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| Junctioning 32A cooker circuit with a 13A spur. |
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| paulca:
--- Quote from: dmills on February 10, 2022, 01:46:05 pm ---A standard UK ring circuit (It is a weird UK thing for the non UK crowd) is typically fed by a 32A breaker, and nobody worries about a 2.5mm spur to a single socket. Seems to me that the 6mm 32A line to the oven switch with a short 2.5mm spur to a socket (or more usefully, a switched fused spur for the igniters) is very much equivalent and should be just fine. Or just change the breaker to a 16A one at the DB and call it good, I don't see the issue. --- End quote --- You have a point. I know single spurs off the ring on 2.5mm are common and as you point out it's basically the same thing. If someone puts a drill through that 2.5mm cable it will get give 32Amps of current from the ring until its breaker pops. Also, good point about the 16A breaker. The oven only needs a 16A fuse, the ignitors are negligible and I can more easily use 16A flex for the socket spur and let the hob fuse it's self at 13Amp. The 60A junction box should be grand for creating the spur. |
| themadhippy:
--- Quote ---Seems to me that the 6mm 32A line to the oven switch with a short 2.5mm spur to a socket (or more usefully, a switched fused spur for the igniters) is very much equivalent and should be just fine --- End quote --- Indeed,but come the time you want to sell the place and mr cartel member turns up to do your electrical safety certificate the potential buyer is paying for he's going to say no because it isnt in the big expensive book of rules,and quote a rip off price to "make it safe" |
| paulca:
--- Quote from: themadhippy on February 10, 2022, 03:50:54 pm --- --- Quote ---Seems to me that the 6mm 32A line to the oven switch with a short 2.5mm spur to a socket (or more usefully, a switched fused spur for the igniters) is very much equivalent and should be just fine --- End quote --- Indeed,but come the time you want to sell the place and mr cartel member turns up to do your electrical safety certificate the potential buyer is paying for he's going to say no because it isnt in the big expensive book of rules,and quote a rip off price to "make it safe" --- End quote --- That's easy to flip the other way. (1) it's on the end of a cable, it's consumer equipment and not installation work. (2) "Fine, I'll remove the cooker/appliances from the sale and remove them on my departure" It's sort of why I like the more cowboy approach as it's IS just consumer side add ons. A 13A extension lead for the hob and the 6mm tail to the cooker. I can switch back to all electric or leave it as it was later. If I start installing actual spurs and fused/switched spur boxes, THEN it WILL have to be to code as it IS installation work.... and if I change my mind later and go back to electric, or switch to induction, I don't need to rip it out and resinstall another setup. EDIT: I think the terms "TO CODE" and "SAFE" and both usable. But many SAFE installations would not be "TO CODE". All I really want is SAFE. SAFE enough that an actual spark would frown, but be happy enough, rather than backing away and refusing to work on it. And I don't want to set my kitchen on fire either. |
| mikeselectricstuff:
UK Regs do allow cable to be protected by fusing at the far end under certain circumstances - I'm not sufficiently familiar with the details to know if this would apply here. Why does the cooker socket need to be on flex ? 4mm cable to that socket would be fine, assuming you can get a 6 and a 4 into the terminals of the isolator. |
| richard.cs:
--- Quote from: mikeselectricstuff on February 10, 2022, 04:46:57 pm ---UK Regs do allow cable to be protected by fusing at the far end under certain circumstances - I'm not sufficiently familiar with the details to know if this would apply here. --- End quote --- This is exactly what applies here, and why 2.5 mm2 spurs are allowed on a 32 A circuit. You have to separately meet these two criteria: 1. Protection against overload unless the load by its nature can't fail so as to produce overload. This can be at any point, so it is met by a downstream 13 A or smaller fuse. 2. Protection against short circuit, assumed to be a zero-Ohm short at the most distant point. There are some assumptions baked into this, but the end result is you can take a 13 A rated flex* off a 32 A circuit to feed the hob, and connect the hob via a FCU** or a 13A plug, (probably with a 3 A fuse, that's plenty***, but you may be able to get away with higher). That fuse protects the cable against overload, because if some weird fault were to make the hob igniter draw say 20 A the fuse would blow before the cable is damaged. Separately, if a short circuit were to occur at the last point in that cable before the fuse, the total loop resistance (external supply impedance + 6mm cable + flex) needs to be low enough that the 32 A MCB would trip quickly enough to protect the cable. You check this by looking at the expected fault current, and corresponding max tripping time, and then you can work out the let through energy and the maximum temperature the cable gets to. You or your electrician should do this calculation, but in practice you'll find it is fine for sensible lengths of flex (too long and the MCB trips too slowly and the let though energy and final temperature is higher). UK wiring regs are like this, you're expected to do actual engineering calculations rather than the US "rigidly follow code" approach. There are upsides and downsides to this. :) Also, why not reduce the MCB feeding the 6mm cable to 16 A anyway? You may find the manufacturer's instructions (which you're supposed to "take account of") require that anyway, and that is a cheap and straightforward job. *Why flex here though? A bit of 1.5 or 2.5 mm2 T&E to a FCU would seem more conventional. If you do use flex you should really use ferrules. **FCU = fused connection unit. It's a thing we have in the UK that takes the same type of fuses as the plugs but is for permanently installed things. *** These ignition things take a couple of milliamps. |
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