1A fuse - legal and available in the UK?

[Darren Blake]

Quicky: I'd like to use a 1A fuse to protect a low power circuit that is wired using 3A flex.

Although I used to have a collection of 1A fuses in plug-top size, they now seem to be unobtainable. Maplins sell 1A fuses in the 20mm x 5mm size. Would this fit in a plug top and would it be legal to use it?

Alternatively, if I were to fit a 3A fuse (the lowest easily available in the correct size), would this actually offer adequate protection for 3A flex? I'm guessing that 3A flex can actually take a bit more than that before letting the magic smoke out.

For info, the actual steady-state draw will be about 0.25A and the load is a 50W halogen lamp, so the start-up current wil be a bit higher (no idea how much higher though).

Thanks in advance.

 

[ban-all-sheds]

Although I used to have a collection of 1A fuses in plug-top size, they now seem to be unobtainable.

Maplins sell 1A fuses in the 20mm x 5mm size. Would this fit in a plug top and would it be legal to use it?

No and no.

Alternatively, if I were to fit a 3A fuse (the lowest easily available in the correct size), would this actually offer adequate protection for 3A flex?

Why do you think that it might not be OK to protect a cable with a fuse rated no higher than the cable?

 

[Darren Blake]

Thanks for the fast reply.

I take it the picture means that you can indeed still get plug-top sized 1A fuses?

Assuming the fuse blows instantly, there's no issue with putting a 3A fuse on a 3A flex. However, I'd feel happier with something lower. As I said in my original post, I suspect that a 3A cable can carry a lot more than 3A, and that a 3A fuse is probably toleranced to blow at less then 3A. That's the sensble way round, however I was worried that some bizarre fault might put 3.5A or something down the line, which would be enough to bother the flex but not blow the fuse. I don't know about the actual tolerances, but you see the kind of scenario I'm getting at.

Anyway, I'd be happy with either a plug-top 1A fuse if I can get one, of a 3A fuse if you say it will adequately protect the flex.

 

[ban-all-sheds]

I take it the picture means that you can indeed still get plug-top sized 1A fuses?

Try clicking on it....

Or this.

of a 3A fuse if you say it will adequately protect the flex.

It'll be fine.

 

[ericmark]

I did hunt net and http://www.byriteelectricals.co.uk/Products.asp?C=8&S=20&Title=HOME ELECTRICAL&STitle=FUSES still list 1 amp fuses but a fuse in a plug is to protect the cable not the appliance and Table 52.3 gives 0.75 mm as min csa of flex which is rated 6 amp. It would be more common to use a BS 646 fuse as used in shaver adapter.

 

[MarkBarl]

I'm not sure about the legality regarding the size of a fuse. However from a PAT testing point of view the guide tells us to look for BS 1362 marking and an ASTA mark and that it is of appropriate rating for the appliance. 3A, 5A and 13A have become the most common (I believe because of common wire sizes), however if you have a smaller rated one and it is appropriate no reason why not to use it.

 

[BS3036]

BS1362 says "The rated current may be any value not exceeding 13A. For use in plugs, the preferred rated currents are 3A and 13A"

The other interesting rule is that the body of 13A fuses must be brown, the body of 3A fuses must be red, and "for all other ratings the marking shall be in black".

 

[Darren Blake]

Ok, that's all good then Plenty of options (well....two anyway).

In the case of the 1A fuse, can anyone calculate or estimate the start up current for a 50W halogen running off a 60VA 12VAC transformer?

 

[RF Lighting]

Less than 1 amp thats for sure.

 

[Taylortwocities]

Not sure where this thread is taking us - it seems unnecessary.

Even if the start up current was as high as 1amp a BS1362 fuse would survive the surge.

Use a 3A fuse and ensure the connecting cable is OK for 3A. No need to spend any more time on it..

 

[Stoday]

can anyone calculate or estimate the start up current for a 50W halogen running off a 60VA 12VAC transformer?

Well, for a 100W 230V GLS lamp the starting transient is over a kW. Totally useless information though, as Taylortwoties says...

 

[Darren Blake]

Okey dokey. Thanks for the replies all.

 

[barclay55]

Well "primary.uk.2008"
at present seems to be selling every BS1362 fuse you might want and more:
http://stores.ebay.co.uk/primary-uk...0QQcolZ4QQdirZ1QQfsubZ256414012QQftidZ2QQtZkm

 

[Click-Sure]

Electric Centre sell 1A, 2A, 3A, 5A, 7A, 10A & 13A.

1A - Part No: AC3364, £3.00 +VAT (catalogue price) for a bag of 10.

 

[ban-all-sheds]

1A - Part No: AC3364, £3.00 +VAT (catalogue price) for a bag of 10.

That's nearly twice what TLC charge, and they aren't exactly renowned for their sharp pencils....