Reverse polarity feed to multipoint boiler.

Ian D J

Ian D J

Michael Fish
Messages
6,216
Name
Ian D J
Edit My Images
Yes
Evening to all at TP. Here's one for the local sparkies.

I've just had my two years old gas multipoint heater in the kitchen freshly serviced by an engineer and he noticed there is a reverse polarity feed to it from the wall switch and needs to be corrected - and for that I'd have to get hold of an electrician. But for now, the engineer quickly checked the electric supply on a couple of wall sockets around the house and all checked out fine and the heater itself will carry on working as normal anyway.

What's got me puzzled is this: I would have thought a reverse polarity feed to an appliance would cause the RCD unit to trip or worse still, a short circuit, but the engineer did say most modern multipoint heaters can take a reverse polarity feed, just that it'll stay "hot" even when switched off at the wall switch.

So, I'm hoping it'll be an easy fix by unscrewing the wall switch (which has it's own fuse) and swapping the wires around. I certainly won't be doing it myself as I do not get well with electrics at all - I don't think anyone are when in contact with 240 volts!

PS: This is here at the UK, if that is of any help to anyone. :D
 
Last edited:
as it's fed with 240v AC the polarity changes 50 times a second his meaning of reverse polarity may well mean the live n neutral are wired the wrong way round and it would be a simple case of swapping them round but without knowing what he really means by reverse polarity it might be a little more complicated but from what you have wrote that would be my thoughts
 
Ian D J said:
So, I'm hoping it'll be an easy fix by unscrewing the wall switch (which has it's own fuse) and swapping the wires around. I certainly won't be doing it myself as I do not get well with electrics at all - I don't think anyone are when in contact with 240 volts!

PS: This is here at the UK, if that is of any help to anyone. :D
Click to expand...

Probably this. Just do it yourself. If you can work a screwdriver why pay somebody else to do it.
Just turn off the mains, swap the wires and turn the mains back on.

Although, it isn't going to hurt by staying the way it is. So if it ain't broke, why fix it.
 
Last edited:
I suspect this is just one of those things that modern Power supplies can cope with .
Its a bit like European plugs they have live and neurtral through the primary two pins and thus can be plugged in both ways, the earth is on a common pin that touches the sides of the socket.
 
NB If it is the wrong way round then IT DOES MATTER!
If the switch controlling it is switched off, or if the fuse supplying it blows, then the unit will still be LIVE as the switch and fuse are in the neutral return and not in the live supply.
Sorry for the caps but this is a dangerous situation if a fault occurs.
ecoleman's last statement should be ignored.
 
Last edited:
Suvv said:
NB If it is the wrong way round then IT DOES MATTER!
If the switch controlling it is switched off, or if the fuse supplying it blows, then the unit will still be LIVE as the switch and fuse are in the neutral return and not in the live supply.
Sorry for the caps but this is a dangerous situation if a fault occurs.
ecoleman's last statement should be ignored.
Click to expand...

The neutral wire is connected to ground at the breaker box, which is connected to physical ground nearby. If you switch the hot line and leave the neutral, then the whole device will be at neutral potential. That's OK. If you switch the neutral, then the whole device will be at hot potential.

Open up your consumer unit or any light switch. The neutral is NEVER used for switching. :rolleyes:
 
Last edited:
ecoleman said:
The neutral wire is connected to ground at the breaker box, which is connected to physical ground nearby. If you switch the hot line and leave the neutral, then the whole device will be at neutral potential. That's OK. If you switch the neutral, then the whole device will be at hot potential.

Open up your consumer unit or any light switch. The neutral is NEVER used for switching. :rolleyes:
Click to expand...

I agree entirely.
Except that if the neutral and live are reversed at the supply then the neutral WILL be used for switching.
 
Suvv said:
I agree entirely.
Except that if the neutral and live are reversed at the supply then the neutral WILL be used for switching.
Click to expand...

If they are reversed at the supply (ie consumer unit) which is very doubtful and which is not what the OP said.

The OP thinks it is reversed at the wall switch, which means that the switch is still on the live but the live and neutral wires to the device are reversed at the switch. This will not cause a problem as when the switch is turned of, the live is still cut.

Of course the poles could be reversed at the connection to the device as well.

If somebody has reversed the poles in the consumer unit, then yes there is a problem and whoever wired it should be shot.
 
Last edited:
The OP says that the switch has its own fuse therfore it is almost certainly a double pole fused connection unit. If the live and neutral are reversed in that unit then the heater will be isolated completely if the switch is off BUT there will still be a live supply to the heater if the fuse blows.
 
i had a new meter fitted today and this subject came up
the engineer who fitted the new meter did a polarity check before he started replacing the old meter
basically as already said he's checking that live n neutral are wired correctly from the consumer unit

never really heard of this check before but it looks like it's standard practice
 
Update:

Just had a sparkie look at the mains switch attached to the boiler - and indeed it was fitted in reverse polarity. All corrected now. :police: :banana:
 
You must log in or register to reply here.
Back
Top