No earth cable on light fitting

[Taylortwocities]

 

[winston1]

Either it is Class II and does not require and should not be earthed

This is often stated, but what harm can come from earthing a class 2 appliance?

Because the metal parts could be made live by a fault elsewhere.

You mean the earth might not be earth. Hm, that argument could be applied to a class 1 appliance as well.

Class 2 stuff often gets earthed with interconnections anyway. Take hi-fi, any one of the components could be class 1 and export the earth via connecting leads. Even if this is not the case I would earth it anyway as the sum of the leakage currents can cause a tingle.

 

[EFLImpudence]

You mean the earth might not be earth.

I don't know what that means.

Hm, that argument could be applied to a class 1 appliance as well.

No, by live to earth fault somewhere else - hopefully disconnected by ADS.

Class 2 stuff often gets earthed with interconnections anyway. Take hi-fi, any one of the components could be class 1 and export the earth via connecting leads.

How does an isolated metal case of a Class II appliance become earthed by CPCs elsewhere?

Even if this is not the case I would earth it anyway

Unfortunately I believe you,

as the sum of the leakage currents can cause a tingle.

Have you earthed your cutlery?

 

[EFLImpudence]

Also, you may just as well say that plastic parts should be changed to metal so that YOU can earth them.

 

[PBC_1966]

This is often stated, but what harm can come from earthing a class 2 appliance?

Because the metal parts could be made live by a fault elsewhere.

You mean by the earth wire to the class II appliance becoming live at its other end somehow? The same could happen with a class I appliance, which would make that an argument for omitting the earth connection on the latter.

How does an isolated metal case of a Class II appliance become earthed by CPCs elsewhere?

Audio & video equipment, as Winston has already mentioned, is a prime example, where the case will end up earthed via interconnecting leads connected to other equipment which is earthed.

Or you might just bolt a piece of class II equipment into a rack frame which is earthed. In some cases, merely standing it on top of some other piece of earthed class I equipment will do it.

 

[EFLImpudence]

Oh, come on.

This is often stated, but what harm can come from earthing a class 2 appliance?

Because the metal parts could be made live by a fault elsewhere.

You mean by the earth wire to the class II appliance becoming live at its other end somehow?

Yes, that's what happens in a Live to exposed-conductive-part fault - all the CPCs and earthed parts become live until the OPD operates.

The same could happen with a class I appliance, which would make that an argument for omitting the earth connection on the latter.

Then the OPDs would not operate in a fault in the Class I appliance, would they?


Earthing is not a good thing in itself; it is a necessary evil to operate the OPD so that e-c-ps do not remain live.

Metal parts being prevented from becoming live (because of faults) by double insulation is considered the better option.

 

[winston1]

How does an isolated metal case of a Class II appliance become earthed by CPCs elsewhere?

Take my case of hi-fi. You have a class 2 amplifier with a metal case. You have say a class 1 FM tuner which is earthed and you connect its output to your amplifier. Voila your isolated metal case becomes earthed.

 

[EFLImpudence]

How does an isolated metal case of a Class II appliance become earthed by CPCs elsewhere?

Take my case of hi-fi. You have a class 2 amplifier with a metal case. You have say a class 1 FM tuner which is earthed and you connect its output to your amplifier. Voila your isolated metal case becomes earthed.

I am not familiar with the appliances but -

Either it doesn't or it's not Class II.

 

[EFLImpudence]

OR - you're doing it wrong.

 

[winston1]

How does an isolated metal case of a Class II appliance become earthed by CPCs elsewhere?

Take my case of hi-fi. You have a class 2 amplifier with a metal case. You have say a class 1 FM tuner which is earthed and you connect its output to your amplifier. Voila your isolated metal case becomes earthed.

I am not familiar with the appliances but -

Either it doesn't or it's not Class II.

Of course it does. If you interconnect a class 1 and class 2 appliance the class 2 one becomes earthed.

 

[PBC_1966]

Whatever classification it might or might not fall under officially, there are numerous pieces of audio & video equipment which are supplied with 2-core cords with no earth to the casing, but the casing is electrically connected to the outers of RCA jacks, BNC's, etc., so if you interconnect with a piece of equipment which is earthed, the casing will end up earthed via those interconnections.

That's assuming, as I said before, that it isn't earthed by some more direct means, such as being bolted to a rack frame which is already earthed, either directly or via the earths on other equipment mounted in the same frame.

 

[ban-all-sheds]

Whatever classification it might or might not fall under officially, there are numerous pieces of audio & video equipment which are supplied with 2-core cords with no earth to the casing, but the casing is electrically connected to the outers of RCA jacks, BNC's, etc., so if you interconnect with a piece of equipment which is earthed, the casing will end up earthed via those interconnections.

In which case you have ignored the instructions concerning earthing the equipment.

That's assuming, as I said before, that it isn't earthed by some more direct means, such as being bolted to a rack frame which is already earthed, either directly or via the earths on other equipment mounted in the same frame.

Ditto.

 

[PBC_1966]

The same could happen with a class I appliance, which would make that an argument for omitting the earth connection on the latter.

Then the OPDs would not operate in a fault in the Class I appliance, would they?

Of course not, but neither could a potential be introduced onto the casing of that class I appliance from a fault elsewhere.

The point I was making is that the argument about some external fault making live the casing of a class II appliance which has been earthed anyway applies equally to an appliance which is class I and designed to have its casing earthed from the outset.

 

[PBC_1966]

In which case you have ignored the instructions concerning earthing the equipment.

Which instructions?

 

[EFLImpudence]

The point I was making is that the argument about some external fault making live the casing of a class II appliance which has been earthed anyway applies equally to an appliance which is class I and designed to have its casing earthed from the outset.

I really don't think that warrants a reply.