I have a new 220V Table saw, but my main panel is full

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Forum topic by Chewmanfoo posted 06-17-2014 11:04 PM 1374 views 0 times favorited 27 replies Add to Favorites Watch
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8 posts in 857 days

06-17-2014 11:04 PM

My first post – sorry if this question is in the wrong thread or somehow inappropriate…

I just bought a new 220V table saw. I have assembled it and it’s sitting there grinning at me. I can’t plug it in yet.

In my 100 amp main panel, I noticed a few double 15amp breakers where two breakers are living in one space. Can I double up a few 20amp breakers to make room for a new 30amp service? Suppose I wanted to add a sub panel closer to my woodshop – could I add a 60amp breaker in my main panel, then string the wire and add my new 30amp breaker in the sub panel? Or, since my main panel is full, do I really need to upgrade the main panel to a new 200amp panel with more room?

27 replies so far

View MrRon's profile


3891 posts in 2661 days

#1 posted 06-17-2014 11:26 PM

Yes! you can double up on your breakers. Add up all the current being used at any one time to see if you have enough capacity to run a saw. Lights should not dim when the saw is starting. If they do, you need to upgrade service.

View English's profile


512 posts in 895 days

#2 posted 06-18-2014 12:05 AM

Panels are usually labeled if you can add tandum breakers. Labels will show something like 12/24 circuits in this example all 12 circuits can be changed to tandum breakers giving you 24 circuit, some panels are labeled 12/16. In this case only 4 of the 12 original circuits can be tandum breakers. There are many other labels, read the labels completely, it should tell you if you can expand the number of circuits.

If you are not sure what to do, please call an electrican. We don’t want to lose any of our LJ family.

-- John, Suffolk Virgina

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Shawn Masterson

1294 posts in 1366 days

#3 posted 06-18-2014 12:16 AM

Your current panel, how many spaces are there? My old panel was 100 amp and only had 20 spaces. I replaced it with a 100 amp panel with 30 spaces. Going to a 200 amp means there may be some other incurred expenses. I believe that you will need a new service from the pole, meter base, and the rest of the house will have to be brought up to current code. I am not a sparkey, but I believe that is what is involved with upgrading to a 200 amp panel.

If I were you I would pull a 220 breaker and put in a sub-panel. I have a 60 amp breaker feeding my sub-panel. from there I have 12 circuits in the shop. it’s really not enough. There is plenty of power, but not enough slots.

View pmayer's profile


845 posts in 2483 days

#4 posted 06-18-2014 03:13 PM

I would install a sub-panel. It’s easy (if you can wire a new circuit you can install a sub-panel), relatively inexpensive, and you will appreciate the flexibility that this affords you.

I added a 100amp subpanel with 20 slots for my shop and I have used nearly all of them. Yes, my wiring is way overkill for a 1-2 person shop, but it is a nice luxury to have.

-- PaulMayer,

View Chewmanfoo's profile


8 posts in 857 days

#5 posted 06-18-2014 03:22 PM

Wow this board is chock full of helpful folks with good ideas!

A few follow-up questions.

(fear not – I have a bachelor’s in Computer Engineering, I understand Ohm’s law etc. I won’t burn down my house!)

I have 100amp service.

If I add an additional 100amp sub panel, that’s OK, just as long as I sum the total amps in use simultaneously (at ANY time of day) in my main panel, subtract that from 100amps, the remaining amps are available simultaneously on my sub panel. So considering lights, computers, TV, HVAC, oven, clothes dryer on the main panel, I come up with, say, 60 amps – then I can have 40 amps simultaneously on my sub-panel without fear. 40 amps is my table saw + dust extraction, for example.

It might be safer to just add a 40 amp sub-panel, correct?


View TheFridge's profile


5672 posts in 904 days

#6 posted 06-18-2014 05:05 PM

Must be an older house.

If the saw draws 16A and the total length is under 100’ #12 on a 20A breaker is more than enough.

You could size the wire up bit I don’t recommend sizing the breaker up to a 30A if the FLA of the saw is 16A or less.

A sub panel would be great if you can do it. You could also get a quad breaker. It’s 2 tandem breakers with handle ties on the inner and outer sets, so you could double up a 2 pole breaker.

Technically, you’re only supposed to use up to 80% of the capacity on any given breaker, from the mains on down to a branch ckt breaker. There are exceptions, but cord and plug connected equipment in a house (your saw and portable power tools) ,isn’t one of them.

