Fused spur question for 3Kw heater

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I noted an old fuse the other day slightly longer than the 13 amp fuse but same diameter and it is marked 12 amp continuous 25 amp blow unlike the 13 amp fuse the fuse wire inside is in air, but we are looking at the wire inside the fuse running near melting point, and a little thought that heat could be concentrated at centre View attachment 210724 or over the whole fuse, I have never really considered the quality of a 13 amp fuse, we see BS 1362 written on them and think they are all the same, but are they?

Those are car fuses designed to be used on 12v (and possibly 24v) systems. Don't use them on 240v. They will explode on heavy overload as there is no sand in them.
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I wonder if this may have been a regional thing, or a PO and not BT, as I've spoken to a number of local BT colleagues [some going back to POT / PO times] with experience in a selection of different sections and none have heard of it.
It's only recently on here [forums] that I've become aware of it.
I seem to recall Red mk plugs with For Gpo Use stamped on them, or am i dreaming
The bit that gets hot is the fuse in the plug. If you put it on a FCU you will have the same problem in the FCU.

The fuse tends to generate some heat and the fuse clips tend to loosen due to the heat, which causes some resistance between fuse end caps and the clips. The problem is much worse with poorer quality/design of plugs and sockets, so best to make sure that if it is intended to regularly run at a regular 3Kw loading, that both are of good quality and the fuse is firmly held by the clips.
The IET BS 7671 now warns of the problem with over 2 kW fixed appliances and suggests over 2 kW should have a dedicated supply
Hi Eric, where did you see that please
Eric is always saying that, but making it sound like much more of a generalisation than it actually is. I presume he is referring to what the guidance of Appendix 15 says about ways of avoiding overloading one of the arms of a ring final, about which it says (but, as you can see, only in relation to cooking appliances) ...


Kind Regards, John
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unlike the 13 amp fuse the fuse wire inside is in air, but we are looking at the wire inside the fuse running near melting point,

13amp and the other similar cartridge fuses are supposed to be silica(?) sand filled, to instantly quell the arc, when the fuse wire burns out. Many of the fake Chinese ones lack the sand filling.
Sure they were post office, never worked in BBC premises in my life, good plugs though and seems big companies thought so too

Hospitals began using their own (rather dangerous) design of round pin plug - where the live pin was the replaceable fuse. If the fuse pin snapped or came unscrewed from the plug, it could leave the fuse live and poking out of the socket.
Personally I think the maximum heat setting is only to initially warm the room up, and then ideally drop to a lower setting after an hour.
This helps with life of the heater and plug

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