GFCI Protection 240V 3 Wire?

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awheeler

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I'm building a 240V kettle with control panel. I have a 4 wire 240V coming from a dryer outlet supplying the control panel and then 3 wire to element. I talked with an electrician and he said a GFCI will not protect the kettle/element since you only have 3 wires going to element. From what I read that sounds correct as you need a nuetral wire to trip a gfci. Does this sound correct?
 
No. A double-pole (240V) GFI breaker watches both "hot" wires and the "neutral" wire independently, so that it can protect a mixture of 120V/240V loads beyond it.

The electrician is, sadly, mistaken.

Here's a relevant snippet from the Scheider Electric website (emphasis added by me):


How does a two pole GFI breaker work?

The GFCI sensor in a two-pole QWIK-GARD circuit breaker continuously monitors the current flow in the two ungrounded ``hot`` load conductors and the neutral conductor. The sensor compares the current flow in all directions. In two-pole applications, the current flows out to the load on the ``hot`` load conductors and back to the source on the neutral load conductor or one of the ``hot`` load conductors. If the current flowing back to the source is less than the current flowing out to the load, a ground fault exists.
 
Hey cscade. Do you know if an in-line GFCI rated for 240v / 30 amps would offer the same ground fault protection if I put a 20 amp plug on the end and used it on a 20 amp breaker? I have a 240v / 3000W immersion heater with a 6-20 plug and I’d like to add in-line GFCI protection to the power cord.

Now I'm using a 20 amp extension cord with the GFCI built in, but would like to add protection directly to the HLT cord so that I don't have the drag out the extension.
 
If I understand your question, you want to do this:

Code:
[240V]
20A double-pole breaker
  -> 30A 240V rated cord with inline GFI protection
    -> 3000W heater

In order to do so, you'll need to cut the ends off of the 30A cord, wire one end directly to the immersion heater, and the other to a plug appropriate to connect to a 20A outlet. Is this correct?

If so, I don't see any issues. As long as you are connecting all the conductors correctly. Your cord will be heavier than it needs to be, but the "30A" part of the cord specification relates to how much current it can safely carry, not anything to do with the GFI. The GFI aspect will continue to work as long as all the same conductors are connected the same way as before the modifications.

As usual, make very sure you know what you're doing, and don't just take my word for it!

Hey cscade. Do you know if an in-line GFCI rated for 240v / 30 amps would offer the same ground fault protection if I put a 20 amp plug on the end and used it on a 20 amp breaker? I have a 240v / 3000W immersion heater with a 6-20 plug and I’d like to add in-line GFCI protection to the power cord.

Now I'm using a 20 amp extension cord with the GFCI built in, but would like to add protection directly to the HLT cord so that I don't have the drag out the extension.
 
Here's some info I posted in another thread. I also had an electrician tell me what you were told, and then we both learned something that day :p Basically you need the neutral wire from your main panel to the gfi connected to allow it to function, but the neutral need go no further than the gfi. BTW that neutral should connect to the ground ONLY in the main service panel.


Do not confuse a neutral wire with a safety ground wire. A 240V GFCI usually has to be connected to the neutral wire of the source cable/line, coming from the breaker panel, to be able to supply the neutral to the load if it requires one, as was described above. If the load does not need a neutral - because it does not have any 120 volt devices such as time-clocks, programmers, etc. - then no neutral wire needs to be run to the load.

However a GFCI needs to have a ground wire from the source so that it can operate correctly to detect fault currents flowing into the safety ground wire coming from the load.

Note that the modern GFCI's other main way of detecting faults is to detect a sufficient difference - usually a difference of only about 30 milliamps - between the current flowing in one "hot" (for example a black wire) compared to the current flowing in the other "hot" (for example a red wire). Such a difference or imbalance must be caused by a leakage current going from one of the hots to ground without going through the protective ground wire: for example from a damp control switch that has cracked plastic insulation to a person's hand and then through his or her body to the damp floor in a kitchen or utility room.
 
Thanks for the information. I wasn't sure if the ability of the GFCI to offer protection had anything to do with amperage rating. You wouldn't want to put 30 amps through a GFCI that was rated for 20 amps, but hopefully a 30 amp rated GFCI will still offer all the same protection when only a 20 amp load is used.
 
You wouldn't want to put 30 amps through a GFCI that was rated for 20 amps, but hopefully a 30 amp rated GFCI will still offer all the same protection when only a 20 amp load is used.

those are MAX ratings... like a speed limit is the MAX speed you can go. you are free to go slower.
and a circuit breaker will work with anything between zero current, all the way up to its max amp rating.
 
