220 outlet in metal box - does it need a ground?

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Old 01-30-14, 10:35 PM
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220 outlet in metal box - does it need a ground?

I am a first time home owner and very new to home-related electrical work, so please bear with me.

I took the faceplate off the 220v plug for my electric dryer to see how it was wired because I've been reading a book called "How to Wire a House" by Rex Cauldwell (great book, btw). What I saw surprised me a bit. The plug is 3-wire with 2 hots and 1 ground, which I know isn't to code, but my house was built in 1956, so it didn't surprise me too much. What did surprise me is that the metal box wasn't grounded with a pigtail. So I have 2 questions:

1) Shouldn't a metal electrical box ALWAYS be grounded?

2) If I go in there and ground the box for safety, is it considered an alteration that would mean I have to bring the whole thing up to code?

Thanks in advance!
 
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Old 01-30-14, 11:23 PM
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The plug is 3-wire with 2 hots and 1 ground
It should have been two hots and a neutral. Was the third wire bare?

Note residential voltages are 120v and 240v. The dryer should be 120/240v not 220v.
 
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Old 01-30-14, 11:36 PM
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Welcome to the forums!

1) Shouldn't a metal electrical box ALWAYS be grounded?
Yes

2) If I go in there and ground the box for safety, is it considered an alteration that would mean I have to bring the whole thing up to code?
No

BTW, you don't have a 220V receptacle for your dryer. It's a 240V receptacle.
 
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Old 01-31-14, 07:55 AM
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Just checking: O/P says two hots and a ground not neutral. If that really is a ground would it be legal for a dryer that is 120/240? If it is really a white insulated neutral would you really connect it to the box since it isn't a ground?
 
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Old 01-31-14, 09:54 AM
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If that really is a ground would it be legal for a dryer that is 120/240?
Probably not.

If it is really a white insulated neutral would you really connect it to the box since it isn't a ground?
Nope, not in a million years.
 
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Old 01-31-14, 10:14 AM
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So Snoogans, we need to know exactly what you have to answer your question. Is the alleged ground bare, green, or white. Bare or green not code compliant for a dryer. If white it isn't a ground and should not be connected to the box. Or is it SE with a braided ground?
 
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Old 01-31-14, 11:39 AM
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Thanks to everyone for the input.

The ground wire is a solid, bare copper wire. The cable is NM of some type, although I didn't see what type exactly and I'm at work so I can't check until I get home.

The NM wire has a black wire, a white wire (which has red electrical tape around it), and a bare ground. The receptacle is 3 prong, and has the hot wires going to the straight terminals and the bare ground going to the "L" shaped terminal.
 
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Old 01-31-14, 01:08 PM
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The NM wire has a black wire, a white wire (which has red electrical tape around it), and a bare ground. The receptacle is 3 prong, and has the hot wires going to the straight terminals and the bare ground going to the "L" shaped terminal.
2-wire NM cable with a bare ground was never allowed by code for a 120/240 volt dryer circuit, not even back in 1956. I would recommend you replace that circuit with 10-3 NM-B cable, which has a total of 4 wires including the bare ground, and a 4-wire dryer receptacle. You'll also have to replace the cord on the dryer with a 4-wire cord.



If it is really a white insulated neutral would you really connect it to the box since it isn't a ground?
Nope, not in a million years.
I am going to disagree. There was a time when 120/240 volt dryer circuits grounded the dryer through the white neutral conductor. The same was true of electric ranges. It's my opinion that the correct thing to do with that type of circuit would have been to ground the box with a pigtail through the white neutral conductor as well, just like the frame of the dryer was grounded.

This would only apply to flush receptacles mounted in a box and not to what I consider more common, the surface type receptacles.
 
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Old 01-31-14, 07:50 PM
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Hmmmm...

I understand that this set-up is not to code. But is it dangerous? Can it damage my dryer? I will fix it, but should I tell my wife not to use the dryer?
 
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Old 01-31-14, 08:05 PM
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Can it damage my dryer?
No, just you and your family. It imposes a current on the grounds which should not be hot. That puts a voltage on the metal case of any grounded appliances. If you should touch a metal faucet connected to a metal water pipe for instance and the stove or refrigerator there is a remote there could be voltage difference between the grounded water pipe and the metal of the stove depending on the conductivity of the soil and other factors.
 
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Old 03-10-14, 02:22 PM
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After doing some digging and thinking, I don't think this answer is correct. Even with a braided neutral as the 3rd wire (which used to be code prior to 1996), it comes to the same in terms of possibly electrifying other appliances or metal object in the house because both neutral and ground wires are on the same bus in the service panel. Your logic would apply then to all outlets and appliances, because they are all interconnected via the fact that all neutrals and grounds end up on the same bus in the main panel (this is taking out the complication of sub-panels, which I know need to have the neutrals and grounds on separate buses). This 240v wiring configuration is no different in that regard.

I mean no disrespect, I just want to get it straight in my head.

What I've read is that the neutral is there in a 4-wire system because some of the electronics in newer washers and dryers use 110v, not 220v. I still can't figure out exactly why the neutral being present is necessary based on the 110v stuff, but it's most likely because I don't really know enough to understand. Is it because for the 110v use there needs to be a place for the current to go when the appliance is only using one leg for the stuff that uses 110v?
 
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Old 03-10-14, 02:40 PM
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A 120 volt load needs a neutral to operate. Straight 240 volt loads do not. Te return path for a 240 volt load is the opposite leg in the circuit.

The electron flow for the neutral is only going towards the panel. It is not going back to the ground screw on the device. The issue with a 3 wire setup for the dryer was that the neutral was bonded to the frame of the dryer. That put a small amount of current on the frame. If someone were touch the dryer and a surface at a different potential there was a chance of a shock.
 
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Old 03-10-14, 03:00 PM
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What I've read is that the neutral is there in a 4-wire system because some of the electronics in newer washers and dryers use 110v, not 220v.box-does-need-ground.html#ixzz2vaz8Cubc
Wrong. Almost all dryers are built as 120 volt appliances then either a gas or 240 volt heat source is added. This is true for driers even before electronics were used. Motors have always been 120 volts even when the timers were electromechanical.

Tech note: Residential voltage is 120 and 240..

Exception: Some European residential appliances built for US sales that are 240 only with 240 controls and motors but they are rare.
 
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Old 03-10-14, 03:04 PM
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A 120 volt load needs a neutral to operate. Straight 240 volt loads do not. Te return path for a 240 volt load is the opposite leg in the circuit.
Thank you for confirming that. It means I'm actually learning something.

The issue with a 3 wire setup for the dryer was that the neutral was bonded to the frame of the dryer. That put a small amount of current on the frame. If someone were touch the dryer and a surface at a different potential there was a chance of a shock.
I think I understand what you are saying about how this imposes a small amount of current on the frame of the dryer itself. Thank you for that as well.

So how does having a bare ground (which is my current situation, see my OP) as the 3rd wire act any differently than having a braided neutral? A wire is a wire, right? Is it because it's bare and therefore has no insulation to stop it from carrying the current to someplace else (other than the NM jacket)?
 
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Old 03-10-14, 03:11 PM
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Wrong. Almost all dryers are built as 120 volt appliances then either a gas or 240 volt heat source is added. This is true for driers even before electronics were used.
OK, that makes sense.

Tech note: Residential voltage is 120 and 240..
Sorry, I'm a newb. I'll try to keep it straight.
 
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Old 03-10-14, 03:26 PM
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If the dryer used SE cable the braided conductor was the neutral.

With a 4 wire setup the neutral is only for return current. The grounding is handled by the bare conductor.
 
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