220 V Outlet Configuration / Sawstop Question

[James H Bennett]

My family an I are patiently waiting for the completion of our home - construction is due to finish the end of this month. One of the garage spaces is called an "RV" spot, and I see that the builder has included a 220 volt outlet, presumably for some sort of RV hookup. We have no RV but my eye is on this large space is not for parking, but for my new workshop - wahoo!

Anyway, I had sold my old Craftsman contractor saw when we left California and the wife said I can buy a new table saw (wahoo #2!). My wish/plan is the 3 HP, 220 volt Sawstop PCS. Looking at the Sawstop web site, it appears that the saw will come with a NEMA 6-15P plug (round ground prong and two flat horizontal hot / neutral? prongs). Well, the outlet the builder has installed has FOUR holes in it: one round ground plug at the bottom, two flat 45 degree holes on the sides, and one flat horizontal hole at the top).

Worst (best?) case would be to have an electrician re-do it but if this is something simple that I can change out I'd sooner do it myself. However, I don't want the new saw to turn into a large flaming mass, either.

I am not familiar with 220 volt plugs or receptacles - can anyone here venture an educated guess as to what the heck sort of outlet this is? I know that the Sawstop manual describes how to replace the supplied cable with one of your choice, but what the heck is that fourth hole for on the outlet?

Thanks, Jim

[Josh Molaver]

The 4 terminals are: hot, hot, neutral, ground. I'm not familiar with RV's, but they must use the neutral to pull 120V/240V power at different places. Your Sawstop has two hots and a ground; no neutral...all the electronics run on 240V.

Switching the receptacle over is trivial - just buy the correct one the Sawstop uses, shut off the breaker (AND TEST IT), open the box, and re-wire it - capping the now unused neutral. You must validate the breaker and wiring are sufficient for the amperage you'd be pulling - validate the breaker is rated at whatever Sawstop recommends, AND the wiring must be rated to support that amperage (i.e. 20 amps or 30 amps).

[William Chain]

Alternatively, if that plug is wired with sufficiently sized wire, perhaps you could have the builder put in a subpanel instead of a huge RV outlet (could be 50 amps, could be 30 amps). Two hots, and a separated neutral and ground would work very nicely for that - then you can put in an array of outlets for your shop.

[Dave Mills]

Excellent advice. I would just add that you might want to check the amperage on the existing RV circuit. If, for example, it is a 50A, then that location would make a nice small breaker box from which several 240V/20A circuits and/or 120V circuits might be run. It would turn it into an electrician project instead of simply swapping the outlet, but if your shop plans include more than just the one 240V tool, it may be worth doing it.

[William Chain]

Exactly, without a photo or some specs, it is hard to know what RV outlet you're staring at. A 50 amp circuit would be a wonderful opportunity. Have the builder do this if possible while everything is still rough, it'll be a game changer for your intended shop.


Excellent advice. I would just add that you might want to check the amperage on the existing RV circuit. If, for example, it is a 50A, then that location would make a nice small breaker box from which several 240V/20A circuits and/or 120V circuits might be run. It would turn it into an electrician project instead of simply swapping the outlet, but if your shop plans include more than just the one 240V tool, it may be worth doing it.

[Rich Engelhardt]

Worst (best?) case would be to have an electrician re-do it but if this is something simple that I can change out I'd sooner do it myself.FWIW - I'd get an electrician out - or - talk to the electrician that did the wiring in your house - and discuss your plans for putting in a shop.

In addition to the one 220V outlet for the saw, you're going to want several 120V GFI outlets - maybe A/C & heat, lights and dust collection.
Plus - that gives you enough to add a 220V plug for an electric vehicle if you have to get one of those things.

I plan to have the electrician put in a 60 amp subpanel in the third bay garage of our new place that's being built.

