Regulations Myths

[ebee]

Most boilers seem to have a FCU not a plug and socket, so hard to plug into a generator in an emergency without the use of a widow maker, also need a locking off device designed for that make of FCU, to lock the switch off. (The fuse only supplies line, so neutral still connected so technically not isolated) Where if using a 13 amp plug, where these

are universal for all 13 amp plugs.

The only reason I can think of, was some regulations back, we did not need to protect FCU with an RCD, however buried cables in wall rule has in the main change that.

I have asked on Plumbing section it does say in some boiler manuals to use a FCU, likely written before the rules on RCD's changed. So other than that's the way we have always done it, why would one use a FCU to supply a boiler? As to being able to unplug locking sockets would stop that

so why are FCU used to supply boilers? These View attachment 373164 will allow us to have central heating even with a power cut, not sure if 600 watt is enough, but since the use of FCU encourages the use of the widow maker, should a FCU be given a code 2 in an EICR!

Some sockets are/were single pole switching is one reason, the other reason is you would also loose the earth connection by unplugging - unless you did what I did on a LA Grant aided rewire to trap the grants inspector (well he was previously a plumbing/heating engineer so I thought he would snag it). Did not work out how I planned though, he never brought the issue up, I was awaiting his challenge that although isolation would be achieved the earth connection would be lost, I had put an earth link from the socket directly into the boiler to maintain earthing even once unplugged,.
That will teach me to be a right smart alec trying to catch him out, it took all of the fun out of it - I must get out more often.

 

[ericmark]

I am not sure @ebee if best to keep earth connected or not? If a broken PEN earth wire is exported to a fuel oil tank, that could be quite dangerous.

 

[JohnW2]

Most boilers seem to have a FCU not a plug and socket, so hard to plug into a generator in an emergency without the use of a widow maker, ...

That's the very reason why I have ignored "how most boilers are wired" and have my entire heating system, including the boiler, supplied via one 13A plug/socket. I could have used a changeover switch, but most of the appropriate ones available are very big and clunky, so I opted for the plug/socket.

 

[ebee]

Yes if you are using only one source for your mains supply (like most of us mere mortals) then OK but if you have alternative supplies then its sometimes a whole new ball of wax

 

[JohnW2]

Yes if you are using only one source for your mains supply (like most of us mere mortals) then OK but if you have alternative supplies then its sometimes a whole new ball of wax

Sure, my I was responding to eric's post which obviously related to those mortals who have generators, even if they are rare

 

[SimonH2]

... but since the use of FCU encourages the use of the widow maker, should a FCU be given a code 2 in an EICR!

That's an interesting thought.

Some sockets are/were single pole switching is one reason

Irrelevant since you have full isolation with the plug out - even with an unswitched socket. And there's something to be said for not having a handy switch on the heating.

the other reason is you would also loose the earth connection by unplugging

So ?
If it has no electrical connection, iit probably doesn't need an earth. If it's determined that it does need equipotential bonding (not earthing), then you simply bond it regardless as the typical 0.75mm² CPC in the flex doesn't meet regs for it.

 

[JohnW2]

If it has no electrical connection, iit probably doesn't need an earth. If it's determined that it does need equipotential bonding (not earthing), then you simply bond it regardless as the typical 0.75mm² CPC in the flex doesn't meet regs for it.

... and, in any event, if the house has copper plumbing and bonded extraneous-c-ps (which is probably the most common scenario) the boiler will be implicitly connected to the installations earthing system (i.e. MET and CPCs) even if one 'disconnects its supply.

 

[ebee]

Irrelevant since you have full isolation with the plug out - even with an unswitched socket. And there's something to be said for not having a handy switch on the heating

I am not disagreeing with that. Yes indeed, full isolation is achieved by pulling the plug out. If only the Live conductors are disconnected by using a switched socket then it is always possible that the switch on the socket is merely SP not DP therefore the N is not disconnected by switching off either.
Of course the E could be difficult to disconnect from the boiler by virtue of parallel paths running to any metal pipework connected to the boiler by virtue of earthing and or bonding therefore complete isolation of any earth reference between one source of supply and any other available source of supply would be extremely difficult to guarantee with any certainty.
How do we achieve total separation of earthing systems both at the time of checking (testing) and guarantee it will remain so at all future times as well? Not easy by any stretch!