Would this be an option? 12 guage wire for 30amp is a bit low.

1
http://www.ebay.com/itm/2Ft-12-Gauge-Pro-Cap-Extension-Cord-Adapter-w-30A-GFCI-/180623669764?pt=LH_DefaultDomain_0&hash=item2a0e027a04
If he had a 240V / 20AMP 6-20 receptacle available, could he switch out the 120V male and female plug ends on the linked extension and replace them with 6-20 ones that were 240V / 20AMP and get GFCI protection for a 4500W element?

No plans to try, just curious if the GFCI works the same for 120V or 240V on these inline units?
Both legs monitored or just one on a 120V GFCI?
 
On a 120V GFI, it only watches the current on the hot and neutral wires. A 120V cord-GFI is only going to have 1 hot, 1 neutral, and 1 ground wire. Whereas a 240V GFI (should) have 2 hots, 1 neutral, and 1 ground (I think... I have never seen a 240V cord-GFI in person, only 240V GFI breakers). Older ones may only have 2 hots and a ground, no neutral, since dryer outlets used to (all) be 2 wire rather than today's 3.

I'm beyond my comfort zone on knowing these answers, but no matter what I wouldn't try to repurpose a 120V part to 240V.

If he had a 240V / 20AMP 6-20 receptacle available, could he switch out the 120V male and female plug ends on the linked extension and replace them with 6-20 ones that were 240V / 20AMP and get GFCI protection for a 4500W element?

No plans to try, just curious if the GFCI works the same for 120V or 240V on these inline units?
Both legs monitored or just one on a 120V GFCI?
 
I think you mean on a 120v circuit the GFCI watches the current on the hot and neutral .
 
First you must understand how a gfci works... If you have a 120V circuit, you have a hot, a neutral and a ground. The gfci has a current transformer inside the measures the sum of the current flowing in the hot and neutral. this value should always be 0 indicating that the current flowing in the hot matches the current flowing in the neutral. You do have a ground in the circuit but its not required to trip the gfci because if you short to another grounded point you will still have some extra current in the hot that does not match in the neutral which will trip the gfci. Think about if you were using a tool outside and you shorted it to the earth rather than the ground conductor, it would still trip even though the fault current did not actually travel back on the ground to your gfci.

Same principle applys to a 240 gfci, it just sums all the current flowing either hot to hot or hot to neutral and looks for a net 0 value. If you develoup a short anywhere in your system to any grounded point (assuming you draw more than the mA trip level) you will trip your gfci.

You can test this out by building an e-stop and running it to a rod driven into the ground as opposed to the ground conductor going back to the panel.

If your electrician does not know this, go find one that knows what he is doing as he is most likely a hazard to himself and you.
 
Reading this thread brings up the following question:

Let's say I have a 240V four wire GFCI feeding my setup. To my element I have 240V three wire, with no ground getting to the kettle. I have my kettle on an insulated surface, again with no real connection to ground. One of the hot wires gets shorted to the kettle. What's going to happen?

My guess is that there is a possibility that the GFCI will see no difference in current flows and will not trip. Since there is no connection to ground at the kettle, there is no where for current to flow. Now if I happen to touch the kettle and a ground point, I would get shocked tripping the GFCI.

Probably a good idea to have your kettle grounded.
 
Reading this thread brings up the following question:

Let's say I have a 240V four wire GFCI feeding my setup. But to my kettle I have only 240V three wire, with no ground to the kettle. I have my kettle on an insulated surface, again with no real connection to ground. One of the hot wires gets shorted to the kettle. What's going to happen?

My guess is that there is a possibility that the GFCI will see no difference in current flows and will not trip. Since there is no connection to ground at the kettle, there is no where for current to flow. Now if I happen to touch the kettle and a ground point, I would get shocked tripping the GFCI.

Probably a good idea to have your kettle grounded.

Of course the kettle should be grounded. Your 3-wire, 240v feed to the element should be H-H-G, and you should test to verify ground continuity.
 
Of course the kettle should be grounded. Your 3-wire, 240v feed to the element should be H-H-G, and you should test to verify ground continuity.

I saw no real mention of grounding the kettle or verifying that ground, in the thread. Which I think is a good idea, and provides the most protection.
 
A gfi is the only way to use a three wire plug on a two wire system by code, the neural hooks to the gfi.
 
A gfci does not need a equipment ground to function. It works by sensing when current is going somewhere that it is not intended. ( leakage)
 
^Very true, but it's still a good idea to ground the kettle, better to have that current leak through the ground wire than the brewer.

