How Many Machines On One Circuit?

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Forum topic by javaboy posted 07-23-2012 02:02 AM 1993 views 1 time favorited 13 replies Add to Favorites Watch
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104 posts in 2163 days

07-23-2012 02:02 AM

Topic tags/keywords: 220v circuits 220v power electric motor amperage ratings question tablesaw

My shop has one 220V 30 amp circuit (yes, it also has a bunch of 110V circuits, but my question is about the 220V circuit).

The only thin connected to the 220V circuit at this time is a Grizzly DC. The motor on that is rated at 18 amps.

I am thinking about buying the Grizzly G0690 TS—its motor is rated at 12 amps.

Can I run both machines on the same circuit? I seem to remember reading somewhere that woodworking machine motors are typically rated on starting amperage only, so I am thinking if I start one machine, and then the other I should be OK. What do you think—can it be done, or will I be better off installing another 220V circuit?

Thanks for any advice!


-- Sow justice, reap peace

13 replies so far

View Arlin Eastman's profile

Arlin Eastman

4234 posts in 2590 days

#1 posted 07-23-2012 02:26 AM


It is not the machines but the AMPs that each machine draws. In your owners manual and on the ID plate it will tell you the amps of the machine.

So if you have a tablesaw drawing 20 amps you have 10 amps let to use before the breaker trips which is not good to do.

But to your question on both of your machines on at the same time is Yes just as long as you do not start them both at the same time

I hope other chime in to add more


-- It is always the right time, to do the right thing.

View Dan Lyke's profile

Dan Lyke

1520 posts in 4154 days

#2 posted 07-23-2012 02:34 AM

There are code issues, I’m too burned at the end of the weekend to figure out the details, but I believe that code says you run one 220v circuit to one outlet.

However… from a practical standpoint the question is: What are you going to use simultaneously. If you’re one person in the shop, if the dust collector and the table saw are pulling 18+12 amps at the same time (presumably you’d want to use the dust collector and the table saw at the same time), that’s 30 amps. On a 30A circuit. Maybe those specs are for startup, and the circuit breaker will let you get away with it if you start them at different times. Maybe that’s actual running load, in which case the circuit breaker would be right in shutting you down.

Me? I’d put ‘em on different circuits (almost 4k watts for a dust collector? I hope that sucker is sucking your shop inside out), but maybe you can get away with it…

-- Dan Lyke, Petaluma California,

View Cole Tallerman's profile

Cole Tallerman

392 posts in 2214 days

#3 posted 07-23-2012 02:38 AM

If you turn them on a couple seconds apart they should be fine. My table saw pulls 15 amps when starting but only 12 under a HEAVY load. Also keep in mind that there is a small loss in amps along the cable. Not a large amount but if your right on the full load line it may play a factor. Turning them on at different times tho should work fine.

View MonteCristo's profile


2099 posts in 2217 days

#4 posted 07-23-2012 02:47 AM

Here in Canada the sustained load (ie when working) on an electrical circuit is only allowed to be 80% of the circuit’s capacity. In your case that would be 24 Amps. As Arlin points out, you can often run two or more machines on a circuit as long as you don’t start them at the same time (motors draw hard on startup). Also, if one machine is just idling (ie not under load) it will draw less and it may be fine to leave it running while you use (one of) the other machine(s). I have two table saws on the same 220V circuit and do this sometimes. I couldn’t have them both working at the same time but I can work one and idle the other which is occasionally handy.

If you are not sure of the actual running AMP draws it is risky to push it as, although you may not pop the breaker you may be over the 80% and that will heat up your wiring – not a good idea.

If you know anyone or can rent a clamp meter you can use it to check the actual AMP draws of your equipment.

In my experience ww motors are rated using the actual AMPS under load, not on start up, although when you hear the term “maximum developed”, which is often used with regards to HP, that is a startup value and is of little use – more of a marketing gimmick to make the thing sound powerful.

-- Dwight - "Free legal advice available - contact Dewey, Cheetam & Howe""

View MJCD's profile


542 posts in 2400 days

#5 posted 07-23-2012 02:53 AM

The other issue is the wiring, itself. The breaker may be labeled for 30 amps, but you need to have electrical wire leading to the equipment which can handle 30 amps. Generally, a 30 amp draw requires a 10 gauge wire – this would apply only if you have the DC and the TS on the same wire run; that is, a portion of the wiring is feeding both pieces of equipment. I say this, as it is unlikely you would have two leads coming from the 30 amp breaker. 10 gauge is uncommon within non-commercial environments.

I’ve had electricians disagree with me on this; though, all of the publish information, and how I was taught by my electrician Father, say 30 amps requires 10 gauge.

-- Lead By Example; Make a Difference

View javaboy's profile


104 posts in 2163 days

#6 posted 07-23-2012 02:58 AM

Thanks for the input, guys! Sounds like it’s worth giving it a try and seeing what happens. If the CB starts popping I’ll have to bite the bullet and install another circuit.

