JimWPB

That was a real nice choice of breaker to use. I had been using breakers that are slightly larger physically because I didn't know that these smaller ones were available.

I have a question about the wire size though. When I look up amp capacity charts, they tell me that AWG #2 is good for around 125 amps & AWG 2/0 is good for around 200 amps. Different charts have a little variation on these numbers, mostly depending on the temperature rating of the insulation & the number of wires crammed into a small area, but the numbers are generally close to what I posted.

That being the case, did you use #2 or #2/0? 2/0 is much larger.

Mr.T

#2 AWG is the answer, which is also typical for the wire leads that come attached with recovery winches for Jeeps and trucks.

The reason for running around double the amperage of tables meant for typical NEC applicable wiring (like the wiring of houses and industry) is that more voltage drop (per foot) is acceptable and the use is short duration.

A couple side notes: A 6 foot run of #2 wiring with 200 amps has about 0.4 volts drop, meaning 14.4V at the battery (engine running) and 14V at the winch motor (~3% loss). Also, if you get access to the internal wiring of major appliances you'll typically find wires carrying much more current than the NEC tables allow for circuits with the same wire external to the appliance!

JimWPB

Thank you for a well explained response.

I'm with you on a lot of it, but I have questions about a few details. It's my understanding that the loss of voltage across the wire is a function of wire size & amperage. Lower system voltage does not protect you from this being an issue. As an example, a loss of 3 volts out of 120 is generally not noticeable. A loss of 3 volts out of 12 is 25%. That can be a big deal. Generally speaking, lower voltage systems require larger wires to prevent noticeable voltage drops, not the other way around. A chart for wire size & voltage drop at a given amperage can be found here - http://assets.bluesea.com/files/reso...on_chartlg.jpg. They don't rate AWG #2 above 120 amps. They only list 2/0 (or larger) for 200 amps. When using this chart, the wire lengths are for round trip from the positive, to the load & back to the negative side of the battery. This means that if a device is 6' from the battery, it is a 12' run in the chart.

Most of the NEC standards are written from the perspective of fire safety, not voltage drop, until you get into very long runs that will not be found in a Jeep. The NEC standards are written by the NFPA, which is a fire safety organization. The chart I listed in the preceding paragraph is specifically for low voltage DC systems. It gives 2 columns, one for 3% loss & another for 10% loss. this is the easy way to look it up. It's also possible to do actual calculations, but that's more involved.

I just found this site. It provides a plug & play calculator for loss across wires of specific sizes & lengths - https://www.rapidtables.com/calc/wir...alculator.html. This might be useful for examples that fall between entries in the chart. According to this calculator, AWG #2 will give about a 0.6vdc drop across 10' with 200 amps & #2/0 will give a drop of about half as much. Neither of these drops are huge, so the motor should run OK. Your statement of 0.4v for 6' also checks out here. ...but that doesn't take into account the effect of the return side drop, so I would be tempted to call it closer to 0.8v total, in theory. I'd be interested to put meters at the battery & at the load to see how well those numbers hold up in the real world. Each connector, crimp, etc. might add a little more to the total drop.

The next question is - will the wire get hot? Since most winches have very low duty cycle ratings at full load, I'm going to guess that high amps will not be present for enough time to smoke the insulation on the wires when running the winch. The potential hazard may come if your wire from the battery to the winch chafes through & touches a ground somewhere. Now you have a situation where 120 amp wire might see something like 190 amps for a very long time without tripping the breaker & that may cause a smoke show. Now the odds of this actually happening are not all that high. In the event of chafing through, there's a good chance that you will draw enough amps to trip the breaker. The window of danger between the safe capacity of the wire & the trip point of the breaker is a relatively narrow window that would require a certain range of partial short to actually start a fire. It could happen, but it's also possible that I might win the lottery this week & I'm not banking on that hard enough to quit my day job.

14.4vdc seems like an optimistic number to use in your calculations. An alternator is only going to keep the system voltage that high under low load conditions. Alternator current capacity ratings are specified for cold conditions. When the alternator gets warm, the actual output goes down a lot. 50% de-rating is not unusual. Lets say that your alternator legitimately puts out 100 amps. That's still an optimistic number, but lets start there. At full alternator output, we are now looking at the resting voltage of the battery. For a lead acid battery (gel, AGM, flooded, etc) it's going to be 12.6vdc when full. As your battery supplies the other 100 amps, the voltage is going to drop from there. The amount of the drop is going to increase after some time passes. If you still have more than 11vdc at the motor, I would be surprised. This is all theory, leaning slightly towards the optimistic side.

