Another tingling light switch thread.
- Thread starter Keithmac
- Start date
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If there is enough height to the CU for RCBOs to be 'easily' installed, then that would be a theoretical possibility - although RCBOs are so much more expensive that MCBs that such an approach would probably not make sense unless you actually wanted RCBOs (which is not a bad idea!). Some would probably argue that doing that would change the CU enough that it counted as a replacement one, in which case it would have to have a metal case - but it looks as if yours might already be metal?
On balance, I would personally think that it would probably make more sense to get a new CU - either dual RCD or 'all RCBO'.
Kind Regards, John
Thanks John, all RCD protected would be nice so it looks like I'll have to start saving the pennies!.
Yeh it is a metal consumer unit.
Main concern is the metal light fittings and metal oven are not RCD protected at the moment.
I have a customer at work who I get on with very well who's and electrician, I may have to bend his ear next time I see him rather than going through the Yellow Pages.
Yeh it is a metal consumer unit.
Main concern is the metal light fittings and metal oven are not RCD protected at the moment.
I have a customer at work who I get on with very well who's and electrician, I may have to bend his ear next time I see him rather than going through the Yellow Pages.
A dual RCD CU (covering all circuits) would currently be quite a lot cheaper than an all-RCBO one - MCBs are typically £2-£3 each, whereas RCBOs are generally over £20 each (and RCDs perhaps about £30 each).
If you know him fairly well, you would presumably at least be fairly confident that he is not a 'cowboy', which unfortunately is not always the case with Yellow Pages etc.!
If you decide to go for a new (or even just 'refurbished with RCBOs') CU, any decent electrician would do fairly extensive tests of the installation before touching the CU - so you could thereby avoid paying separately for an inspection/testing.
Kind Regards, John
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It should be pointed out that RCDs are for personal protection.
It makes absolutely no difference to your lights, or other appliances, whether there is an RCD or not.
As you have discovered, should one of your unearthed light fittings have become live in the event of a fault then, had you touched it, an RCD might have saved your life. An RCD might have caused disconnection IF there were a path to earth prior to it being touched, but this is unlikely until you become that path.
As it is now earthed, such a fault will result in disconnection of the supply by the MCB before anyone gets there.
Indeed, provided that the fault is of sufficiently low impedance that enough current flows through it to trip an MCB. If the impedance is not that low, the 'touch voltage' is almost certainly not going to get high enough to represent a threat to life (for most people), although they might get a significant shock if they touch it and something (else) 'earthed'.
RCD protection would prevent more than a tiny persistent 'touch voltage' ever occurring.
Kind Regards, John
Well, yes, it's supposed to be. Why would it not be (on a 6A circuit)?
Well, yes, but that's just saying "If things don't work as they should then things will not happen that should, and something that should not happen will".
Not if the light body is live and unearthed.
As you know, the only requirement is that the fault current should be adequate to magnetically trip the RCD is the presence of a 'negligible' (aka 'zero') impedance L-E fault. If the Zs of a circuit is only just low enough for that, then any finite fault impedance will mean that the MCB will not trip magnetically and, if the fault impedance were sufficiently high, not necessarily ever trip.
I don't really understand that comment. I was merely saying that if the circuit's Zs is compliant, then the R2 is going to be sufficiently low that the touch voltage of the exposed-c-p would never get up to what is regarded as a 'dangerous' level, no matter what the fault impedance.
I was talking about the situation in which the light body is earthed - and persistently 'live' (because of an L-E fault) only to the extent of the VD in the CPC - say about 0.12V in the case of a 30mA RCD and a (very pessimistic) R2 of 4Ω.
In contrast, again with R2=4Ω, a B6 should not ever trip unless the touch voltage reaches 6.78V, and not necessarily trip magnetically unless the touch voltage reaches at least 120V.
Whether that means that the level of 'risk to persons' justifies RCD protection is, as you know, something I'm not so sure about.
Kind Regards, John
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