Does copper h/w cylinder need bonding?

[tireetim]

Does a copper hot water cylinder with an immersion need earth bonding? All pipes to and from it are plastic and there is a single immersion element. Appologies if the answer is on here somewhere, had a look but couldn’t find it.
Thanks.

 

[EFLImpudence]

No.

Not even if the pipes were metal.

It will be earthed by the Circuit Protective Conductor (earth wire) of the immersion cable, but that is a separate matter and nothing to do with bonding. I just thought I'd mention it.

 

[tireetim]

Thank you !

 

[ban-all-sheds]

No.

Not even if the pipes were metal.

But if the latest provisions re supplementary bonding did not apply, and the pipes to/from the cylinder did need bonding in the bathroom, then the location where the cylinder is might be a good, and appropriate, place to do it.

[edit]unfortunately omitted word added[/edit]

 

[JohnW2]

In the context of this thread ....

.... All pipes to and from it are plastic ....

 

[bernardgreen]

It will be earthed by the Circuit Protective Conductor (earth wire) of the immersion cable,

in which case there can be no harm in bonding it to the MET.

Of course there is the possibility of an immersion heater being fitted in a pocket in the cylinder. Depending on the design of the pocket and the way the immersion is fitted into the pocket the earth in the immersion cable might not have a reliable connection to the metal of the cylinder.

 

[ban-all-sheds]

In the context of this thread ....

And in the context of a reply to what EFLI wrote, what I missed was a significant word from my reply, not what the OP wrote.

 

[EFLImpudence]

in which case there can be no harm in bonding it to the MET.

Well, it is already earthed to the MET so there would be little point bonding it to the MET but it is true that any so-called bonding (actually further earthing) would do no harm.
What good, though, do you think it would do?

Bonding to the MET would usually be main bonding. Do you think the cylinder (plastic pipes, don't forget) is an extraneous-conductive-part?
If so, how and why?
If not, and it is supplementary bonding then why to the MET. Are the MET and the cylinder simultaneously accessible?

Of course there is the possibility of an immersion heater being fitted in a pocket in the cylinder. Depending on the design of the pocket and the way the immersion is fitted into the pocket the earth in the immersion cable might not have a reliable connection to the metal of the cylinder.

All the better then.
The cylinder will not become live in the event of a fault - UNLESS you have unnecessarily so-called bonded (actually earthed) it.



Your washing machine is earthed; there can be no harm adding another earth wire even if you call it bonding. Have you done thet?
It would be better - safer - if your washing machine did not need to be earthed at all, but it does.

 

[bernardgreen]

but it is true that any so-called bonding (actually further earthing) would do no harm.

and would enable protective devices to operate if there was a double fault situation which without the "unecessary" bond to the cylinder would have made the cylinder live.

Your washing machine is earthed; there can be no harm adding another earth wire even if you call it bonding. Have you done thet?

No because the hose pipes are plastic and the risk of the machine's case becoming Live when unplugged is very small. If it did become Live ( due to a fault elsewhere in the plumbing ) then the resistance of the water in the hoses is high enough to (hopefully) prevent a lethal current being taken from the machine. The double fault os machine not earthed and a fault elsewhere making some pipe work Live.

It does worry me that a lot of electricians only considered single fault situations and seem unable / unwilling to consider what is possible in a double fault situation.

 

[JohnW2]

It does worry me that a lot of electricians only considered single fault situations and seem unable / unwilling to consider what is possible in a double fault situation.

In the general situation think it depends upon what sort of faults one is contemplating. Some faults are so uncommon/improbable individually that to contemplate two of them arising simultaneously is probably on a par with be worried about stepping out of one's house, go up stairs etc.

One also has to consider the totality of the situation. Unnecessarily earthing something (whether or not it is called 'bonding') increases risk in some (rare) situations, so one has to decide whether that (very small) risk is greater or less than the (very small) risk of a 'double fault' if one does not earth it.

Kind Regards, John

 

[EFLImpudence]

and would enable protective devices to operate

That is not the function of bonding. You therefore admit that your suggestion is supplementary (additional) earthing.

if there was a double fault situation which without the "unecessary" bond to the cylinder would have made the cylinder live.

Why would the necessary immersion CPC not achieve that? Why would a second CPC be necessary?

No because the hose pipes are plastic and the risk of the machine's case becoming Live when unplugged is very small.

Edit - see below.

If it did become Live ( due to a fault elsewhere in the plumbing ) then the resistance of the water in the hoses is high enough to (hopefully) prevent a lethal current being taken from the machine.

Edit - Does the same not apply to the cylinder? So-
If not then the immersion CPC will do its job.
Please test the resistance/conductivity of the water in several meters (or one metre) of plastic pipe.

Even if it were metal, main bonding (as you suggested) is just not required and neither is supplementary bonding in the location.

The double fault os machine not earthed and a fault elsewhere making some pipe work Live.

The pipe is (in this case) plastic and cannot become live.

It does worry me that a lot of electricians only considered single fault situations and seem unable / unwilling to consider what is possible in a double fault situation.

It should not worry you.

You are favouring protecting against an extremely unlikely scenario and introducing a much more likely hazard of touching an earthed object when getting a shock from a live conductor.
We cannot protect against everything so protecting against the more likely is accepted as the best compromise.

It is difficult not to ridicule your suggestions.

 

[EFLImpudence]

Ah. I misread your post and the bit about the washing machine.

So, cannot the washing machine unplugged become live in the unlikely occurrences you envisage.

 

[John D v2.0]

Earthing is to disconnect the supply when a fault internal to an appliance causes the case to become live.
Bonding is to prevent a conductive item introducing an unwanted potential into a location where it may cause a danger due to there being other potentials already introduced (eg supplier earth)

Theoretically a building without a electric incoming supply at all, but with gas and water in metal should be bonded.

 

[JohnW2]

Theoretically a building without a electric incoming supply at all, but with gas and water in metal should be bonded.

I would say that's rather debatable. There would only be a point if one really believed that there was a significant risk that one of the supply pipes might introduce a potential dangerously different from that of the other supply pipe.

As you know, the usual reason for bonding metal supply pipes (or other extraneous-c-ps) is because of the risk that they might introduce 'true earth potential' into a building within which, under certain circumstances, the 'earthed' exposed-conductive parts of the electrical installation could be at a potential significantly different from true earth potential.

Although theoretically not impossible (and acknowledged by the regs' definition of an extraneous-c-p) it is incredibly unlikely that a metal supply pipe would introduce a potential which was dangerously different from true earth, and even less likely that two supply pipes coming out of the ground in the vicinity of the same building would have a dangerously different potential between them.

Kind Regards, John

 

[John D v2.0]

Well, as you've pretty much covered, ecps may introduce a potential, which is usually local earth. However I suppose that means that you'd have to satisfy yourself that they really did have a good enough connection to local earth before any other connection.
How about one supply sleeved in conduit eg gas tracpipe and the steel frame of the building well connected to local earth.

As you say, not likely without an electric supply, but if it happened, id bond.