Installing 240V Circuit

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Forum topic by tblake1984 posted 12-31-2015 10:15 PM 786 views 0 times favorited 35 replies Add to Favorites Watch
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28 posts in 588 days

12-31-2015 10:15 PM

I have a Ridgid R4512 table saw that is rated at 13A. Doing the math and assuming a 70% efficiency on the motor, that means I am getting 1.5hp max out of this thing. I bogged it down and tripped the breaker cutting some raised panels with it two weeks ago and it freaked me out a bit. My question is this; If I convert it to 240V, does the amperage go down to maintain the same wattage or will I actually get more power out of the saw? Basically, I figure the equation would then be (240*13)-30%=2184W=2.9hp. Is that right?

If so, I want to run it on 240v. Here are the options I am considering for the circuit.

[1] Hire an electrician to install a dedicated 240V 15A circuit. This is obviously the smartest way to go but also the most expensive. I have a basement shop (aka, a concrete cave with unfinished walls) so installing a dedicated outlet box and conduit is a PITA.

[3] Install the circuit myself and replace a pre-existing 1-gang 120v outlet box with a 2-gang outlet box so I can have a 120V and a 240V outlet in the same box (I would also use the pre-existing conduit as well with 12-3 NM wire and a 15A breaker). This would be much cheaper and seems easy enough to do on my own but I’m not sure if running 120 and 240 in the same conduit is a good idea.

I will be replacing the whole cord assembly on the saw with something longer as well. Also, what are your thoughts on making this a 20A circuit despite Ridgid’s recommendation of 15A?

35 replies so far

View OggieOglethorpe's profile


1172 posts in 1527 days

#1 posted 12-31-2015 10:16 PM

I LOVE Internet discussions on electric questions!

View Parabola's profile


9 posts in 294 days

#2 posted 12-31-2015 10:23 PM

For your motor power question:
A motor is built for a specific power output. Doubling the voltage will divide the current in half. (P = I*V)
Many motors will show the amperage draw for both voltage configurations and they always reduce the current when you up the voltage.

I won’t speak to the electrician questions as my answers may not be correct.

View MadMark's profile


965 posts in 870 days

#3 posted 12-31-2015 10:36 PM

To get both 110vac and 220vac you’ll need two hots, a neutral, and a ground. A cordset would require a NEMA14-20 connectors. Do NOT try to use the ground as a neutral. Put a 20A breaker in line (no point in doing all this for 15A)

If you are in a basement run your wiring thru the first floor joists. If the ceiling is finished put a NEMA14 on the wall next to the existing breaker panel and run a cordset to where you need it.

220vac is actually two 110vac lines 180° out of phase. so yeah, you can mix 110vac and 220vac in the same box / cable.


-- Madmark -

View CharlesA's profile


2971 posts in 1215 days

#4 posted 12-31-2015 10:41 PM

I think your equation should read:


-- "Man is the only animal which devours his own, for I can apply no milder term to the general prey of the rich on the poor." ~Thomas Jefferson

View SirIrb's profile


1239 posts in 647 days

#5 posted 12-31-2015 11:26 PM

Took me 6 tries to get through college algebra with a 74. I will choose to not add anything to a discussion on math. You need @TheFridge, resident electrician.

-- Don't blame me, I voted for no one.

View Cato's profile


693 posts in 2729 days

#6 posted 12-31-2015 11:47 PM

I think your HP will basically remain the same just draw less amps.

View CharlesA's profile


2971 posts in 1215 days

#7 posted 12-31-2015 11:48 PM

Some folks argue that a 240v setup is more efficient than 120, but it would be in the single digits %, not 100%.

I have a Craftsman that is very similar to the Ridgid. Some thoughts: use a thin kerf blade, make sure you keep it sharp, and feed particularly hard or thick wood more slowly.

I’ve cut 8/4 Jatoba without much trouble. The only lumber I’be had a hard time with is 2×12 floor joists (I ripped in strips to make my work bench), and it would curve back together and squeeze the blade.

-- "Man is the only animal which devours his own, for I can apply no milder term to the general prey of the rich on the poor." ~Thomas Jefferson

View dhazelton's profile


2283 posts in 1714 days

#8 posted 01-01-2016 12:55 AM

You’d have to look at your local electrical code to see if you could put both circuits in the same box. The conduit would also have to be large enough so things aren’t tight or bunched up in it. I would keep them separate myself. If the only thing keeping you from doing it yourself is the concrete get a Ramset or buy some masonry screws or anchors. Screws work best in green concrete, so I might go with the Ramset. You can also just drop a large piece of wood down from a ceiling or rim joist and attach your box to that.

View clin's profile


485 posts in 413 days

#9 posted 01-01-2016 02:18 AM

Just another confirmation that yes, going from 120 V to 240 V, will cut the current draw in half.

If you are going to run new wire, run the largest wire (largest amp circuit) you can. While there may be code restrictions on how much you can load your panel, I’m pretty sure there is no limit on how large a wire you can run (just how large a breaker you can put in it). The point being, larger wire allows you the option to draw more amps if you need to, even if you only want 20 A now.

Also, you may want to consider putting in a sub-panel. For example, run a 60 A circuit, and put a small breaker panel in your basement. Then you can add on more easily in the future. This way, you are running just one new set of wires (though larger), but can then expand easily.

As always you need to understand what your electric codes are, but adding a sub-panel, is actually quite easy to do.

