I think however a 40A 3036 (not checked availability yet) and appropriate cable is a better route.
What type of board is it? 45A (not 40A) 3036 do exist but you need a board which will take them...
I think however a 40A 3036 (not checked availability yet) and appropriate cable is a better route.
That sounds a bit like a classroom example of potential non-discrimination!Have you tried using a single B40 amp breaker to feed a small consumer unit, containing three B16 breakers, one per heater, wired in appropriate cable for the lengths involved, ending in a 13amp fused spur box for each hand wash heater?
Indeed, and if I may add a little explanation, since this ties in to a thread I started this afternoon...When BS3036s are used the CCC of the cable must be derated by a factor of 0.725.
The standard CCC tables assume the use of a Type B MCB, or something with equivalent characteristics. For such a device, I2 (current required to cause operation within 1 hour) is 1.45 times In (the 'rating' of the MCB). Hence, for example, if the tables give a CCC of, say,10A, that means that the cable can safely carry 14.5A for an hour.
With a BS3036 fuse, I2 is 2 times In (as compared with 1.45 times In for the MCB). A cable protected by a 10A BS3036 therefore has to be able safely carry 20A for an hour. The tabulated CCC figure therefore has to be adjusted, by a factor of 1.45/2 (i.e. the ratio of I2/In values), which is 0.725.
Kind Regards, John
Technically/theoretically speaking, no, it couldn't possibly apply, since that 'rule' only results from the current that could flow (for 1 hour) in the event of an overload before a BS3036 fuse operates. If it is deemed that "overload cannot happen" (always an iffy concept, IMO), then that situation obviously cannot arise.Does this 0.725 rule apply if overload protection is not needed?
That sounds a bit like a classroom example of potential non-discrimination!Have you tried using a single B40 amp breaker to feed a small consumer unit, containing three B16 breakers, one per heater, wired in appropriate cable for the lengths involved, ending in a 13amp fused spur box for each hand wash heater?
Kind Regards, John
If the building is three-phase, one 16A breaker on each phase wired in 2.5mm terminating in a 20A DP isolator to which the water heater is connected?????
Ooooh!one should really be able to actually 'up-rate' it, by multiplying by a factor of 1.45 - but try convincing anyone about that!
You were talking about a B40 MCB feeding three B16 MCBs which, in turn, were feeding three 13A FCUs. You obviously would get no signicant discrimination between the 13A fuses and the 16A MCBs. As for discrimination between the B16s and the upstream B40, that's pretty marginal. With a 3x differential, you would hope to get discrimination, but 40/16 is only 2.5x, so I certainly wouldn't put my shirt on that discrimination.John, please explain why this looks to be a case for none discrimination. I'm guessing this is because you were thinking that the 45A upstream fuse was 3036 and the 16A was a 60898? Even so I think discrimination would have been satisfied (please feel free to check as this is the first time I've considered discrimination).
Fine, and that makes sense. In that case you wouldn't need to have both B16s and FCUs, so that discrimination problem goes away. However, I would still not put money on a B16 and B40 discriminating. The ideal, of course, would be to have the three B16s in a CU fed from it's own switchfuse from the main supply, with, say, a 60A or 80A fuse in that switchfuse. Then you would certainly hope to get discrimination from the B16s.As for the MIs it only calls for the use of a FCU if we're taking a spur of the ring.
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