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Forum topic by tealetm posted 12-01-2017 01:31 AM 316 views 0 times favorited 10 replies Add to Favorites Watch
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tealetm

87 posts in 694 days


12-01-2017 01:31 AM

Ok- current setup is 20 amp service to my small shop. I’m pushing the limits with my current equipment- only tripped it once with all the lights, older craftsman tablesaw and a shop vac.

Anywho, I started digging into my existing service. 4 10ga wires run underground.

So question: can I install a subpanel feeding off a dual pole 30 amp breaker in my main panel? It’d be limited to 30amps overall of course, but that would give me the option to get a 220v saw. Maybe a 20amp 220v circuit and a 20amp 120v circuit in the sub panel?

Thoughts? Is a 220v vintage Unisaw ok off a dual pole 20amp breaker? Or does it need a larger feed And I should forget the bigger saw and use what’s working?

New shop in a year or so so I’m not going to run larger feed to this one at this point.


10 replies so far

View Fred Hargis's profile

Fred Hargis

4757 posts in 2329 days


#1 posted 12-01-2017 11:51 AM

Well, technically what you want to do will work. But if the feed is 10-2, you won’t have a neutral for the 120V circuit. I suppose you could tie the ground and neutral together together (I’ve seen “pros” do this). No doubt this will start a very long discussion of the “code” and what’s right/wrong with your idea…..but the bottom line is you’re idea will work (again, technically). If you need an approval of some sort, you may not be able to get it.

-- Our village hasn't lost it's idiot, he was elected to congress.

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jonah

1455 posts in 3135 days


#2 posted 12-01-2017 12:41 PM

He said there are four wires, so likely it’s 10/3, not 10/2. It will work fine. You can definitely put a two 20A circuits in a 30A sub panel.

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tealetm

87 posts in 694 days


#3 posted 12-01-2017 01:05 PM

Yes, I have 10-3 running out there.

I haven’t been able to find a 30amp subpanel with a main breaker and more than three breaker lugs yet though… buying a larger 100amp subpanel is excessive, even if it’s limited by the 30amp breaker in the main.

So a vintage 220v Unisaw draws less than 20a? Original motor, haven’t seen a data plate yet though.

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jonah

1455 posts in 3135 days


#4 posted 12-01-2017 02:18 PM

Older saws will have 1-2hp motors. At 240V, 1hp is like four amps or less.

One horsepower is ~750 watts.

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Firewood

164 posts in 1470 days


#5 posted 12-01-2017 02:30 PM

You can run a 3hp saw on 240/20A. The 100A sub may actually be cheaper then one more specific to your size needs. If it were me, I’d put in the (1) 240V and (2) 120V circuits. Put the 240 on breaker slots 1-3 and 120V on 2-4. Label your outlets so you can device your loads as evenly as possible.

-- Mike - Waukesha, WI

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tealetm

87 posts in 694 days


#6 posted 12-01-2017 02:35 PM

Great- thanks guys.

Mike- I think you’re right from what I’m seeing regarding panel pricing.

Any reason the main breaker in the sub panel has to be reduced, as long as the main panel breaker is correct for the main-to-sub wiring size?

View Fred Hargis's profile

Fred Hargis

4757 posts in 2329 days


#7 posted 12-01-2017 04:18 PM

Nope, the main panel breaker will protect it.

-- Our village hasn't lost it's idiot, he was elected to congress.

View rbrjr1's profile

rbrjr1

95 posts in 42 days


#8 posted 12-01-2017 05:15 PM

You’re going to have a tough time putting a subpanel in AND running 120 AND running 240 off it.

even the 70A sub panels I’ve seen only have room for a single double pole breaker or 2 tandem single pole breakers.

if you want both 240 and 120 off the sub panel, you’ll have to get a 70A subpanel, wire up 4 of the 1/2” breakers in it and use the “middle two” with a breaker link for your 240v circuit and each of the outer breakers will be your 120v circuits.

obviously, you’ll also have to make sure that the 10/3 is coming off a 30A breaker in your panel.

at least it’s my understanding that this will be what is required.
(even with the two 120v and single 240v circuits, you’ll be limited to the 30A total draw)

-- measure twice, cut once.

View tealetm's profile

tealetm

87 posts in 694 days


#9 posted 12-01-2017 09:24 PM



You re going to have a tough time putting a subpanel in AND running 120 AND running 240 off it.

even the 70A sub panels I ve seen only have room for a single double pole breaker or 2 tandem single pole breakers.

if you want both 240 and 120 off the sub panel, you ll have to get a 70A subpanel, wire up 4 of the 1/2” breakers in it and use the “middle two” with a breaker link for your 240v circuit and each of the outer breakers will be your 120v circuits.

obviously, you ll also have to make sure that the 10/3 is coming off a 30A breaker in your panel.

at least it s my understanding that this will be what is required.
(even with the two 120v and single 240v circuits, you ll be limited to the 30A total draw)

-

That’s my plan as of now- although I’ll pick up a 100amp panel so o have more spaces.

Or maybe a load center that doesn’t have a main breaker (don’t need one since I will have less than 6 breakers)

Thanks all- you pointed em in the right direction

View bigblockyeti's profile

bigblockyeti

4697 posts in 1557 days


#10 posted 12-01-2017 10:04 PM

When in doubt, Unisaw! You should be fine with your setup and you’ll appreciate having a Unisaw now vs. getting something smaller and then wanting to upgrade later.

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