DIY Doctor

Electric Shock from Flex-Outlet plate

Postby Stu Magoo » Sat Jan 09, 2021 12:46 pm

Hi,
I've received an electric shock from the screw heads of a Flex Outlet-Plate in my airing cupboard. It connects the hot water cylinder thermostat to the Boiler controls downstairs. The Thermostat is working fine.
I've partially removed the plate and looked at the wiring behind. I've discovered a 3 core and earth cable feeding into the plate. The Earth has a green sheath covering it completely and is not attached to anything. The Live and Neutral are connected to their respective L & N on the plate. The remaining "Switch" wire which is yellow is connected to the Earth terminal of the plate.
The flex from the thermostat is wired Live & Neutral to their respective L & N plate terminals the same as the cable feed.
The earth of the flex is wired to the earth terminal of the plate the same as the yellow "Switch" cable. This appears to be what is making the screw heads of the plate live.
What is the correct way for me to wire this ?
Any help or advice would be appreciated.
Thanks
Stu
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Stu Magoo
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Postby Mr White » Sat Jan 09, 2021 9:28 pm

Why were you touching it, and what were you doing before?

There is no reason the yellow can not be used for an earth connection, it should be sleeved though to indicate such. Maybe the original earth is severed?

How is the other end of the cable connected.
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Postby ericmark » Sun Jan 10, 2021 10:29 pm

Sorry can't work out exactly what I am looking at, however the regulations say an earth must be run to every point even if not required, before 1966 it was permitted not to run earths to light fittings, but today only the flex ceiling rose to bulb can be run without an earth.

However it seems plumbers are unaware of these rules, and I have seen again and again were earths are missing and/or the wire marked green/yellow has been used for other than earth with no over sleeving.

In theory where one is running multi multi core cables you can over sleeve the earth cores in all but one cable, I think personally bad practice but way the regulations are worded, it is allowed.

The result is some times with central heating green/yellow are not earth, C Plan, W Plan and Y Plan all need three wires to the tank thermostat, and it seems often plumbers used the green/yellow as line, and I would guess the result is some one has assumed green/yellow is earth when it is not.
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Postby Stu Magoo » Fri Jan 15, 2021 5:28 pm

Thanks for your replies - sorry it took a while for me to reply.
I happened to wipe the face of the flex plate with a damp dusting cloth and was preparing to paint the walls.

The thermostat on the hot water cylinder has 3 connections:
Constant live
Neutral
Live Switch - to which the yellow/green flex wire is connected. There is no Earth connection.

At the flex plate the yellow/green wire from the thermostat (Live Switch)is connected to the Earth terminal of the flex plate as is the Yellow wire (Live Switch) from the Cable feeding into the socket.

The Earth terminal of the flex plate is connected to the crew heads of the plate itself by a solid metal plate and is being used as a cable connector for the Live Switch wire. Subsequently when the thermostat is calling for heat the screw heads are live, when its satisfied they are no longer live. This is how I received the electric shock.

I'm tempted to just get a connector block and use it to connect both the live switch wires from the earth connector in the plate and then at least the screw heads will not be live when the thermostat calls for heat. I'll sleeve these wires brown to identify them as live.
How is a Thermostat flex normally wired into a flex face plate ?
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Postby Mr White » Fri Jan 15, 2021 8:41 pm

In light of what you have said, I would strongly recommend you get an electrician to come round and have a look to see what is what and change any damaged cable.
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