Why is there a 4 wire dryer plug?

[skeezix]

I know that code changes in '96 required dryer plugs to be converted from a 3-wire setup to a 4-wire setup. The 4th wire being ground. Is that to prevent shock hazard, fire hazard, or to protect the equipment. I'm not sure if I should go ahead and add a 4-wire setup, or just convert my dryer to a 3-wire setup. Thanks.

[kactuskid]

A 4 wire cord is definatly safer and protects against shock, but whether you "need" to change anything is still unknown. Existing 3 wire dryer circuits are still allowed, they just can't be extended, and if a new dryer is purchased a 3 wire cord can be attached to it.

If installing a new circuit then a 4 wire circuit is required. So, please provide a bit more info of what your project is so we can help you out.

[skeezix]

I decided to go 4 wire... but I probably didn't need to. I guess I am just paranoid. Ran a new circuit to the panel on Saturday. We did find out that our dryer cord was miswired by the appliance store, and we had been running it without ground for the last 7 years. Oops.

[kactuskid]

So I take it that the appliance store never installed the ground strap that connects the neutral wire (center conductor) to the dryers frame when they installed your 3 wire cord. That's a dangerous thing to mess up on. Sorry to hear that, but glad to hear you found it out before someone got hurt. Thanks for the feedback and let us know if you need anything else. Below is a link that'll show you how it's supposed to be done for a 4 wire cord in case you wanna check your work out. Be sure that the neutral wire and the ground wire are totally separated at the back of the dryer now for your 4 wire connection.

http://www.selfhelpandmore.com/switc...ryer/index.htm

[Phelps]

Here is the reason why:

A 3 prong dryer has 2 hots and a neutral/ground strap. Because of the 110 motor and other things that work on 110, that means power is coming into one of the 110 hot legs and steadily flowing out the neutral/ground. And since the case of the dryer is grounded, this technically means that the flow of juice(albeit reduced) is thru the case! Normaly you won't get shocked if the floor is not wet and you have shoes on. And even so, you may still not feel much of or any shock. BUT, if one of the electrical components shorted out, then there WOULD be full current flow into the case, on it's way to ground at the panel box.

But, with the 4-prong set up, they can now remove the ground neutral -to-case grounding strap, isolating the neutral from the ground, until it enters the panel box. That means that the 110 juice that flows thru the motor and other things can now go into the neutral without ever being in contact with the case! The 4th (ground) wire is now available just for safety backup in case there is a short. And then if it does (short), it will directly go through the wire to the panel box ground terminal rather than ever going through the case.

Oh. In this scenario, 3 prong or 4 prong isn't really going to matter, but I thought I'd share this odity with you: I have seen elements sometimes burn in half and drape on the case where even though the 220 current flow is now broken, their still is the ability of 110 to flow through the element and directly into the case, producing 110 (instead of the normal 220) heat and the dryer can get hot with the dryer off and not even spinning!

[suprheat]

With a three wire system current DOES NOT flow thru the case unless the ground wire is broken in its path back to the panel - even if a component is shorted. However, I suppose that if you physically took the so called neutral wire feeding the components inside the cabinet and moved it to the case away from the netral/ground wire connection then current would flow thru the case to the neutral/ground wire. But who would do that? Current flows thru the path of least resistance and that is the wire to the panel. So don't worry about gettting shocked if all wiring is up to snuff.

[gbehl]

reason for the change

In the old style receptacle the assumption had been made
that if Line "Y" shorted it was fine to have a single alternate
pathway to ground. Remember 220v appliances actually run
with no actual need of a ground or common wire other than
for safety reasons.

This assupmtion left out the possiblity that maybe both "Y"
and "X" could become shorted and that could cause 2x the
current to be carried on the "alternate carrier" which in many
cases is already downsized. This could cause a severe over
current condition which is not only an electrical problem, but
is a fire hazard which is what the electrical code is actually
for. After all the NEC is put out by the NFPA.

[richbrich]

Why is there a 4-wire dryer plug? - I did that... :>(

Referencing 'Suprheats' remarks (excerpted here: "...With a three wire system current DOES NOT flow thru the case unless the ground wire is broken in its path back to the panel - even if a component is shorted. However, I suppose that if you physically took the so called neutral wire feeding the components inside the cabinet and moved it to the case away from the netral/ground wire connection then current would flow thru the case to the neutral/ground wire. But who would do that?...
Well, I did just that...at first the dryer ran ok (I guess) for a minute or so, and my wife said she thought it smelled a little 'funny'. Very definitely heat was coming into the dryer. Opened the door, turning it off, a couple of times, and then discovered that heat no longer is produced and comes into the dryer - only unheated air. Did some reading, discoveredm my error, and then disconnected from a screw in the cabinet, the wire that came from the above control panel, and then connected it to the 'neutral' connection (where the white wire from dryer plug is connected. Still no heat at all. What happened?
Note: this is about a 10 year old kenmore and switched it from 3-wire to a 4-wire connector (installing in a mobile home).
Would miswiring it as I explained, damage some component? If so, any ideas at all? Anyone else ever done this? If so, what did you find was damaged?
I'm quite puzzled and have found very little info about this particular info...
Thanks for any input.
- richbrich