3 prong dryers on a sub-panel

[akronman]

I'm a darn good electrician, but not perfect. I have 2 electric dryers, 3 prong cords, wired into a 100Amp SUBPANEL. The subpanel is properly wired with all grounds isolated from all neutrals until they get back to the main box. I also have all dryers and washers simply cabinet grounded to pipes, outlet conduit boxes, etc. As I wire in my 3rd 3prong dryer, it just occured to me, three minutes ago, that the dryer's internal terminal block, with ground attached to neutral, breaks that rule entirely. I have never had electric problems with any dryer, nor any electric problems in the house at all. Do I need to detach the ground from the neutral in the dryer terminal block/box and instead ground that dryer green/ground wire directly to the overall metal outlet box, properly grounded on the wall, via the conduit pipes, thereby separating it from the neutral until it's back to the main box?

 

My strong guess is yes, and it will take 5 minutes per dryer, and I would NOT have to do this with if these dryers were from the main box instead of a subpanel. I'll use the gas ones until someone answers, and thanks in advance.

 

[neptunebob]

I don't know if I can answer the specific question you have, but you could peace of mind if you switch to the 4 prong cords and outlets, but I know, that is a bit more work.

 

[kenmore71]

It's probably a good idea to do if you're not going to switch to 4 wire cords and wiring.

That said, I can't see how it would pose any real safety hazzard. I've always been a bit fuzzy on the whole bonded neutral issue in general.

Also, I bet there are tens of thousands of electric dryers operating in this country under the exact conditions you are describing.

 

[limitededition]

4 prong plug

I am no electrician but in all of the installations that I have seen I do not believe that you can use the conduit as any of the conducters this is why in 4 prong installations the cable is BLACK & RED AS HOT WIRES THE WHITE AS NEUTRAL AND THEGREEN AS GROUND, and I believe as to current electrical code the conduit may not be used a a conducter it is not like a cold water copper pipe that is soldered for continuity depending to the type of conduit soft or rigid the connector are either screwed or mechanically connected which could allow corrosion, remember current always seeks the easiest path to ground and conduit with one or more high resistance connections could make you the easiest path

Rick

 

[akronman]

grounding correction

I wasn't clear earlier---all of these conduit-outlet installations include a 10ga bare copper conducter from the isolated ground bar of the subpanel, running inside the conduit,  to the final wall mounted metal outlet box, very securely screwed in to the box as I attach it to the wall. On 2 so far, I even left the uncut spare 6 or so inches run out a small hole in the metal box and attach the dryer cabinet ground directly there. So the continuity and security of the ground is not a concern. My question goes back to the terminal block inside the dryer, I believe I need to separate the ground there from the neutral lug, and connect directly to the above described ground.

Again, thanks--sorry I wasn't clearer earlier--

Mark

 

 

 

[kenmore71]

Here is what the 2011 NEC has to say about the issue of combining neutrals and grounds:

250.142 Use of Grounded Circuit Conductor for Grounding Equipment.

(A) Supply-Side Equipment. A grounded circuit conductor shall be permitted to ground non–current-carrying metal parts of equipment, raceways, and other enclosures at any of the following locations:
(1) On the supply side or within the enclosure of the ac service-disconnecting means
(2) On the supply side or within the enclosure of the main disconnecting means for separate buildings as provided in 250.32(B)
(3) On the supply side or within the enclosure of the main disconnecting means or overcurrent devices of a separately derived system where permitted by 250.30(A)(1)

(B) Load-Side Equipment. Except as permitted in 250.30(A)(1) and 250.32(B), a grounded circuit conductor shall not be used for grounding non–current-carrying metal parts of equipment on the load side of the service disconnecting means or on the load side of a separately derived system disconnecting means or the overcurrent devices for a separately derived system not having a main disconnecting means.

So, technically what you are proposing is the "proper" and most safe way to do it.

 

[arbilab]

I have never seen a 4th/green wire on a dryer or for a dryer socket. But I've never lived anywhere newer than 1985. My understanding is like yours, that neutral/white/current ground and safety/green/non-current ground are not supposed to meet at the load end. But I and my 'understanding' are quite old.

 

[circlew]

Yes, you should disconnect the grounding strap from the neutral on the dryer. The best method to ground the dryers is by using a 4-wire cord and plug with the proper receptacle.

The 4-wire setup has been required for many years in mobile homes and circuits originating at a sub-panel. The high school I attended was the first time I ever saw 4-wire dryer and range receptacles. These circuits were, of course, fed from a sub-panel.

 

[akronman]

Thanks All

I'm glad I asked, dryers ground is now seperated from the neutral on all 3 machines, very securely independently grounded, I feel safe and "up to code."

 

[combo52]

Grounding Electric Dryers With Three Wire Cords

I would leave the neutral ground strap in place on the dryers terminal block, two good grounds are better than one. But in reality it wouldn't make any real difference,  but I would be concerned if I was relying on only a separate ground wire that it might become disconnected and present a real hazard. The good thing about the old way of just using a three wire cord that is neutral grounded is that if the ground connection ever fails the dryer won't even start so you will look for and correct the problem quickly. With the new four wire cords you have no idea if the machine is properly grounded as it will run just fine ungrounded, you just have to hope it is LOL.