The existing cooker circuit is 6mm² on a B40. The customer wants to replace the free-standing cooker with 2 built-in ovens and an induction hob. Will each cable from cooker outlet to device need to be the full 6mm², (e.g HO7RN-F) or can I get away with anything smaller and more convenient (e.g. what's supplied with each oven/hob, if anything)? The final purchasing choice hasn't been made yet, so I don't know whether any of the devices will be suitable for a 13A plug/FCU, which can obviously accept a smaller cable.
Are you sure it is not enough ? Usually it is, the range of Zs for a far end fault for which the 2.5mmsq cable does not get too hot in the breaker trip time is quite wide.
For a period of 5 seconds or less, the relationship I2t = k2S2 characterizes the time in seconds during which a conductor of c.s.a. S (in mm 2) can be allowed to carry a current I, before its temperature reaches a level which would damage the surrounding insulation. so for 2,5mmsq, say 0.08 x 106, l say 80 000 allowable thermal stress for cables I2t (expressed in ampere2 x second x 106) so for a typical 40A breaker
so any fault less than about 4kA, and high enough to take out the breaker fast, say 5* 40A plus 10% for luck, say any fault current in the range from 250A to 4000A will be just fine for full fault protection for a 2.5mm cable on a B40.
Are you sure it is not enough ? Usually it is, the range of Zs for a far end fault for which the 2.5mmsq cable does not get too hot in the breaker trip time is quite wide.
For a period of 5 seconds or less, the relationship I2t = k2S2 characterizes the time in seconds during which a conductor of c.s.a. S (in mm 2) can be allowed to carry a current I, before its temperature reaches a level which would damage the surrounding insulation. so for 2,5mmsq, say 0.08 x 106, l say 80 000 allowable thermal stress for cables I2t (expressed in ampere2 x second x 106) so for a typical 40A breaker
so any fault less than about 4kA, and high enough to take out the breaker fast, say 5* 40A plus 10% for luck, say any fault current in the range from 250A to 4000A will be just fine for full fault protection for a 2.5mm cable on a B40.
