Kva
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Totterdown - William Street, to be exact!!
Did a rewire job there.
Did a rewire job there.
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ban-all-sheds said:
BAS's installation sounds pretty standard and i'm sure there are many out there with exactly this type of arrangement happily working on a 100 Amp CU. How can you reconcile a 134A Max demand after applied diversity on a 100 Amp Cu?
Are the sugested diversity figures in the regs wrong or am I confused on the calculation/ interpretation of the result?
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the thing not covered really by the diversity rules for domestic situations is the fact that you are very unlikely to shower and cook and fully load your rings at once
also rings in domestic settings very rarely cover the full 100 square meters
also with the coming of central heating bar fires and fan heaters are used a lot less than they used to be so while a ring may be capable of supplying 30A it is very unlikely to ever be supplying that in practice (we lived with our rings on 15A fuses for years and the only one we ever blew was the kitchen and that only happened every few years)
also rings in domestic settings very rarely cover the full 100 square meters
also with the coming of central heating bar fires and fan heaters are used a lot less than they used to be so while a ring may be capable of supplying 30A it is very unlikely to ever be supplying that in practice (we lived with our rings on 15A fuses for years and the only one we ever blew was the kitchen and that only happened every few years)
The former, I would suggest.brown-nought said:
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My ring's always fully loaded...
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I agree with BAS.
This area seems open to too much interpretation. Regs state diversity can be allowed for by a "competent person" but there are some suggested formulas/values in table H2 of GN 1. Now if we use these figures/formulas as BAS did in his example we often arrive at a value of over a 100 Amps event though we know from experience that it unlikely the electric shower, oven, all the lights etc will all be on together.
So this leads to two questions:-
1) Are the regs any real help when it comes to Diversity
2) Are you happy to sign an installation cert (pink or not) with MD figures arrived at from experience rather than tabulated “standard” calculation. (Cable sizing etc isn’t this open is it?)
I mean what happens in the unlikely situation on Xmas day when the family roast is on, dishwasher, toaster, kettle all going, mum in the shower, granny roasting by the fan heater and dad in the shed playing with his new arc welder and it all goes bang. How hard will it be for barristers to rip into your “design” when they discover you didn’t follow the regs diversity suggestions? (Do you know better than prof. CEng etc…)
And I haven’t even mentioned part P have I.
(I know it might sound like I have contradicted myself, but experience would be valid for 999 out of 1000 cases. But it is that one case where it is wrong that you would have to justify your decision.)
Rant over … this just seems to be one area where I always feel let down by any guidance. Has anyone ever seen a descent book on diversity in electrical design??
This area seems open to too much interpretation. Regs state diversity can be allowed for by a "competent person" but there are some suggested formulas/values in table H2 of GN 1. Now if we use these figures/formulas as BAS did in his example we often arrive at a value of over a 100 Amps event though we know from experience that it unlikely the electric shower, oven, all the lights etc will all be on together.
So this leads to two questions:-
1) Are the regs any real help when it comes to Diversity
2) Are you happy to sign an installation cert (pink or not) with MD figures arrived at from experience rather than tabulated “standard” calculation. (Cable sizing etc isn’t this open is it?)
I mean what happens in the unlikely situation on Xmas day when the family roast is on, dishwasher, toaster, kettle all going, mum in the shower, granny roasting by the fan heater and dad in the shed playing with his new arc welder and it all goes bang. How hard will it be for barristers to rip into your “design” when they discover you didn’t follow the regs diversity suggestions? (Do you know better than prof. CEng etc…)
And I haven’t even mentioned part P have I.
(I know it might sound like I have contradicted myself, but experience would be valid for 999 out of 1000 cases. But it is that one case where it is wrong that you would have to justify your decision.)
Rant over … this just seems to be one area where I always feel let down by any guidance. Has anyone ever seen a descent book on diversity in electrical design??
thats why we have the service fuse
so that in the event of significan't overload it will blow before any real damage is done
imo any sparks who put a 100/80 or worse 100/63 split on a 100A service fuse are asking for trouble
so that in the event of significan't overload it will blow before any real damage is done
imo any sparks who put a 100/80 or worse 100/63 split on a 100A service fuse are asking for trouble
But does it cover 100m²?securespark said:
I've got just this dilemma - I'm going to be erecting an outbuilding, supplying it either via a 63A MCB in its own enclosure, or a 63A switchfuse, and of course I'll also have the 100A house CU.plugwash said:
Even with oven (don't have electric hob), house shower, outbuilding shower and a few other odds'n'sods going, the chances of me drawing considerably more than 100A for an extended period are very small (outbuilding shower will probably only be used a few times a year).
But I guess there is the potential to create an overload, (which AFAIK is illegal, isn't it?).
My plan right now is to put a 100A switchfuse immediately after the meter, and hope that if it does all go pear-shaped, my fuse will go before the supplier's one does.
Anybody know if the service fuse is also a BS88?
Because?...
its imo very bad practice to have a device that could (albieit unlikley) be overloaded without overloading any breaker/fuse in the system
something like
[code:1]
100A service fuse-100A isolator---80A rcd---3 32a breakers for rings
|
2 6a breakers for lights
[/code:1]
in this situation if there was heavy load on the rings then the 80A rcd could be overloaded while the 100A fuse was still within rated current
something like
[code:1]
100A service fuse-100A isolator---80A rcd---3 32a breakers for rings
|
2 6a breakers for lights
[/code:1]
in this situation if there was heavy load on the rings then the 80A rcd could be overloaded while the 100A fuse was still within rated current
So why do they ever make 100/80 or 100/63 boards?
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