Fuse information

[martin_t]

Hi

Can someone explain what "Continuous" and "Fusing" mean when talking about the specification of a fuse? I guess "Continuous" means will support a continuous current up to the spec of the fuse, but what does "Fusing" mean? This is the specification in the Vehicle Wiring Products catalogue I am lookin at.
Also I am putt a 60amp cable from my battery to my temporary dash for starting (this cable will feed all my necessary instruments and warning lights), and I want to put a fuse in line near the battery. Do I assume I simply put a fuse in less that 60amp? I don't really know what I will be drawing, the items on the temp dash etc will be:

Fuel pump
Fan
rev counter
oil pressure gauge
Water temp gauge
oil pressure warning light


any help appreciated

Thanks

Martin

[wilf]

One at a time then:

"Continuous rating" for a fuse means the current it will pass forever without rupturing.

"Fusing" - a little ambiguous, could mean the act of putting a fuse in a circuit, or a fuse rupturing due to excessive current.

The circuits you describe can probably live off a 35 - 40A fuse. That way you protect the cable as well. (fuses should always be rated less than the actual cable they supply).

Your appreciation is appreciated..........

[martin_t]

Originally Posted by wilf

One at a time then:

"Continuous rating" for a fuse means the current it will pass forever without rupturing.

"Fusing" - a little ambiguous, could mean the act of putting a fuse in a circuit, or a fuse rupturing due to excessive current.

The circuits you describe can probably live off a 35 - 40A fuse. That way you protect the cable as well. (fuses should always be rated less than the actual cable they supply).

Your appreciation is appreciated..........

Thanks for that Wilf!

[oglyoodoo]

Looks like Wilf beat me to it whilst typing a reply...
Bear with me as I've just got back from the local town beer festival and very nice some of the ales were...
You are right that Continuous current is intended to mean the current a fuse will carry without it blowing.
Fusing current is a bit misleading as it also has a time element to it. Fuses are effectively thermal devices. The more current you put through it the hotter it gets and there comes a time when it gets so hot it will go Pop. A 30A fuse carrying 30A may well carry this for many hours but it is likely to fail in time as it is getting pretty hot. If you pass 35A through a 30A fuse it may take several minutes maybe hours before it blows. Putting 50A through it, it will fail cause it to fail much quicker and if you have a short somewhere it will blow in milliseconds when called upon to pass a few hundred amps.
A single fuse won't, in my view, protect your temporary dash properly although it is probably OK for a start up. You have a Fan which will draw some 10 to 20A, a fuel pump which could draw say 5A maybe much more whereas you also have instruments doubtless with thin wiring drawing a fraction of an amp which could fuse quicker than your fuse.
If you want to protect things for a start up with a single fan I would be inclined to use a 30A to 50A fuse for the Fan and Pump and a smaller fuse say 5Amp to protect the instruments and oil pressure lamp.
You are using a cable rated at 60A. This is the current the cable is expected to take without overheating or excessive voltage drop. It will no doubt carry several hundred amps for short periods and certainly long enough to blow a 30A fuse as long as the cable isn't too long.
I personally would measure what the fuel pump and Fans draw and then make a decision on what fuse rating to use. Bear in mind that anything with a motor or lamps will draw a much higher inrush current at switch on so the fuse will need to be rated higher to cope with this without failing.
Fuses seem simple items but I could probably write a couple of pages about them.
HTH
Denis

[martin_t]

Hi Denis

I didn't give all the information which may have made things clearer!! I am intending to feed a "distribution post" on my temporary dash with the 60amp fused cable from the battery. From the distribution post, all my other instruments, dials, fan etc etc are fed, first going through a fuse box with mainly 5-8amp fuses. The exception is the fan which I have got a 30amp fuse protecting it. What I don't understand is what current is coming from the battery up the 60amp cable to the distribution post and then on to my temporary fuse box before the instruments. Will that just blow my 5amp- 8amp fuses? (as you see, I'm no electrician!!!).

Confused

Martin

[Purple AK]

What Dennis said Bearing in mind that a 16" fan will spike to well over 50amps on startup

[Purple AK]

Originally Posted by martin_t

Hi Denis

I didn't give all the information which may have made things clearer!! I am intending to feed a "distribution post" on my temporary dash with the 60amp fused cable from the battery. From the distribution post, all my other instruments, dials, fan etc etc are fed, first going through a fuse box with mainly 5-8amp fuses. The exception is the fan which I have got a 30amp fuse protecting it. What I don't understand is what current is coming from the battery up the 60amp cable to the distribution post and then on to my temporary fuse box before the instruments. Will that just blow my 5amp- 8amp fuses? (as you see, I'm no electrician!!!).

Confused

Martin

The current coming up the 60amp cable will be whatever is being drawn by what is connected to the end of it (your fuse box) A 60amp cable should be fine as the spike from the fan/fans is only a split second thing. You just need to ensure the fan fuse is man enough.

[oglyoodoo]

Martin
It sounds like you have the electrics properly sorted with separate fuses for items drawing lower current. Your 60A fuse is only there to protect against a short at the input to your Terminal Post and separate fuses in other words it's just to protect the 60A cable against a short and possible smoke. As Purple AK says the current in the 60A cable will be the sum of all the other loads so a 50-60A fuse should be fine. It won't blow your other fuses. Fitting a large fuse is a wise precaution but I dare say many temporary startups don't fuse that single heavy cable if everything else is fused. Just make sure everything is well insulated and can't possibly short to chassis. Good luck...

Denis