Earth funnies and phantom voltages on lighting circuit

[JohnW2]

It's just occurred to me .....

.... much of the recent discussion has concerned 412.2.3.2 which requires that a CPC to be run to, and terminated at, each point/accessory in a circuit, but only if that circuit supplies one or more items of Class II equipment.

I feel sure that it must exist somewhere, but off the top of my head I cannot think of a corresponding reg which requires a CPC to be run to every point/accessory in a circuit (e.g. a standard sockets circuit) which does not 'supply one or more items of Class II equipment'

 

[EFLImpudence]

I feel sure that it must exist somewhere, but off the top of my head I cannot think of a corresponding reg which requires a CPC to be run to every point/accessory in a circuit (e.g. a standard sockets circuit) which does not 'supply one or more items of Class II equipment'

Do you mean that because this regulation insists on fitting something which is not necessary then there should be a similar regulation stating that that thing must be fitted where it is necessary?

Would that not be covered by the likes of a regulation stating that exposed-conductive-parts etc. must be earthed?



So, with reference to your sometime query about whether plastic light switches are actually Class II, if they are not then a CPC to them is not required.

 

[JohnW2]

Do you mean that because this regulation insists on fitting something which is not necessary then there should be a similar regulation stating that that thing must be fitted where it is necessary?

Yes, I suppose I am - or, perhaps put a different way, I would have expected the regs to indicate where it IS necessary.

Would that not be covered by the likes of a regulation stating that exposed-conductive-parts etc. must be earthed?

Not necessarily. A plastic socket does not have any exposed-c-ps, but there is obviously a need to 'run a CPC' to it.

So, with reference to your sometime query about whether plastic light switches are actually Class II, if they are not then a CPC to them is not required.

Unless I'm missing something then seemingly not - unless the circuit concerned "supplies one or more items of Class II equipment", in which case there is seemingly a requirement for a CPC to be run/terminated at ALL points & accessories in the circuit (including any light switches).

 

[yartin]

Pre 1966 lighting circuits, without an earth wire, do not accommodate metal fittings.

That's not accurate information. Light with metal fittings which are CLASS II DOUBLE INSULATED NO EARTH REQUIRED can be used. Many such wall/ceiling lights are available in the market, one example below:

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www.thelightingsuperstore.co.uk

 

[plugwash]

That's not accurate information. Light with metal fittings which are CLASS II DOUBLE INSULATED NO EARTH REQUIRED can be used. Many such wall/ceiling lights are available in the market, one example below:

Loading…

www.thelightingsuperstore.co.uk

In principle they can.

In practice, actually installing class 2 metal lights to existing UK lighting circuits while maintaining their class 2 status is problematic. Often resulting in those lights being installed in ways that effectively render them "class 0".

 

[Jurassicspark]

That's not accurate information. Light with metal fittings which are CLASS II DOUBLE INSULATED NO EARTH REQUIRED can be used. Many such wall/ceiling lights are available in the market, one example below:

And if installed correctly.

 

[JohnW2]

And if installed correctly.

One source of confusion, given that one is required to "take account of" (but not necessarily comply with) manufacturer's instructions, those instructions for Class II items often include (and often in bold uppercase, as here) "THIS ITEM MUST NOT BE EARTHED", or something like that.

I think that is misleading. Whilst it is true that it is always undesirable to create any unnecessarily earthed touchable metal within a property, I cannot see that, from the point-of-view of the 'item', there is ever any problem with earthing any touchable metal parts it may have.

 

[EFLImpudence]

I think that is misleading. Whilst it is true that it is always undesirable to create any unnecessarily earthed touchable metal within a property, I cannot see that, from the point-of-view of the 'item', there is ever any problem with earthing any touchable metal parts it may have.

It is thought that double-insulated is safer than having earthed items therefore it would be better to have all double-insulated appliances and no earthed items in the home.

You are free to disagree.