[James H Bennett]

Guys - thanks for the replies! I neglected to mention that I also would be using the outlet for nightly charging of my hybrid SUV. I can schedule that for the wee hours of the morning. But, after reading the replies, I think my best bet is to bite the bullet and have an electrician come out to assess the amperage capacity of that line and if possible, add one or two other 220 outlets for my woodworking equipment.

Thanks again, Jim

[Bill Dufour]

remember if it is say a 30 amp outlet you can run a 100 amp panel off of it. Thiis gives you lots of extra space for latter expansions. Rule of thumb is any panel should have at least two empty slots for latter additions. So if you need 6 slots now get at least eight in the new panel. A 240 circuit uses two slots, a surge protector uses two more slots. So it adds up fast. I see saw, ac, welder, planer, car. so right there it is 10 circuits plus 120 stuff. Keep lights on there own breakers not on the general use 120 outlets.
Is is convenient to use the same make of breaker as existing in the house so you can swap stuff around for testing etc. Or if something fails sunday night you can pull and replace the more critical use for a day. Just not Zinsco or federal pacific. I like square D QO breakers. still being sold 50 years latter. Lots of cheap used ones for sale.
Bill D

[Jim Becker]

Just put a 240v 4-wire plug that matches your receptacle on the saw. The neutral will not get used... This preserves the outlet "as it" for other applications such as your EV charging. You can, of course, make a pigtail to "adapt" the saw's "native" plug, but that costs more money than just changing the plug.

[lowell holmes]

I agree with Jim. My table saw is jumpered to 220. It does not bog down. You will wire the wall plug with proper outlets which if I remember correctly, can be purchased at Lowes or Home Depot.
If you are nervous doing it, hire an electrician.

[Charles Coolidge]

You want the breaker sized to your saw, you want it to trip in a fault condition not hit the saw with 50+ amps before it trips. I say run a 2nd 220v outlet for the saw and a 3rd 220v for a dust collector each sized appropriately. I have a 5hp ICS and 3hp cyclone, went with 30 amp twist lock plugs and outlets for both.

[Patrick Varley]

remember if it is say a 30 amp outlet you can run a 100 amp panel off of it.

I don't think this is true, though I'd second getting an electrician out. It's all going to depend on the gauge of wire at that outlet. A 100 amp panel would require (at least) 3AWG copper. A 30A outlet likely only has 8 or 10AWG.

I'd echo the idea of having a 50A sub-panel put in in place of the existing outlet, then wiring some combination of new 220 and 120 circuits based on the equipment you have.

[Jim Becker]

You want the breaker sized to your saw, you want it to trip in a fault condition not hit the saw with 50+ amps before it trips. I say run a 2nd 220v outlet for the saw and a 3rd 220v for a dust collector each sized appropriately. .

The breaker is to protect the wire, not what's plugged into it. Electricity doesn't "hit" anything with the maximum amperage; it supplies what is requested from the device using the energy. There is no electrical benefit to replacing the existing four wire receptacle and breaker for the OP's saw. Any benefit would be purely for convenience. In this case, there would actually be inconvenience because of the stated intent to use that circuit for charging an EV, too.

That said, I do agree with adding circuits to the OP's shop space for tools like a DC which should be on dedicated service.

[Andy D Jones]

You want the breaker sized to your saw, you want it to trip in a fault condition not hit the saw with 50+ amps before it trips. I say run a 2nd 220v outlet for the saw and a 3rd 220v for a dust collector each sized appropriately. I have a 5hp ICS and 3hp cyclone, went with 30 amp twist lock plugs and outlets for both.

It is NOT the responsibility of the breaker to protect whatever is plugged into the outlet! The breaker is there to protect the fixed wiring, thus preventing a structural fire. It is the responsibility of the unit plugged into the outlet to protect itself and its portable cord.

Example: most kitchens and dining room outlets are rated at 15 amps, but they are on a 20 amp breaker (with in-wall-wiring to suit: 12 ga). This is all IAW NEC. So clearly, the breaker is not capable of protecting any appliance plugged into those outlets.

