Hello, It appears that my whole lighting circuit has no earth. We are family of four with young children, but it's me who usually handles the lights ;-) Is this a clearcut case for a rewire or is there an easier way remedy or avoid the problem. Fred
No, its fine, provided you have plastic (or double insulated) light fittings and switches. Metal switches (and many metal fittings, such as spots/ceiling fans) are unlikely to comply with this.
However, such a circuit is likely to be old. If done in PVC, there is little to worry about. However, many old circuits will be done in rubber, which WILL indicate the need for a rewire.
Christian.
If the cable is rubber, then you need to schedule a rewire as a matter of some urgency, and until then, DON'T TOUCH IT -- any movement can lead to insulation falling away as a powder, which is pretty unrepairable except by a rewire. Don't unscrew a light switch to check this -- look at the wiring in the loft or somewhere else where you can do so without moving it.
If the insulation is PVC, then you should schedule a rewire, but it's not necessarily so urgent. What you should do immediately is make sure all your light switches are plastic (not metal) faced and the light fittings are all double insulated.
As someone who has experienced a shock from simultaneously touching a metal screw retaining a double insulated switch into a metal backbox that was contacting the live feed, to a metal carpet join strip that I was standing on in my socks I can confirm it hurts.
Someone ought to provide M3.5 durable plastic screws - but I don't think they do!
A far more acceptable and viable solution is to install or extend the RCD to protect the whole house and forget rewiring (unless its rubber) Of course if you are concerned that loosing all the lights is a problem then stick a few emergency lights around the place.
You can get plastic caps that clip into the screw holes.
Christian.
Isn't this advised against in the regulations ? On the basis that if the RCD were to trip out, you wouldn't want to try and find your fuse box in the dark ?
I think a small maintained emergency light over the CU (driven from the circuit that would otherwise provide illumination for the CU) would be a very good idea in this circumstance.
If the wiring is rubber, it will be very old and normally in a dangerous state, and need rewiring. If its pvc, you have more options:
There is also the option to fit an RCD to the lighting circuit and use any existing metal fittings. It wont give perfect safety but is a huge improvement in cases where rewiring is unaffordable. I mention it cos there are a few in that position.
NT
Good point. Affordability is one issue, a family of four quite another. Must be one of the worst jobs to get done whilst living in the house with young children. Found the boiler swap hard enough to stomach, but going on holidays whilst the electrician rips up all the floors? Hard to take I must say. Will therefore look into the RCD - and also consider what other electrics need doing, but it's not looking good I am afraid. Fred
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There seems to have been a fashion around here at some time in the 1960s for lighting circuits with no earth, wired through backboxes with plastic inserts into which the screws for the faceplate screwed. Thus, although the backbox was metal there was no connection to the metal screws.
Hwyl!
M.
Even with a missing earth I wouldn't RCD a lighting circuit, unless it was required by TT earthing.
Christian.
Pretty certain RS Components do nylon screws.
However, there's no reason a metal back box should ever be live if the wiring was well done in the first place.
I would, benefits outweigh downside, especially with kids, but its only fair to point out to Fred that if something in the lighting develops or has already developed an earth fault, which is possible with no earth wire, you might find the rcd just trips. Its posible. If thats so, its best you dont use the circuit really.
The main q really is do you have rubber or pvc. If its pvc you shuold be ok, if its rubber, youve got a mess that needs replacing as soon as poss.
If its so bad you need to disconnect it, temporary wiring is easy, just not pretty. If youre stuck, plug in lights are fairly practical.
NT
Yes I just noticed they do supply M3.5 but at the time they were unavailable certainly from the main distributors (Farnell/RS/Vero/STC/ etc) and if I recall correctly one of the major nylon pillar/screw manufacturers only did M3 and M4
Anyway the whole point was that if the backbox is not earthed then if as in my case the screw connection to the switch was slightly high resistance it degraded the insulation gradually (over a period of
10-15 years) This was sufficient to cause contact between the wire and the backbox - this would have been trivial if non metal screws had been used or if the backbox had been earthed the MCB/ fuse would have blown.I suspect the fault had been there for quite a while though and it was only accidental simultaneous contact from the fixing screw via sweaty feet to the carpet strip that was sufficient to be felt - badly especially as it was a cross chest shock. If I'd been wearing shoes or been fully on the carpet I doubt there would have been anything felt at all.
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