Hi all
I am looking at adding a separate power circuit for a kitchen re-work - currently the kitchen feed is included in the downstairs ring. Both upstairs and downstairs rings (2 x 30A) are currently protected by a
63A RCD covering a split bus bar. If I break out the kitchen and put it onto a separate 30A ring, do I have to uprate the RCD to 100A to cover the 3 x 30A circuits?TIA
Phil
Probably not. You can probably apply diversity of ring circuits here, which is 100% of the current of the largest, and 40% of the current of the rest. That's 30 + (30 + 30) x 0.4 = 54, which is within the 63A rating. Note that you should only apply this in the case of no better information being available. For example, if you already know your two rings get loaded up to maximum, then you shouldn't apply this diversity, but that's unlikely.
I would also suggest you provide a non-RCD protected circuit to your kitchen. At a minimum, you can use it for the fridge/freezer so you don't lose their contents if an RCD trips whilst you are away, and the boiler if it's in the kitchen so you don't come back to a frozen house with burst pipes. Another good candidate is the oven if you have one which runs from a 13A outlet, and then any of the other non-portable applances. The last two kitchens I've rewired I have put in two rings, one RCD protected for all the worktop and other accessible socket outlets, and the other not RCD protected for all the fixed/stationary appliances with sockets positioned such that they are not readily accessible for general use.
Thanks Andrew
Excellent "food for thought" there!
Phil
Yup. Some washing machines and dishwashers seem to have a habit of tripping RCDs rather randomly. Although it's arguable an RCD is just showing a fault which should be dealt with asap.
Might be worth going one further, and providing a dedicated non RCD radial circuit shared between freezer and boiler. Cable's cheap, after all.
Would this not contravene Prat P? Or is this the point where you have to run 4mm?
Phil
In message , TheScullster writes
Why?
No, you can run a 20A radial circuit in 2.5mm^2 T&E cable protected by a
20A MCB. I've done exactly as Dave suggests in fact in my kitchen. (subject to limitations on floor area served - 50m^2? IIRC)
No - you simply use a 16 amp MCB. More than enough for a freezer and boiler circuit.
For a 2.5mm² radial circuit, which you might want to use for other things too, I would make it a a 20A MCB, and unless the earth fault loop impedance was on the edge, a Type C so it shouldn't have any problems if separate fridge and freezer compressors start up at the same time, with anything else also on the circuit.
Doubtful, since its quite unusual to have more than a 60A leccy board fuse running the whole house.
Actually I think you'll find most houses for last 25 years are 100A supplies. 80A was also quite common prior to that. For older installations, at least prior to deregulation (not tried since) it was free to upgrade a cutout to 100A providing the existing supplier's wiring and the CU were suitably rated.
Is there anything to go in the FAQ about what DIY people can do, and not do, in Part P? That would be useful as it is one of those confusing topics that comes up every week. Andy's Wade and Hall seem to write a lot about Part P.
What would be useful is how to get around some of the points of Part P, not in a view to make matters unsafe mind you.
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