Another example: we have dual-amperage receptacles (e.g. 15 & 20 amp plug compatible.) How would it be possible for a breaker to provide no more than 15 amps when a 15 amp device is plugged in, yet provide 20 amps when a 20 amp device is plugged in? The breaker and wire serving the outlet are required to safely handle at least the 20 amp load, while the device plugged in protects itself.

The saw (or any other line-powered device) is required (via UL, et al) to provide overload protection to prevent a fire in any of its wiring (including inside the motor). Extension cords are protected by their receptacle not allowing anything incapable of protecting the extension cord to be plugged in.

Generally, tools' built-in protection breakers are much faster reacting, to protect the unit from damage, and personnel from injury. Panel breakers are slower reacting, to prevent a fire (between breaker and outlet) while reducing nuisance tripping, Their reaction time is often long enough to damage the power tool if the power tool is what caused it, except for UL/CSA required protection in the tool.

-- Andy - Arlington TX

[Charles Coolidge]

The breaker is to protect the wire, not what's plugged into it. Electricity doesn't "hit" anything with the maximum amperage; it supplies what is requested from the device using the energy. There is no electrical benefit to replacing the existing four wire receptacle and breaker for the OP's saw. Any benefit would be purely for convenience. In this case, there would actually be inconvenience because of the stated intent to use that circuit for charging an EV, too.

That said, I do agree with adding circuits to the OP's shop space for tools like a DC which should be on dedicated service.

Yes the breaker is to protect the wire. Now if the wire and breaker are capable of delivering 50 amps in a fault situation then what's going to happen, there you have it.

[Charles Coolidge]

It is NOT the responsibility of the breaker to protect whatever is plugged into the outlet! The breaker is there to protect the fixed wiring, thus preventing a structural fire. It is the responsibility of the unit plugged into the outlet to protect itself and its portable cord.

Example: most kitchens and dining room outlets are rated at 15 amps, but they are on a 20 amp breaker (with in-wall-wiring to suit: 12 ga). This is all IAW NEC. So clearly, the breaker is not capable of protecting any appliance plugged into those outlets.

Another example: we have dual-amperage receptacles (e.g. 15 & 20 amp plug compatible.) How would it be possible for a breaker to provide no more than 15 amps when a 15 amp device is plugged in, yet provide 20 amps when a 20 amp device is plugged in? The breaker and wire serving the outlet are required to safely handle at least the 20 amp load, while the device plugged in protects itself.

The saw (or any other line-powered device) is required (via UL, et al) to provide overload protection to prevent a fire in any of its wiring (including inside the motor). Extension cords are protected by their receptacle not allowing anything incapable of protecting the extension cord to be plugged in.

Generally, tools' built-in protection breakers are much faster reacting, to protect the unit from damage, and personnel from injury. Panel breakers are slower reacting, to prevent a fire (between breaker and outlet) while reducing nuisance tripping, Their reaction time is often long enough to damage the power tool if the power tool is what caused it, except for UL/CSA required protection in the tool.

-- Andy - Arlington TX

You are missing the point entirely. Are the components in a machine rated for 220v 20amps capable of handling 50 amps when connected to a 50 amp circuit? Why even bother to specify the circuit for the machine at 220 20 amps, heck connect it to a 100 amp circuit by your logic. Just run some 00 wire in the shop and connect all the machines to a 100 amp circuit breaker, the wire is protected.

[David L Morse]

Are the components in a machine rated for 220v 20amps capable of handling 50 amps when connected to a 50 amp circuit?

Are the components in your phone charger capable of handling 20A when connected to a 20A circuit? By your logic you would need a 0.2A circuit for that. Jim and Andy are correct.

[Steve Fish]

I would definitely go for a sub panel and a few extra receptacles now. Way less hassle, mess, and exspense vs doing it later in hindsight.
Also, I’m curious why nobody has suggested changing the plug for the sawstop to the 4 prong and simply leaving the neutral slot empty on the saw side of the plug? I would think having the receptacles in the walls wired for neutral gives more flexibility long term

[Jim Becker]

Yes the breaker is to protect the wire. Now if the wire and breaker are capable of delivering 50 amps in a fault situation then what's going to happen, there you have it.