 

[yartin]

It is thought that double-insulated is safer than having earthed items therefore it would be better to have all double-insulated appliances and no earthed items in the home.

You are free to disagree.

I am not disagreeing, I am not an electrician only a DIYer keen to learn; if you can explain why would it be safer?

I fitted bathroom light, I think it was IP44 and and was also class 2 double insulated no earth required, I wasn't expecting class 2, found out after arrived.

 

[Harry Bloomfield]

I think that is misleading. Whilst it is true that it is always undesirable to create any unnecessarily earthed touchable metal within a property, I cannot see that, from the point-of-view of the 'item', there is ever any problem with earthing any touchable metal parts it may have.

The example earlier, from Yartin, the light fitting with all that exposed metal, I would despite the manufacturer classifying it as double insulated - I would insist on thoroughly checking it, and were there any risk, I would make a point of earthing it.

 

[yartin]

In principle they can.

In practice, actually installing class 2 metal lights to existing UK lighting circuits while maintaining their class 2 status is problematic. Often resulting in those lights being installed in ways that effectively render them "class 0".

I can't see why will render them class 0. I have seen a couple of class 2 lights, the only difference is that L & N are both in a thick sleeve which assume acts as protection.

 

[Jurassicspark]

I think that is misleading. Whilst it is true that it is always undesirable to create any unnecessarily earthed touchable metal within a property, I cannot see that, from the point-of-view of the 'item', there is ever any problem with earthing any touchable metal parts it may have.

If it wasn’t earthed and the fitting got damp whatever is in proximity will have a potential that could be dangerous if touched. Earthing whatever it is will cause the RCD to trip for e.g water ingress caused by a plumbing leak.

 

[plugwash]

Earthing provides a path for fault currents, tripping a breaker in the event of a fault, that is better than the fault causing the case to become and remain live. However, there is still a brief window between when the fault makes the case live and when the protective device trips. Furthermore, earthed metal can act as a "second point of contact" for a shock originating from another peice of equipment.

The idea with "double insulated" design is that the equipment is designed such that a fault making the case live is "very unlikely", with the result that there is no reason to, and possibly a detriment from, earthing the case.

How well that works in practice depends on how good a job the manufacturer and installer have done to render faults to the case very unlikely.

For a metal cased item "double insulated" design generally means that individual conductors carrying hazardous voltages should not be in a location where, if they came lose from their terminal, or if their insulation failed, they could come in contact with the case. Sheaths, barriers, terminal boxes or similar should be used to prevent that from happening.

What all too often happens is that the manufacturer provides a small terminal box inside the light. This terminal box is designed to provide cable restraint for the supply cable and enclose the connection such that the individual conductors, even if they were to become disconnected or their insulation were to fail, cannot come in contact with the enclosure of the light.

But in a typical UK installation the installer is faced with not one but three cables coming out of the ceiling, furthermore the outer sheath on said cables is often stripped back so it is flush with the ceiling. The terminal box is usually too small to take three cables and even if it was big enough, there is often not enough usable length on the cables.

So the light ends up being installed such that individual conductors with only basic insulation are exposed inside the main body of the light fitting, as are additional terminals with no sub-enclosures or cable restraint. At that point the fitting can't reasonably be considered class 2 anymore.

There are also some fittings that are sold as class 2, but simply fail to meet class 2 standards even if installed correctly.

 

[Harry Bloomfield]

There are also some fittings that are sold as class 2, but simply fail to meet class 2 standards even if installed correctly.

So the safer option, where there is doubt, is to connect them as a class 1?

 

[EFLImpudence]

I am not disagreeing, I am not an electrician only a DIYer keen to learn; if you can explain why would it be safer?

I fitted bathroom light, I think it was IP44 and and was also class 2 double insulated no earth required, I wasn't expecting class 2, found out after arrived.

Excellent answer from Plugwash.

I cannot add to that - except to say that generally speaking people think earthing is a good thing; it is not; it is a necessary evil.