Danger high voltage!
September 4, 2012 11:33 AM   Subscribe

Another home wiring question: Old apartment, and I want to plug a three-prong plug (for a small fluorescent grow light) into the only two-prong outlet. For the past couple of days, I've been using a cheater plug, but I supposing this is not a good long-term solution. Should I just bite the bullet and use an extension cord to a grounded outlet?

Small grow light to try to grow basil inside during winter. Ideally, the light should be on all day. There is a two-prong outlet very close to the plants, but the light has a three-prong plug.

I've had an electrician there before to ask about upgrading to a three-prong, but (for whatever reason), he said he couldn't put one there. It's an old building, and we're renting, so we're not really apt to throw any money at this.

Electric afficionados, should I just suck it up and get a three-prong extension cord to run to the grounded outlet across the room? Is it unsafe to have a cheater plug with this small fluorescent lamp running while we're out, for essentially the next 8 months?
posted by Admiral Haddock to Home & Garden (23 answers total) 2 users marked this as a favorite
Get a three-prong extension cord that is rated high enough for what you want to do (e.g. an appliance-rated extension cord). I hate those cheater-plugs with a passion and I wish they were outlawed.

Even still, a heavy rate extension cord shouldn't be your permanent solution, especially if you could trip over it.

I would go one step further and suck it up to move your grow light so that it reaches a three-prong outlet on its own. (My house has both types of outlets and I have put much effort into arranging and decorating in a way that lets me plug things in correctly--it's what drives the decor of my house to a point, unfortunately.)
posted by TinWhistle at 11:40 AM on September 4, 2012

The reason your electrician won't wire the plug is that it's possible that there are no ground wires in the wall, and the plugs won't be up to code. We were told the only way we can do it was to put GFCI's in. I elected to get plate covers and call it a day (I wanted to put in nice, new, clean plugs.)

Here is an interesting article.

I'm thinking that your existing set-up should be fine.
posted by Ruthless Bunny at 11:41 AM on September 4, 2012 [1 favorite]

I would continue to do what you're doing, but I'm old and foolish.
posted by HuronBob at 11:57 AM on September 4, 2012 [1 favorite]

"Small Grow Light" is...what? I've got several "small grow lights" and all are 2 prong plugs, the only 3 prong I have is a fluorescent fixture. Unless we're talking "small" but "high draw" (mercury, halogen, sodium vapor, some kind of funky high lumen LED array), I'd continue to do what you're doing.
posted by TomMelee at 12:04 PM on September 4, 2012

"I hate those cheater-plugs with a passion and I wish they were outlawed."

Not to derail the convo, but TinWhistle, can you explain why? I'm using several of these: in one place I could just as well take it out because I only have a two-pronged cord plugged in anyway, but in the other I have a three-pronged surge-protector strip plugged in. Now your comment has me worried—what's the potential problem? I was thinking with the converter plug + surge protector, my electronics would be a-ok.

OP, I'd be inclined to run a high-end extension cord. But...given my above question to TinWhistle, by all means, take my suggestion with a large helping of salt.
posted by Eicats at 12:09 PM on September 4, 2012

IIRC, a surge protector will often try to redirect a surge of energy through the ground. With a cheater plug, you have no ground (unless it's one of those that screws into the outlet, and even then maybe not), so the surge protector will probably be rendered ineffective.

However I have never understood why you wouldn't want to use a high-rated extension cord as a permanent solution. I do this. As long as you're not tripping over it and it's rated for the load, I've never seen what the problem is.
posted by zvs at 12:18 PM on September 4, 2012

(Also I was displeased to find that the previous owners of my house had plugged the dryer into a cheater plug! In the event of a ground fault within the appliance, the whole case could become hot and kill you if you touched it. Brilliant.)
posted by zvs at 12:19 PM on September 4, 2012

I wouldnt do it as a long term solution. I have lights set up for my apt garden consisting of an appliance rated extension chord which is running 2 leds currently and one giant cfl. That setup is about to change as I expand with removal of the leds to a different area and the addition of 3 more large cfls. Make sure you do the math to ensure safety with how much you are drawing from a single circuit.
posted by handbanana at 12:20 PM on September 4, 2012

I do use the cheater-plugs that screw in...but wouldn't an extension cord also have the problem of no ground?

Again, sorry if these follow-ups are not helpful to the OP.
posted by Eicats at 12:31 PM on September 4, 2012

The amount of power isn't the issue.

The third prong is the earth ground. In a two prong outlet, you have a hot and neutral. In a three prong, you have a hot, neutral and ground.

The hot and neutral are the only two wires required to make the light work. The ground wire is there to add the protection against some major damage or loose wire (usually from the hot wire) from connecting to the conductive surfaces of the thing you are powering... in the case of the lamp, perhaps a switch or metal cover. If such a thing inexplicably happened, having the surface connected to that ground lead would assure that the fuse would blow at the fuse/breaker panel and it would render the defect safe. A two wire would not, and you may have an inadvertently hot external surface that would be risky IF THERE WERE A DEFECT AND IF YOU WERE AT THE SAME TIME TOUCHING IT AND A CLOSE BY GROUNDED OR NEUTRAL WIRE OR SURFACE.

