I don't understand the problem you envisage...
Switch fuse - Minimum fuse rating
- Thread starter AndyPRK
- Start date
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What assessory were you thinking I would beconnecting the tails to?
433.2.2
Nope - and I probably never will, even though there are five 800KMFs there in total. However, I suppose that I'm a born pessimist, in that I always try to avoid (sometimes 'cost permitting!) having only a single spare for anything - through fear that, should a spare ever have to be deployed, it might possibly prove faulty and itself fail almost immediately! ... and, of course, if I stored the second spare anywhere other than where you have seen, I would probably never be able to find it 'years down the road' if ever I needed to!Have you ever needed either of them?I've got more than him
Kind Regards, John
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What's that then?
John - a fair point. If one blows a second is likely to if fault is still present.
Why not look it up?
True, but that's not really the main thing I was thinking of - since I would hopefully identify and remove the fault before subjecting a replacement fault to it!
It was more the possibility that the fuse might prove 'faulty'. I obviously check them for continuity before 'clipping them to the wall', but that doesn't preclude the possibility that it will blow (at a normal operating current) soon after being put into service (maybe many years down he road) - I've certainly experienced that with 'small' cartridge fuses.
I suppose that lamps/bulbs (particularly filament ones) are a classical example of a situation in which I would not consider it wise 'to keep only one spare', for much the same reasons (we've all heard that 'ping' from a new lamp!).
Kind Regards, John
433.2.1 Except where Regulation 433.2.2 or 433.3 applies, a device for protection against overload shall be installed at the point where a reduction occurs in the value of the current-carrying capacity of the conductors of the installation.
NOTE: A reduction in current-carrying capacity may be due to a change in cross-sectional area, method of installation, type of cable or conductor, or in environmental conditions.
433.2.2 The device protecting a conductor against overload may be installed along the run of that conductor if the part of the run between the point where a change occurs (in cross-sectional area, method of installation, type of cable or conductor. or in environmental conditions) and the position of the protective device has neither branch circuits nor outlets for connection of current-using equipment and fulfils at least one of the following conditions:
(i) It is protected against fault current in accordance with the requirements stated in Section 434
(ii) Its length does not exceed 3 m, it is installed in such a manner as to reduce the risk of fault to a minimum, and it is installed in such a manner as to reduce to a minimum the risk of fire or danger to persons (see also Regulation 434.2.1).
So your point is that I don't need to have tails coming in ?
I could put smaller diameter wires into a henly I guess.
Where am I going to find 1G "panel-mount fuse" that I can fit a 20A or 30A fuse ?
Yep, I presume that's what BAS was getting at. If, as you said, the outgoing cables from the fuse are going to be 1.5mm² or 2.5mm², with a fuse appropriately small to protect that cable, then the regs (I mean BS7671) allow that the incoming cable to the fuse (and switch) need not be any larger in CSA than those outgoing cables. Whether the DNOs see it the same way when the only upstream protection to the cable is their fuse, I don't know, since they work to different regulations.
As for 'putting smaller diameter wires into a Henley', that's obviously possible, but you need to bear in mind what I initially said about the 800KMF - that you need to be careful putting a small conductor into a screw terminal designed for up to 16mm² or 25mm².
No-one has actually asked you yet - out of interest, where is this SWA going that requires only such a modest CSA?
Kind Regards, John
Ok. To complete the story.
I saw the plastic switch fuse going cheap. I know people liked them on here. And considering buying it, and thought it could be of use for this task (if it ever happened) or something else.
It was to power a garage which has 2 light tubes and a 16A radial socket circuit. (no heavy loads)
I think its about 20m away.
I saw the plastic switch fuse going cheap. I know people liked them on here. And considering buying it, and thought it could be of use for this task (if it ever happened) or something else.
It was to power a garage which has 2 light tubes and a 16A radial socket circuit. (no heavy loads)
I think its about 20m away.
OK. Do I take it that you don't have a spare way in your CU for this purpose, or have some reason for not wanting to do it that way (e.g. no non-RCD ways available)?
BTW, if you worked with a design current of 20A and wanted to be really strictly compliant with the (VD guidelines in the) regs, then (if I've got my sums right) 20m of 1.5mm² (VD=5.04%) would not provide a quite low enough VD even for sockets, let alone lighting, and even 2.5mm² (VD=3.13%) would not provide quite a low enough VD for lighting. However, you would only be exceeding the guidelines by a tiny and trivial amount. Of course, things would be worse if you worked to a design current greater than 20A, or if the total cable run were greater than 20m. There would certainly be minimal margin for 'future proofing' even with 2.5mm².
Kind Regards, John
It would be far from easy to route it to the CU.
This leaves connection to either the kitchen ring or the meter cupboard.
Even the kitchen ring wouldn't be tidy.
Thanks for the calculations John. So 2.5mm minimum then.
Out of interest, I shouldn't need an RCD to protect the SWA then? Its a PME supply.
There is an RCD in the garage.
This leaves connection to either the kitchen ring or the meter cupboard.
Even the kitchen ring wouldn't be tidy.
Thanks for the calculations John. So 2.5mm minimum then.
Out of interest, I shouldn't need an RCD to protect the SWA then? Its a PME supply.
There is an RCD in the garage.
OK. Is the meter cupboard (is it an outside one?) a long way from the CU, then?
Your decision, although I agree thatis probably the minimum. As I said, even 2.5mm² is technically pretty marginal, and provides little, if any, 'future proofing'.
That is correct.
Kind Regards, John
Wouldn't have to be quite that small...
Anyway - apologies for any confusion - I thought Andy was concerned about not being able to get tails into the switch. Which he can't, if they are more than 10mm², but a 32A switch (which will fit a standard 1G box) will take 10mm² conductors, and give that everything would be contained within the meter cabinet, I don't see a problem with using that size.
Yes the meter cupboard is outside.
The meter and CU are just within the 3m limit, but I'm not exactly sure of their route
The meter and CU are just within the 3m limit, but I'm not exactly sure of their route
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