Do I input 120 V or 240 V in wire-size calculators?
It’s pretty far…180 feet. A particular amperage is not required…would like 60A, but cost will likely move me lower.
240V, but you also change some other stuff.
The default 3% is wire-salesman bullpuckey. It's not in Code at all. Put 5.5% and see what it says.
Also change the ampacity to your more realistic actual expected load
. The usual mistake is to use the breaker trip number (e.g. 60A), but even that is wrong
, because you're not allowed to plan to use more than 80% of that. (e.g. 48A for a 60A trip). So putting more than 80% is simply an error.
When you factor for 80%, you will not need a wire-size bump at 180' and can just use the statutory minimum wire size. For instance the common/standard 60A circuit with 4 AWG Al wire, at 180' your voltage drop is only 3.29% at 48A actual. That is totally fine, even by the wire salesman's standards.
Why does lowering amps help? Because voltage drop is caused by amps actually flowing at that moment. No amps / low amps = no/low voltage drop. A solitary 120V tool flowing 12A on that hypothetical #4 Al will only drop 1.64%. If you added a 120V 12A dust collector *on the other leg*, that would actually reduce voltage drop to 0.82%.
I would advise all of my clients to install conduit; it is a no brainer.
One exception: if theft is a serious risk. Theft from conduit is easy, just bash into one end, tie it to the trailer hitch and drive away. Stealing direct burial line buried to 24", a bit harder.
you need to use #4 copper wire.
[or] AL, but it will probably be #2 AL.
Yes it is #2 AL wire which gives a 2.64% VD for 60 amps.
I think you miscalculated on that one. But hey, if you're going to #2 Al, you might as well go a half-size larger and go #1 Al. That'll put you at 100A, as carmusic proposes.
Remember, voltage drop is not a code requirement, it's considered a preferable practice (by wire salesmen lol). That means if you bump to #1 aluminum wire *for voltage drop reasons*, you are perfectly welcome to "call it" a 100A circuit and put a 100A breaker on that, since #1 Al is the correct wire for a 100A circuit. And then just limit your draw to 60A lol.
I would like to use direct buried UF (Underground Feeder) cable, and avoid conduit. The largest caliber I can find in UF (with 4 conductors needed for separate neutral & ground) is 6 gauge. This looks to be $3 or $4 per foot.
That's correct. UF cable stops at 6 AWG. At that point you switch to other direct-burial types such as URD
or MH feeder
6 AWG is the wobble-point at which you should seriously be evaluating aluminum at 2 sizes larger (numerically smaller). There is nothing wrong with aluminum wire as feeder, however Code requires it be the new AA-8000 alloy, a rule made out of an abundance of caution. The lugs on the subpanel will be aluminum anyway, so this averts a dissimilar-metal problem.
I don’t understand how two conductors each with 120V looses less over distance than one 120 V conductor.
Because voltage drop *doesn't actually happen* as a percentage, it happens as an absolute volt drop. So if you have 2.4 volts drop at 120V, you just dropped 2%. If you have 2.4V drop at 240V, you only dropped 1%. Further, if you can run the same load at 240V instead of 120V, that means current drops in half. So the voltage drop reduces by half *again*.
Subpanel rating: If you lived in Wyoming with 80 mph posted freeway limits, would you want R-rated (85 mph max) tires on your car? Probably not, because you don't want to run your car tires at absolute redline. So why would you put a 60A rated or even 100A rated subpanel on your 60A circuit?
Subpanel main breaker rating: A subpanel in an outbuilding does not need any main breaker at all. It needs a disconnect switch. Usually the cheapest way to get a disconnect switch is get one with a main breaker. The main breaker size does not matter; it's only a disconnect switch. So if you find a panel you like with a 200A main breaker, that is fine.
Subpanel spaces. I see it all the time where people overspend on wire (weren't you ready to buy #4 Cu!?) and then scrimp on the subpanel. Then they immediately run out of spaces and go "woe is me!" The cost difference for more spaces is trivial at the time you are buying the panel. So go stupidly huge on spaces. Get the largest panel that won't get you kicked out of bed. Gosh, so you miss out on a couple of pizzas.
This means when you get a wild hair to develop a wood shop, 240V saw (2 spaces) got em. 240V dust collector (2 spaces) got em. 240V planer got em. 240V jointer got em. 240V radial arm (2 spaces) got em. *fwiff* we just went through 10 spaces just like that. See, when I say get a 30-space panel, I'm not insane.