BTW I hope anyone going electric would know enough not to try to wire a 240 element with H-H-N, I mean where would they put the neutral? (Don't say on the grounding screw...)


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BTW I hope anyone going electric would know enough not to try to wire a 240 element with H-H-N, I mean where would they put the neutral? (Don't say on the grounding screw...)

The neutral could go to the ground screw, but I imagine it would trip the GFCI. Dryers on a three wire circuit have their neutral and ground bonded in the dryer.

Also, I guess once the element is grounded it would be pretty hard for the kettle to not also be grounded. Unless there is something I'm missing.
 
Reading this thread brings up the following question:

Let's say I have a 240V four wire GFCI feeding my setup. To my element I have 240V three wire, with no ground getting to the kettle. I have my kettle on an insulated surface, again with no real connection to ground. One of the hot wires gets shorted to the kettle. What's going to happen?
I guess my original question wasn't what was going through my mind. I was thinking more of if I had an existing 240V three wire (H-H-N) circuit in my house that I wanted to use for my system. I would have no ground wire available at the element/kettle. I install a GFCI on that three wire circuit. Is that GFCI going to afford me the protection I need in all cases?

My thoughts are that while a GFCI may not require a ground wire to function, it's still probably best practice to use a four wire circuit to supply your system.
 
I guess my original question wasn't what was going through my mind. I was thinking more of if I had an existing 240V three wire (H-H-N) circuit in my house that I wanted to use for my system. I would have no ground wire available at the element/kettle. I install a GFCI on that three wire circuit. Is that GFCI going to afford me the protection I need in all cases?

My thoughts are that while a GFCI may not require a ground wire to function, it's still probably best practice to use a four wire circuit to supply your system.
Inorder to provide GFCI protection with that set of circumstances you need to wire the Spa Panel in a very specific way so that ground will be developed for your set up.

This is how it should be wired:


power-panel-6.jpg
 
Inorder to provide GFCI protection with that set of circumstances you need to wire the Spa Panel in a very specific way so that ground will be developed for your set up.





This is how it should be wired:








power-panel-6.jpg


Thanks P-J. Going through this thread I didn't think it was clear on what you would need to do to provide GFCI protection under those circumstances. In my case, I've already switched my dryer receptacle over to a 4 wire.
 
In the three wire picture, wouldn't that be feeding power back through the ground if you had a 120V device connected?
 
I thought that three wire dryers were wired HHG, not HHN; two hots and an unshielded ground. No neutral.
 
I thought that three wire dryers were wired HHG, not HHN; two hots and an unshielded ground. No neutral.
Clothes dryers are 120V/240V devices. Power supplied to them using a 3 wire power feed are wired as hot, hot and neutral. The wire used at that time appear as you describe but it is actually "two hots and an unshielded neutral"
 
Isn't the typical home spa panel a single phase device? Whereas the 6-50R is intended for split phase usage, where each hot serves as the out-of-phase neutral for the other hot. You need to be sure your panel is wired to provide both phases if you are going to use type 6 wiring and connectors, most home panels are not setup that way. Or that is how I understand it.
 
I was planning on running my brewery on the welding outlet. That is why I was asking. My welders are usually single phase but use the 6-50 ends. Definitely a different application than brewing though.
 
So wait a minute...am I reading this correctly. I could take my spare 30amp dry outlet that's hot, hot, unshielded neutral, and put a 50 amp spa panel in and wire it as illustrated in the photo and I'd have a safe gfci protected outlet now? This would save me a tremendous amount of time, money and hassle.

I was advised in the past I'd have to run a completely new line directly from my main and couldn't make my spare outlet work.

I would be pretty thrilled if this could work.
 
So wait a minute...am I reading this correctly. I could take my spare 30amp dry outlet that's hot, hot, unshielded neutral, and put a 50 amp spa panel in and wire it as illustrated in the photo and I'd have a safe gfci protected outlet now? This would save me a tremendous amount of time, money and hassle.

I was advised in the past I'd have to run a completely new line directly from my main and couldn't make my spare outlet work.

I would be pretty thrilled if this could work.
IF your outlet is indeed a "spare" dryer outlet - the answer is Yes. Is certainly can be done. Three wire dryer outlets provide 240V and Neutral to the dryer.
 
IF your outlet is indeed a "spare" dryer outlet - the answer is Yes. Is certainly be done. Three wire dryer outlets provide 240V and Neutral to the dryer.
and if your three wire dryer outlet is like mine, and many others out there, you may have a ground wire in the box just not connected to anything. Then you can convert it over to 4 wire.
 
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