Now, back into the real world. You have had this install for a few years now. You haven't posted about having any problems. I'm going to guess that it's been working fine. I'm curious if you've ever been actually drawing 200 amps or not. I'm going to guess that most big winches on Jeeps (9,000-13,000#) don't see much more than 25% of max load ever, if that much. I've pulled my Jeep up a 30 degree incline with a silly little 2,500# winch before. There are actually 2 reasons why I expect that most winches on Jeeps never see more than 25% load. The other is that, these days, the winch mounting plates on off-road bumpers are often no more than 3/16" thick steel. I expect that 10k# of mechanical stress would leave a permanent twist in that kind of sheet metal.

...but the bottom line is - I'm curious how hard you have pulled with this thing & if you noticed the wires getting hot or not. ...and if you've twisted up a winch mount or not. Theory is theory, but when the rubber meets the road in the real world, that's when the truth gets told. ...and I'm listening.

Edit:
Sorry, the question was already answered. I just reread the end of post #1

Mr.T

Very glad post #1 had the info. Yours was a most detailed and well thought out reply-question, so I'm going to try and match you!

Usage over the last 11+ years has been infrequent, the winch has been reliable, and the breaker has never tripped. Mostly I've kept to running roughly 20 seconds on and 20 seconds off as mentioned in the "Testing" paragraph of post #1.

A few additional notes:

• The 0.4 voltage drop at 200A with 6 feet of #2 was actually an estimate for the total round-trip voltage drop, essentially the same as the drop across 12 feet of wire. The phone app I used assumes a resistance of 0.15591 ohms per 1000 feet of #2 AWG (0.00015591 per foot). This online wire resistance calculator says 0.156 ohms when 1000 feet is entered for the length and #2 for the size. So that ends up being 200(12)(0.00015591) = 0.375 volts (~0.4 volts) using ohms law. But as we know, wire is not exactly the same, so the ohms per foot varies a bit. I just tried the Rapid Tables Voltage Drop Calculator that you linked to above and it gave the exact same result: 0.375 volts drop round-trip, entering 6' for the one-way distance. (See note *** on the web page for the example of entering 10' for length with a circuit using two 10' wires).
• You're correct that 14V at the winch motor is very unlikely at 200A. That was a poor example on my part, over simplified to illustrate voltage drop from 6' of #2 wire. A realistic (engine running ~2000 RPM) voltage at the winch motor is more like ~12 volts. There's a bunch of individual voltage drops to sum up (e.g. alternator, battery, terminals, connectors, plus the wire itself that we're mainly discussing). The alternator and battery are the big ones, and without a running engine it might be ~10.5 volts. Battery choice and condition are huge factors, just like with a starter motor.
• The heat dissipated (200A on #2 wire) is about 75 watts over two 6 foot long wires, or 12.5 watts per foot. No problem for an intermittent load like a winch motor. The motor windings will fry long before the #2 wiring. But it is too much current for a higher duty cycle circuit -- I'll guess that 200A for 10 minutes straight could overheat the insulation. And, that's why the BlueSea chart you referenced above, which is based on the ABYC (marine equivalent to the NEC), rates #2 wire at 120A. Engine bay temperature is way more of an issue.
• If the winch motor current gets to 400A the voltage drop from #2 wiring will hit ~0.75 volts. Sounds like a lot, but the battery and alternator will drop a lot more -- And I'm guessing my winch will self destruct if current stays that high for more than a minute, less if it's already warm.
• I have doubts that my new & expensive AGM battery + alternator can keep the voltage high enough to get to 400+ amps without the winch motor stalling (or nearly stalling). In a perverse way, typical voltage drop can limit winch abuse because the user notes the motor slowing to a stall at slightly below full load, and lets off the switch. With dual batteries, a heavier duty alternator, potentially larger wiring, the winch will draw more current, produce more power, more heat, and self destruct easier! I think what I'm trying to say is that maximum amperage and winch-pull ratings are likely at best-case supply voltage, should be short duration, and despite all that still work fine for the vast majority of installations.
• EDIT -- Another thought: Regarding the concern that a wiring fault to ground could draw amps less than what it takes to trip the breaker, but high enough to overheat the wire. First, the breaker should be off when not in use, so someone would likely notice and mitigate this rare problem. Plus, I'd bet it would eventually draw much more current, and trip the breaker as more bare copper is exposed and the short circuit gets worse. The bigger problem is that it suddenly becomes a 1000+ amp wire fault causing a battery explosion, subsequent fire, injury, and a total loss -- There was a video of this happening, which was my inspiration for all this.