GFCI outlers for ungrounded circuits

[Terry Beck]

I have always been told that you can gain ground fault protection in older homes with ungrounded wiring by replacing ungrounded outlets (i.e. kitchen, bath, etc) with GFCI outlets (and I assume breakers as well). I know that the GFCI circuit monitors the difference between the hot and neutral, and does not rely on a grounding conductor.

Previously I have scoured the GFCI manufacturer's websites, and other sites, but I have not found any documentation on installing GFCI in ungrounded systems.

Talking with an electrician, he told me that installing GFCI on ungrounded circuits does provide this protection, EXCEPT when the GFCI circuit has shared neutrals (multi-wired circuits). He says this is also true (not really effective) when installing AFCI breakers for ungrounded circuits with shared neutrals. One recent house I inspected had AFCI breakers on old ungrounded circuits, and the AFCI tested OK with my Ideal Circuit Analyzer (I didn't see any recognizeable multi-wire circuits at the panel).

It sort of makes sense I suppose, but I am having trouble understanding it. Also, being a little dense, where would I normally see circuits with shared neutrals? Any help?

[Jerry Peck]

A multi-wire circuit is a problem for GFCI devices in that the GFCI monitors the current going through the hot and through the neutral, comparing both to each other, and, if both are the same, the GFCI protection remains 'on'.

If there is a 5 ma +/- 1 ma difference between the current in the hot and in the neutral, then the GFCI trips.

Now, lets take a fully balanced multi-wire circuit, say 20 amps on each leg, there is *no* (-0-, nada) neutral current - i.e., the GFCI would immediately trip 'off', thinking that there was a 20 amp ground fault somewhere. :)

[Matt Fellman]

Another thing to keep in mind with ungrounded outlets is that GFI provides the safety protection but does nothing for equipment grounding. Meaning if you plug in your new three prong computer there is no way for it to dissapate static electricty. So, while the safety is there, which is the most important thing, your electronics are at risk. This is why there is supposed to be (rarely is) a sticker on the outlet that says 'no equipment ground'.

As time moves forward and two conductor wiring becomes more outdated, most manufacturers of electronics assume (or require) a grounded three prong plug. That is usually the fineprint on the tag at the end of the plug that gets immediately ripped off and thrown away.

[Gunnar Alquist]

Terry,

I would think you would find what you are looking for in the installation instructions provided with the GFCI device.

[Jim Robinson]

You can install it with a shared neutral, but you can't use it to protect "down stream" like you normally can. Each receptacle needs its own GFCI, and you add jumper wires so that each GFCI only has one black wire and one white wire coming into it, and nothing leaving it. Hope that makes sense.

[Jerry Peck]

You can install it with a shared neutral, but you can't use it to protect "down stream" like you normally can. Each receptacle needs its own GFCI, and you add jumper wires so that each GFCI only has one black wire and one white wire coming into it, and nothing leaving it. Hope that makes sense.

Correct, I failed to mention that as I was assuming (probably incorrectly) that he was referring to installing the GFCIs and trying to protect downstream receptacles with it.

Of course, that would require a GFCI device at each receptacle, but that is 'doable' (I hate that term and terms like that - why did I use it???).

[Terry Beck]

How much of this also applies to AFCI breakers and/or AFCI protected circuits?
(though I'm not sure how you would run a multi-wire branch off a single pole AFCI breaker)

[Michael Thomas]

BTW, recently ran across this on the Mike Holt's board:

"250.114(3) has particular application.

Even though all the receptacles have been changed out to grounded type and they are all given GFCI protection, if there is no actual equipment ground conductor connected to the grounded terminal of the receptacle, then a number of cord and plug devices can't use those receptacles.

Quote:
250.114 Equipment Connected by Cord and Plug

Under any of the conditions described in 250.114(1) through (4), exposed non–current-carrying metal parts of cord-and-plug-connected equipment likely to become energized shall be grounded.

Exception: Listed tools, listed appliances, and listed equipment covered in 250.114(2) through (4) shall not be required to be grounded where protected by a system of double insulation or its equivalent. Double insulated equipment shall be distinctively marked.



(3) In residential occupancies:

a. Refrigerators, freezers, and air conditioners

b. Clothes-washing, clothes-drying, dish-washing machines; kitchen waste disposers; information technology equipment; sump pumps and electrical aquarium equipment

c. Hand-held motor-operated tools, stationary and fixed motor-operated tools, light industrial motor-operated tools

d. Motor-operated appliances of the following types: hedge clippers, lawn mowers, snow blowers, and wet scrubbers

e. Portable handlamps



I would argue that it is better to leave the 2 wire receptacles as such, replace the worn ones with new 2 wire receptacles, use GFCI protection if you wish, and work equipment ground conductors to the locations that serve items listed above."

