# Anyone Using a GFCI With their 240V Table Saw?



## ras61 (Mar 27, 2014)

Hi - I'm planning to run a 240 line for a table saw, and was thinking a GFCI circuit breaker would be a good idea. In researching this, I've seen hints that at start-up the 240 motor might cause a voltage imbalance and trip the GFCI breaker. Before going to the expense of adding one of these breakers, I was hoping for some real life feedback from anyone who's also done this. Thanks for the help.

Russ

PS This is a spin off from another topic that I thought deserved it's own thread.


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## bigblockyeti (Sep 9, 2013)

Not with a tablesaw, but we did have a 240V circuit in one part of the shop where I worked for the old compressor and it was equipped with a GFCI breaker. This was done in part to the condensate puddle that could accumulate if someone didn't properly hook up the hose when draining the compressor. I think you may be right on the voltage imbalance issue as this was a 5hp motor spinning up a compressor with a large flywheel and did so much slower than a tablesaw spins up to full speed. The breakers (2) only lasted about three months before failure. After going through two of them we reverted back to the original non-GFCI setup and fixed the root problem with a properly plumbed automatic condensate drain.


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## oldnovice (Mar 7, 2009)

I have a 2 pole GFCI on my 220 VAC, 30A, line for over a year and, knock on wood, have had no problems.
Code required the GFCI as the outlet was in my garage.


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## teejk (Jan 19, 2011)

I would never use a GFCI on anything that doesn't pose the risk they were designed to protect against. That is generally limited to anything where liquid is possible (code says outside, garage, kitchen, laundry, bath, sump pump and I guess 1 near the panel). If you don't have danger of moisture near your saw, keep it simple. I've had to replace a few of those outlets after only a couple of years because they failed.


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## ras61 (Mar 27, 2014)

Teejk - the reason I'm considering a GFCI is because the saw will be in a detached garage where there is a utility sink, the possibility of rain getting in if the doors are open, or just people walking in from outside with wet shoes. The GFCI breaker is $70, a small price for peace of mind, but a waste of money if it won't work with the saw motor.

Oldnovice - not sure of code rules where you live, but here a garage outlet only needs to be protected if it's 120V, 240V is still exempt (don't ask me why). As electrical codes only become more conservative over time, I'd bet money that 240V lines will also require GFCI protection sooner rather than later. As I understand it, a new code book comes out every 3 years, and I think we're due for a new one in 2014, so it will be interesting to see if things change.

Also, what kind of saw and motor are you running on that 30amp GFCI breaker? Thanks.


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## TopamaxSurvivor (May 2, 2008)

ras61, New code comes out this year 2014 edition, you are correct. I have always wondered why for lots of things in the code. For instance, if you have a 15 or 20 amp pool motor circuit, 120 or 240 volts, it required GFCI, but if the circuit was 30 amp of higher, it did not require GFCI. For 2014 they have changed that, now all of them require it regardless of the circuit amperage and voltage. I would imagine they will eventually require GFCI for 240 volt circuits in garages and out buildings.

The saw start up should not cause any nuisance tripping.


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## oldnovice (Mar 7, 2009)

*Russ*, I mislead you in thinking that the 220 Volt was on my TS when it was actually on my 2.2 HP spindle!


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## ras61 (Mar 27, 2014)

Thanks for the reassurance Topamax, your pedigree in the realm of ether and sparks truley gives both credibility and comfort (thanks!). Once I ACTUALLY get a TS, I'll roll the dice and try a GFCI breaker. I'll then report back then on how things work out (hopefully sooner rather than later).


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## Ocelot (Mar 6, 2011)

I've had nothing but trouble from the 120v GFI do-dads in my shop. After any saw has been on them for awhile, they buzz constantly 24-7. They don't trip, they just drop voltage, so the saw (or DC) won't start. They probably get hot too. I've taken 2 of them out. One of them is still in the wall buzzing. It may even be a fire hazard. We previously had a freezer plugged into one, and it kept tripping and threatening to spoil our food, so we got rid of that one too. I don't think GFI does well supplying power to motors.

-Ocelot


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## TopamaxSurvivor (May 2, 2008)

Ocelot, They are supposed to be tested monthly and replaced if not working properly.


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## Ocelot (Mar 6, 2011)

Wow! How many homeowner's know that they are supposed to be tested monthly? Why are they so fragile? It must be that there is a way to build this thing where it won't be so prone to breaking, or at least so that GFI devices that are so fragile would be banned from sale.