You can for the most part eliminate this risk with an isolation transformer, which breaks the galvanic connection between the wall and the load. It's cheaper than running a ground lead to the fuse panel (a home run) ground, and while not quite as safe, is an alternative for an informed consumer. You only need about 100 VA transformer to isolate that load, and if you get killed, it will be because you are INSIDE the lamp where you don't belong.

You may want to inquire of your electrician if he would be able to locate one for you. Ideally, it would be two wire and in a non-conductive box.
posted by FauxScot at 12:35 PM on September 4, 2012

Eicats - To clarify I think the people recommending an extension cord are saying run the cord to a (presumably present but farther away) 3-prong grounded outlet.

Ruthless Bunny's article is actually quite informative, so thanks for that.
posted by Wretch729 at 12:39 PM on September 4, 2012

Response by poster: Thanks to all for the responses so far. To clarify, if it's helpful--

The cheater plug is screwed in to the faceplate (it's the old style, with a wire, which I'll replace; I know the risk the wire could come loose and go into the other socket). That said, I'm not convinced that the plate itself is attached to anything that's grounded, so I'm not sure the cheater is "working."

This is the grow light.

Yes, Eicats, the extension would be a three-prong cable going to a properly grounded outlet across the room (in another room, actually). The trade-off is a theoretical risk of a short with a cheater plug, or a real and constant risk of tripping on the cord for the next 8 months.
posted by Admiral Haddock at 12:44 PM on September 4, 2012

FWIW, I was commenting on the draw of a high power use item across an extension cord, vs the amount of power in a 2 vs 3 plug outlet, as the trip/sever/smash risk of running a permanent extension cord is non-zero.

That light is grounded because it's a metal casing and because of the transformer inside the ballast of the fluorescent fixture is right up next to that metal housing. If it were I, I would continue to use a 3-to-2, versus running an extension cord.

Total sidebar, Basil doesn't need anywhere near that much light, even grown indoors, and if you are using fluorescents make sure that the bulb is no more than about 3 inches off the top of the plant. (hydroponic gardener here)
posted by TomMelee at 1:27 PM on September 4, 2012

My electrician brother in-laws advice for our house, install a GFCI outlet at the spots your worried about. It's like the one near your kitchen or bathroom with the red reset button. They are not dependent on a ground and have a fuse to stop erroneous current flows...I.E getting shocked or a short.
posted by couchdive at 1:50 PM on September 4, 2012

While I wouldn't say this is the "correct" thing to do, if it were me, I'd continue to use the 3-to-2 adapter, screwed into the outlet faceplate.

If you want, you can use an outlet tester (under $10 at Home Depot and other places) to see if the ground is good, once you have the adapter on there. Be sure that there isn't old paint or other crap keeping the little tab on the adapter from making good contact with the screw in the center of the outlet faceplate. And pay attention to the hints in the WP article for detecting a false ground created by shorting Neutral to Gnd; you'll need a multimeter to check that.

Even in an old house with 2-prong plugs, there should be a ground provided via the metallic jacket of BX cable and the metal box, if the wiring and subsequent additions to it were done properly. It could be that the wiring in your apartment wasn't done correctly, and the original ground has now lifted and is floating, which is bad. But I'd at least test things out to see if it's the case. If it is, I'd move on with my life.

If there's no ground in the outlet box, then the proper thing to do is probably to replace the old 2-wire outlet with a 3-wire GFCI outlet. This is allowed by code in most places provided that the outlet is clearly marked "No Equipment Ground". More info here.
posted by Kadin2048 at 2:04 PM on September 4, 2012

Hey folks, you realize that even when a box of some sort is grounded, well, taking zvs' dryer as an example, if there is a ground fault, the box is hot, but it's hot with some sort of return so that if you touch it, it's more like a bird sitting on a wire than making yourself the only path to ground.

If you touch your grounded, faulty appliance and something like a water faucet at the same time, you might find you're more conductive than you thought. If the light you're using is in good working condition and not placed where it could fall into the sink while you're doing dishes, a grounded outlet probably doesn't buy you that much safety relative to other things that people do all the time.

TLDR: Grounding gives you an advantage if something is goes seriously awry, but it is not a substitute for GFCI.
posted by Kid Charlemagne at 2:48 PM on September 4, 2012

Almost certainly, the wire behind your socket has only 2 conductors, so simply putting a 3 prong outlet there would be the electrical equivalent of your cheater, but would (falsely) imply that you had a proper ground. That's why your electrician can't do it.

The right solution is to run 3 conductors to where the light is. An extension cord would do this, but is dangerous insofar as it can be stepped on & damaged.

Another possibility is (or used to be, I'm not sure if it's still up to code) running some sort of a surface conduit (one consumer brand is wiremold).

Finally, as was mentioned above, your electrician can install a GFCI outlet which will have 3 prong plugs. This is OK because the circuitry detects even a very small discrepancy between the currents on the 2 wires, and trips before there is time to do much damage. This appears to be up to code.