Just rules of thumb. You usually don’t need to upgrade your service unless you are adding a large appliance (bigger A/C), or a generator.

And if you double up a ckt from a cable that has 2 hots and are sharing a neutral, make sure the 2 hots are on opposite phases or the neutral will carry a double load. Which isn’t good.

Sub panel or doubling up. Up to you really.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View Chewmanfoo's profile


8 posts in 857 days

#7 posted 06-18-2014 06:03 PM

My saw ( says 5HP, 14amp, minimum circuit 30amp.

I’ve decided to put a sub panel in the wood shop (attached garage) about 50 ft away from the main panel. I’ll put in a 30amp and a 20amp circuit in it, as well as some 15 amp circuits for lights, a PC and chargers etc.

Now, to figure out how big a wire is required for this sub panel. Googling this little conundrum is yielding quite a disagreement among the “experts”!

View nicksmurf111's profile


361 posts in 868 days

#8 posted 06-18-2014 08:31 PM

Yeah, your correct. You would need a 30 amp breaker. That must be an efficient motor though if it’s 14 fla.

-- Nicholas

View crank49's profile


3979 posts in 2389 days

#9 posted 06-18-2014 09:04 PM

I could understand a 15/30 amp rating. That would be the amp loading for 230/115V.
But if it says minimum circuit 30 amp then you will need a 30 amp circuit. Probably due to inrush current for starting a 5 hp motor.
NEC (National Electrical Code) specifies #8 awg = 50 amps . . . #6 awg = 65 amps . . . #4 awg = 85 amps.
These ratings are for maximum of 3 conductors in a conduit or cable. These ratings get reduced by 0.88 for 104 degrees F.

-- Michael: Hillary has a long list of accomplishments, though most DAs would refer to them as felonies.

View Chewmanfoo's profile


8 posts in 857 days

#10 posted 06-18-2014 09:07 PM

You guys are great!

so, if I wanted to have room for reasonable future expansion, i need to run a #4 3 conductor wire from my main panel to this sub-panel?

View nicksmurf111's profile


361 posts in 868 days

#11 posted 06-18-2014 09:11 PM


You have to do the calculation for the length of conduit you will be using. I would suggest pulling a permit and run your plans past the inspector. Or at least have an electrician go over your plans with you. Depending where you put the sub-panel, the grounding requirements will be different.

-- Nicholas

View Chewmanfoo's profile


8 posts in 857 days

#12 posted 06-18-2014 09:23 PM

Why does the notion of pulling a permit fill me with dread? I’m completely ignorant of that whole process.

View Richard H's profile

Richard H

483 posts in 1098 days

#13 posted 06-18-2014 09:32 PM

Depending on if you have AC or not and if you use electric heat or gas 100 Amps is a good sized service for most residences. A sub panel is probably the best long term answer but the easiest solution if you don’t see yourself needing to expand much in the future and if your panel is rated for it would be to go with the tandem breakers.

Panel work is something I always just hire out myself. It’s not that I don’t understand the work I just feel like it’s better in the long run to get someone who does that kind of work everyday to do it. You could run the wire to the new outlet and install the box and have a electrician do the actual panel hookup. They should also be able to quickly tell you when quoting the job if you need a sub panel or not. Think of permitting the work as a safety net. If the inspector finds issues with either your or the electricians work than they are pointing out things that may potentially end up costing you much more in the future to fix than to just resolve when you install it.

View Shawn Masterson's profile

Shawn Masterson

1294 posts in 1366 days

#14 posted 06-19-2014 12:42 AM

You need a 4 conductor wire. You have to have your grounds and neutrals separate in the sub-panel. I can say I know that #4 aluminum will get you 60 amps. Yes aluminum is fine for a sub-panel, and will save some money.

View ColonelTravis's profile


1154 posts in 1312 days

#15 posted 06-19-2014 02:42 AM

I’m in your same situation, Chew. Made an extension cord for now but long-term I need a sub-panel. I can do outlets, ceiling fans, lights, etc. But with panels, I’m with Richard above. That’s a whole new level I don’t want to deal with – not because it’s difficult. It doesn’t seem to be, I’ve watched videos and read stuff, blah, blah, blah. but I wouldn’t know if I messed up until the house burned down. I don’t have the background to check and double-check everything properly.

My wife’s uncle does a lot of electric work, he’s going to come over for my garage, so you don’t have to hire an electrician off Angie’s List. Poke around, maybe you can find someone who won’t charge you an arm and a leg, because that kind of work ain’t cheap.

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