Wiring new electric range

[Roly]

The white wire is just under another screw on the box. The OP said it attached to the old range. It was just another chassis ground. Probably a good idea with a 30YO appliance but I'd be concerned that a modern appliance may do something extraordinary with the chassis.

I'd wire the new up exactly like the old one, just skip the extra white wire they have used for a ground. Just unscrew it and set it aside.

 Your correct . I missed that the wire was connected to the old range.   Roly

[Mr_Mike]

Other than removing the odd white wire used to bond the old stove, why do anything else?

Assuming your new cord matches the old receptacle, do nothing. You stove is apparently already set up with the chassis ground connected to neutral as is required for three wire. (but double check that) Nothing particularly wrong with the existing receptacle.

Given this circuit is on a main panel and not a sub-panel, it is a valid configuration on old work. The ground wire on the circuit is redundant, but hurts nothing.

[TDKPE]

A 50A 4-wire, 3-pole surface receptacle is only $13 at the BORG. http://www.homedepot.com/p/Leviton-50-Am.../202077645

The existing is an ungrounded receptacle, but connected to an equipment grounding conductor that it wasn't designed to utilize. It's only a backing plate, and 'grounding' it has no real utility. Using it as a junction block for an equipment ground, though, is definitely not copacetic.

Use one protocol or the other (3-wire vs 4-wire), but not both.

Edit: Leaving that equipment ground from the panel to the backing plate of the existing receptacle isn't hurting anything, so if staying with the existing 3-wire setup, I would just leave it there. And lose that white 'ground wire' to the stove. Just to clarify.

[Roly]

"not copacetic.  "

 I hadn't heard that term in quite a while.     Agree on just changing the receptacle but the old way works too.   Roly

[ez-duzit]

OP--you didn't bother to post a photo of the new stove's plug but, assuming it is a Nema 6-50, just change out the old receptacle.

[Phil Thien]

He already wired the stove/range with a cord set w/ a 10-50, he indicated as such in the OP.

So if he changes the receptacle, he needs to change the cord set, too.

Meh, I'd leave it.

It is compliant, new stoves get installed on 10-50 receptacles all the time.

[Phil S.]

Thanks for all the feedback, guys.  So it sounds like I can simply remove the extra wire, checking to be sure there is contact between the neutral and the stove frame (green screw).  I was not familiar with the idea of grounding via the neutral connection.  Looks like whoever wired up the old stove wasn't either.  How does that work? Why does that work on a 240v system, but not on a 120?  Is there a way to check the connection, say with a VOM meter, to be sure everything is copacetic, mainly safely grounded?  I'm still a bit nervous about this setup thinking there must be a reason why a 3 wire setup no longer meets code for new installations.

The plug I installed is a new one bought with the stove compatible with the existing 3 prong outlet.

[TDKPE]

I'm still a bit nervous about this setup thinking there must be a reason why a 3 wire setup no longer meets code for new installations.

It was changed in the '96 cycle because if you lose the neutral, the frame becomes energized.  There are both 120V and 240V circuits within the stove (lights are 120V, for instance, and sometimes heating elements can be), and a 120V circuit within the unit uses the neutral to hold one end to zero volts, just like all the other 120V loads in your house.  If that neutral loses continuity, there will be no current flow (and the light or clock won't work), but the frame (that's bonded to that disconnected neutral) will go to 120V to ground.  Also, it's possible that 120V portions will see a gross over- or under-voltage condition, which happens in your house if you lose the neutral out to the transformer (and which will usually bring a POCO repair crew out quick).

Dryers historically had 120V motors, lights, and controls, and a 240V heating element.  Same deal.

Also, as the neutral carries current, the voltage at the stove/dryer frame will be drawn away from zero volts (relative to ground) in proportion to the amount of current carried, and in proportion to the increased resistance of the neutral due to the poor connection.  The end game is zero continuity, and even the controls or a light bulb can bring the frame to 120V.

So to eliminate that potential hazard, especially the life safety part, the code was changed so that the frame is always grounded with an independent grounding conductor which carries no current under normal conditions, and therefore has experiences no voltage drop, and remains at zero volts to ground.  If you lose the branch circuit neutral, the stove will probably just not work, or some parts of it won't work.  But the frame won't go hot.

Separate grounding, independent of the neutral, is consistent with standard practice for everything else in your house.  But yes, you could bond the frame of a 120V load to the neutral, but again, if you lose the neutral, the frame goes to 120V.  So it's not done.

Sorry you asked?

[kencombs]

Another vote for a proper 4 wire recept and plug since you already have a 4 wire connection up to the recept. If the wire didn't include both a ground and neutral I'd say use the 3 wire cord but, The code was changed for a reason.

[Phil S.]

Well - I pulled the single wire, had continuity between the neutral post and the stove frame, buttoned everything up, plugged in the stove and threw the breaker.  No smoke, bad noises and my hair didn't stand on end when I touched the stove.  Clock and oven light worked as they should.  Filled up the tea kettle  and brewed some tea so I think I'm good to go.  I'll keep an eye on the clock and if it is out when I still have power to the house I'll pull the breaker and investigate.