ECN Forum
Posted By: Chester 3 wire dryer circuit question... - 04/25/04 01:49 AM
Hi all,

I am an electrical student, actually having finished my course work now. I have worked with my electrician family for hands on experience, yet there are still some things I come across that throw me off a little. Today, I added a 4 prong 240v dryer receptacle for a friend. This is a task I have done many times. In fact, this is something I seem to need to do more than anything else. Well, I took off the old 3 prong receptacle, and when I did I noticed the cable was a three wire cable. I tested them to ensure their function. Here were the wires: one black, which was a hot 120v; one white, also a hot 120v; and one bare copper wire, (non current-carrying, no voltage) which was being used as a neutral on the old receptacle. Now, it's clear that the house was wired previous to the 1996 code changes, which now require the four wire, four prong setup on dryer circuits consisting of two line, one neutral, and one bare grounding wire. Anyway, I wired the new four prong receptacle as follows: the white and black hots into their corresponding slots, and then I wired the bare copper wire into the neutral slot, considering that it (the neutral) is sometimes needed to carry unbalanced currents. I, of course, left the grounding slot of the receptable open. Was this correct? My textbook says that it is not required that new cable be installed if one runs into this situation, only that the electrician use a "harness" to tie the neutral somehow to the ground, which would then tie them together to the frame of the dryer. Should I make a tie/bond between the neutral and gounding slot, as technically there is not grounding protection on the dryer scheme as of right now. Of course, the dryer works just fine, but I want to do this according to "the book." Please help. I very much appreciate it.

[This message has been edited by Chester (edited 04-24-2004).]
Posted By: iwire Re: 3 wire dryer circuit question... - 04/25/04 02:09 AM
Welcome Chester and glad you are asking questions.

It sounds like you installed a 4 wire receptacle on the end of a 3 wire cable.

This is not good. [Linked Image]

If this is an existing building you should have put a 3 wire receptacle on the end of the three wire cable.

As it is now you have a grounding type receptacle with no grounding means.

I ask you to change this ASAP.

Bob
Posted By: Chester Re: 3 wire dryer circuit question... - 04/25/04 02:27 AM
Bob, are you saying then that I should have just kept the old 3 wire (with no grounding slot!) receptacle on there, and then simply changed out the dryer cord from modern four prong, to outdated 3 prong? Would I not simply be dropping down in safety level by doing this? As I said, the code gives my permission to do this, if I adequately tie the frame via ground to the nuetral slot of the receptacle. Are you getting what I am saying? Please tell me where I'm going wrong. I can paste my textbook instruction I am basing my statements on, if you would like. Thanks....
Posted By: iwire Re: 3 wire dryer circuit question... - 04/25/04 03:18 AM
Chester you have not raised the safety level at all as you sill have only three wires heading back to the panel.

If you want the safety level to increase run a four wire cable and install your new 4 wire outlet.

You have created a situation where the next person that comes along sees a 4 wire grounding type receptical and plugs in a dryer set up for that.

This new dryer will run great with no grounding.

Quote
250.140 Frames of Ranges and Clothes Dryers.
This section shall apply to existing branch-circuit installations only. New branch-circuit installations shall comply with 250.134 and 250.138. Frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be grounded in the manner specified by 250.134 or 250.138; or, except for mobile homes and recreational vehicles, shall be permitted to be grounded to the grounded circuit conductor if all the following conditions are met.

(1)The supply circuit is 120/240-volt, single-phase, 3-wire; or 208Y/120-volt derived from a 3-phase, 4-wire, wye-connected system.

(2)The grounded conductor is not smaller than 10 AWG copper or 8 AWG aluminum.

(3)The grounded conductor is insulated, or the grounded conductor is uninsulated and part of a Type SE service-entrance cable and the branch circuit originates at the service equipment.

(4)Grounding contacts of receptacles furnished as part of the equipment are bonded to the equipment.

