Discuss MCB sizing in the UK Electrical Forum area at ElectriciansForums.net
show us how. us plebs can only do the < and >. and i can sometimes enter "a" without activating the caps lock.Or could be... Iz≥In≥Ib or Ib≤In≤Iz
(just showing off as I've just discovered how to do those symbols)
(still working on how to do subscript on here)
Yes, and put a couple if smiley emoticons on thd post as well!show us how. us plebs can only do the < and >. and i can sometimes enter "a" without activating the caps lock.
BS 7671 specifically stated that ceiling roses etc. can be connected to a circuit with a protective device rating not exceeding 16A, so yes - it's in black and white that you can do it.So when is over load protection needed? In theory you could run a lighting circuit of a 16amp breaker then as long as the cable is correct for 16 amps?
1.5mm cable on a 16a breaker will work perfectly fine. It's how they do it in some other countries.So when is over load protection needed? In theory you could run a lighting circuit of a 16amp breaker then as long as the cable is correct for 16 amps?
1.5mm cable on a 16a breaker will work perfectly fine. It's how they do it in some other countries.
Ah i didn't take into account any potential difference in fitting ratings. I continue to learn !some lighting accessories, switches and connections in the U.K. are only rated at 5/6amps...
that said even running at 15-16 Amos I doubt they would over heat
a) Where the circuit load is not limited to below the cable CCC by design, i.e. the user could plug in or dial up more load on the equipment until the cable is overloaded.So when is over load protection needed
So i'm presuming a fault on 6a stuff wouldn't spike sufficiently to allow the 16a breaker to detect it
So my understandings is it’s more about fault current to trip the breaker under fault conditions the higher rated breakers will need a lower impedance to satisfy the required disconnection time. The breakers primary function is to protect the cable from over heating so as long as the cable is rated higher then the breaker. As for (a) what are examples of overload situations?a) Where the circuit load is not limited to below the cable CCC by design, i.e. the user could plug in or dial up more load on the equipment until the cable is overloaded.
b) Where equipment manufacturers specify it. Or rather, they will sometimes specify a maximum MCB or fuse size, not necessarily as overload protection but as short-circuit protection for the wiring and components inside the equipment. E.g. you might choose a 32A MCB to protect a 6mm² cooker circuit, where the oven is connected by 2.5mm² flex, and so long as the adiabatic is satisfied the flex will be protected against short-circuit. The flex won't handle 32A but the oven can't draw 32A for long enough to damage it, even in the event of an element failure. But the oven instructions might well specify a maximum 20A MCB because the oven internal wiring splits into multiple 1.0mm² cables, and for those the 32A MCB does not offer adequate short-circuit protection.
IMO the extractor fan 3A fuse business is just daft, though!
What governs the level of fault current available to trip the MCB is not so much the normal load rating of the 'stuff' but the resistance of the wiring supplying it. It takes a higher fault current to trip the larger MCB, which puts a lower ceiling on the loop impedance, and might require heavier cables. A long lighting circuit might have to be wired in 2.5mm² simply to enable a 16A MCB to trip fast enough, which is pointless if the total load is less than 6A.
Simple case is someone putting on too many heater (or kitchen appliances of comparable draw) on their 13A sockets.As for (a) what are examples of overload situations?
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