Possible to wire GFCI into 240v circuit with 3-prong receptacle?

[monathedog]

I've done some digging around on this and other sites but have not found an answer to my specific case. Basically I'm using a Nema 10-50 240v receptacle to power my heating element. See attached drawing to see what is looks like. It is an old receptacle design that has 2 hots and one neutral wire. The philosophy of the time was that the appliance would use its frame as the ground and so there is not a ground wire in the circuit.

I purchased a 240v Square D breaker with GFCI, planning to protect the circut from the circut breaker. However, deep inside the booklet that came with the GFCI it says not to use the breaker in circuits which have appliances whose frames serve as ground. I am pretty sure that this applies to my circuit, and it makes sense since the GFCIs monitor the ground path for a fault. Anybody know about this and can shed light on whether or not this would work?

The element is wired such that the two hots go to each of the two terminals on the water heater and the neutral wire is connected to the kettle, as a ground wire would be. I have test fired it and poked around with a voltmeter and everything appears to work properly...the kettle is not electrified =D

Anyone have any ideas to make this setup safe? I am using a PLC as a controller and have GFCI'd the 120v circut powering the enclosure and pump. Thanks you for input!

 

[bsperr]

I think your breaker would still work to protect the circuit. A 120/240 GFCI breaker will measure the return current on the hot leads and grounded/neutral conductor. It doesn't monitor the grounding/green wire.

I'm not sure why the instructions would tell you not to use it on circuits with appliances that are grounded to their frame. Maybe it could lead to nuisance tripping. Since you already bought the breaker, I would install it and see if you have problems with nuisance tripping because of the dryer. If you bought it from Lowes, HD, etc., I'm sure they wouldn't have any problems with you returning it if it doesn't work out.

There's always the option of using a spa panel if the breaker route doesn't work.

 

[monathedog]

Thanks for your reply. You're right, I'll install it and see how it works. Worst case I remove it and return it. I am okay with some nuisance tripping if it will make things a little safer

 

[pogden]

I'll jump in on this as I have related questions about my setup, which has *some* similarities, and I have some partial knowledge to share.

I want to power my 240V 5500W kettle off my 4-wire 30A dryer circuit. Like you, I purchased and installed (with the help of a licensed electrician) a Square D Homeline 30A 2-pole GFCI breaker in place of the non-GFCI 30A breaker that came with the house. As soon as we restored power, the thing tripped. We reset it it probably a dozen times, sometimes it stayed closed, others it tripped again right away. After getting it to stay closed, we went and turned on the dryer (not the motor or the heater, just the control panel) and it tripped immediately. We did this several times. The dryer, by the way, has been working fine for 7-8 years.

The electrician, who had some homebrewing in his past and was fascinated with my e-keggle and SSVR-based controller, suggested we plug it in to see what would happen. The crazy thing is, it worked just fine! I powered on the controller, gave it a little juice - enough to feel the element start to get warm - no problem. I even cranked it up to ~50% for a second, and it got quite warm - again, no problem. Plugged the dryer back in and it tripped immediately.

Admittedly, my 2 second test is probably not conclusive - maybe the breaker would trip after the thing was running for a while, I don't know. But the dryer tripped instantly, leading me to the conclusion that:

1. The breaker is faulty (sigh - bought it on eBay, though the seller was reputable and the thing looks brand new).
2. The dryer has a ground fault.
3. The breaker is not compatible with my dryer.

A guy I work with who does a lot of DIY stuff pointed me to the same disclaimer from Square D that you referenced in your OP. His advice: disconnect the frame ground on the dryer, if there is one, as it shouldn't be needed (as I have a 4-wire setup). That may be my "next next" step in troubleshooting this.

My next step is to rule out a faulty GFCI breaker, so I ordered another one from HD. Adding to the plausibility of a defective breaker (aside from the fact that it was sourced from eBay) is that my controller is all 240V. Perhaps there is a problem inside the breaker itself that causes it to always sense a difference in current between either of the hots and the neutral (basically a false 120V ground fault) but not between the the two hots. This could explain why the dryer trips the breaker and my controller/element did not.

If the new GFCI breaker doesn't work, I may try finding/disconnecting a frame ground in my dryer and see what happens. Need to think about that some more - seems like it might be okay as long as the there's also a ground connected to the power cord. Frankly, I'll probably just go the spa panel route.

So, back to you. I agree that your 240V element circuit should be protected. But you may find that if you have a range or dryer plugged into that same receptacle when you are not brewing will have problems (nuisance tripping being most likely).

 

[ChuckO]

Admittedly, my 2 second test is probably not conclusive - maybe the breaker would trip after the thing was running for a while, I don't know. But the dryer tripped instantly, leading me to the conclusion that:

1. The breaker is faulty (sigh - bought it on eBay, though the seller was reputable and the thing looks brand new).
2. The dryer has a ground fault.
3. The breaker is not compatible with my dryer.

A guy I work with who does a lot of DIY stuff pointed me to the same disclaimer from Square D that you referenced in your OP. His advice: disconnect the frame ground on the dryer, if there is one, as it shouldn't be needed (as I have a 4-wire setup). That may be my "next next" step in troubleshooting this.

Most modern dryers that I have seen have a ground connection jumper between the dryer frame and the neutral terminal for connecting the cord. This is to ground the frame when used in a 3 wire installation. Installation manuals should reference removing this jumper strap for a 4 wire system.

 

[pogden]

ChuckI, you nailed it. My dryer does indeed have such a strap, and it was not disconnected as it should have been for my 4- wire receptacle. I disconnected the strap and everything is fine. Dryer works, and more importantly I now have power to my brewery!