Does a steel staircase need to be earthed?

[ed110220]

Maybe an odd question, but when I was refurbishing my hallway the other day I found an old electrical cable bonded to the staircase at one end and running to the area of the meter and CU at the other. No longer attached at that end. From the look of it dated to when the house was built in 1949, with old style brown non-PVC insulation and I'm guessing was an earth cable. Everything has since been rewired at least once so it hasn't been used for a long time.

But should a steel staircase (and steel framed house) be earthed?

 

[securespark]

If the steels are exposed.

I did a job wiring up a steel-framed house. I attached the frame to the MET and then tapped off the frame locally for the water MEB.

 

[plugwash]

There are generally two reasons for connecting metalwork to the earthing system.

The first (referred to as "earthing" by electricans) is to disconnect hazards in the event that a live conductor comes into contact with the metalwork, usually as a result of failed/damaged insulation.

The second (reffered to as "bonding" by electrians) is to avoid potential differences between different "earths". When faults (or the use of combined neutral and earth conductors by suppliers) cause currents to flow in an earthing system that can create voltages between different parts of the earthing system and between the earthing system and "real earth".

On the other hand if somehow a live conductor does become exposed and someone touches it at the same time as an item of non-electrical metalwork then it is better if the non-electrical metalwork is NOT earthed.

Opinions have shifted over the years, at one stage it was the done thing in at least some areas to earth/bond everything metal and to add "supplementary bonding" in kitchens and bathrooms, nowadays practices have shifted more towards only bonding stuff that is actually in contact with the ground or actually used to contain electrical conductors.

 

[ericmark]

In 2008 the rules changed, and with RCD protection many items no longer need bonding.

The death of Emma Shaw highlights the problem, had the stop tap not been earthed she would not have died, also if the metal frame had been earthed she would not have died, and if RCD's had been fitted she would not have died.

So there is danger both in earthing and not earthing, with the tooth brush supply in a bathroom we ensure there is no earth to make it safe, but this only works with one item, with multi items the isolation transformer does not help, but the RCD has made it easier, and now bonding is only done with items coming in from outside, gas pipe, water pipe etc.

When I first started even metal window frames were bonded.

 

[JohnW2]

If the steels are exposed.

If some of the steel staircase (or metal fittings/things connected to it) are exposed, then what really matters most is whether or not it is is in electrical continuity with the steel frame of the house and whether, in turn, that steel frame is in contact (hence electrical continuity) with 'the earth' (ground/soil etc.). If it is, then main bonding would be necessary. If not, as plugwash has implied, it might well be considered safer not to connect it to earth.

Kind Regards, John

 

[SUNRAY]

When I first started even metal window frames were bonded.

I did a lot of new build work in the 70's for a builder friend, SEEBoard would come in and do their inspection before making the final connexion. We had to 'bond all exposed metalwork' that meant metal handles and hinges on wooden windows, kitchen cupboard handles (an ali extrusion along the top or bottom of doors and drawers was common), the standard row of coat hooks on a wooden plate... yeah you get the message.
It got to the stage SEEBoard would be called in much earlier before such accessories were fitted.

 

[ed110220]

If some of the steel staircase (or metal fittings/things connected to it) are exposed, then what really matters most is whether or not it is is in electrical continuity with the steel frame of the house and whether, in turn, that steel frame is in contact (hence electrical continuity) with 'the earth' (ground/soil etc.). If it is, then main bonding would be necessary. If not, as plugwash has implied, it might well be considered safer not to connect it to earth.

Kind Regards, John

Yes, the steel staircase is exposed apart from being carpeted (sides, underside, banisters are exposed). It will definitely be in continuity with the steel frame of the house as it is bolted onto a steel beam at the top, and all the steels of the house are bolted together. What I don't know is whether/how well the whole steel frame is in contact with the ground electrically. It sits on a concrete foundation but I don't know what effect that has.

 

[JohnW2]

Yes, the steel staircase is exposed apart from being carpeted (sides, underside, banisters are exposed). It will definitely be in continuity with the steel frame of the house as it is bolted onto a steel beam at the top, and all the steels of the house are bolted together. What I don't know is whether/how well the whole steel frame is in contact with the ground electrically. It sits on a concrete foundation but I don't know what effect that has.

That's roughly as I suspected would be the case. The last point you mention is usually the potentially 'difficult' one. An electrician could attempt to determine, by measurement, whether the steel frame was in electrical contact with the ground, but that is far from foolproof. For a start, there might appear to be no electrical connection if the measurement was undertaken during a very dry period, but that could change if/when the foundation (and vicinity) became very wet. Also, it is more than likely that the steel frame will be connected to 'earth' (in the form of the electrical installation's earthing system) in 'incidental' ways (e.g. by being in contact with metal plumbing pipes which, in turn, were 'earthed' by contact with electrically 'earthed' things like boilers, CH pumps/valves etc.).

You certainly would need an electrician to provide an opinion/judgement about this but, given the uncertainties I mention, I suspect that many would advise 'bonding' of the steel frame (connecting it to the electrical installation's Main Earthing Terminal with a fairly substantial cable). Once the steel frame was bonded in that fashion, there would be no need to also bond or earth other metal things which were in contact with it (like your staircase).

Kind Regards, John

 

[studentspark]

You need to confirm if it is an extraneous conductive part. (Not part of the electrical installation but can introduce a potential)
Is it possible to come into contact with exposed conductive parts (Such things as metal light switches) whilst on the steps?

 

[JohnW2]

You need to confirm if it is an extraneous conductive part. (Not part of the electrical installation but can introduce a potential)

Although we haven't used that technical term, that's precisely what we have been discussing.

Is it possible to come into contact with exposed conductive parts (Such things as metal light switches) whilst on the steps?

I don't think that there has been any suggestion, or any reason to think, that the steel staircase would be an extraneous-c-p, since, in itself, it will presumably be entirely within the building.

As has been discussed, what matters is the steel frame of the building (which may well be in electrical continuity with the staircase). The important question is whether that steel frame is an extraneous-c-p (and I have suggested that one probably should assume that it at least might be) - and, if it is (an extraneous-c-p) then it (the frame) needs main bonding. However, as I said, once that was done, the staircase itself (which is not an extraneous-c-p) woulds not need to be separately bonded.

Kind Regards, John

 

[flameport]

It will definitely be in continuity with the steel frame of the house as it is bolted onto a steel beam at the top, and all the steels of the house are bolted together.

The steel structure requires bonding.
The stairs do not require bonding separately, as they are already connected to the rest of it.