What size wire to earth my steel conduit?

[STEVEROG]

I've got a steel conduit running under a concrete floor. It's protecting the cable feeding the cooker/hob.

What size earth wire should be used to earth the conduit?

 

[mfarrow]

You can work it out using the adiabatic. But... if you use the same size as the E in the equivalent T&E for the circuit, you won't be going far wrong.

 

[xr4x4]

Common sense would say the same size as the earth running inside it, as a minimum..!

 

[Cliffy88]

25mm will be fine for singles or t+e.

 

[Cliffy88]

Sorry miss read there is no need too earth the conduit but rule of thumb Is half the conductor size if you want too.

 

[sparkwright]

Welcome to the forum Cliffy.

I would say there is a need to earth the metal conduit...

 

[Cliffy88]

If the conduit comes out of the ground and can be touched yeah earth it, 6mm t+e 2.5mm cpc( earth) 10mm t+e 4mm cpc

 

[xr4x4]

I would guess the supply cable is 6 or 10mm.

 

[Cliffy88]

Yes it depends what the cooker is pulling 6mm on a 32a b braker or 10mm on 40a braker for future use

 

[STEVEROG]

The cooker cable is 6 mm.

 

[ban-all-sheds]

Surely the conduit is threaded, and bushed into boxes which are connected to the cpc?

 

[sparkwright]

Surely the conduit is threaded, and bushed into boxes which are connected to the cpc?

Exactly.

Is this a continuous length of conduit going from a metal back bo to another metal back box?

Or is it just a piece of conduit in the floor only, and the rest of the run isn't conduit? If so, you need some sort of caps at the end of the conduit so the cable can't catch on any rough edges.

Is it twin and earth cable or singles you are using?

4 mm or greater for the earth lead in my opinion, anything smaller may require further protection from mechanical damage.

 

[JohnD]

25mm will be fine for singles or t+e.

 

[Cliffy88]

Read the next post john d, I thought he wanted size of conduit I read the question wrong

 

[STEVEROG]

Thanks for the input gents, some more information.....

It' just a single short length of metal conduit buried in concrete floor.

The conduit has a 6 mm T&E cooker cable running in it.

The conduit takes the cable from the edge of the room across to the kitchen island in the middle of the room

The conduit isn't connected to anything at either of its ends.

I filed the ends of the conduit smooth before pulling the cables through

So it sounds like a 2.5mm^2 earth wire is just about sufficient but a 4mm^2 would be preferred. Now, what's the preference, single or multi-core wire? Where's the best place to purchase (I don't want a whole reel).

Regards,

Steve