2-wire receptacle - Mike Holt's Forum (http://forums.mikeholt.com/showthread.php?t=79178&highlight=250.114%283%29)

[John Steinke]

250.114 is being misapplied by the poster. It is one of those code sections that is aimed at manufacturers, and dovetails nicely with the UL standards under which the appliances are tested.

Indeed, were it not got the grounding of the appliance case, there would be very little reason for that third wire, and we'd still be using two-prong plugs and receptacles.

Let's put it all in context: this requirement, and the debates behind it, go back at least to WW2, with a particular surge in the early '60's, as three-prong receptacles were becoming common. UL really had, up until then, no basis to require the case to be grounded. There was even a time when the case was commonly ungrounded, or bonded to the neutral. FWIW, the two-prong plug was modified (neutral side made wider) specifically to prevent the case becoming 'hot' by inserting the plug wrong.

So ... we're up to the '60's. The three prong cord has become common - what to do when the home has two prong receptacles? Not until decades later - after the GFCI had proven itself - was an alternative to rewiring the house accepted by the NEC.

After great debate, it was accepted that a GFCI was an acceptable substitution for grounding the appliance, and that you could use three-prong receptacles, with GFCI protection, in these cases. This applies no matter what appliances are installed. In short, the code folks felt GFCI protection was preferable to removed ground prongs.

The one area where the use of a GFI, in place of grounding, has problems is one of utility, not safety. That is, some electronics (certain fluorescent lamp ballasts, certain surge suppressors, certain timers and photocells, etc) need an effective ground path to operate properly.


As for multi-wire circuits .... AKA "shared neutrals" .... the run of wire from the panel to the first junction box is very often a multi-wire branch circuit. That is, there are two 'hot' wires using the same neutral wire. At that first junction box, the circuits separate, going off in different directions.
This was done to reduce the clutter, and number of wires, in the panel. The practice also resulted in fewer wires having to enter the panel, or clutter up the attic.

Where a neutral is common to two circuits, you need to either use a two-pole AFCI or GFCI breaker ... or install the protection after the circuits are separated.

A two-pole GFCI breaker will meet the code requirements for replacing two-prong receptacles with three-prong ones. No AFCI breaker will meet these requirements.

An AFCI is NOT a GFCI. You will still need to put a GFCI in the circuit somewhere, if you want to change the receptacles.

[Gunnar Alquist]

Where a neutral is common to two circuits, you need to either use a two-pole AFCI or GFCI breaker ... or install the protection after the circuits are separated.


John,

I had thought that the two-pole or handle-tie rule was only if the circuits were connected to the same device, such as when they are attached to different outlets of a duplex receptacle outlet. I see this at dishwasher/disposals regularly. At least, this is the way I learned it. Could this have changed in the past few years?

1999 NEC
Article 210-4 (b) Dwelling Units. In dwelling units, a multiwire branch circuit supplying more than one device or equipment on the same yoke shall be provided with a means to disconnect simultaneously all ungrounded conductors at the panelboard where the branch circuit originated.

[Jim Robinson]

I think he means that the two pole GFCI breaker can be used on this type of circuit to provide GFCI protection (if required or desired), not that the two pole breaker would be required if the GFCI protection was not required.

[Jerry Peck]

I think he means that the two pole GFCI breaker can be used on this type of circuit to provide GFCI protection (if required or desired),

That's what I think John means, but, he needs to explain it as that goes against everything I can think of about GFCI protection on a multi-wire circuit.

You have two 120 volt loads, one common neutral (which may, or may not, have the same current as either of the hots, or not have any current on the neutral).

That goes against the way a GFCI operates - at least to my understanding - and is why the GFCI protection needs to be installed after the device is tapped off the multi-wire circuit ... where the neutral and hot current will be the same (unless there is a ground fault).

[Gunnar Alquist]

Ohhh... I get it.

[John Steinke]

Hmm ... grammar, changing horses in mid-stream, train of thought derailed ...

Don't confuse "code requirements" with the laws of physics, please.

We're talking about GFCI's, AFCI's, and multiwire branch circuits (AKA "shared neutrals." We're not talking about any other multi-wire branch circuits ... just those that you desire to place the other sorts of protection on.