Bob
Posted By: caselec Re: 3 wire dryer circuit question... - 04/25/04 03:30 AM
From your description of the cable it sounds like it is type NM cable. If that is the case this installation was never code compliant. The bare wire in type NM cable is not to be used as a grounded conductor. I agree with Bob that you haven’t made this installation any safer and have made the problem worse. The frame of the dryer is not grounded at all now. I recommend getting a qualified electrician to replace the cable and install the 4-wire receptacle.

Curt
Posted By: Chester Re: 3 wire dryer circuit question... - 04/25/04 04:09 AM
Thanks for the continued help here Bob. Please tell me if I am right - I have two choices at this point. 1) Put back on the 3 prong receptacle and swap out the current four-prong dryer cord to a 3 prong or 2) install a 4 wire cable with two hot, a nuetral, and a grounding conducter....correct? Thanks again Bob.
Posted By: pauluk Re: 3 wire dryer circuit question... - 04/25/04 08:46 AM
Welcome to ECN Chester.

The problem with the 3-wire set-up is that the current-carrying neutral is also used as the protective grounding conductor.

That means that in normal use, if there should be a break or bad connection on that neutral, then the frame of the dryer could become energized at 120V via the control circuits.

Swapping the 3-wire receptacle for a 4-wire one while leaving only a 3-wire feed doesn't really accomplish much. If you had linked the neutral wire to both the neutral and ground connections of the new 4-w receptacle (which I believe is against code anyway), then all you've done is make the system 4-wire from the receptacle to the dryer. A bad neutral on the feed would still result in the same situation as described above.

Leaving the grounding terminal open on the new receptacle means that there's no protective ground on the dryer at all now.
Posted By: Chester Re: 3 wire dryer circuit question... - 04/25/04 05:52 PM
Thanks Paul, I gotcha there. See, I have already inherited a bad situation here. The cable being used was inadequate, it was meant for a 120v circuit and not a 240v. There are three wires in it, a black, a white, and a bare copper. The guy who did the install was using the black (hot) as a 120v hot in the receptacle, the white (supposed the be the neutral in 120v circuit) as the other 120v hot, and he was using the bare GROUNDING conducter as the neutral! Incredible! I was a bit thrown off when I saw this, as I have done this job numerous times for folks, and never saw this terrible scheme being used. Well, this shows me it was bad to begin with, with the wrong type of cable being used to begin with. As I see it, I only have one choice here: to install a new proper four wire cable with the new standard four slot receptacle. This is the only choice I see. Am I correct? What do you guys think? Thanks for sticking with me here.

[This message has been edited by Chester (edited 04-25-2004).]

[This message has been edited by Chester (edited 04-25-2004).]
Posted By: Lostazhell Re: 3 wire dryer circuit question... - 04/25/04 06:12 PM
Chester..
Thats the way I'd do it... 10/3w/ground from the 30A 2pole at your panel, Make up your 4 wire recept with the proper connections & you should be in the green [Linked Image] A bare conductor in romex is not meant to be a current carrying conductor, therefore I'd certainly rerun this with the proper amount of conductors

Welcome to ECN btw [Linked Image]

-Randy
Posted By: Attic Rat Re: 3 wire dryer circuit question... - 04/25/04 06:21 PM
... Chester, I totally agree with all these guys..."Do it right..or don't do it at all".. I'd effect repairs ASAP!!
Russ
Posted By: Chester Re: 3 wire dryer circuit question... - 04/25/04 06:40 PM
Attic Rat, "do it right or don't do it at all" is the very reason I am here asking these questions. I would hope I have made this abundantly clear.