Of course it might be easier just to move the light to where the 3 prong outlet is.
posted by mr vino at 3:44 PM on September 4, 2012

Even in an old house with 2-prong plugs, there should be a ground provided via the metallic jacket of BX cable and the metal box, if the wiring and subsequent additions to it were done properly.

unless the wiring is so old that it isn't BX, but knob and tube. All 3 of the houses I've owned (in the Boston area) had at least some knob-and-tube wiring.
posted by mr vino at 3:45 PM on September 4, 2012

Also I was displeased to find that the previous owners of my house had plugged the dryer into a cheater plug! In the event of a ground fault within the appliance, the whole case could become hot and kill you if you touched it. Brilliant.

The adapter may be just fine. Up until about the year 2000, most dryers were wired with 3-prong plugs that had two hots and a neutral with no ground. The appliance chassis was internally bonded to the neutral. A hot fault to the chassis would go to the neutral and pop the breaker. So the dryer was just fine, per pre-2000 code.

If you have a 4-prong dryer and a three prong socket, the adapter connects the dryer chassis ground to neutral exactly as for the 60 previous years of the electrical code. This saves having to re-wire your home to use newer dryers and is no less safe than older dryers.

If you have a 3-prong dryer and a 4-prong socket, the adapter just connects the two hots and neutral exactly as they were for the 60 previous years. The dryer chassis is grounded to the neutral.

In either case, with a proper adapter, the chassis will not be floating.
posted by JackFlash at 4:00 PM on September 4, 2012

Yes---right, but 220v across a normal, 110v plug? Wouldn't you have to jury-rig that supply wire or something, to get it onto a normal plug? Or are we talking an apartment sized dryer or something? The warehouse I used to manage had intensely stupid wiring (200A service, split into 4 sub panels, and the first panel was split into 2, 50A breakers, from which the other 4 panels were served. 200A straight to 100A @ 50A each box. Dumb.) We had a big, in-wall air conditioner in the receiving area, and it was plugged into a normal, 110v outlet. (And not one of the fancy red 25A or 50A jobbers, either) It was one of those units that can take either 110 or 220, it was just on 110. Well, one day there was a festival at the skate park next door, and the grounds folks came to steal some power, so I directed them to that plug.

I have NO IDEA how the workman saw it, but he happened to see that the switch on the A/C was set to 220, and it was on and working fine. So he grabbed his Fluke out of the truck, and sure enough--220. So we opened the box, 3 wires inside. White, green, black. Tracing them back, both green and black were hot----and each came from a DIFFERENT CIRCUIT. And no, the box wasn't grounded. That's when I really started looking, and discovered that in individual junction boxes I had white/green/red/black/yellow wires that were ALL hot (nothing taped), and others of the same colors that were not, and almost all switches broke neutral. Super, mega, awesomely cool.
posted by TomMelee at 6:46 PM on September 4, 2012

Assuming the doorway doesn't have a functioning door go with the properly rated extension cord because the hazard (tripping and potentially a damaged cord causing a shock hazard) is visible and avoidable (especially if you duct tape the cord to the wall rather than letting it lay on the floor) while the shock hazard from an ungrounded 3 prong plug is serious and most importantly invisible until you get shocked.

If you feel up to changing the outlet a GFCI will provide similar protection to a grounded plug for about $20. Be forewarned however that getting a modern GFCI with TR shutters into an old, small, metal box (especially if the box isn't terminal IE: wires enter and exit the box) can be nigh impossible.

A third option is for an inline plug in GFCI. Just plug it into your 2-3 prong adapter and then plug it into 2 prong outlet. This doesn't provide an equipment ground but your light should work fine. Just don't plug a motor or surge protector into it. The inline GFCI are fairly expensive though and not terribly reliable in my experience. Note that a plug in GFCI test will not pop a GFCI installed this way.

couchdive writes "My electrician brother in-laws advice for our house, install a GFCI outlet at the spots your worried about. It's like the one near your kitchen or bathroom with the red reset button. They are not dependent on a ground and have a fuse to stop erroneous current flows...I.E getting shocked or a short."

GFCIs do not have a fuse and therefor do not protect against excessive current draws. They only detect an imbalance in flows between the hot and neutral.

Kadin2048 writes "Even in an old house with 2-prong plugs, there should be a ground provided via the metallic jacket of BX cable and the metal box, if the wiring and subsequent additions to it were done properly."

YMMV on this a lot. There are plenty of 40s and 50s houses here with 2 conductor Vulcanised India Rubber (VIR) insulated cable. The boxes wired with this cable won't be grounded in any way.
posted by Mitheral at 6:52 PM on September 4, 2012 [1 favorite]

Sorry for the confusion. This thread is pretty fun. It's a gas dryer and only draws 110V, so only one hot on the outlet. However, it was installed pre-2000. Do they make cheaters for 220V plugs? Terrifying.
posted by zvs at 12:49 PM on September 5, 2012

Thank for the correct info, Mitheral!
posted by couchdive at 1:49 PM on September 5, 2012

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