If you want to add GFCI or AFCI protection to a multi-wire branch circuit, you can do it two ways.
You can do it "after the split" .... after the point where the neutral is shared ... by using a device. OK, I've yet to see an AFCI device, but there is a code opening for such a thing to exist.
"Before the split" .... where both circuits are using the same neutral ... you need the widget that provides the protection to monitor both "hots" as well as the neutral. In practical terms, this means that you need a two-pole breaker.

Let us, just for the sake of discussion, assume that BOTH of the 'hot' wires are drawing one amp. Since the two 'legs' are exactly out of time with each other, they will cancel each other out on the neutral wire. While, out at the loads, each neutral will be carrying a single amp .... once the neutrals join into that shared neutral, the neutral load will be ... zero. This is what makes shared neutrals work.
A two pole breaker will be able to consider this in deciding whether there is current leakage.

The same issue arises with both AFCI and GFCI devices, simply because the AFCI devices have a (30ma) GFI function, as well as the "arc fault" function within them. (Compare this to the 5ma setting of GFI devices).

Absent the need for the AFCI / GFCI to monitor ALL wires of a circuit in order to work, there is absolutely no (physical) reason for the two 'hots' to be terminated to breakers next to each other. They need to be on different 'legs' - or the neutral will be carrying too many amps - but they need not be next to each other.

The 2008 NEC makes some major changes in this area, but that's for another forum.

[Jerry Peck]

Don't confuse "code requirements" with the laws of physics, please.

I'm not, so make sure you don't.


We're talking about GFCI's, AFCI's, and multiwire branch circuits (AKA "shared neutrals." We're not talking about any other multi-wire branch circuits ... just those that you desire to place the other sorts of protection on.

Correct, a simple multi-wire branch circuit one desires to install GFCI protection on. Let's drop the AFCI as that does not pertain to this discussion.


If you want to add GFCI or AFCI protection to a multi-wire branch circuit, you can do it two ways.
You can do it "after the split" .... after the point where the neutral is shared ... by using a device. OK, I've yet to see an AFCI device, but there is a code opening for such a thing to exist.

That part I agree with and understand, it's the next part you will need to explain.


"Before the split" .... where both circuits are using the same neutral ... you need the widget that provides the protection to monitor both "hots" as well as the neutral. In practical terms, this means that you need a two-pole breaker.

A two-pole GFCI breaker is not going to work on a multi-wire circuit, not as I understand how GFCI protection works. That's the part you need to explain - how it works like that.


Let us, just for the sake of discussion, assume that BOTH of the 'hot' wires are drawing one amp. Since the two 'legs' are exactly out of time with each other, they will cancel each other out on the neutral wire. While, out at the loads, each neutral will be carrying a single amp .... once the neutrals join into that shared neutral, the neutral load will be ... zero. This is what makes shared neutrals work.
A two pole breaker will be able to consider this in deciding whether there is current leakage.

No, the GFCI monitors and compares the current in the hot to the current in the neutral in determining if a ground fault is present.

With a two pole breaker monitoring two hots, let's use your one amp in each hot, you could also have one amp in the neutral from two one amp loads on one leg and one one amp load on the other leg, how does that breaker know that the one amp is (or in this case, is not) a ground fault when it cannot compare it to anything meaningful?

On a 240 volt circuit ONLY, no current should be flowing on the neutral, thus the neutral could be set up to trip the breaker at 5 ma, however, on a multi-wire circuit, you could have all the current flowing on one hot and the neutral, or on both hots, or on both hots and some of the current flowing on the neutral.

You need to explain it better, or differently, for what you are saying to make sense and hold true.

[John Steinke]

A two pole GFCI breaker has connections for both hots, as well as the neutral. While the exact manner is unknown to me, the electronics 'do the math' and decide whether the returning neutral load is consistent with the amps being drawn by the two circuits.

From an academic standpoint, this would be particularly interesting when applied to circumstances where the power comes from a three phase system.

Therefor, they will work with multi-wire branch circuits. Indeed, many "hot tub" use exactly this sort of breaker ... while the tub has both 240 and 120v loads.

[Jerry Peck]

A two pole GFCI breaker has connections for both hots, as well as the neutral. While the exact manner is unknown to me, the electronics 'do the math' and decide whether the returning neutral load is consistent with the amps being drawn by the two circuits.

From an academic standpoint, this would be particularly interesting when applied to circumstances where the power comes from a three phase system.

Therefor, they will work with multi-wire branch circuits. Indeed, many "hot tub" use exactly this sort of breaker ... while the tub has both 240 and 120v loads.

John,

You are not making any sense in what you are saying.

You are describing something made for one use (on 240 volt equipment) and then trying to apply that to something which does not have any 240 volt loads (multi-wire circuits do not have any 240 volt loads, by definition).

