RCD Spur for Shower Pump Ask questions and find answers to many subjects relating to electrics and electrical work

[Heeber]

hi folks,
I've taken a spur from the fused switch for the immersion element in the airing cupboard.

I converted the existing single box to a dual box ( http://www.screwfix.com/prods/22772/Ele ... Lining-Box )
so I could easily put the fused switch back in. I connected the single RCD switch ( http://www.screwfix.com/prods/83049/Ele ... 3A-RCD-FCU )
off the feed to the fused switch - i.e. a very short spur!

I've connected up the pump to the RCD unit, however, it does not seem to display any lights on the switch when pressing Reset/Test buttons.

I have not yet plumbed in the pump, so it's not going to be drawing any current - so is that the reason no light shows, or have I committed some schoolboy error?

Many thanks,
Heeb

[ericmark]

I see no reason why the light should not come on. But reading the instructions they look as if they have been OCR scanned and no corrections made i.e. S instead of 5 so can't be sure.

[Heeber]

OK, so had a further check.

The switch I was hooking into is on a spur, but as I was wiring as if a double socket, I thought this would be ok.

However, just went back with the multimeter :

(across the feed coming into the first switch)

across L - N : 18v (would have expected 240v)
across L - E : 240v
across N - E : 222v (would have expected 0v)

There are plenty other wires under the airing cupboard (feeding the CH work) but the spur I'm using comes straight out floor, into the switch.

There are no other sockets near to this to tap into, so this is a potential disaster (i.e no shower pump!).

help!?

Thanks,
Heeb,

[ericmark]

You have lost your neutral connection. The 222v is going through the neon etc of your RCD unit which is why neutral is considered as a Live wire and the Phase wire on a single phase supply is called Line not Live to differentiate phase and neutral.

As to where you have lost the neutral is something I can't really help with.

[Heeber]

Thanks for that, worrying, but at least explained.

Question though, is this likely to be a fault or something deliberate?

As I said above, the existing switch directly feeds the element in the water tank. My fear being that this is something that couldn't be "fixed" without compromising the element feed. (Which I don't ever use!)

Is there an alternate way to wire up the RCD switch in this scenario?

Many thanks,
Heeb

[ericmark]

You need to find break in neutral feed, can't really help remote needs hands on well at least being there to work out where or why the neutral is missing.

[Heeber]

Had a look at the switch in the kitchen marked "water heater" (only have ever used the GCH to heat water since we moved in).

Similar story. It's on a spur, and reads :

across L - N : 197v (would have expected 240v)
across L - E : 244v
across N - E : 42v (would have expected 0v)

There is a whole raft of switches on the wall (previous owners!), feeding under-cupboard lights and sockets. The closest switch has no load on it, and cross-checking, I get continuity between it and the Water Heater switch on Live, but not Neutral. Is that correct, or is this the break?

If this is the prob, then I'm gonna have a log of tiles to take off!

(PS - and before, is there any sense that this might be deliberate?)

Thanks,
Heeb

[ericmark]

I am sorry but it is a little more complex than just measuring volts as with any cables running next to each other there is some capacitance and inductance so without loads you can get some funny readings. From the reading you give:-
across L - N : 197v (would have expected 240v)
across L - E : 244v
across N - E : 42v (would have expected 0v)
I would expect there is still a neutral problem. There is normally a N – E reading but not as high as you show. I think from what you say you may have reached the stage where you need to get an electrician to sort it out for you. I think your talking about grid switches and they would normally have both line and neutral feeds to each switch but not always which is why I would be happier if you got some local help.

Yours Eric

[Heeber]

just to let you know - got a spark in.

traced prob back to consumer unit - all the neutrals were loose!

now sorted - shower saved!

thanks for help,
Heeb

[ericmark]

Thankyou for letting us know. Always nice to see how well we did.
Eric