immersion heater/FCU

[Mr a.m.p]

Hi, I'm new to this so please bear with me.

In my airing cupboard is a switched 13a FCU with red neon.
This is connected to a 3kw immersion heater.
When the fcu is switched off The red neon glows ie is lit dimly but not at full brightness.
When the fcu is switched on the neon lights up as normal ( full brightness)
Am I right in thinking that when switched off, the neon should be completely off?
I'm worried this may start a fire so I've removed the fuse for now at the fuse board.
Why & how do I fix it?

 

[Chri5]

Has it been recently fitted?

An incorrectly wired neon f/ spur such as the load terminals having the supply wiring and the supply terminals having the load cable (in other word wrongly wired) can show the conditions you mention.

Take the fused spur plate off (having isolated the circuit at CU fuse) and have a look

 

[Chri5]

Oh, and don't ask me how I know the neon stays on when the wiring is the reverse of being correct

 

[Mr a.m.p]

Hi,thanks for speedy reply,

Not sure when it was fitted as I've just bought the house & probably will never use the immersion heater in the later future.
There are 4 terminals ( not including earth ) in the unit two are "L" and two are "N" but none indicate wether they are load or supply.
Hope this makes it clearer?

 

[ban-all-sheds]

Surely if you swap load & supply the neon just stays on full brightness all the time?

I can see how an unlikely combination of swapping load & supply on the phase only, and an element leaking to earth might cause this, but that's all.

It would be good to know how the switch is wired.

 

[Mr a.m.p]

I haven't a clue either why the neon stays on even, it is only very dim but from your reply I'm guessing its just a case of swapping them over as the supply is in the load and load is in the supply.

Many thanks.

 

[ban-all-sheds]

How do you know that if the terminals are unmarked?

 

[Mr a.m.p]

Hi, here,
Here goes with an explanation of how the switch is wired ;


At the back of the plate behind the fuse ;
On top is a the "L" from the supply
Below this is the "N" from supply

At the back of the plate behind the switch ;
At the top is the "L" from the load/immers heater
Below this is "N" from the load

So the supply is wired to the fuse side and the load is wired to the switch side.

Sorry if that confuses things,tried to keep it short and simple.

 

[JohnD]

it might be easiest to just turn off the supply and fit a new one. If it is on a dedicated 15A or 15A circit it does not need an FCU, just a 20A DP switch (pref with neon) which will only cost you a few pounds.

You can make sure you wire the new one correctly.

If there is still a problem then you may have a wiring fault which will need investigation and correction. Have a look for Green and Yellow wires supplementary bonding the earth of the circuit to the copper pipes and tell us what you can see.