Thus, multi-wire circuits *are only* working with the two hots and the single shared neutral, which does not work with the way a GFCI functions.

[John Steinke]

Jerry, I can't understand your objection. If the two-pole GFI breaker was intended for only 240v loads, it would not have that neutral wire; there would be no need. Nor could it work at all on a three phase system, as the two "hots" would fail to cancel each other out.

[Randy Clayton]

I brezed through of some of the posts and just said whhhhaaatt!
Look it up in the code book and its evan there in the code check books;gfci outlets and 2 wire systems are handled...

[Jerry Peck]

I brezed through of some of the posts and just said whhhhaaatt!


Good, maybe you can contribute to the thread then?


Look it up in the code book and its evan there in the code check books;gfci outlets and 2 wire systems are handled...

Explain how 240 volt GFCI devices protect multi-wire circuits.

We *already know* that if multi-wire circuits feed receptacles in the given locations for GFCI protection that GFCI protection is required, the discussion has been ... How? Do you need to use GFCI devices (receptacles) or can you use a GFCI breaker?

Care to contribute and answer that, and explain 'how' the GFCI breaker would work in monitoring the current for the neutral and the how to provide that protection, or, explain how it otherwise provides that protection?

Your explanation is welcomed.

Currently, though, I'm waiting for an answer back from Siemens, my inquiry was forward up the channels to the engineers, so I'm waiting on their response.

[Jerry Peck]

Care to contribute and answer that, and explain 'how' the GFCI breaker would work in monitoring the current for the neutral and the how to provide that protection, or, explain how it otherwise provides that protection?

Your explanation is welcomed.

Currently, though, I'm waiting for an answer back from Siemens, my inquiry was forward up the channels to the engineers, so I'm waiting on their response.

I received my answer back from Siemens, stating that all of their double pole GFCI breakers have a 120 volt / 240 volt rating and will work on shared neutral circuits (multi-wire circuits) - without the asked for explanation as to how they would work, however, a double pole GFCI breaker which is not rated for 120 volt / 240 volts (is only rated for 240 volts) will not on multi-wire circuits.

I gave their answer much thinking as to "how" that would work without coming to any success. I finally e-mailed the engineer who answered my question explaining that I had thought of all of the circuitry 'which I could think of' which could be used but could not think of how a double pole breaker would work on a multi-wire circuit and asked if he would explain it to me.

He called me back (instead of e-mailing me) and asked if I know how GFCIs worked. I said yes and explained how they work, at least how I've learned that they work. He said I was correct and that is why it will work on a double pole 120 volt / 240 volt breaker. I said 'That's why I said 'which I could think of' and I had not thought of what he explained to me. He said, yes, many people think they can think of it all and then don't understand when the answer is something they did not think of, because I knew it was something I was not thinking of, the explanation was easy to do as he started explaining it and I finished explaining it, I just needed to be started out on the right track. (Wish I had thought of this myself, but, obviously, I did not.)

This is how GFCIs work: (most of us already know this)

The neutral and hot conductors are routed through a coil, a current transformer, and the current's magnetic fields cancel each other out when the current flowing through both are equal.

When the current is not equal in each, the difference causes a current and voltage to be induced into the coil, which is calibrated so that 5 ma +/- 1 ma will trip the switch mechanism.

I kept trying to use two coils, hot and neutral in each coil, the same neutral, being compared to two separate hots ... and it just would not work out where it would work. :(

However, with double pole 120 volt / 240 volt GFCI breakers, the two hot conductors AND the neural (all three conductors / current paths) are run through the coil, when the two hots are in balance, the magnetic fields created cancel out. When the two hots are not in balance, the additional current is carried by the neutral, the magnetic fields created still cancel out. Thus, when there is no leakage, the currents in the two hots and the neutral always cancel each other out.

However, when there is leakage current from either hot or the neutral, there is an imbalance of current between the two hots or the two hots and the neutral, and that imbalance creates the magnetic field which generates the current and voltage in the coil which is calibrated to trip the GFCI switch at 5 ma +/- 1 ma.

Thus, *IF* the double pole GFCI breaker is rated at 120 volts / 240 volts (and all of Siemens double pole GFCI breakers are), then that double pole breaker *WILL* work on a multi-wire (shared neutral) circuit.

[Brandon Chew]

Cool. I knew the current was being "monitored", but never gave much thought to "how". Once you said all the ungrounded and grounded conductors passed through a single coil, it all made perfect sense. Any "missing" current, which is flowing through the equipment grounding conductor or by some other path to ground, will cause a current to flow on the transformer coil.

Thanks for tracking that info down!