 

[ericmark]

and guarantee it will remain so at all future times as well?

This does not only apply to the earth, it applies to all we install, my boiler was installed likely 25 years ago, and at that point, we were not having loads of power cuts, OK the Winter of Discontent which was the point I vowed never again to rely on one fuel, but never had a gas power cut that I remember, and electric not that often, and in the main short-lived.

So at the time, using a FCU in the flat, would mean unlikely anyone in the flat would switch off/unplug the central heating and DHW resulting in the main house not having central heating or oil heated DHW. And in my case, since the switch from DNO supply to battery and inverter supply is automatic, and the boiler is the only item in the house not RCD protected, then to continue with a FCU is really the only way. It would not comply if I used a plug and socket.

But I would think I am the odd one out? In the main, people's central heating is RCD protected, so it would better future-proof to give the option to use a simple plug in power supply, be it a battery bank, or a generator. So even if no generator seen when installing, to give the option seems to make sense, these

are becoming more and more popular, and safer than outside sockets if we consider loss of PEN, an easy way to get power to the BBQ, and of course great stand by for the short power cut.

 

[SimonH2]

If only the Live conductors are disconnected by using a switched socket then it is always possible that the switch on the socket is merely SP not DP therefore the N is not disconnected by switching off either.

It's really irrelevant whether the socket is SP or DP switched - for isolation you pull the plug since I can't recall ever seeing a domestic BS1363 socket with anything remotely resembling a lock off facility.

Of course the E could be difficult to disconnect from the boiler by virtue of parallel paths running to any metal pipework connected to the boiler by virtue of earthing and or bonding therefore complete isolation of any earth reference between one source of supply and any other available source of supply would be extremely difficult to guarantee with any certainty.
How do we achieve total separation of earthing systems both at the time of checking (testing) and guarantee it will remain so at all future times as well? Not easy by any stretch!

Do we bother ?
The days when the DNOs came round disconnecting local earth rods when applying PME (I recall it happening to a friend) are long gone - I assume. Having a local earth connected with the DNO earth no longer seem to the the taboo it once was, and it seems to be actively encouraged now - it was rumoured that Ed18 rev 2 would make it mandatory.

 

[JohnW2]

It's really irrelevant whether the socket is SP or DP switched - for isolation you pull the plug ...

Indeed. Although they seem to be becoming more common (I'm not sure that they even existed in the not-too-distant past), I'm not at all sure why anyone would want a DP switch in a socket!

 

[Murdochcat]

Indeed. Although they seem to be becoming more common (I'm not sure that they even existed in the not-too-distant past), I'm not at all sure why anyone would want a DP switch in a socket!

Probably for sockets in tricky locations where unplugging is difficult and switching off is easier

 

[plugwash]

Indeed. Although they seem to be becoming more common (I'm not sure that they even existed in the not-too-distant past),

I'm pretty sure MK logic plus has been DP switched since it's introduction in the 1990s. I don't know about prior to that.

I'm not at all sure why anyone would want a DP switch in a socket!

It was certainly marketed as a safety feature.

I can see the argument both ways. On the one hand, completely disconnected is surely safer than mostly disconnected. On the other hand, a DP switch is more "things to go wrong", and there is the risk that if one pole of the switch were to fail you could end up in an "off but live" situation.

 

[JohnW2]

Probably for sockets in tricky locations where unplugging is difficult and switching off is easier

I suppose so - but, in most cases, if one can switch it off, one could probably also unplug it.

 

[JohnW2]

I'm pretty sure MK logic plus has been DP switched since it's introduction in the 1990s. I don't know about prior to that.

Fair enough but,as I said, I wasn't really aware that any of them were DP back then.

It was certainly marketed as a safety feature.

I'm sure it was, but am not so sure that I understand - other than in the (I would think pretty unusual) situation Murdo mentioned - of it being easy to switch off but difficult to unplug, because of the location.

I can see the argument both ways. On the one hand, completely disconnected is surely safer than mostly disconnected.

Indeed, but provided one can do it, unplugging is the ultimate in "completely disconnected", isn't it?

On the other hand, a DP switch is more "things to go wrong", and there is the risk that if one pole of the switch were to fail you could end up in an "off but live" situation.

Quite - and I would say that is definitely an "UNsafety feature" (albeit I imagine very rare). !