GFCI for 220?

[Hank Keller]

Is there such a thing as a GFCI for a 220 circuit?

[Bob Johnson2]

Yes there is, but they are expensive and fairly hard to find. I found thew Borg carries them in the higher amperages but I had to go thru an electrical supply house for 15 and 20 amp. I think I paid $80 via an electrician at work.

[Andy Fox]

Hank,

I looked into these a while back while doing my garage wiring guesstimate. One online electrical supply house has 20 amp 240V GFCI circuit breakers for around $150. I don't think anyone manufactures 240V GFCI receptacles. I'm not sure if GFCI is required on 240V receptacles; this probably varies with the local codes and inspectors. In either case, it's definitely safer for anywhere there's bare concrete or moisture.

Andy

[Rob Russell]

In our area, 240v GFCI circuit breakers are readily available. Our local Home Depot carries them and that's where I got the 60amp/240v GFCI breaker we needed for our hot tub. They aren't cheap. I don't remember what I paid for the breaker 5 years ago, but it was about $100.

There is no NEC requirement for 240v GFCI protection for normal use circuits just because you're in a garage or a basement. In other words, you don't need 240v/GFCI protection for your machine circuits in your garage/basement workshop.

In terms of things varying with "local inspectors" - the inspector shouldn't make a difference. If I were told that I needed GFCI protection for my 240v workshop machine circuits, I'd politely ask to see the code section that requires such protection. Spas/hot tubs do require the GFCI protection, but there is a specific article in the NEC that is specific to that type of installation.

Rob

[John Cavanaugh]

Its not required in my area either, but I am planning on using them even though they are expensive. We spend so much time in woodworking trying to be safe from the flying blades, I figured it was only prudent to do the same with potenial flying electrons...

--
John Cavanaugh

[Rob Russell]

I don't think you'll get the sort of safety out of a 240v GFCI that you think you will.

A GFCI works by comparing the current going out to a device to the current returning via the neutral leg. On a 240v GFCI, it's looking at the net difference in current that's going out between the 2 hot legs and comparing that to what's returning on the neutral.

For a regular 240v motor load, there is no current that returns to the panel. In such a circumstance, you could be frying away at the end of the circuit and the GFCI breaker will never trip.

Bottom line - from my perspective - spending the money for 240v GFCI breakers for your shop is a waste of money and will give you minmal protection from shock. The only time the GFCI should trip is if you have a 120v load running off of that circuit, in which case there should be current returning on the neutral. If you're being shocked by that part of the 240v circuit, the GFCI should trip.

Rob

[Todd Tolhurst]

Are you sure about that? A 240V GFCI should measure the sum of the currents in the 2 hots and the neutral. If the sum is non-zero (which means that some current entering the circuit didn't return through the opposite hot phase or the neutral), it should trip.

[Rob Russell]

Are you sure about that? A 240V GFCI should measure the sum of the currents in the 2 hots and the neutral. If the sum is non-zero (which means that some current entering the circuit didn't return through the oppsite hot phase or the neutral), it should trip.

The sum of the currents (if you're taking signs into consideration) would be the difference between the currents in each hot leg.

On a 240v motor - there is no neutral and no current return. That's why I don't think the GFCI will trip on a straight 240v load, whether it's a motor or us being fried.

[Brad Schmid]

Hank,

220 GFCI is common in RVing circles. Mine is 30A 110, but most campgrounds we go to have hookups for both 50A-220 and 30A-110, both GFCI. You might check to see if you have a Camping World or similar in your area. They might be able to lead you in the right direction.

Edit: Now that I thought about this for an hour, I'm not sure I know if it's right. Since I don't use the 50A circuits, I guess I never paid that close attention. I think they might be 110 too... Oh well, just ignore me
Brad

[Mike Henderson]

A 220/240 GFCI actually works the same as the 110 Volt GFCI. You have two wires providing power. If the net current in those two wires is not zero, the GFCI trips.

The fact that one of the wires in a 110 volt circuit is connected to ground makes NO difference - what's important is that the current in the two wires nets to zero.

In a 110 volt circuit, if current "leaks" from the black wire to ground (maybe through you), the net current in the black and white wires will not be zero and the GFCI will trip.

In a 220 volt circuit, current can "leak" from either wire. Unless both wires "leaked" exactly the same amount at the same time, the net current in the two wires will not be zero and the GFCI will trip.

So let's say you have GFCI on a 220 volt circuit supplying a table saw. You forget to unplug the saw and you start to work on the switch. You touch one of the hot leads and current flows through you to ground - the GFCI trips.

Now, let's say that you have the same situation but you have good rubber sole shoes on and you grab the two power leads, one each with each hand. This time, you're fried because the current goes through you (none to ground) and the GFCI thinks everything is working normally. The same thing can happen on a 110 volt GFCI.

And just an added comment. Even with a 220 volt circuit, the potential between each lead and ground is only 110 volts.

The people who designed our power distribution architecture were really thinking - it's as safe as they could make it. But GFCI adds to the safety.

Mike

[Todd Tolhurst]

A 240V motor, with no neutral, still has a current "return". 60 times each second, current flows from one hot lead, through the motor windings, and back out through the other hot lead; then the current flow reverses direction.

In a 240v-only circuit (no neutral present), the current flowing in one hot lead should be equal to, but opposite in sign, the current flowing in the other hot lead. If the currents are not equal, some current is leaking to ground rather than returning through the opposite phase.

Now, this won't protect you if you manage to place yourself across both hot leads, but neither will a 120V GFCI trip if you contact both the hot and the neutral; the GFCI only detects current which leaks to ground.

[Barry O'Mahony]

GFCI = Ground Fault Circuit Interrupter. And that's exactly what they are: they interrupt a circuit upon detection of a "Ground Fault"; i.e., leakage of some of the circuit's current to someplace it's not supposed to be going to. If the leakage were large enough, the fault current would trip an overcurrent circuit breaker. GFCI's are typically required in situations where damp conditions may lead to leakage currents large enough to be hazardous, but less than that required to trip an Overcurrent Protection Device.

They are available in 1-pole and 2-pole configurations. 1-pole devices connect to the Line and the grounded Neutral conductor on 120V branch circuits. 2-pole devices connect to the 2 Line conductors on 240V branch circuits, or the 2 Line and the 1 grounded Neutral conductors on 120V/240V multiwire branch circuits.

GFCI's operate by summing the vector sum of the currents in the 2 conductors (1-pole devices) or the 3 conductors (2-pole devices), and trip when this vector sum (which represents the leakage current) exceeds about 5 ma. In 240V branches there is no neutral so this terminal is left unconnected, although the line side neutral pigtail must still be connected in order for the device to operate.

See http://automation.usa.siemens.com/re...duct/s3014.pdf for a description and wiring diagrams.