Earthing Galvanised Steel Conduit

ColmLaw

Hi All,

I'm looking to have an electric shower installed and as part of this will have a 10mm cable running through a galvanised steel conduit behind plasterboard.

In terms of earthing this conduit, where should the earth wire be linked to the circuit? Does a separate earth wire need to run from the consumer unit to the earth clamp on the conduit or can an earth be tapped from elsewhere?

2011

ColmLaw wrote: »

Hi All,

I'm looking to have an electric shower installed and as part of this will have a 10mm cable running through a galvanised steel conduit behind plasterboard.

In terms of earthing this conduit, where should the earth wire be linked to the circuit? Does a separate earth wire need to run from the consumer unit to the earth clamp on the conduit or can an earth be tapped from elsewhere?

What is the purpose of the earth cable?
Is it for equipotential bonding or is it for a CPC (circuit protective conductor)?

Why are you using steel conduit? It is unusual to use steel conduit in this way. Not that there is anything wrong with this.

Equipotential bonding is all about electrically connecting simultaneously accessible conductive parts together. This keeps them at the same electrical potential so that a person touching more than one conductive part at one time will not get an electric shock.

A CPC provides a return path to the MET (main earth terminal) for a fault current.

Tuco88

You could run a seprate earth, or come from the shower isolator(pull cord) or local bonding. You could use pipe bonding clamps on the steel conduit.

Risteard81

Typically steel conduit will be run as part of a complete containment system, e.g. drops from steel trunking. Then the Earthing would be achieved with mechanically sound connections, e.g. flanged couplers screwed tightly with a bush spanner. BS951 clamps would not typically be seen with conduit, which is an exposed conductive part and must be earthed (and may be utilised as the cpc).

2011

Risteard81 wrote: »

BS951 clamps would not typically be seen with conduit, which is an exposed conductive part and must be earthed (and may be utilised as the cpc).

These clamps are frequently used on steel conduits in many industrial installations in particular ATEX installations.

Risteard81

2011 wrote: »

These clamps are frequently used on steel conduits in many industrial installations in particular ATEX installations.

Perhaps, but I doubt that a domestic shower will be located in a hazardous area!

2011

Risteard81 wrote: »

Perhaps, but I doubt that a domestic shower will be located in a hazardous area!

.....and I doubt that a domestic shower will be wired via metal trunking
We don't know that this is a domestic installation, steel conduit would suggest that it is not.
As it happens emergency showers are frequently installed in hazardous areas.

However my point remains:
Using BS951 clamps to bond steel conduit is very much standard practice.

Risteard81

2011 wrote: »

.....and I doubt that a domestic shower will be wired via metal trunking

I completely agree, which is why I find the notion strange.

But as you have pointed out we do not know that this is a domestic installation, although my interpretation of the original post was that it was but for whatever reason a steel conduit drop was wanted, perhaps for earthed mechanical protection.

As said typically, at least in this part of the country for general electrical installations it would not be standard practice to install a BS 951 clamp on steel conduit, and usually connections between trunking and the accessories would be done with flanged couplers. Although not common nowadays a Ductor tester should be used to test the continuity of the containment, where a loose connection would spark (so obviously not talking about potentially explosive atmospheres).

2011

Risteard81 wrote: »

But as you have pointed out we do not know that this is a domestic installation, although my interpretation of the original post was

To be honest this is what I thought too.

As said typically, at least in this part of the country for general
electrical installations it would not be standard practice to install a BS 951
clamp on steel conduit

It is very normal nowadays, I see this all the time in many different installations.

This is particularly popular when steel conduit is used as cable containment for cables with larger bending radius such as NYMJ, Silflex or SWA. "Open bends" are frequently used with these cables. This is when the conduit stops and starts either side of a bend. Flange couplers, bends and conduit boxes are avoided for ease of wiring. In these cases BS951 clamps are used to bond the conduit across a break.

Risteard81

Essentially then the steel conduit is being used for some additional mechanical robustness, as opposed to required mechanical protection for non-sheathed singles.

Notwithstanding galvanised drops with FP200 for many/most fire alarm installations, I would generally use conduit with BS 6491B (LS0H) / BS 6491X (PVC) singles. Certainly I wouldn't be looking to protect SWA with conduit - the earthed armouring should achieve that nicely.

2011

Risteard81 wrote: »

Essentially then the steel conduit is being used for some additional mechanical robustness, as opposed to required mechanical protection for non-sheathed singles.

No, when steel conduit is used with armored cables generally the intent is that the conduit forms part of a cable containment system as opposed to providing additional "robustness".

Certainly I wouldn't be looking to protect SWA with conduit - the earthed armouring should achieve that nicely.

As above conduit is normally used in this fashion as containment. This practice and bonding the conduit with earth straps is considered normal practice in Ireland.

Tuco88

2011 wrote: »

These clamps are frequently used on steel conduits in many industrial installations in particular ATEX installations.

I agree, I work in a large pharma plant and it's very common. You would see swa cables being "sleeved" in conduit open ended as we call it. And then earthed with the clamps.

Risteard81

2011 wrote: »

This practice and bonding the conduit with earth straps is considered normal practice in Ireland.

In parts, perhaps. But certainly not in the north of Ireland. Nor is it something I have encountered whilst working in the south of Ireland, but I accept that it may be common practice amongst some.