Freewill

Don't get me wrong. I have a lifetime of experience designing and installing electrical systems - everything from micro-current controls to power distribution well over 1000 amps. I'm a fanatic about good wiring practices and protecting wiring with over-current devices. In most cases I would be the one pushing for protection.

But in this case I just don't believe a 4-500 amp fuse is any kind of protection. The current capacity of a starter or winch cable is no more than around 150-200 amps tops. The only reason the cable can carry the peak load of the starter or winch is because the duration of the load is very short. But, if that cable gets a short and starts to heat up, the cable is going to get hot enough to start a fire long before a 4-500 amp fuse blows.

I can get behind a disconnect because the disconnect can be left "Off" except when the winch is needed. A cable that is not connected to the battery can't heat up and start a fire. During winch operation, the switch can be turned off if something starts to smoke. During winch operation if a person is worried that the switch is not accessible because a fire is already burning then someone was not paying attention! If there is great fear about not being able to reach the switch, then a switch that can be rigged with some sort of remote pull cord would be the solution.

JK-Ford

If you are as good as you say. Then why does your circuit design not make any sense? Why would a profesional design a circuit with a fuse that is to large to protect the circuit.
200 amp load = 4 / 0 cable = 200 amp fuse with time delay for motor protection.
And you should also be aware that ( for an instantaneous short or even an overcurrent situation ) a fusible link is the only 100% garantee for circuit protection. A disconnect ( switch ) is only used as a safety device for maintenance. The switch doesn't provide any circuit protection ( during opperation). And it seems quite obvious that you have never seen a circuit fault. By the time that your eyes tell you that there is a problem, the dammage has already occurred.

WCDAVE

I am not sure about the laws in Arkansas, but this would not be the case in many states. It IS VERY CURIOUS that no winch manufacturer includes or advocates a fuse.

OzzyPotter

Is there a fuse in-line with the starter motor from the battery?

Freewill

This discussion has been about about how to work with what we have. Using the stock winch cable requires a compromise, and a compromise is not usually the best design.

(Wire sizes and ampacities below are for single insulated cables in free air. Ampacity has not been derated for cable bundling or for location in a hot engine compartment.)

The Warn M8000 draws 435 amps at full load, yet Warn only provides (what appears to be) 1ga cable good for around 250 amps. But a winch is an intermittent load, so the 1ga cable does not have time to seriously overheat.

A 1ga cable would use a 250 amp fuse for protection, but the winch motor may draw 435 amps so a 250 amp fuse is likely to fail when the winch is under full load. The fuse needs to be big enough to handle the load AND small enough to protect the cable. If a 450 amp fuse is needed, then cable much larger than 1ga is required. If a smaller slo-blow fuse will hold the winch, then the cable size can be chosen based on the smaller fuse size.

I agree that a fuse provides instantaneous protection when the overload is greater than the fuse rating.

I don't agree that a disconnect is only for maintenance, although it is critical for that purpose. A disconnect is a useful way to kill a circuit for any reason the owner or operator chooses. Battery disconnects are common in the RV/automotive/marine field.

Circuit failures happen and I've seen my share. At worst they are explosive, hot, and violent. (FWIW, failures happen on protected circuits too, so protection is not 100%). The point is that a violent failure at least makes itself known so a person can try and react. What worries me are the small insulation failures from abrasion or pinching that slowly and silently build up heat and eventually start a fire in a Jeep parked in the garage. A big fuse will not help much with this hazard, but a disconnect will.

It comes down to finding the best design for the circumstances, along with regular maintenance and inspection - because nothing is foolproof.

So, what would my best-practice design look like? 1. Install a fuse sized to support the winch. 2. Use cable large enough to be protected by the required fuse. 3. Provide a disconnect. This gives the best protection against sudden failure during operation, and against a compromised cable overheating when not in use.

JK-Ford

OK. Now you are sounding more like a profesional. And finally this thread is headed in the right direction. But I still think that it is necessary to do some fine tuning in your reasoning on a couple of points.

This is why it is critical to make careful selections on wire and fuse sizes. A highly resistive short ( wire chafe ) acts exactly like any other load. IE: motor, light bulb, radio, ect, ect. As the current ( and heat ) builds, so does the amperage. So, when the current reaches the critical stage OF CIRCUIT DESIGN, the fusable link will react. If "YOU" design the circuit improperly. It will react improperly.

I guess this is all realitive depending how you look at it. My only issue is calling a disconnect switch a "circuit protection device". A disconnected circuit needs no protection. Only people need protection when a circuit is disconnected. A disconnected circuit is nothing more than a hunk of different metals and plastic. It only hase purpose when it is "live".

Finaly someone else has seen the light.

JK-Ford

If you buy an electric pool pump motor, does it come with directions that tell you how to install it?. If you purchase an electric stove, does it come with a fuse. If you burn down you your house installing an electric water heater. Do you think the manufacturer of the water heater will buy you a new one. But all these devices give the installer the information required ( on the nameplate ). So that he can properly design and install a matched circuit to support that piece of equipment.

ShakyJake

Incorrect. My Superwinch came with a circuit breaker. I replaced it with a better one, and would never run any electrical device off my battery without one. Have you priced modern automotive electronic replacement parts? Fuse or circuit breaker= insurance. For safety items like winches and trailer ebrakes, an auto resetting circuit breaker is preferred.

JK-Ford

Not on our jeeps. But I have seen this arrangement before. However, the electrical systems on modern vehicles electronicaly monitor lots of different things.

ronjenx

The winch being switched off doesn't kill the positive lead. A chafed wire will still create a direct path to ground, and a fire hazard.
A switch near the battery end of the cable will kill the positive lead.

It's a big world out there. There has to be thousands of winch circuit related fires.