeded the faster it will blow or trip. But a fuse or MCB of say 30 A rating will allow 40A to pass for a few minuted before blowing or tripping, so the earth cable has to be big enough so that any earth fault will allow a big fault current to flow, tripping the protective device within the specified 5 seconds for a fixed appliance.

An RCD works on a different principle. If there is no fault, an appliance will have say 10A flowing into it via the live and 10A flowing out of it via the neutral. If there is a difference, then there must be an fault to earth. It will trip if the difference is as low as 30mA for longer than 30mS. Before you would even feel it so definately recommended.