Large Gauge Cable Questions

Hey all,

Is there ever a reason to run 2/0, 3/0, or 4/0 battery cable in an automotive application? Maybe extreme competition audio? High end race?

For reference, 1/0 AWG = 50sq.mm

Also, what could one expect for amp ratings for cables like this? It seems the information varies online, and I trust this source here at HPA more.

Is 1/0AWG (50sq.mm) in good quality cable something like a 200A cable?

Thanks!

Can't think of one, unless it's an electric vehicle.

Maybe an engine that's hard to crank over at a high enough speed, like a large capacity supercharged engine with a lot of drag and you need to minimise the voltage drop in the cables to maximise the starter motor torque and/or there is a long run to, and from, the battery/ies.

Modern geared starter motors have drastically reduced the currents required, though.

I like Gord's EV suggestion, in addition to competition audio you mentioned Zach. It's not something I've needed a normal street or motorsport application.

Forgot the second part of your post - every conductor (other than super-conductors) has resistance, which causes a voltage drop along its length, and heat to be produced within the conductor.

The first is important because the device being driven may be voltage sensitive and its working voltage will be the supply less the voltage drop to, and from, it. This is especially true for things that use power, as the power available is the square of the voltage - lose 10% of the potential voltage and you lose 10% of the power.

The second is important because you don't want the conductor getting hot enough to damage the insulation, or nearby wiring or components. I will usually have a rating at a specified ambient temperature, but that can be drastically down-rated if it's enclosed in the middle of a loom, and/or hot environment, etc. Depending on the specific wiring insulation, and use, that 1/0 is normally rated between 150 and 170A.

In practice, you will usually check the minimum gauge for the maximum acceptable voltage drop over the ENTIRE circuit, and the current vs heat limit for the wire and insulation you want to use. The insulation is important, especially as most common insulation has limits that can easily be reached in the modern vehicle's engine compartment - that's one reason why people pay for high end product, they have much higher temperature resitance, other advantages are they're tougher, and lighter.

It might make more sense if you check out some of the on-line spec' charts, such as

https://www.engineeringtoolbox.com/wire-gauges-d_419.html

https://www.powerstream.com/Wire_Size.htm

https://www.cerrowire.com/products/resources/tables-calculators/ampacity-charts/

@Mike, Thanks for the response. I really appreciate it.

@Gord No

Thanks for the info!

According to the second link you provided, maybe I should consider going with cable between 1AWG and 2/0AWG for most applications, especially for a customer/client......it is saying that 2AWG is good for 94A power transmission--- an amperage that might be acceptable, but certainly not in the safe zone if we are talking sizing a cable for the max output of a modern alternator.....it might work alright for a classic car or older one with an alternator of 75A or so, but I like having a little more buffer and a lot of modern alternators seem to be rated above 100A, which 1AWG cable and bigger would be best matched to? If I am reading your reply correctly.

Thanks again.

I don't have a specific suggestion - partly because I tend to up-size power handling wiring, but some comments. Perhaps others can add to/correct them?

There are two basic alternator designs, those that are voltage referenced and those that aren't.

Voltage referenced will have a voltage reference wire from the battery to ensure the battery voltage is correct - details will differ, and the older type where the voltage is regulated at the alternator and may lose some voltage by the time the battery receives it.

Some alternators are grounded directly through their body and mount to the engine, whereas some will be mounted on insulated mounts which are used to reduce vibration and, sometimes, heat transfer from the engine. You shouldn't need a separate ground for the first but it will be required for the second - and on that, I had a vehicle where the resistance of the ground wire was enough to melt the insulation from the heat generated, so I used a pair in parallel. It's something that's often overlooked.

The normal, running output of the alternator will be equal to the total electrical draw on the system - the electronics, fuel pump(s), lights, heater, fans, etc, that may be in use. If the battery was discharged, there will be an additional drain there, too. When you consider that, it's would be a smart move to size the wiring for the maximum output rating for the alternator, even though that may be higher than the nominal draw, because you probably don't know what will happen.

On alternators, even with the above suggestion, they're usually rated to much higher amperages than needed, but this is because at lower rpm they aren't as efficient, and there needs to be sufficient capacity at lower rpm to meet the loading. In winter, commuting in the dark, in slow moving or idling traffic, with lights and heaters on, it's not uncommon for the drain to exceed supply, and the battery to discharge over time - if it applies to you, you could fit a higher capacity alternator, or purchase a small battery charger to trickle charge the vehicle when it's parked overnight, or at work - but those depend, obviously, on how secure your parking is at those places.

@Gord No, Thank you sgain for the reply.

Ah, yes Ive seen the ones with insulated mounts, that makes sense.

And yes, that makes sense as most of the time youre not really gonna get much more than 100A draw at the battery if, say, you have 40-50A worth of accessories going (which i feel like is harder to do, the newer the vehicle) and 50A draw from the Alternator.....

So sizing it a little bit on the side of caution isnt a bad thing, not to mention you dont necessarily know what the end user is going to do with the vehicle after the power handling system leaves your bay or leaves your hands. However, even with all the accessories on, even an old car isnt likely to draw over the rated amperage of the alternator is what youre saying?

If thats the case, then 2AWG would be sufficient for a lot of applications, but the more "bells and whistles" a vehicle has, the more i may want to start sizing up?

Seems like it may be very application dependent, although you said you size them up often anyway.