[This message has been edited by Chester (edited 04-25-2004).]
Posted By: Attic Rat Re: 3 wire dryer circuit question... - 04/26/04 02:49 AM
... Clear as driven snow,...I was just being redundant..No worries dude,.. [Linked Image] [Linked Image]
Posted By: Lostazhell Re: 3 wire dryer circuit question... - 04/27/04 11:41 PM
[Linked Image from safetycenter.navy.mil]

Might wanna check the contacts on that dryer outlet! [Linked Image]

-Randy
[Linked Image] [Linked Image] that is ugly one there . for some other peoples want to know why i did talk about that with air compressor [see my area about the air compressor hook up ]

that one reason why for " soft molded plugs" are curpits with connetions and they are common found in window a/c usage but diffrent plug arrangements but same result when they get hot.

merci, marc
Posted By: Chester Re: 3 wire dryer circuit question... - 04/28/04 02:00 AM
Hey guys,

Well, I am nearly finished with putting in the new Romex cable, the proper one for the job here - 10-3 with ground. Well, when I opened up the panel, I found a real mess there. I guess a guy who worked for the city utility department, or something like that, lived in the house previously. I assume he is the one who did the "rewiring." There I found grounding wires going into the neutral buses, and neutrals going into the grounding bus. They were mismatched all over the place! Plus, for the range and the heater unit, I found the same scheme as the previous one. He was using 10-2 on both, with the neutral acting as the other hot. I believe it is against the code to use white neutrals as hots, unless they have been properly remarked with black...anyway, it's a real mess, and I don't know if I wanna do all of these circuits myself. I worked very hard tonight....let me know what you think of all of this. BTW, if the neutral and the grounding bus in the panel are bonded together in the panel itself, (I believe they are) why can't neutrals go into the grounding bus, and vice versa?
Posted By: Attic Rat Re: 3 wire dryer circuit question... - 04/28/04 03:14 AM
... If the panel you're referring to is a "Service Disconnect" with a "Main Breaker",then all the grounds and neutrals will land on the same bar..if it's a "Sub-Panel" that is derived from another panel,the grounds and neutrals MUST be kept separate..so that any errant current flowing on the neutral does not contact equipment grounds,..(chassis,etc.) and pose a very hazardous condition..this is my understanding...The rest of the gang here can probably illustrate this clearer for you.. Guys,..any takers??
Russ
Posted By: pauluk Re: 3 wire dryer circuit question... - 04/28/04 09:09 AM
If you didn;t keep neutrals and equipment grounds separate in sub-panels, then you could end up with parallel paths for the neutral current via grounding conductors, including exposed conduit, raceways, etc.

Chester,
I don't want to confuse you too much by introducing irrelevant "foreign 'lectricity," but this is one topic where different parts of the world see things a different way.

Over here on the east side of the Big Pond, for example, we keep neutrals and grounds separate even in the main panel. The bond, if used at all, is made before the meter.
Posted By: Chester Re: 3 wire dryer circuit question... - 04/28/04 01:00 PM
OK....guys, I am referring to the main panel in the garage, which does have a main disconnect at the top of the panel. This large breaker turns off the whole house, plus this panel receives the service cables. I don't even think this small house has a sub-panel. Anyway, given this situation, I take it, it is okay if neutral wires are attached to the grounding bus, and grounding wires to the neutral buses? (Three buses total on this main panel.) This is how the electrician wired it when the house went up, so I assume it is fine. Please let me know. (My textbook does not detail all this bus stuff very much.)

Thanks,
Chester
Posted By: rizer Re: 3 wire dryer circuit question... - 04/28/04 10:25 PM
yes, that is corrrect you can put either one on the grn bar or the neutral bar provided the neutral bar has been "bonded" to the box. this is usually accomplished by a dissimilar looking screw which runs through the bar itself and into the back of the panel. as you said "busses" (bars) i am assuming that there are two neutral bars which are factory bonded together. at times this is not readily apparent as the sometimes run the jumper bar behind plastic and you can only see the connection between the two bars. hope this helps, this can only be done like this at the main service.

[This message has been edited by rizer (edited 04-28-2004).]
Posted By: triple Re: 3 wire dryer circuit question... - 04/29/04 08:32 PM
If the ground bar is an "add-on" that is screwed separately to the panel case, then you cannot have neutrals attached to it.
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