That's not how it works, however...

[Jim Becker]

You are missing the point entirely. Are the components in a machine rated for 220v 20amps capable of handling 50 amps when connected to a 50 amp circuit? Why even bother to specify the circuit for the machine at 220 20 amps, heck connect it to a 100 amp circuit by your logic. Just run some 00 wire in the shop and connect all the machines to a 100 amp circuit breaker, the wire is protected.
Charles, the wire and breaker "allow" up to 50 amps to be requested without damaging the in-wall wire, receptacle and breaker. They do not "send" 50 amps of current to anything that doesn't ask for it. If your device only needs/asks for 2 amps, that's all it will ever see. Your 20 amp saw will not ask for more than 20 amps of current (outside of possible a startup spike which is normal and handled by modern breakers) and will never, ever see 50 amps of current on that circuit.

[Ken Combs]

I no longer have a SawStop, but going from memory, the one I had used a motor with a thermal breaker, like most quality motors used on power tools. That is where the responsibility for protecting tool lies, not with supply circuit.

One should never put a receptacle on a circuit with a lower rating than the wire and breaker. A 30a recpt would overheat if used to the capacity of a 50a circuit for instance. There is a common exception already mentioned,15a recepts on a 20a household circuit, that is an exception as they are rated 20a pass through and 15a for connected appliances.

[Wes Grass]

Yeah, outlets don't push power, your tools suck ;-)

We've got an RV outlet here. It's 50A as I recall. Currently (ha) disconnected to run a feed to a hot tub.

I had a 50A circuit and outlet in my garage, presumably for a welder. I used it a couple times to back feed the main panel with a generator (yes, I turned off the main first). I rewired it to a sub panel. I think I have 1 20A, and 2 30A breakers in it. Or 2-20's and a 30? So either 70 or 80A potential draw, but if I were to load all of those to capacity it would trip the breaker in the main. Not likely I'd ever have the TS, BS, Planer, and DC all running at the same time and each pulling a real load.

I've also got 2 outlets on each of those breakers. I kept the BS and Planer plugged in to a single circuit, but they were never run at the same time. Probably would have been fine if I started the Planer first. Had no desire, or need, to test it. But the 50A in the main would have done it's job and the beefy cable buried in the wall would have been fine.

[Andy D Jones]

I no longer have a SawStop, but going from memory, the one I had used a motor with a thermal breaker, like most quality motors used on power tools. That is where the responsibility for protecting tool lies, not with supply circuit.

One should never put a receptacle on a circuit with a lower rating than the wire and breaker. A 30a recpt would overheat if used to the capacity of a 50a circuit for instance. There is a common exception already mentioned,15a recepts on a 20a household circuit, that is an exception as they are rated 20a pass through and 15a for connected appliances.

Receptacles are required to limit the maximum size of (fixed) wire to which they can be attached, to correspond to the maximum current which they can safely handle, regardless of the physical safeguard of the receptacle itself (i.e. the current rating of any plug that can be mated with the receptacle).

Thus you cannot physically install (and pass inspection with) a receptacle that will not safely handle the current suppliable by the breaker, if the requisite minimum size (or larger) wire is used.

-- Andy - Arlington TX

[Rod Sheridan]

Yes the breaker is to protect the wire. Now if the wire and breaker are capable of delivering 50 amps in a fault situation then what's going to happen, there you have it.

Fault current could be in the 1,000 to 1,500 ampere range regardless of whether it’s a 30 or 50 ampere breaker.

I presume it’s a 30 ampere feeder which would be fine for the saw.....Rod

[Rod Sheridan]

You are missing the point entirely. Are the components in a machine rated for 220v 20amps capable of handling 50 amps when connected to a 50 amp circuit? Why even bother to specify the circuit for the machine at 220 20 amps, heck connect it to a 100 amp circuit by your logic. Just run some 00 wire in the shop and connect all the machines to a 100 amp circuit breaker, the wire is protected.

