9 replies to this topic

[Northernpower]

I've just fitted a radiator fan that runs at 80 watts which by my reckoning it just shy of 7 amps. Am I right in assuming a 5 amp blade fuse will protect the relay supply circuit?

[Swift_General]

Rating for blade fuses relate to their continuous value. So 7A through a 5A blade will result in a slow blow situation, so you would need a higher rated fuse. And obviously cable of a suitable rating.

[Northernpower]

Rating for blade fuses relate to their continuous value. So 7A through a 5A blade will result in a slow blow situation, so you would need a higher rated fuse. And obviously cable of a suitable rating.

I've used 16 amp cable so I'm happy with that, I'll use a 10 amp fuse, I was getting mixed up with the continuous rating and the blow rating.

Edited by Northernpower, 31 August 2017 - 11:42 AM.

[slidehammer]

10 amp should be fine that will allow a bit of lye way on initial start up of the fan when it will probably draw an amp of 2 more

[Northernpower]

10 amp should be fine that will allow a bit of lye way on initial start up of the fan when it will probably draw an amp of 2 more

Interesting, I managed to finish the wiring off and it blew the 10amp. I've had to go to 15amp, double checked it was 80 watts.

[CityEPete]

Don't blade fuses need rating by half compared to glass ones? So a 7amp running load would need double or the nearest fuse being 15amp in a blade, 10 in a glass one?

[Northernpower]

Don't blade fuses need rating by half compared to glass ones? So a 7amp running load would need double or the nearest fuse being 15amp in a blade, 10 in a glass one?

I don't know that's why I asked?

[Swift_General]

Blade fuses are normally rated at continuous values and would generally blow at about double that figure.

Edited by Swift_General, 31 August 2017 - 04:53 PM.

[CityEPete]

Blade fuses are normally rated at continuous values and would generally blow at about double that figure.

Do you half it the other way then? 10amp glass fuse or a 5amp blade?

[Swift_General]

Blade fuses are normally rated at continuous values and would generally blow at about double that figure.

Do you half it the other way then? 10amp glass fuse or a 5amp blade?

Potentially yes, for example the old 35A glass fuses you'll find in many minis will only be continuously rated for about 17.5A. However if you replace a glass fuse it is always worth checking with your supplier as the glass fuses I have bought recently have been marked with their continuous and not blow rating, i.e. the same as blades. I guess this standardisation makes sense if everyone is aware of it, however it brings with it the risk that you replace a fuse with double the rating it should be - so your 35A glass fuse in your mini now blows at 70A with the obvious dangers that brings.

Edited by Swift_General, 31 August 2017 - 07:25 PM.