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I found this warning in the instructions for a Siemens 2-pole 30 amp GFCI breaker which will be installed for a dryer circuit:

To obtain maximum protection against electric shock, electric ranges and clothes dryers whose frames are grounded by connection to the grounded circuit conductor should not be connected to the load circuit of this device.

So this is basically saying don't use this breaker on a 3-wire dryer circuit that is wired as hot-hot-neutral (not an issue here as the circuit is 4-wire). In fact it seems to be saying that “maximum protection against electric shock” is obtained by not using the breaker in that situation. Why??

My understanding is that 3-wire dryer circuits are supposed to be hot-hot-ground. In that case there is no neutral to run through the breaker. Leakage current to ground would result in an imbalance between the hots and the breaker would trip as desired. A 120-volt load inside the dryer, such as for the controls, would have its return current run through the ground, which would also result in an imbalance and trip the breaker. That’s a problem for sure, but it doesn't reduce “protection against electric shock.”

For a 3-wire dryer that is actually wired as hot-hot-neutral, with the neutral running through the breaker, you could have a fault where a person touching the “wrong” thing provided a current path between one hot and the case. That current would return through the neutral, and the breaker would not see an imbalance and would not trip. So the breaker would not provide protection there – but it doesn't make things worse either.

So am I missing something in understanding the current flows here that would actually result in less protection against shocks with the GFCI breaker than without? Or is this more likely just poor wording or a legal CYA or something like that?

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    "grounded circuit conductor" is another name for insulated neutral wire(I think). Neutral is a circuit conductor that is grounded at the main panel. Ground wire is usually not used as a "circuit" conductor. Hot, hot, neutral circuits has been discontinued/banned, for being unsafe. These circuits mainly used the old NEMA 10 receptacles/plugs
    – crip659
    2 days ago
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    @crip659 yes "grounded circuit conductor" is the neutral. That's one reason the warning seemed odd, it describes a hot-hot-neutral setup as if it were normal, but I would not expect to see that unless it were wired in error.
    – trawson
    2 days ago
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    @JonCuster Did read another question a few weeks ago that also described neutral as a grounded circuit/current conductor being different from just a ground conductor(in posted instructions). If remember correctly it also described hot/live as ungrounded conductors. It is weird/odd phasing to us, but think it is more for international use, odd translation.
    – crip659
    2 days ago
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    @JonCuster I guess we have to agree to disagree. "Ungrounded conductor" is NEC terminology for what we call "hot". "Grounded conductor" (also "grounded service conductor" or "grounded circuit conductor") is what we call "neutral" (at least in a 120/240 system) and can carry current when the system is functioning correctly; it is grounded through the main bonding jumper in the main panel. "Grounding conductor" or "Equipment grounding conductor" (EGC) is what we call "ground" -- e.g. the bare wire in a piece of NM, etc. -- and does not carry current when the system is functioning correctly.
    – trawson
    2 days ago
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    The confusing terminology here is that the Neutral wire is the "grounded" conductor (because it's connected to ground in the main panel), while the Ground wire is Grounding conductor. The Neutral is "intentionally grounded", bit it is not the "grounding" conductor.
    – brhans
    2 days ago

3 Answers 3

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The old clothes dryer receptacles were NEMA 10-30. This had two hots and a neutral, but no ground. That is because going way back nothing had grounds. As grounds were added (witness the progression over the last 75 years or so from most ordinary 120V receptacles having 2 prongs to having 3 prongs), clothes dryers were supposed to be migrated to NEMA 14-30, which has two hots, neutral and ground. But as a fallback measure to provide some limited protection and backwards compatibility (i.e., new dryer with old receptacle), clothes dryers were allowed to be installed with ground and neutral connected in the dryer. The presumption was that over time the receptacles would be replaced, and all new receptacles would be NEMA 14-30.

That worked for new construction. But for old construction, instead people got new dryers (they don't last forever) and continued to connect them to NEMA 10-30 receptacles. And it has gotten so bad that there are numerous questions here where people open up their "old" 10-30 and find that it actually has a separate ground wire available! And people continue to ask questions about how to convert their 4-wire receptacle (14-30) to 3-wire (10-30) because they got a used dryer that only has a 3-wire cable. When in fact the proper thing to do (and actually easier than replacing a receptacle) is to replace the dryer cord and remove the neutral-ground bond in the dryer.

On to the question:

GFCI in general is a great way to provide protection in lieu of ground. If you have a 2-wire receptacle with no ground available (no ground wire lurking in the back of the box or just outside the box, no armored cable, no metal conduit, no easy path to add a ground wire) then you can replace the ordinary 2-wire receptacle with a GFCI/receptacle and get substantially the same protection as a properly grounded receptacle would provide. Actually quite a bit better protection in certain respects. Note also that the receptacles are supposed to be labeled so that any user knows that this is not an ordinary grounded receptacle - i.e., if they truly need ground (e.g., for surge suppression) then the ground pin is not connected and therefore useless.

However, a clothes dryer is a different beast. You can't put in a GFCI/receptacle because nobody (or at least nobody that I've found) actually makes one. If you could do that then you would remove the neutral-ground bond in the dryer and install a 4-wire (ground not connected because unavailable) 14-30 GFCI/receptacle and be reasonably protected just like a 120V NEMA 5-15 with GFCI. But that isn't an option.

