Space heater with no ground?
January 8, 2022 7:37 PM   Subscribe

I want to run a 1500w space heater in a bedroom that has old two-prong outlets with no ground. The space heater's scary warning tags recommend against this. Would it be safe to run the space heater on a "no equipment ground" GFCI?

I could maybe supply a real ground wire to the outlet, but I'm lazy and I'd rather not if I don't have to. There's a crawlspace directly below, but getting a ground wire up into the gang box without opening up the wall seems hard.

FWIW, this isn't knob and tube wiring, but it's from some time pre-1980 when the house had a major remodel but they didn't bother updating the outlets in this room.
posted by qxntpqbbbqxl to Home & Garden (7 answers total) 1 user marked this as a favorite
If you've got all-metal plumbing, and can see a metal pipe in your crawlspace, wiring that up as your ground might be your easiest choice. I wouldn't run an appliance that pulls that much power ungrounded.
posted by mhoye at 7:58 PM on January 8, 2022 [1 favorite]

Best answer: It's safer but not as safe a using a grounded outlet. I wouldn't worry about the theoretical difference in your case between the two though. Just continue as if you were protected.

Have you got a breaker panel? If so what brand? You may be able to replace the breaker for that circuit with either an Arc Fault or a combination Arc Fault/GFCI breaker. The latter would be best though an arc fault breaker with GFCI receptacle is also good (or vice versa depending on what you can actually buy supply chains being what they are). Arc Fault protection is a good thing to have on this sort of circuit/load (it protects the structure from fire rather than the user from electrocution).

BTW the GFCI receptacle doesn't have to be installed at the particular outlet you are using. You can install it at any receptacle on the same branch that is between the breaker and the receptacle you are using. You would then have to swap the two prong receptacle with a three prong and attach a sticker to the wall plate that comes with the GFCI. I mention it because you might not have space in the box for the GFCI depending on what else is going on in there.

However space heaters really load the circuit they are on. If there are any marginal splices etc on that circuit they'll show up (though a no ground, non-K&T usually has soldered connections which are pretty fool proof if the wiring hasn't been messed with). The absolutely best would be to run a dedicated circuit for the heater just because it is such a large load. With a crawl space under the desired location it's pretty easy to add a receptacle at that end. If you can get to your breaker panel easily this might be something to consider.
posted by Mitheral at 8:40 PM on January 8, 2022 [2 favorites]

Best answer: * First, I would replace the outlet - you may discover there's a ground wire already present you can use, and in any case, a fresh 2 prong outlet will be much safer than an old, worn out one. Spend the extra $1 to get the higher quality outlet, and install it using the screw terminals (rather than the backstab ones).
* here's an example of an oil filled radiator which looks to have a 2 prong plug: link
* some space heaters have a Low mode, which uses about 750 watts. If you are unsure about the quality of wiring, it may be safer to use a lower load.
posted by soylent00FF00 at 7:25 AM on January 9, 2022 [3 favorites]

Best answer: The other side of soylent's comment - I bought a house that had been remodeled, I had a grounded outlet where I wanted my computer, but it tested non-grounded.
I went under the house, and found the most jacked up bodge of wiring I have ever seen. In the end, it was powered off old knob and tube. Why the house hadn't burned, I don't know. I pulled new wire from the panel.
While not OP's situation, it pays to verify the grounding with at least one of those cheap little plug in testing devices. Two prong recept's are getting hard to find at the big box stores, I think previous owner just bought 3 prongs and installed those.
posted by rudd135 at 7:42 AM on January 9, 2022

Best answer: The principal risk is the same as with any other touch-exposed device: if the heater was designed with the case / controls / etc. connected to earth ground, it relies on that connection to protect the user from operation or wiring faults. Imagine slowly melting a wire support so the hot conductor touches the case: the case is now live and no protection can catch it. (Double-insulated things like two-prong power tools have an additional protective layer of insulation in case the functional insulation fails. For cost reasons, your three-prong heater almost certainly doesn't.)

Basically, the heater will *work* but the three-prong plug should be screaming at you "not designed to work without access to protective ground!"

As noted above, an upstream GFCI will theoretically protect you (someone touches the hot controls, becomes the path to ground, the GFCI detects that I_line minus I_neutral is no longer zero and hopefully opens the circuit), but that protection doesn't activate until someone is already getting shocked. I personally would not rely on it.
posted by introp at 11:42 AM on January 9, 2022

Best answer: I believe that the non-grounded GFCI meets the US National Electrical Code, and I would personally be comfortable using such an arrangement for this.

However, there are many 1500 W electric heaters that do not even have ground plugs and thus are presumably double-insulated. If you have lingering doubts, perhaps one of these heaters could set you at ease.
posted by Juffo-Wup at 4:42 PM on January 9, 2022

Looking at both my space heaters, none has the 3 pin plug, both have the normal 2 pin plug.
posted by Ferrari328 at 10:48 AM on January 10, 2022

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