Following a bit of a discussion prompted by yours truly failing to do due diligence ....
I was assailed by doubt, and got more uncomfortable with the idea that you could put a 19.1kW appliance on a 4mm² cable. Plus "diversity" is (almost?) always covered in "Maximum Demand and Diversity".
But, of course, you can't put a 19.1kW appliance on a 32A circuit - the 10A+(fl-10)*.3 calculation does not change the characteristics of the MCB. 19.1kW may well result in a post-diversity current of 31.9A, but on switch-on a B32 isn't going to put up with 83A for very long.
But up with what will it put?
"1.45In within 1 hour" is satisfied by 1.45In within 10ms. Can you rely on it being able to pass 1.45In for any length of time at all? Is the only figure you can properly rely on the non-tripping current of 1.13In? Should you probably not put anything larger than an 8.316kW appliance on a B32?
We've all seen the time-current curves for BS EN 60898 devices, but are they typical? Are they the maximum times (i.e. worst performance) you can expect from them? Is there any official guarantee that any device won't work much faster than those curves?
If I built a very sophisticated device which would pass 1.13In indefinitely (as required) but tripped "instantly" at 1.14In (ticks the box for 1.45In within 1 hour) would it comply?
Interestingly, when I got out my copy of the IET's Electrical Installation Design Guide, I read that (with my emphasis) "The demand of a circuit or of an installation is the current taken by the circuit or installation over a period of time, say 30 minutes", which does put my original concern firmly to bed.
Without any tea.
Actually, what was the interesting bit, and this probably goes a long way to answering previous questions about leeway on cable ratings, tolerances, all the malarkey about how one must use actual voltage rather than nominal or ones house will explode etc, at Iz a PVC cable takes 1 hour to get to 70°C.
Yup.Fair enough. Does that mean that you agree with my interpretation (which, as I said, seems to be the basis of most advice one sees being given about diversity)?
I was assailed by doubt, and got more uncomfortable with the idea that you could put a 19.1kW appliance on a 4mm² cable. Plus "diversity" is (almost?) always covered in "Maximum Demand and Diversity".
But, of course, you can't put a 19.1kW appliance on a 32A circuit - the 10A+(fl-10)*.3 calculation does not change the characteristics of the MCB. 19.1kW may well result in a post-diversity current of 31.9A, but on switch-on a B32 isn't going to put up with 83A for very long.
But up with what will it put?
"1.45In within 1 hour" is satisfied by 1.45In within 10ms. Can you rely on it being able to pass 1.45In for any length of time at all? Is the only figure you can properly rely on the non-tripping current of 1.13In? Should you probably not put anything larger than an 8.316kW appliance on a B32?
We've all seen the time-current curves for BS EN 60898 devices, but are they typical? Are they the maximum times (i.e. worst performance) you can expect from them? Is there any official guarantee that any device won't work much faster than those curves?
If I built a very sophisticated device which would pass 1.13In indefinitely (as required) but tripped "instantly" at 1.14In (ticks the box for 1.45In within 1 hour) would it comply?
Interestingly, when I got out my copy of the IET's Electrical Installation Design Guide, I read that (with my emphasis) "The demand of a circuit or of an installation is the current taken by the circuit or installation over a period of time, say 30 minutes", which does put my original concern firmly to bed.
Without any tea.
Actually, what was the interesting bit, and this probably goes a long way to answering previous questions about leeway on cable ratings, tolerances, all the malarkey about how one must use actual voltage rather than nominal or ones house will explode etc, at Iz a PVC cable takes 1 hour to get to 70°C.