Plug fuse vs Consumer unit fuse

mark19 · Posted: Fri Nov 23, 2007 7:20 pm Post Subject: Plug fuse vs Consumer unit fuse

Could somebody explain why a plug fuse should not be used in place of a consumer unit fuse for a lighting circuit (5amp). In other words, what is the difference between a plug fuse and a consumer unit fuse. Many thanks for your replies.

plugwash · Posted: Fri Nov 23, 2007 7:29 pm Post Subject:

afaict the main issue is that it is a bit oversized and so will put strain on the carrier.

Adam_151 · Posted: Fri Nov 23, 2007 7:33 pm Post Subject:

Plug fuse is to BS1362, consumer unit fuse is to BS1361

1) Slight difference in size firstly, could lead to a bad connection

2) Different fusing factor, somwhere between 1.6 and 1.9 for a plug fuse, needs to be 1.45 or less for consumer unit fuses unless we want to start applying extra factors to check compliance of the wiring (as we do with 3036 fuses)

3) different breaking capacity, a BS1362 isn't garenteed to break anything above 6ka, if BS1361 fuses were used because of a high PFC then not a good idea to fit something with a lower breaking capacity

4) Anyway the board was designed for BS1361 fuses, anything else won't have been type tested with it. etc, etc

plugwash · Posted: Fri Nov 23, 2007 7:41 pm Post Subject:

playing devils advocate for a bit.

Adam_151 wrote:

2) Different fusing factor, somwhere between 1.6 and 1.9 for a plug fuse, needs to be 1.45 or less for consumer unit fuses unless we want to start applying extra factors to check compliance of the wiring (as we do with 3036 fuses)

I will assume we are talking about 5A fuses because those are the only ones that are reasonablly close in physical size between the two types. That means lighting circuits and those tend to have plenty of slack for such correction factors.

Quote:

3) different breaking capacity, a BS1362 isn't garenteed to break anything above 6ka, if BS1361 fuses were used because of a high PFC then not a good idea to fit something with a lower breaking capacity

True but assuming this is a domestic situation the service fuse should be providing adequate back up protection.

it's a bodge but IMO it is not a particularlly dangerous one.

JohnD · Posted: Fri Nov 23, 2007 8:27 pm Post Subject:

I have a feeling he is thinking about the price difference.

Another prob is that plugtop fuses also come in 13A which would be undesirable on a lighting circuit.

kai · Posted: Fri Nov 23, 2007 8:57 pm Post Subject: Price difference.

The best way round that is to replace the 5amp holder in the CU with a 15amp one, with a length of 2.5.mm cable from the 15amp fuseway to a fuse-connection unit next to the CU, then the wiring for the lighting circuit starts from the FCU, with a 5amp plug fuse in it - my lighting was done like that in a former home - solves all problems.