Dual RCD Consumer Units
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JohnD said:There are also double-decker CUs where you (can) have an RCD on each rail, fed from a common main switch, the idea being that a trip on one rail will not bring down the other.
However, RCDs being what they are, I suspect that there could be odd leakage current that sometimes would, unless one of them was delayed.
For example:
If your needs are more modest you can also do it on a single rail
John: Am I having a thick moment? Please correct me if I am!!
Isn't that set-up effectively the same as a split-load set up but without the S type RCD?
What's to stop the 100mA tripping when a fault occurs on the 30mA side?
The double-decker one isn't like a split, because a fault to earth on the top rail (should) trip the top-rail RCD but not the bottom one, and vice-versa.
If you had a TT Split Load with a 100ma S-type as main switch, a fault on, say, the lights would trip the delayed one; and, as it was effectively the main switch, you would lose all sockets as well, on the 30mA RCD circuits.
Now I look again at the single-rail CU in the lower picture, I see it has been assembled with no RCDs; I can't see the point of that config.
(p.s. I can put up a pic of the innards of a double decker tomorrow, if you like. but the way it works, the top deck looks like an ordinary CU, it has been assembled with the RCD to protect all top-deck circuits.
The main switch also has P and N busbars running down to the top of the RCD in the lower deck, which again looks like an ordinary RCD protected CU.
The top-deck RCD protects only the top-deck circuits; and the bottom-deck RCD protects only the bottom deck circuits.
You could swap either RCD for a 100A DP switch if you wanted; or remove it and have an extra two MCBs or RCBOs instead. you could also take out the top Main Switch and replace it with a S-type RCD.)
If you had a TT Split Load with a 100ma S-type as main switch, a fault on, say, the lights would trip the delayed one; and, as it was effectively the main switch, you would lose all sockets as well, on the 30mA RCD circuits.
Now I look again at the single-rail CU in the lower picture, I see it has been assembled with no RCDs; I can't see the point of that config.
(p.s. I can put up a pic of the innards of a double decker tomorrow, if you like. but the way it works, the top deck looks like an ordinary CU, it has been assembled with the RCD to protect all top-deck circuits.
The main switch also has P and N busbars running down to the top of the RCD in the lower deck, which again looks like an ordinary RCD protected CU.
The top-deck RCD protects only the top-deck circuits; and the bottom-deck RCD protects only the bottom deck circuits.
You could swap either RCD for a 100A DP switch if you wanted; or remove it and have an extra two MCBs or RCBOs instead. you could also take out the top Main Switch and replace it with a S-type RCD.)
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That's right, they aren't in series.
However leakage currents often travel up and down unexpected paths, so you still might find they both tripped together, unless the lighting circuits were delayed.
(sometimes a fault in one house will trip the RCD next door! Currents probably passing up water-pipes through main bonds.)
However leakage currents often travel up and down unexpected paths, so you still might find they both tripped together, unless the lighting circuits were delayed.
(sometimes a fault in one house will trip the RCD next door! Currents probably passing up water-pipes through main bonds.)
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I have experienced several times now energising of a circuit on the NON-rcd side of a regular split board causing the RCD to trip out.
Very unusual though this is, it could also happen in your arrangement, John!
Don't know a way round it, though...
Very unusual though this is, it could also happen in your arrangement, John!
Don't know a way round it, though...
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Steady on, fella!!
I'm sure I can rearrange these letters into a recognisable order....
C O R B
I'm sure I can rearrange these letters into a recognisable order....
C O R B
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