hot fuse!

[norton41]

A fuse in main fuse box recently blew, I was a bit concerned as it had got really quite hot to the touch...I have not replaced it yet as I am worried that the fuse box could be at fault. Does anyone know whether these old style fuses get very hot before they blow?

 

[BSBS]

What rating was the fuse and what does the circuit supply??

Fuses can get hot before they blow especially if they are supplying a circuit that draws near or just over the fuses operating current..

For example i went to a customer who had problems with here Night storage heaters they were 3.2kw and had been connected through 13a Fused spurs, she had turned them right up to max so they were drawing the full current (a touch over 13A) the fuses did blow but not before the fuse carrier had melted..

 

[Adam_151]

What rating was the fuse and what does the circuit supply??
Fuses can get hot before they blow especially if they are supplying a circuit that draws near or just over the fuses operating current..

Yeah, I know at my old school the guy from the DNO had to use a chisel to remove the service fuse, becuase the carrier had been melted ,it was either 100A or 300A, mate of mine asked the DNO guy what the supply was, and he said 300A, not sure if he meant 300A total, or 300A per phase, but thinking about it, reckon must have been per phase, becuase its quite a big building, with loads of lights, electric cookers, workshops, canteen, etc recently installed aircon, along with stage lighting in use at the time pushed it over the edge

 

[norton41]

It was a 30amp fuse. At the time,we had washing machine, dishwasher and a small tumble dryer on at the same time on this circuit....the downstairs ring main.

 

[HDRW]

It was a 30amp fuse. At the time,we had washing machine, dishwasher and a small tumble dryer on at the same time on this circuit....the downstairs ring main.

Right, and each of these could have been drawing 13A so the total could be 39A (check the ratings plates to see what they actually draw). A 30A fuse doesn't hold at 30A and blow instantly at 30.1A, it's a time/overload combination. It will blow "instantly" on a dead short (hundreds or thousands of amps) and may hold for several minutes at 100% overload - I forget the actual figures.

So yes, when it has a small overload you would expect the fuse to get hot, and then eventually blow, and it looks like a small overload is what you had.

So you either need to install a new circuit and split the heavy-load devices between them (don't forget the electic kettle if you have one), or to use only two of them at a time, so the maximum load is 26A. The latter is *much* easier to do!

As I said above, check the ratings so you know exactly what you are dealing with on each appliance.

Cheers,

Howard[/b]

 

[Qedelec]

A 30A BS3036 (rewirable) will handle about 50A continously

 

[Steve]

A 30A BS3036 (rewirable) will handle about 50A continously

really? continuously? forever? surely it would blow after, say, 5 mins or less?

 

[Qedelec]

Page 195 of BS7671
Look at the graph for BS3036 semi enclosed fuses.
Its about 55Amps
70Amps will blow in 20 seconds.

This is the reason your house can burn down before a BS3036 fuse blows.