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## TopamaxSurvivor (May 2, 2008)

I don't know that they are really that fragile. Just like anything else, there will be some bad ones in the pile. Most last for many years.

When I have been on service calls, many people do not even know what they are. I seriously doubt if very many are ever tested, much less monthly.

The lasted code will require arc fault to all residential circuits. More buttons to push and test every month ;-)


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## Ocelot (Mar 6, 2011)

All 3 of them in my shop have gone bad, and one that I replaced quickly went bad too. I suspect that the surge current at motor turn-on is the problem. The surge can be much more than the stated continous circult limit. The breaker is slow enough that it doesn't trip, but the GFI's solid-state components can't take it.

The first one started to go bad just running a little 120v hoist that I used to pull stuff up into the attic.

-Ocelot


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## TopamaxSurvivor (May 2, 2008)

My guess would be there are other issues in the system affecting the GFI operation. Sensing a few milliamps difference in the current of a motor should not cause them to go bad. If they are 15 amp and opening a lot, I suppose they might go out due to motor load, but the contacts would be closed during normal operation. Closed contacts do not burn up. Closing heavy loads will burn them up if they are not rated for the use. If they are opening all the time, there is a leak to ground in the utilization equipment.


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## teejk (Jan 19, 2011)

Topamax…I've had problems on houses I bought so I agree with the "overload" thing on GFCI's. But they do contain electronics that go beyond the normal circuit breaker/outlet (which when boiled down to their basics are not much more than big wire-nuts). Electronics can be "fickle". But back to the OP…can you even get a 240v GFCI? Somebody explained to me years ago that 240v ran on three wires instead of 4 because of how 240v automatically balanced load. Smaller 240v appliances now seem to require the separate ground but I've read that is solely for back-up in case either the green or white wire failed. But as long as I have your attention, I've never found a sparky that can explain the need for arc-fault circuits. I Pulled my housing permit before they became mandatory so I didn't have to deal with what would have been a costly addition at the time.


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## ras61 (Mar 27, 2014)

Teejk - You can't get a 240V GFCI outlet (at least not yet), but you can get a 240V GFCI circuit breaker and protect the line at the panel. The rest of your questions I'll leave to Topamax or someone else qualified to answer.

Ocelot - Maybe if you tried a 120V GFCI breaker you'd have better luck, might be worth a try?


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## TopamaxSurvivor (May 2, 2008)

teejk, All I can say is I have not yet come across a recurring GFCI failing that I could not determine the cause. It is normally high resistance ground.

GFCI technology comes in about any voltage and amperage you care to specify. Beyond 15 and 20 amp at 120 volts it is only available in circuit breakers.

240 volts works on 2 hot to ground wires. 120 volts works on 1 hot wire and one grounded wire. Normally, a transformer will have a center tap that is grounded. You get 120 from each 240 volt hot to the center tap. The grounded center tap facilitates activation of short circuit protection if either hot were to become grounded. The ground is very important to stabilize the 120s. If your compressor started on one side of the 120 and your tv was on the other side and there were no other loads and a poor ground connection, your TV would see 210 +/- volts, the compressor would see 30 +/-. The compressor would not start, the TV would blow up and you would have neither working. The ground is the most important part of the system. sort of like your car; if the brakes do not work, you probably do not want it to start.

The '240 volt balancing" of the load comes when you have, say a 5 amp 120 volt load on one end of the 240 volt transformer and a 10 amp load on the other end. If you just had the 10 amp alone, the center tap would carry a 10 amp load. Same for the 5 amp alone. With both on at the same time, the center only carries 5 amps; half of the 10 amp load. The other half of the 10 amp load balances with the 5 amp and goes through it.

Smaller 240 volt equipment will have a white neutral if it has 120 volt load which is normally a control circuit or possibly a small motor if it is a heat generating device. Green is ground the world around. It is always there to facilitate the operation of short circuit protection and to make sure the device is not hot when some one touches it.

I'm not going to explain the need for arc fault other than it is required by the code. I am not sure about the current state of the technology. It is current sensing that looks at wave forms to determine if there is an arc which will generate heat and possible a fire. There have been a lot of issues getting it to find problems without just being a nuisance. Since I do not do residential other than an occasional service call, I really haven't paid much attention to it.


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