So the next best option, and required by NEC 2020 for new circuits, is to install a GFCI/breaker, like the Siemens referenced here. The problem is that if you combine it with a 10-30 receptacle without ground and a dryer withe neutral-ground bonded then you will have a false sense of security since a ground fault will go to neutral and not be seen as a problem by the GFCI. Using a GFCI/breaker would actually hide a very real problem. In theory the GFCI would still help in case of user touches dryer with ground fault when it is on, but it is far from an ideal setup.

In addition, there are only three groups of people who are likely to install a GFCI/breaker for their clothes dryer circuit:

  • New construction under NEC 2020 rules - 14-30 is mandatory, since 1996. So this warning says "don't cheat".
  • New circuit in old construction under NEC 2020 rules - 14-30 is mandatory, since 1996. So this warning says "don't cheat".
  • Owner is a safety fanatic and wants the best protection (e.g., they just bought a house and are fixing all the old problems and getting everything up to NEC 2020 code even where not strictly required). This warning says don't put in the GFCI/breaker unless you also replace the old receptacle. Which is very good advice.

I find it extremely unlikely that someone would decide to simply add a GFCI/breaker to their clothes dryer circuit as a half-way measure to improve safety. Those breakers are expensive, the solution is not perfect, replacing the receptacle is the right thing to do anyway (how many people are using pre-1996 dryers and really want to put in 240V 30A GFCI breakers?), and I'd bet that in almost all pre-1996 homes (because afterwards any 10-30 should be an improper retrofit and a ground wire hiding in back from the original 14-30) that I've seen, the laundry room is in the basement and electrical, including running either a new cable or at least a ground wire, is easy to do. The older the house, the more likely that is the case.

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    Thanks! Awesome answer and I appreciate all the historical detail. I always thought of the 3-prong dryers as H-H-G not H-H-N but I see at some point they had to be H-H-N because there was no G. So I get that what they mean is "don't cheat" and "go to 4-wire before you install this". Would be much clearer if they had said "for maximum protection use a 4-wire circuit with this breaker" instead of "for maximum protection on a 3-wire circuit don't connect it to this breaker." The latter implies you need to connect to something else for maximum protection, which isn't really right.
    – trawson
    2 days ago
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The key here is maximum protection which is not in any way saying than a GFCI breaker is more hazardous that a non-GFCI breaker in this application. If you interpret it that way, you're not reading what they wrote.

What it says is simply that the protection the GFCI affords when continuing to use a NEMA 10 dryer/range connection that has been outlawed for new applications for more than 25 years (at present) is not maximum - since a proper 4-wire NEMA 14 is clearly safer, for either kind of breaker.

They, and I, would much prefer that people with hazardous old dryer connections rip them out and install NEMA-14s - and presumably their legal team likes that if anything bad happens to people who did not, they violated code by not following manufacturer instructions when installing the breaker.

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My understanding is that 3-wire dryer circuits are supposed to be hot-hot-ground.

No. Dryers have a 240V heater and 120V everything-else, for this reason. Ovens, same reason and the #1 120V load is the oven light. (time was, every house in America had a whole box of 120V incandescent bulbs in their junk drawer).

In 1966 a positively deranged compromise was made to allow dryer and ranges (only) to be quote, "grounded", unquote, by attaching their chassis to the neutral wire. This was banned in 1996.

Adding a GFCI helps - a shock between dryer chassis and, say, the sink will be caught by the GFCI. But internal ground faults from hot to chassis will not concern the GFCI. There is the coverage gap.

How do we fix this cheap? Easy.

In the 1960s, all legal 3-wire cables, "/3 no ground" and #10 SEU, started to be exhausted. Once they ran out, the only legal cable was 10/3 w/ground. So, many NEMA 10s actually have a ground hiding behind it, or metal conduit which qualifies as a ground. In which case simply swap to a NEMA 14.

If you find /2 w/ground cable, with ground being abused as neutral, that was illegal the day it was installed! You must run new cable.

Otherwise...

  • Wire the range/dryer correctly for a NEMA 14-30 or 14-50 connection, with bootleg strap removed/stowed so neutral is isolated from ground.
  • Install a NEMA 14-50 or 14-30 socket, and simply do not install ground.
  • Label the NEMA 14 socket "GFCI Protected / No Equipment Ground" per 406.4(D)(2)(c).
  • (almost forgot) Install a GFCI breaker.
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    Of course that makes sense. Now I don't know where I ever got the idea that the 10-30 receptacles were hot-hot-ground. Maybe an old house had one wired that way?? I'm not sure. Anyway glad to have it clarified. Here we just got a new dryer and did exactly what you said. There was a 10-30 with a ground hiding in the box (not even connected to the box). We swapped it for a 14-30, grounded everything properly, put a 4-wire cord on the dryer, and removed the dryer bonding jumper.
    – trawson
    yesterday
  • @trawson perhaps you got the idea from "type 6" receptacles, which are hot-hot-ground ?
    – P2000
    yesterday
  • Well, if the NEMA 10 circuit is fed from the main panel, it wires exactly the same as a NEMA 6. One could hardly believe that ungrounded circuits were still being installed in the 1990s, so someone who hadn't looked up the pinout on a NEMA 10 might naturally assume it's ground. that's why I created that one graphic I use a lot. yesterday
  • Agreed. In this house there was a lot one can't quite believe -- e.g. dryer receptacle with the ground just laying in the box, 6/3 SJ marked “not for use in wet locations” and buried 3” deep across the lawn, hidden junction boxes with the added bonus of hot / neutral swaps within some of them, etc. Cleaning things up as we find them.
    – trawson
    yesterday

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