Sparkyadrian
New member
Will I require to change the rcd sockets to standard if I fit rcbo's to the db?
Existing Rcd Sockets With Rcbo's
- Thread starter Sparkyadrian
- Start date
Help Support Talk Electrician Forum:
- Joined
- Jun 21, 2008
- Messages
- 17,025
- Reaction score
- 47
Or change up stream RCD to a time delay to give some discrimination.
- Joined
- Feb 5, 2009
- Messages
- 5,612
- Reaction score
- 1
Yes its best to as they wont discriminate between each other.
TBH, I would leave the RCD sockets in situ.
Non-discrimination is not always a bad thing.
The best case scenario is that a socket will trip before the RCBO, which prevents nuisance trip on the rest of the circuit
The worst case scenario is that the RCBO trips before the socket, which is the same as switching to standard sockets.
I've been away from the Regs for a few years, but I don't think it conflicts with BS7671 guidance. I expect to be possibly shot down!
Non-discrimination is not always a bad thing.
The best case scenario is that a socket will trip before the RCBO, which prevents nuisance trip on the rest of the circuit
The worst case scenario is that the RCBO trips before the socket, which is the same as switching to standard sockets.
I've been away from the Regs for a few years, but I don't think it conflicts with BS7671 guidance. I expect to be possibly shot down!
I often fit series RCD's, that is 30mA RCD s.o. with upstream instantaneous 30mA RCD, as redundant protection.
That is at least one of them will trip under fault hopefully, even if they have not been tested every 4 months.
It is not specifically against the regs, however there will be no discrimination as to which trips under fault conditions.
That is at least one of them will trip under fault hopefully, even if they have not been tested every 4 months.
It is not specifically against the regs, however there will be no discrimination as to which trips under fault conditions.
davetheglitz
Electrician
I always thought that RCD sockets worked slightly differently to a standard RCD as when the earth is connected there is a low impedance to earth - hence instructions to disconnect when doing insulation tests.
My concern is that the RCD socket may make the tripping threshold of the upstream RCD just that bit closer.
Personally I would change them - and recycle them as appropriate!
My concern is that the RCD socket may make the tripping threshold of the upstream RCD just that bit closer.
Personally I would change them - and recycle them as appropriate!
No Dave,
The instructions to disconnect are because they are electronic devices in the main and could be "fried" by 500V to earth!
In the experience I have of fitting dozens of these in a redundant role as I explained above, testing @ the "new" upstream RCD & the downstream RCD s.o. the RCD s.o. has no affect on the disconnection time in reality.
Remembering that an RCD should be tested with all downstream loads disconnected, and a cable is seen as a load by an RCD...
Stupid that an RCD can pass test under BS7671 but still fail to disconnect in the event of a fault when in circuit, and this is OK, unlikely but OK!
The instructions to disconnect are because they are electronic devices in the main and could be "fried" by 500V to earth!
In the experience I have of fitting dozens of these in a redundant role as I explained above, testing @ the "new" upstream RCD & the downstream RCD s.o. the RCD s.o. has no affect on the disconnection time in reality.
Remembering that an RCD should be tested with all downstream loads disconnected, and a cable is seen as a load by an RCD...
Stupid that an RCD can pass test under BS7671 but still fail to disconnect in the event of a fault when in circuit, and this is OK, unlikely but OK!
davetheglitz
Electrician
Thanks - I've always appreciated the 'Frying Tonight' issue - but when I've done overall insulation tests as a health check before fitting a new CU (generally at 250v until I know what's going on with L+N connected) I've found that there is a low impedance to earth when there is an RCD fused spur fitted.
This wouldn't occur with a conventional RCD as there no connection to earth.
Whether this materially affects trip times - I don't know - I've never tested it - but I'll bow to your experience!
Must confess I never test RCDs with cables disconnected - surely when testing we're looking system rather than individual components.
This wouldn't occur with a conventional RCD as there no connection to earth.
Whether this materially affects trip times - I don't know - I've never tested it - but I'll bow to your experience!
Must confess I never test RCDs with cables disconnected - surely when testing we're looking system rather than individual components.
No mate, the cables act as a load & a capacitance, the meters we use are too dumb to know the difference between the disconnection time of the RCD on its own, or the disconnection time of the RCD plus the voltage decay from any connected cable capacitance.
Hence why RCD only.
RCD in circuit is not as per regs.
Hence why RCD only.
RCD in circuit is not as per regs.
davetheglitz
Electrician
Blimey - love this forum - learnt something new!
Thinking about it - as soon as a very small resistive load is connected the cable capacitance would be completely swamped.
If the RCD is passing trip times with cables connected surely this is worst case?
Thinking about it - as soon as a very small resistive load is connected the cable capacitance would be completely swamped.
If the RCD is passing trip times with cables connected surely this is worst case?
Last edited by a moderator:
davetheglitz
Electrician
Love it! Sorry - I edited the post as I engaged my brain!! Friday night is whisky night - I won't do it again!Canoeboy said:
davetheglitz
Electrician
Bloody right I haven't invited him! If it was whiskey it might be different!
:coatCanoeboy said:You on the Whiskey and Steps hasnt been invited ?msl:
yer, wont get me on that watered down girly whisky. :|
thats NOT whiskeyCanoeboy said:
thats whisky
You bought a bottle of Whisky for a customer @ £1500, you must be mad!
Sparkyadrian
New member
Thanks for all the replys really appreciate them. Thanks again
what ones?
the electrical ones, or the best sort of whisky/whiskey ones? :slap
yet another thread that stayed well on track, :shakehead
