3-Wire Vs. 4-Wire GFCI

I’ve been using a Brutus 20 clone for awhile & decided that I would like to add an Electric HLT to the brewery to save on propane costs & simplify the brewday.

I had planned to run the element @ 240V, convert my control panel from 120V and power the whole thing with a single 240V 4-Wire Plug. So I bought a 30A 4-Wire GFCI for it… I then got around to moving the dryer & discovered that I only have a 3-Wire 240V Outlet to work with.

Now comes my question: Would the GFCI still function properly if I rewired it using a 240V 3-wire plug and simply ignored the neutral wire?

I would add a separate 120V input to the control panel to power pumps, valves…

Thanks,
Theo

You would not ignore the neutral (white wire). That is the main return current circuit. If anything, the ground wire (green wire) would be ignored. Actually its not ignored, its just wired to ground all the equipment that might get energized.

Since you have a 3 wire plug why not just use the ground from that plug as your neutral and ground. I mean yeah you aren't supposed to do it. But ground and neutral are actually the same thing in the breaker box. It wouldn't pass codes inspection but shoot ask any electrician it will work just fine.

Have you turned your breaker off and removed the dryer plug? I bet you have a forth wire in there.

I don't consider myself an expert but here's what I think.

On older dryer plugs (3 wire) the ground prong was missing. Somewhere around 2000, the NEC or NFPA required new installations to be 4 wire (two hots, neutral and ground).

Your GFCI should still work. It doesn't measure current on the ground wire... it compares the current leaving the breaker to current returning to the breaker. So the wiring at the panel will be the same. Your two pole GFCI breaker will have two hot lines and a neutral to hook up. The white coil (pigtail) will be tied to the panel's neutral bus.

You don't need to add a separate input for 120Vac... you'll still have 120Vac between either hot and neutral. The breaker will still operate properly if you have the pigtail hooked up to the neutral bus and the outlet's neutral to the breaker.

I actually had problems running my 120 v march pumps and my 240 elements on the same circuit. It created enough current imbalance(notsurenthe right term) that it would throw the breaker. I had an electrician confirm this for me.

mabrungard said:

You would not ignore the neutral (white wire). That is the main return current circuit. If anything, the ground wire (green wire) would be ignored. Actually its not ignored, its just wired to ground all the equipment that might get energized.

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I'm no expert, but I believe its the voltage difference between the 2 hot lines that creates 240V. I know its 120V between either hot line & neutral. So I reasoned that since this circuit is just for the 240V element the neutral line could be ignored.

milldoggy said:

Have you turned your breaker off and removed the dryer plug? I bet you have a forth wire in there.

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I'll have to take a look at that tomorrow.

SeattleMatt said:

I don't consider myself an expert but here's what I think.

On older dryer plugs (3 wire) the ground prong was missing. Somewhere around 2000, the NEC or NFPA required new installations to be 4 wire (two hots, neutral and ground).

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My understanding is that the 3 wires are 2 hots & ground with the neutral wire missing

I bought one of these on ebay too, I took it apart and re wired it to a 4 wire pigtail, the two hots go through the GFI the the ground and neutral go under the circuit board. In these pictures you can see the black and white wires are the original to hot leads, I connected them to the black and red of the dryer pigtail, and routed the white and green wires of the dryer pigtail around the gfi.

I have not tested it yet, so don't take my word for it yet, but I can't see any reason it wont work.







DON'T DO THIS...IT DOES NOT WORK...I figured this out the hard way, these are monitoring both wires at the same time so when pulling of one leg to run your 120V equipment the GCFI will trip. just get a $50 spa panel...

milldoggy said:

Have you turned your breaker off and removed the dryer plug? I bet you have a forth wire in there.

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Well, I'll be damned once I pulled the outlet I found there are 4 wires hiding in there. Thanks for that.

Now I just gotta rewire the dryer & convert it to a 4 prong outlet.

There you go, might want to test the forth wire and make sure it is wired to the ground bar in the panel. Not sure how to do this, but someone on here can tell you how.

flananuts said:

I actually had problems running my 120 v march pumps and my 240 elements on the same circuit. It created enough current imbalance(notsurenthe right term) that it would throw the breaker. I had an electrician confirm this for me.

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Your 240 VAC GFCI breaker is comparing one leg to the other (it doesn't need the neutral). When you use a single pole device on a 2 pole GFCI, it'll trip because it sees it as a fault.

On many older 240 VAC devices (dryers, A/Cs, ovens, etc.) the neutral was not hooked up because it wasn't needed. The currents on the two legs cancelled each other out. Appliances now have more electronics in them (lighting digital displays, etc.) that are 120 VAC, so they need an insulated conductor for the neutral. There's really no need to rewire your dryer (unless you want to).
A 3 wire 30A GFCI for all your 240 VAC stuff and another 120 VAC GFCI circuit for the rest.

milldoggy said:

There you go, might want to test the forth wire and make sure it is wired to the ground bar in the panel. Not sure how to do this, but someone on here can tell you how.

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Open up the panel and check the cable coming in. It should be 10/3 (black, red, white and ground). Follow the white wire to the neutral/ground "bus." If it's not connected, find an empty slot on the bar and screw it in. If all the neutrals are on one side and all the grounds are on the other, follow suit. If it's been cut short, wire nut a short length of #10 AWG so it can reach the bus. Pete

Thanks for all the info, it's really appreciated

petey_c said:

Open up the panel and check the cable coming in. It should be 10/3 (black, red, white and ground). Follow the white wire to the neutral/ground "bus." If it's not connected, find an empty slot on the bar and screw it in. If all the neutrals are on one side and all the grounds are on the other, follow suit. If it's been cut short, wire nut a short length of #10 AWG so it can reach the bus. Pete

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Can't you test with meter also?

BigBobsBrews said:

Well, I'll be damned once I pulled the outlet I found there are 4 wires hiding in there. Thanks for that.

Now I just gotta rewire the dryer & convert it to a 4 prong outlet.

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You said there were 4 wires in the outlet box. Which 3 of the 4 were connected to the outlet?

The dryer is probably wired with the 240V plus the neutral. Most are. When you complete the change to a 4 wire system and install a 4 wire cord on your dryer, you must remove the green jumper clip between the neutral connection and the dryer cabinet. The green wire from your new dryer power cord will then go to the dryer cabinet where that jumper clip was.

HTH

Gents,

There are 3-wire and 4-wire GFCI devices available; spa panels are of the four wire variety so you can run both 240V and 120V circuits through the same GFCI. Pulling a 120V circuit from a 3-wire GFCI will cause it to trip. From what I understand, the 4-wire variety sums the current draw of both hot legs and compares it to the neutral leg; the GFCI will trip if any current leaks to the ground.

milldoggy said:

Can't you test with meter also?

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Yes. Check for continuity between the neutral and ground wires. If it's not a sub panel (and it's wired correctly) you should get zero ohms or an indication of continuity on your meter. The neutral and ground are electrically at the same point.

pvtschultz Good to know. Thanks, Pete

Mission accomplished gentleman. I installed a 4-Prong outlet & rewired the dryer. Now I just gotta convert my control panel to 240V.

Even found out where all my socks have been disappearing to when I moved the dryer.