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Three prong outlet question #5398864 04/09/20 10:13 PM
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FirstNissan Offline OP
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Hi, I have a few two plug outlets in my garage and most of my power tools / LED shoplights are 3 prong. I have in the past used 3-prong-to-2-prong adapters. My neighbor recently made a comment that I should have the outlets changed because the adapters are "a fire hazard". Any truth to this?

Thank you


2017 Toyota Sienna
2019 Toyota Camry
Re: Three prong outlet question [Re: FirstNissan] #5398876 04/09/20 10:32 PM
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blufeb95 Offline
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They're more of a shock hazard than a fire hazard, devices with a 3 prong plug generally have a metal casing that is grounded if something goes wrong usually the fault to ground will blow a fuse in the device and prevent you from getting electrocuted, however without the ground if the live wire becomes shorted to the case then if you touch the case and you have enough of a connection to ground you'll be in for a nice shock, generally it's a good idea to replace old two prong recepticals with a GFCI if they can't be rewired easily that way if the ground fault ever occurs it'll trip and you might get a quite a zap but not a fatal one.

Re: Three prong outlet question [Re: FirstNissan] #5398889 04/09/20 10:53 PM
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Chris142 Offline
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The adapters are designed to have the screw that holds the plate down pass through a circular dealio. If that is done and the wires are in conduit it should ground ok.


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Re: Three prong outlet question [Re: FirstNissan] #5398892 04/09/20 10:55 PM
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clinebarger Offline
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I know just enough about A/C current/voltage to be dangerous grin My house was built in 1929 & fitted with electricity sometime after that. There was no earth/ground at all......Just Neutrals & Hots (2 wire cloth wrapped) ran willy nilly from a 4 glass fuse panel. I had to drive a brass rod into the ground & ground all my plumbing along with rewiring the entire house & a new service.

What I'm getting at...You might not be grounded?


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Re: Three prong outlet question [Re: FirstNissan] #5398896 04/09/20 11:04 PM
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Oildudeny Offline
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If you're not comfortable working with electrical, have an electrician install weather resistant Gfci's in the garage

Re: Three prong outlet question [Re: FirstNissan] #5398904 04/09/20 11:26 PM
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ripcord Offline
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Chances are you only have two wire romex going out to those outlets.

Re: Three prong outlet question [Re: FirstNissan] #5398931 04/10/20 12:49 AM
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Wolf359 Offline
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Technically the answer is that it's not to code. That's it. You could do the GFCI to get around not having the ground. Or run a ground wire all the way back to the panel.

Re: Three prong outlet question [Re: FirstNissan] #5399018 04/10/20 07:24 AM
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ragtoplvr Offline
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GFCI outlets tested regularly are the answer.

Rod

Re: Three prong outlet question [Re: FirstNissan] #5399120 04/10/20 09:29 AM
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Donald Offline
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Originally Posted by FirstNissan
Hi, I have a few two plug outlets in my garage and most of my power tools / LED shoplights are 3 prong. I have in the past used 3-prong-to-2-prong adapters. My neighbor recently made a comment that I should have the outlets changed because the adapters are "a fire hazard". Any truth to this?

Thank you


You will need to open up the outlet and look. Going to a 3 prong GFI is the proper thing in a garage. In some houses they used BX cable and the outside metal part of the cable is ground. So there is a chance the box is already grounded. But you will need to verify. In a garage it should be a GFI.


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Re: Three prong outlet question [Re: blufeb95] #5399124 04/10/20 09:32 AM
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Dave9 Offline
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Quote
They're more of a shock hazard than a fire hazard, devices with a 3 prong plug generally have a metal casing that is grounded if something goes wrong usually the fault to ground will blow a fuse in the device and prevent you from getting electrocuted, however without the ground if the live wire becomes shorted to the case then if you touch the case and you have enough of a connection to ground you'll be in for a nice shock, generally it's a good idea to replace old two prong recepticals with a GFCI if they can't be rewired easily that way if the ground fault ever occurs it'll trip and you might get a quite a zap but not a fatal one.


This is not quite accurate. Yes a GFCI would trip and is a good safety measure, but practically nothing has a fuse that will blow from a ground fault before it gets to a dangerous level (though some products like hair dryers may have their own GFCI built in), not in the equipment and not at the circuit fuse/breaker panel. There is an exception, if you took a ground wire and touched it to a live chassis, that might blow a fuse, but going through the human body, there is far too much resistance to trip a fuse, and a potentially lethal amount of current is under 100mA.