It depends upon the withstand rating of the components. My 16 ampere jointer/planer is restricted to a circuit capable of not exceeding 5,000 amperes symmetrical.

As for overload capability that’s provided by the machine, not the feeder.....Regards, Rod.

[Kyle Iwamoto]

You are missing the point entirely. Are the components in a machine rated for 220v 20amps capable of handling 50 amps when connected to a 50 amp circuit? Why even bother to specify the circuit for the machine at 220 20 amps, heck connect it to a 100 amp circuit by your logic. Just run some 00 wire in the shop and connect all the machines to a 100 amp circuit breaker, the wire is protected.

I think you are the one that is missing the point. As someone else mentioned, breakers do not push current, tools suck current. Just because the breaker CAN supply 50 amps, it will not. If the tool draws the entire 50 amps, the breaker will let the current through. The breaker will not push 50 amps into a 20 amp saw. But 20 amp saw can draw over 50 amps if it shorts and/or catches fire, then it will trip. The saw is probably toast at this point. The breaker saves the wire in the wall and the house from burning down.

[Charles Coolidge]

The maximum overcurrent protection (MOP) is the maximum circuit breaker size required to properly protect the equipment under anticipated fault conditions...the MOP is the maximum allowable circuit breaker size that will properly disconnect power to the equipment under any anticipated fault condition.

[Curt Putnam]

I did not read the whole thread. I just wanted to point out that two flats @45° and a round is also the configuration for 30 amp 120V RV plugs, Just wanted to suggest that you be sure you have a 240v setup as opposed to the RV setup @ 120v.

[Scott Winners]

Wow. I read most of this. OP, you need a local electricion involved who is aware if any local subtleties not covered or different from the National Electrical Code (NEC).

Local to me I could put in a 220 VAC breaker at 50 amps, with wire suitable for 220V at 50Amps, drop that from the ceiling in my garage with a 50amp receptacle on it, and then use adapters to plug in say a planer that runs on 220VAC at 20 amps, or a different adapter to plug in a tablesaw that runs on 220VAC @ 30 amps. Within the NEC this is a kosher thing to do, but the further east you are, or the closer you are to Chicago (where they had a big fire once upon a time) the more likely you are to find local regulations more restrictive than the NEC.

If it is legal for you to do and you have a 50amp RV outlet in your future shop, I would leave the build alone, not pay any more to the builder, and just come up with adapters to use the 50amp outlet you might already have. If it is legal. One thing I don't do is play fast and loose with my homeowner's insurance. If you have a significant claim the "adjuster" that visits your home isn't there to put a dollar value on the damage, that individual is coming over to find a reason to deny your claim.

[Bruce King]

The maximum overcurrent protection (MOP) is the maximum circuit breaker size required to properly protect the equipment under anticipated fault conditions...the MOP is the maximum allowable circuit breaker size that will properly disconnect power to the equipment under any anticipated fault condition.

Exactly. Outdoor HVAC units always have a max breaker size listed on them. They are expensive units and no one is watching them. Not all malfunctions are dead shorts which can cause an unprotected device to smolder and possibly catch fire. Installed a bath fan/infrared heating unit ceiling unit once that required a max 15 amp circuit. If you like your device you will operate it on a reasonably sized circuit even if they failed to put a max circuit size on it.
The cell phone charger argument does not cut it. For one it’s not a dumb device and two, it has small wires that would burn open very quickly resulting in no issue. Anything on a y adapter or extension cord is just plain wrong, those are temporary wiring items. Wood working tools are usually supervised so errors of judgment usually are not a problem.

[Andy D Jones]

I have yet to see a MOP requirement for plug-in equipment. Only hard-wired (like HVAC).

I'll admit, I have not seen every manual on every machine ever sold with a plug...

-- Andy - Arlington TX