Confusing earth at switch

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Hi, I am confused with the wiring on my dimmer switch...please help.

Basically, when i measure with my DVM between the earth connection and the switched live (ON) on my dimmer switch it shows 101VAC. Is this normal as i am concerned with the state of our wiring, we recently moved in !!

With the switch off it still measures 25VAC between the earth and the live terminal (which is off).

thanks !
 
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what voltage do you get beteween Neutral and Earth? Is this the same as at a socket? And at another light switch which is not a dimmer?

what sort of main earth does your house have?
 
Sounds like a floating CPC.

This is were you have an 'earth wire' (CPC) at the switch, but it isn't actually connected to earth at the other end.

This is not good.
 
Thanks for your quick replies...

I have checked a standard mains socket and have the following -

Between Neutral and Earth = 0VAC
Between Live and Earth = 245VAC
Between Live and Neutral = 245VAC

is that bad :cry:
 
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No, thats good, as it shows there is an earth to the property.

Could you trace the wire from the switch to where ever it goes? (probably either a junction box or the ceiling rose)
 
That is good, but the switch - not so good.

The earth at the switch sounds floaty-floaty : IE - Not connected to earth at the other end.
 
the socket sounds fine


I expect Rf is right about your lighting circit

Have a look at a few more light switches and ceiling roses and you will wotk out if it is a general problem

Houses built pre about 1969 often had no earth on the lighting circuit. You can manage round that by using only insulated (not metal) lamps and light switches. On a newer house it is more likely to be a fault or a bad connection that can be remedied.
 
Phew, that's not so bad then !

The house was built in 1935 so it sounds as though the lighting circuit may not be earthed.....seems strange but hey.

I checked another switch, also downstairs and on same fuse circuit, which measured 120VAC between switched live and earth.

The dimmer switch is currently brass and was already fitted when we moved in. It seems ok and i can't "feel" any voltage on it (i've experienced voltage shocks as i'm an electronics engineer) but this is obviously different to electrical engineering.

I was planning on replacing the switches with newer nicer metal one's and also have new metal light fittings to put up. Is this a problem without the earth?
Is there a way that i can earth the lighting circuit?

Unfortunately i can't get to the conneting rose as it is well hidden.

For information the mains consumer unit is an RCD trip type.

thanks again.
 
Lets just take a couple of steps back here.

You have dimmer switche(s), and you are testing switched live > earth.

What is the reading permanent live (common) > earth?

I would think your house has been rewired since the 1930s, as you have an earth wire (albeit non functioning) 30s wiring doesn't have an earth at all.
 
...I was planning on replacing the switches with newer nicer metal one's and also have new metal light fittings to put up. Is this a problem without the earth..?

YES

Is there a way that i can earth the lighting circuit?


Yes, you can have a good poke round and see if when it was last rewired, it was done using cable which included an earth wire (CPC). if so, you may be able to connect it where not already done, and rectify any defects. If not, then the lighting circuits (at least) need rewiring.
 
Hi,

On the back of the dimmer, between the permanent Live and the Earth, measures 123 VAC.

As for connecting the earth of the lighting circuit to the earth of the rest of the house, could i just have a look in the consumer unit, see if there is an earth wire in the cable that goes to the appropriate rcd switch for the lighting circuit and connect that to all the other Earths?
 
Can I suggest you get a competent electrician to take a look for you?
I would suggest at the minimum that the lighting circuit in question should be tested and inspected with any faults or rewiring being rectified ASAP.
 

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