RE: Re: [OT] Wiring - RCD's

["Paul Gale" <groups@xxxxxxxxxxxxxxxx>]

Thanks David.

Paul.



> -----Original Message-----
> From: David Buckley [mailto:db@xxxxxxx]
> Sent: 15 March 2004 03:53
> To: ukha_d@xxxxxxx
> Subject: [ukha_d] Re: [OT] Wiring - RCD's
>
> --- In ukha_d@xxxxxxx, "Paul Gale" <groups@s...>
wrote:
> > Anyone know if you can fit two RCD's in line?
>
> Yes, you can put multiple RCDs in line.  The way they work is to
> measure the difference in current flowing in the phase and neutral
> conductors, and if they are different by more than a certain amount,
> then to open the circuit.
>
> However, ensuring the right one trips is harder.
>
> If you use different current threshold ratings (your example of 30ma
> and 100ma) then for a 50ma leak, the RCDs should discriminate
> correctly.  Put a 500ma leak on, and its a crap shoot.  Either could
> win.
>
> Under these circumstances, the best approach is time
> discrimination.  The idea is that the faster unit will always trip
> first.  This approach is widely used in circuit breakers of all
> sizes from the home consumer unit to the national grid.
>
> However, i've not seen any RCDs with either adjustable or delayed
> trip action.
>
> Also, if your higher RCD is also protecting other stuff of the plug-
> in variety, then you would not want either to delay the trip, nor to
> have a higher trip current.  You want to live.  It could be argued
> that a slower trip would have negligable impact on permanently wired
> loads such as water heaters, cookers, lights etc.
>
> Advice:  get a non-RCD feed for your garage, and put the sole RCD
> nearby.
>
>
>
>
>
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