Also, no big deal mounting conduit to block or concrete, just get the correct fasteners and appropriate drill. You may need a hammer drill for concrete.

Also, you may want to consider framing the basement wall(s) so you can easily run wire and add shelves or cabinets. I.E., rather then individually mounting things like conduit to the masonry wall, bite the bullet once and get some framing attached to them, then more easily attach to that as needed.

-- Clin

View conifur's profile


955 posts in 569 days

#10 posted 01-01-2016 02:26 AM

Just another confirmation that yes, going from 120 V to 240 V, will cut the current draw in half.
I do believe that is per leg, not total.

-- Knowledge and experience equals Wisdom, Michael Frankowski

View WhyMe's profile


574 posts in 978 days

#11 posted 01-01-2016 02:27 AM

You need a 20A 120V circuit for that saw. Don’t worry about putting in a 240V circuit. Not worth the trouble.

View REO's profile (online now)


883 posts in 1491 days

#12 posted 01-01-2016 03:50 AM

This is easy lol amps times volts is watts right?! The WATT is a unit of power not amps not volts! so many are correct in their statements but their conclusions are misguided! here is a real example that cant be argued.

10 amps times 110 vollts equals 1100 watts which equals 1.475 hp
5 amps times 220 volts equals 1100 watts which equals 1.475 hp
that should clear up the HP problem!
when you pay your bill for electric you pay for WATThours not volts not amps so its easy also to determine that regardless of which voltage you use the final bill will be the same because you pay for 1100 watts times the amount of hours you have the saw running AT rated HP either way

View conifur's profile


955 posts in 569 days

#13 posted 01-01-2016 04:05 AM

I worked for an electric utility for 20 years, last I knew a kilo watt was 1000 watts not 1100!!!!
you pay for 1100 watts times the amount of hours you have the saw running AT rated HP either way

-- Knowledge and experience equals Wisdom, Michael Frankowski

View JBrow's profile


741 posts in 337 days

#14 posted 01-01-2016 04:15 AM


As you know, changing your circuit from 120V to 240V is a lot of work and expensive. Perhaps that would solve your problem, perhaps not. I would troubleshoot the circuit and the saw first.

The breaker tripped because:

1) The circuit was getting too many amps for the 15 A breaker. You did not mention whether the table saw circuit is dedicated or whether other devices are also powered on this circuit. If the circuit is carrying load other than the table saw, the combined load when the breaker tripped caused the trip. Some shop lights (or other household load) plus the table saw on this circuit could have taken the circuit down. If the table saw circuit is not a dedicated circuit, ensuring any other devices on the circuit are off while operating the table saw will probably solve the problem. Alternatively installing a new dedicated 15 amp circuit could also solve the additional load problem.

2) The circuit breaker itself is defective. The only way I know to determine if the circuit breaker is defective is to replace the circuit breaker. If you can do the work of replacing the circuit breaker safely, this would cost maybe $10. I do not how much an electrician would charge, but his time would be minimal.

3) The saw motor is defective. I have no suggestions for troubleshooting the motor but doubt that this is your problem. If the saw normally works ok and been ok since the breaker tripped, I would think the saw is ok. Others have already suggested methods for reducing the load on the motor when making cuts.

Even though you did not say you planned to simply install a 20 amp breaker in place of the 15 amp breaker, I have a strong word of caution since this is tempting. I WOULD NOT simply replace the 15 amp breaker with a 20 amp or larger breaker. This is a REAL FIRE HAZARD. A circuit with a 15 amp breaker, in all probability, has 14 gauge copper wire somewhere in the circuit. 14 gauge wire can safely handle 15 amps. If more than 15 amps is put into 14 gauge wire, it will heat up, damage the insulation encasing the wire, and could start a fire!

If you know with absolute certainty that the circuit has 12 gauge or larger wire is running throughout, then increasing from a 15 amp breaker to a 20 amp breaker would be ok. If the motor has overload protection (a reset button somewhere on the motor), the additional amperage from a larger 120 volt circuit would probably not damage the motor, since the internal circuit breaker on the motor would probably trip if the motor draws too much current. I have read manuals from various manufacturers who recommend a circuit breaker larger than the motor rating. But then these motors may have overload protection.

If you plan to replace the power cord on the saw, I would recommend a 12 gauge power cord, which is a little more money than 14 gauge power cords. This increase in size would reduce voltage drop due to resistance inherent in copper. I believe that voltage (the force pumping the current through the circuit) decreases for a given size wire as distance increases. Increasing the size of the wire for a given current (e.g. 15 amp) would increase the length of the cord before voltage loss effects the motor. Admittedly, using 12 gauge wire instead of 14 gauge wire over a short distance would only reduce the impact of voltage drop slightly. Also, unless your existing table saw power cord is small and long, I doubt that replacing the power cord would be beneficial. Additionally, I doubt the power cord has any effect on the problem of the tripped breaker.

Hope this helps and good luck!

View Moron's profile


5032 posts in 3310 days

#15 posted 01-01-2016 04:28 AM

paid to weed through the crap on my end
pending what you get paid and I suspect it isn’t much : (
I’ld skip the need to explain and just plug it in and make music with dust instead of words that waste bandwidth

” I bought an air conditioner ”
“What would you do “

Its like getting a remote control for a tv, and forgetting it takes batteries

-- "Good artists borrow, great artists steal”…..Picasso

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