Last edited by Dave9; 04/10/20 09:37 AM.
Re: Three prong outlet question [Re: FirstNissan] #5399308 04/10/20 12:32 PM
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exranger06 Offline
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Here is the purpose of the 3rd prong/ground wire:

An appliance or tool that has a metal enclosure, or any metal part that someone can touch that could accidentally become energized, will generally have a 3 prong cord. If a live wire inside the appliance were to come loose and touch the metal enclosure, the circuit breaker protecting the outlet will trip. Without the 3rd prong, the circuit breaker will not trip and the enclosure of the appliance will just stay energized, and you'll get a shock when you touch it.

Here is the reason the breaker trips if the live wire touches the grounded enclosure:

If you connected the hot leg directly to the neutral wire (NOT the ground, the neutral), you'd have a dead short. A dead short = a LOT of current going through the wires. When there's a lot of current going through the wires, the breaker trips. (A 15 amp breaker will trip anytime the current goes over 15 amps, that's why it's a "15 amp breaker!")

The ground wire is bonded to the neutral bar in the breaker panel. So, if the hot leg contacts the ground wire (or a grounded enclosure), it's essentially the same thing as the hot leg contacting the neutral wire and also results in a dead short. This makes the breaker trip as soon as possible, thus de-energizing the appliance and eliminating the shock hazard. This is NOT to say that the ground wire is the same as the neutral wire, and you CANNOT simply use the neutral as a ground wire. The ground wire is to remain "dead" at all times and ONLY used to clear faults!

And this hopefully clears up the misconception that the ground wire sends current to "the ground" (the literal ground you stand on). The ground rods you have going into the ground serve a completely different purpose. The ground wire doesn't send fault current to the ground rods, it sends it back to the source (the transformer), the same place that the hot legs and neutral originate. Remember, the goal is to essentially create a short circuit between the hot leg and the neutral, which both come from the transformer, NOT "the ground."

I really hate those 2 prong adapters. They serve no useful purpose, if you use them the way they were designed (which NO ONE ever does), and they're just plain unsafe if you use them improperly (which EVERYONE does). You're supposed to connect the round tab on the adapter to the screw that holds the outlet cover plate on (which no one ever does). Not connecting this tab is unsafe because if the exposed parts of the appliance become energized, the breaker won't trip and you'll get shocked if you touch them. Even if you DO connect the tab to the cover screw, it still won't do anything if the outlet box is not bonded to ground!

If the outlet box IS bonded to ground, then there's no reason you can't just swap out the 2-prong outlet for a 3-prong outlet and just bond it to the outlet box, thus eliminating the need for those stupid adapters. And that is why I hate those adapters. smile


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Re: Three prong outlet question [Re: FirstNissan] #5399454 04/10/20 03:18 PM
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Re: Three prong outlet question [Re: exranger06] #5399500 04/10/20 04:09 PM
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blufeb95 Offline
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Originally Posted by exranger06

I really hate those 2 prong adapters. They serve no useful purpose, if you use them the way they were designed (which NO ONE ever does), and they're just plain unsafe if you use them improperly (which EVERYONE does). You're supposed to connect the round tab on the adapter to the screw that holds the outlet cover plate on (which no one ever does). Not connecting this tab is unsafe because if the exposed parts of the appliance become energized, the breaker won't trip and you'll get shocked if you touch them. Even if you DO connect the tab to the cover screw, it still won't do anything if the outlet box is not bonded to ground!


Actually probably one of the worst case scenarios is someone uses a cheater plug attached to a screw or puts a 3 prong receptacle in on an outlet where they think there is ground but it's a poor quality path back to the breaker box because their house was wired with pre-1959 AC cable (BX cable) with no bonding strip down the length of the corrugated steel conduit so when a short to ground happens there's going to be a rather high impedance path to ground through that long strip of rusted old steel so the breaker might not trip and either the device with short in it can possibly catch fire or the corrugated steel conduit will become a nice heating coil and start a fire in the attic or crawl.

Re: Three prong outlet question [Re: Wolf359] #5399634 04/10/20 06:34 PM
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zzyzzx Offline
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Originally Posted by Wolf359
Technically the answer is that it's not to code.


Not to current code. You aren't required to change everything every time codes change. It's perfectly fine if it to code for when it was built.

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