.....do you mean intergalactic cabers are not sensible?.............
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I know what you mean. Plowman's cabers are odd.
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...having beamed down from heavy cabering...he says......
.....he does need prescribing anti-caber pills....
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......garbage is garbage and he does come out with it in truck loads....Sad but true.....
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OK, last time.
You have stated that an arrangement where there is a RCD protected ring final circuit designed for supplying sockets in a house, has an FCU installed. From this FCU (fused at 13A) is fed a SWA cable to an outbuilding. In which the SWA terminates at another CU which supplies a ring final circuit for power, and (rather oddly) a ring circuit for lighting.
There are several things wrong here, but let us just take one: Discrimination. The design described above does not provide it. BS7671 requires it, therefore the design is non compliant.
If you wish to assert that my statement above is incorrect, then you will need to explain how your design will discriminate under fault conditions. In particular:
See two simple questions. If you can't answer them, then the system does not comply. Simple huh?
While you are at it, you may want to explain the logic of the design decision to include a 30mA RCD in the supply to the outbuilding lighting circuit. How for example do the lights stay on should that RCD operate?
(it is also poor design to place circuits run to outbuildings on RCDs shared with other house wiring since they are more likely to give rise to spurious trips)
Just for added entertainment, would you care to provide some design details from your own version of this design:
Does your outbuilding have its own RCD or just a switched incomer?
What rating / type CPD is protecting the ring circuit in your main CU?
What rating fuse is in the FCU?
What rating / type CPD is protecting the power circuit in the outbuilding?
What rating / type CPD is protecting the lighting circuit in the outbuilding?
I am not making accusations. I am stating that the arrangement you have thus far described will not comply with the wiring regs for several reasons, some of which I have stated above.
Please note also that I am not disputing your claim that this has been implemented in the past, or will not be again implemented in the future, I am just pointing out it is non compliant, and poor design.
I'm a bit puzzled by the title of this thread...
I thought it was going to be about rebuilding engines, but it seems someone's taken the P...
I thought you'd have been familiar with IMM speak by now?
Feeling rather awkward here (for obvious reasons) this is worryingly similar (although not identical) to the arrangement I found myself with here.
The house has a CU with one RCD protecting all circuits. It's more than a 30mA trip - I can't remember exactly how many, and can't get to it at the moment (I've got a gout infested knee) to check. May even be
100mA [hmm - I see from another thread that this might indicate TT earthing. I don't remember a sign on the CU (I've done nothing to the electrics here apart from change a few light fittings, so aren't too aware of all the details. There is certainly no other RCD to protect any of the internal sockets: perhaps the theory is that with a garage, no-one is going to power external devices off the house circuit, but this explains my posting a few days ago talking about adding an RCD protected external socket]One MCB protected circuit of this feeds a small CU in the garage, which has a 30mA RCD built in. This has two circuits: one the lights and one the sockets, each with their own MCB.
Now you've explained everything, I realise that this isn't right and should be fixed. Ooops - I can't do that now, thank you Mr Prescott. Better leave it as it is.
No need to worry too much - its not as bad as the setup described above. The setup you have would not meet current standards (for some of the same reasons discussed above), however there is no requirement to bring existing work up to scratch unless you are planning to alter it anyway.
It was quite common at one time to stick a 30mA RCD in for the whole house. It is not done these days because of the problems associated with losing lighting circuits at times you really would rather not.
It could well be a 100mA one. There will not usually be any label to say you are on a TT system (the only one that usually gets explicit mention is PME). However the clues would be things like if you received your power via overhead wires, or if you have an earth stake in the ground outside.
This again is much better than the bodge drivel was talking about with a CU fed off a spur off another unrelated circuit - you at least have a dedicated supply to the garage CU and it is not restricted to a total load of only 13A. It would not meet current standards because of the problem of discrimination - i.e. a trip of the MCB in the garage would lose the lights there as well. You also have the potential problem that if the main house RCD is a standard one (i.e. no time delay), then a trip fault in the garage could also trip the house RCD. (just because the garage will trip at a lower current imbalance, it does not mean it will always trip first or instead of the upstream one)
Either that or give Prescott all the respect he deserves and fix it anyway ;-)
You could actually make a number of improvements as "minor works".
Adding a battery maintained emergency light (i.e. one that comes on when the power fails) to the garage would solve the problem with lack of discrimination between its circuits there - a RCD trip would still remove power from both its circuits, but the light would ensure you are not plunged into darkness while waving your hands about near the sharp end of a power tool.
If you are on a TT system, then swapping the RCD in the main house CU for a time delayed one, plus adding a RCD protected socket for use outside would solve most of the other issues. If you are not on a TT system, then you could replace the main RCD with a switch and add a 30mA trip RCBO onto the downstairs socket circuit.
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