RCD or not RCD?

[deanmacken]

All circuits on my CU are covered by an 80ma RCD, just installed a whirlpool bath and it came with an 30ma RCD. Should this be used even if spurring off the ring main that is covered by the RCD on the CU? if so why?

P.s. i know this is notifiable. mostly curious

 

[flameport]

No, as there will be no way of knowing which RCD would trip. Could be either one or both.
Probably supplied like that as many existing circuits won't have an RCD on them.

(presumably you mean an 80A, 30mA rcd, not an 80mA one?)

However you shouldn't really have all the circuits in the CU covered by a single RCD, as this will mean total power failure in the event of any fault.

 

[spark1]

Hi Dean

Will you just confirm the Specification of the RCD on the Consumer Unit.
Should that have read 80A /30mA ?

 

[sparkyspike]

You won't need the supplied RCD. They tend to supply them as standard. Stick it on eBay!

 

[deanmacken]

Yep sorry its says 80Amp, .03a which i presume is 30ma?

i know all circuits shoulnt be on this but the CU was in here when i moved in, i think new split load CU is on the cards. we do get nuisance trips that kill all power.

 

[spark1]

If you install the seperate RCD there will be no discrimination. i.e in the event of an earth leakage problem it is likely both will trip.[ No great problem though] I would Personally fit it if you already have it as it cannot cause nuiscance tripping on the rest of the installation, it can only enhance the safety of your whirlpool bath installation...who knows the one in your consumer unit may be out of spec !

 

[davelx]

I'd have thought that the chances are that the main RCD would trip at a lower leakage current in the whirlpool spur than the dedicated RCD, because the main RCD will already be a little out-of-balance due to L-E leakage in other appliances/circuits which it feeds.

 

[ericmark]

Basic rule as one moves down line the size of RCD reduces by 1/3. Sometimes time delay is also used but basic if main board has 30ma then next one would be 10ma.