Workshop wiring help

[MICHAEL S HILL]

What gauge wire do I need for a sub panel, of either 60 or 100 amps, with a run of 100 feet through a conduit to the main? I have a 3hp Unisaw, 2hp planer, 1.5hp jointer, 1.5hp band saw, and a 1.5hp dust collector, all on 220 volts, along with the usual 110 volt bench top stuff. This would be a one man shop.

[Doug Palmer]

60 amp circuit requires a minimum of #6 awg wire.
100 amp circuit requires a minimum of #3 awg wire.

#6 wire is good for 65 amps. 100 ft will result in upto 5.9 volt drop at the end of the line, which is 2.68%. Not a problem.
#3 wire is good for 100 amps. 100 ft will result in upto 4.9 volt drop at the end of the line, which is 2.23%.
Again, not a problem.

Note: Some like to see less than 2% voltage drop, to me 3% is acceptable. It would matter even less if you actual voltage is closer to 230-240 volts with the motor rated at 220v. As you can see, 5.9 volts below 220 is only 214.1 volts at the end, so that is marginal. 5.9 volt drop from 230 is 224.1 which is fine. If you have a volt meter check your line voltage. If it is already low, step the cable sizes up to #4 for the 60 amp circuit, or #2 for the 100 amp. Your voltage is more likely a little higher, so you could use the smaller wire.

Also, the voltage drop is calculated based on full load of the circuit. As the current load goes down, so does the voltage drop. If your maximum load at any one time is never over 45 amps, the 60 amp circuits voltage drop will be less than 2%. For the 100 amp circuit, if your maximum load is below 90 amps, your voltage drop will be below 2%.

A long answer, but the first two sentence most likely is the answer you need.

[Don Jarvie]

60 amps should be fine for a 1 man shop. Add you the amps from the Unisaw, dust collector and any heat/AC that may run at the same time. You'll probably be well under 60.

Are you doing it yourself? If so the cost of the wire may be a factor. I got 100 ft of 6g (one line not separate lines) and it was 2.50 a foot. It was cheaper than buying 4 separate 6g lines but it was a pain to pull. If I would do it again I'd buy the 4 separate lines. I have a 50amp breaker in my box and at the main. I ran the line off my house box. I can kill the power in the house or in the garage.


Suggest you buy a full panel instead of a sub. I have 20 slots so I can have everything on separate lines and still have slots to spare.

[Dave MacArthur]

If I was running 100 feet of cable, I sure wouldn't want to undershoot it and end up amperage limited... and IMO 60A is marginal, while 100A should allow whatever growth you do in the future.

For the cost of the wire, you almost double your potential. And you can use SER (service entrance cable) instead of #6 or #3 for significantly less $$.

I had the same machines as you basically, and wired my shop using 6AWG (I think), and a 60A breaker feeding a 100A sub panel. My original calculations showed 30.5 A max use in the shop....
That was 4 years ago. Now I wish I had pulled wire to allow the full 100A at the sub-panel. I've upgraded to a 5HP DC, 5HP sawstop, 5HP bandsaw. Sometimes I find I want to also run my 1.5HP DC at the same time because I haven't finished putting up my ducting everywhere. And I don't have any heating or cooling to do yet, but could certainly see putting an airco in to cool my shop when it's 115 F in the summer.

Strongly recommend looking at the relative costs for SER options to feed a 100A sub.

[George Brown]

I ran 100 amps via aluminum SE cable to a subpanel with 4 220V and 10 110V circuits. I also put in a watt-hour meter to know how much I use.

[Jason Fastenau]

I'd second, (or third), going 100 amp. Although 60 should really be fine for a 1 person shop as noted by somebody else, I think it's a good idea to overbuild the electrical capacity in case your needs increase in the future, and retrofitting would be crazy expensive.

[MICHAEL S HILL]

Thank you all for your advice!

[Ian Parish]

Aluminum wire Vs. Copper? Under Ground or through the Wall? Conduit may or may not be needed. These are questions to consider, I am by no means and Electrician nor do I play one on the Internet so consider these questions and ask an expert.

I know AL wire is way way way way cheaper than copper, but you need at least one size larger than the listed copper sizes. Wire for underground needs to be rated for underground with a USE wet rating and ran in conduit, but inside walls you can get SER wire bundled like Romex and not require conduit. I think running the bundled wire in conduit is also not recommended or allowed.

I ran AL wire for 125 amps to a panel on the outside wall and then ran SER wire to another panel in the shop dedicated to tools with Motors and sharp blades. This way when my second panel is off all dangerous tools and the compressor are off.

Good Luck
Ian

[Rob Russell]

60 amp circuit requires a minimum of #6 awg wire.
100 amp circuit requires a minimum of #3 awg wire.

#6 wire is good for 65 amps. 100 ft will result in upto 5.9 volt drop at the end of the line, which is 2.68%. Not a problem.
#3 wire is good for 100 amps. 100 ft will result in upto 4.9 volt drop at the end of the line, which is 2.23%.
Again, not a problem.

I agree with your statements, but only if you're talking about THHN/THWN individual conductors pulled through conduit. If you are talking about something like 6-3NM, then it's only good for 55 amps.

I ran 100 amps via aluminum SE cable to a subpanel with 4 220V and 10 110V circuits. I also put in a watt-hour meter to know how much I use.

I hope that you ran 1/0 SER. If you used 2-2-2-4 aluminum SER, that's only rated for 75 amps.

[Rollie Meyers]

I agree with your statements, but only if you're talking about THHN/THWN individual conductors pulled through conduit. If you are talking about something like 6-3NM, then it's only good for 55 amps.



I hope that you ran 1/0 SER. If you used 2-2-2-4 aluminum SER, that's only rated for 75 amps.

1/0 SER if on the 2008 NEC is 100A, code revision in that edition requires SER to be sized in the 60 degree column in table 310.16.