On wiring the split load CU, will it be OK to put both the cooker and hob onto the RCD'd busbar? or should they go onto the non RCD side? I was thinking of putting both ring mains on the RCD and the cooker/hob, and putting both lighting ccts on the non RCD side so I'm not plunged into darkness if there is a fault elsewhere !!
CU is 100A, 80A rcd
cheers
Perform some risk benefit analysis.
When you get electrocuted by a faulty hob/oven do you want the lights to remain on? Or, when the RCD trips because of an earth leakage on the hob/oven would you prefer salad for dinner?
Maybe you don't like salad :)
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Don't worry - there is lots of info regarding split CUs in the d-i-y archives. After a lengthy study, I have come to the conclusion that the cooker stays off the RCD (as you have suggested) as most cookers 'leak' anyway.
I would normally put the cooker on the non-rcd side. However, if the cooker switch is of the sort that also has a 13amp socket on it and it is likely that the socket may be used to power outdoor powertools then it must go on the RCD side of the CU.
Adam
Cheers, what about the seperate Hob? RCD it?
Same applies, for "cooker" read "hob".
Adam
Thanks
Which is fine right until the point the oven element fails and the break in the earth conductor in the consumer unit that has gone un-noticed for months/years/forever means the fuse doesn't blow and the oven casing rises to mains potential.
A fatal shock is about the 6 inches of reach between the oven and the nicely bonded "split level" gas hob sat right above it.
Apart from the last bit which was narrowly avoided by the owner switching off the cooker at the wall switch the above is actually what happened on an installation a few weeks ago. The earth had failed right in the middle of a sleeved run in the consumer unit. A simple visual examination wouldn't have picked it up.
Put the cooker on the RCD!
I'm now as confused as a baby raccoon !!!
My first thought was to RCD everything apart from the lights, is this sound? the cooker and hob both have seperate radials as they are more than 2m apart (as per regs). What size MCB should serve the cooker & hob (seperateley) the CU came with five 32's one 40 three 6's and one 16.
A simple installation test or PIR would have picked that up.
Adam
The MCB needs sizing in accordance with whatever size cable you are protecting. Without these "unknowns" it's just a guessing exercise.
The guess could be 32A, 20A or 16A :)
6mm cable (4mm is like hens teeth around here for some reason) and cooker 8m hob 11m long
I think the best compromise is a 100mA RCD for everything, with 30mA RCD or RCBO for where there is a real danger.
In practice, although I haven't gotten to the 30mA RCBO for outside sockets, I now have almost zero nuisance tripping on a BIG house, and yet whenever there has been a genuine fault, the RCD has tripped.
(extension cable in the rain outside. 2Kohm short between washing machine motor coil and earth)
You have to make your mind up whether its better to be left in the dark everytime there is a power surge or a big motor cuts in, or whether you are prepared to risk being fried by 100mA .
Even 30mA will kill you if you are unlucky.
But two sweaty hands measures at about 3k, which is like 80mA on a 250v circuit.
Which is why they are EARTHED.
Put it on a 100mA full house trip. Put socketry on 30mA as per regs.
The stove will normally leak enough to get a tingle off if its not earthed.
Welcome to the 'safety mens falling down the stairs in the dark, because you have a 30mA trip and the electronics draws 31mA' brigade.
Look. Houses all 'leak' a bit. Apart from stuff like cookers and kettles that have to balance insulation integrity with high temperatures and cheap cost, steamy rooms and a sweaty thumb print can cause a few mA leakage, every RFI filter in every bit of electronics adds one or two more, the wiring capacitance of all your wires adds a bit more..
I don't regard any wiring as potentially untouchable, so I like an overall RCD including lights.
BUT experience shows that a full house 30mA trip is always tripping for no bloody reason at all. Especially if you have as many TV's, computers, mast head amps, routers, printers and the like as I have.
HOWEVER the regs state that outside sockets have to be on a 30mA RCD.
In practice this means split load or RCBO.
I personally like an RCD protected HOUSE, but set at a level that doesn't do nuisance trips., Here its 100mA. In a small house or flat,
30mA is probably OK on everything.
Depends on the cooker wiring. And the cooker rating. The MCB is there to protect the wiring to the cooker though.
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It turns out not to be a particularly useful size. Wholesalers sometimes don't even stock it.
Use a 32A to protect the cable, although if you feel the need to fuse more closely a typical oven at around 3kW would be "happier" with 16A.
errm what do you think I was doing to even pick up the fault in the first place! I'm not in the habit of walking round kitchens, turning on an obviously faulty oven, finding a bit of well earthed metal and then simultaneously dabbing a hand on each to check for any wiring defects :)
How often do people really have their installations checked? I'd bet some have never been touched in 20 years, maybe more.
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