Monte Cristo—You’ve given me a lot to think about. Could the wires actually develop enough heat to be dangerous without popping the circuit breaker?

MJCD—I am pretty sure the wiring is 10 gauge.



-- Sow justice, reap peace

View MonteCristo's profile


2099 posts in 2217 days

#7 posted 07-23-2012 04:32 PM

javaboy : About the heat thing, I am not sure but I think so, especially if you are running over that 80% I was talking about because the breaker won’t pop until you hit its full (100%) rating (in your case 30 AMP). Things would be even more acute if the breaker is too large an AMP capacity for the actual wiring – I would make darn sure that this is not the case.

I’ve done a few renos over the years and it’s intertesting to see how the sheathing on old wiring has gotten brittle. I am pretty sure some of that it due to it being heated up from time to time.

As I understand it, most house fires are caused by this sort of issue, often skiny extension cords that heat up and the breaker doesn’t pop because the breaker and internal wiring are capable of much higher AMPS.

It’s safer to be cautious and, in the long run, likely cheaper too. You are paying good money on your electric bill to create that heat !

-- Dwight - "Free legal advice available - contact Dewey, Cheetam & Howe""

View Grandpa's profile


3259 posts in 2704 days

#8 posted 07-23-2012 08:14 PM

I think you will be pushing it to the limit with the set up you are looking at. I would install a second circuit. Once in a while we all do something that isn’t too smart and I have done most of those things. I got a heavy extension cord hot enough to melt the plug and it didn’t trip the breaker. The wiring in the wall was near the point of a fire. Not a good thing. Install the circuit and sleep better.

View cutworm's profile


1075 posts in 2822 days

#9 posted 07-24-2012 01:53 AM

The ampacity of #10 awg Romex is 30 amps and that’s continuous. Distance from the breaker is also a factor because of voltage drop. If it is over 50’ or so you will lose horsepower. It’s been a while but I believe the code states that any single device can’t exceed 80% of the breaker rating. I don’t see a situation when you would run both for more than 3 hours so heat shouldn’t be a problem. Wire length may be a problem though and that would hurt the performance of your saw.

-- Steve - "Never Give Up"

View javaboy's profile


104 posts in 2163 days

#10 posted 07-24-2012 03:29 AM

cutworm : Actually, I rarely ever run the TS for more than barely a minute at a time—max. Typically I turn the machine on, push a board through it, then shut it off. Then I go around to the out feed side and retrieve the wood. Then I walk back around and get ready for my next cut. Slow and inefficient I may be, but I take that whole “never reach over the blade” thing very seriously. The DC will usually run for longer periods because I am not constantly turning it on and shutting it off like the TS. The only way both those machines would be running for 3 hours is if I dropped dead in the shop.

That said, I will sleep better knowing I’m not pushing the electric system into possibly dangerous territory, so I will be putting in another 220V circuit.

Thanks everyone who replied—I greatly appreciate all the advice!


-- Sow justice, reap peace

View MrRon's profile


4800 posts in 3272 days

#11 posted 07-27-2012 08:26 PM

I would abide by the codes and rules that were put in place. They are there for your safety. if you follow them, everything will work like it’s supposed to. Of course if everyone did this, there wouldn’t be a need for this forum. I seem to recall that code requires all 220V appliances to be on separate circuits. Sounds like smart choice to me.

View dhazelton's profile


2771 posts in 2325 days

#12 posted 07-27-2012 09:32 PM

I was staying at a friends house during the heat wave we had in the Northeast last week. He has two ceiling fans running off a switch and in the middle of the night I smelled something acrid. I got up to turn on the light and saw the ceiling fan switch glowing cherry red. I woke him up panicked and he shut down the circuit. I pulled out the still-hot switch—it said it was rated for the amperage of one fan only. FOLLOW CODE! The electrician who installed this switch didn’t and it could have led to a fire.

View Sawkerf's profile


1730 posts in 3097 days

#13 posted 07-27-2012 09:49 PM

You need to know what your AHJ (Authority Having Jurisdiction) calls for to meet whatever they’re using for code. (Electrical codes are NOT universal). If they’re happy, you should be fine.

You should be able to determine the gauge of your wire by pulling a receptacle (turn off the breaker first) and looking at the wire jacket. Typically, they’ll have printing telling you the gauge AWG10 would be 10 gauge. AWG20 would be 20 gauge. If your 220v circuit has AWG12 or AWG14, don’t even turn the breaker back on. – lol

You’re probably ok with your DC and TS on the same circuit. Mine are on a 30 amp circuit with 20 gauge wire and do fine. My sequence is to start the DC before the saw so I’m not hitting the circuit with two startup loads at the same time.

-- Adversity doesn't build reveals it.

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