3 prongs dryers

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Esthy said:
I am going to look deeper on Tuesday about. I opened the back plate and I saw the only the neutral and the two ungrounded (hots) connections. The grounding is missing (no green and no green connected to the neutral) and this installation generates at the basement sub-panel.

In existing 3 "prongs" residential, I jump the grounding to the neutral IF the installation is to the main, but if that goes to the sub, them I add the 4 (grounding) wire and go for the 4 prongs. It is the first time I am looking a high-rise building (18 stories) and I am confused.
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Like I said earlier, check with a ohmmeter, some of the newer dryers out there are not quite so obvious that the bonding jumper is in place, I like the old strap better that was only a couple inches long and went directly from the neutral terminal to the frame. Many newer ones have a green wire that is not easy to trace where it ends up but if you check with an ohmmeter it is connected somehow to the neutral terminal, and is usually shipped connected to the green screw where you are to land the EGC if you have a 4 wire cord. If you don't remove this green wire and insulate it you end up making a neutral to ground bond when you plug that dryer in, and defeating the whole purpose of running them separately.
 
iwire said:
With or without the insulated neutral the frame of the dryer or range would be at a difference of potential in refrance to grounded objects due to voltage drop on the feeder(s) to sub panels.

By requiring the circuit to come directly from the service panel lessens this problem.
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And even if it originated from the main panel the dryer motor would still cause voltage drop creating a difference in potential to anything else grounded like the washer. If the NEC truly found this to be an issue they would never have allowed for the neutral to be used as a ground in the first place. You cheat the isolation rule regardless of origin. The rise in potential on an average feeder to a sub panel would be less than a few volts at most. A long run in 10/3 without ground carrying 6 amps on the neut would probably cause more voltage drop just by itself. CMP took so long to change 3 to 4 wire because old habits are difficult to change.

The rule for SEU was made because you can easily bridge the neutral bar and can with the bare concentric neutral in a sub. You could connect it to the ground bar but then the ground system would be carrying current, a big no no.

I know thousands of condos/apartments built before 1996 with sub panels feeding ranges and dryers with non grounding NEMA plugs. All of the inspectors have said as long as the neut is insulated its ok.







Esthy said:
I am going to look deeper on Tuesday about. I opened the back plate and I saw the only the neutral and the two ungrounded (hots) connections. The grounding is missing (no green and no green connected to the neutral) and this installation generates at the basement sub-panel.

In existing 3 "prongs" residential, I jump the grounding to the neutral IF the installation is to the main, but if that goes to the sub, them I add the 4 (grounding) wire and go for the 4 prongs. It is the first time I am looking a high-rise building (18 stories) and I am confused.
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If the box only has 3 wires you dont add a 4 slot outlet and jump the ground over. You add a 3 slot like before. As long as the neutral is insulated it doesn't matter where it comes from. Iwire is incorrect on his interpretation of the code IMO. Excluding mobile homes I have never seen a pre 1996 home or business get a 4 wire home run because of a sub panel.
 
mbrooke said:
I know thousands of condos/apartments built before 1996 with sub panels feeding ranges and dryers with non grounding NEMA plugs. All of the inspectors have said as long as the neut is insulated its ok.
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Same experience for the most part here. But don't know for certain if it was NEC compliant or not, as dwelling inspections just were not happening until about then in this area. So there was nobody rejecting such installations if it were wrong.
 
The oldest code book I own is the 1990 NEC here is the wording from the section at the time.

I will do my best to copy it perfectly.

250-60 Frames of Ranges and Clothes Dryers

(c) 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.
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In my opinion it is very clear that they list two allowed wiring methods but either one used must originate from the service panel.
 
To me the 1990 code wording is even more emphatic through its use of a semicolon.
This separates the first part (insulated) from the entire second part.
The lack of any commas at all in the second part is non standard, but I see the AND of the three remaining items as being the alternative to "insulated".

Tapatalk!
 
although it puts me to changing horses midstream, I would have to that I see the wording as (a) insulated OR (b) SE cable originating in the service panel.
Thankfully, it's a mute point for today's install.
 
iwire said:
OK, can you explain to me why reading that makes sense from an electrical safety standpoint? :)
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You know that is a pretty severe standard to apply to the language of the NEC.
But the earlier argument about the uninsulated neutral accidentally creating a ground to neutral bond if brought into a subpanel carries a lot of weight for me.

Tapatalk!
 
To which I counter that I do not see any particular reason why running an insulated neutral from a subpanel is any worse than running it from the main.
The additional voltage drop (and hence neutral ground offset) from the feeder wire length may not be any worse than the VD from running the SE all the way back to the main.

Tapatalk!
 
GoldDigger said:
The additional voltage drop (and hence neutral ground offset) from the feeder wire length may not be any worse than the VD from running the SE all the way back to the main.
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May not ... very likely could be.


I am willing to read it the other way if someone could explain why the concern of a difference of potential is greater when the conductors are buried in a wall or a box .... is greater than where a person actually comes into contact with the items?

It is my belief that goal is to keep the grounded conductor as close to ground potential as possible by mandating it go back to the bonding point.
 
iwire said:
OK, can you explain to me why reading that makes sense from an electrical safety standpoint? :)
Click to expand...

250-60 Frames of Ranges and Clothes Dryers

(c) 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.
Click to expand...

before trying to determine what it says you must forget anything that has ever changed in this section since 1990 or it can effect your interpretation.

As quoted, and putting myself back in 1990 mindset as best as I can, I see a "one or the other" situation and the service equipment commentary goes with the second option, not an "either this or that", plus another condition that applies to both.

I don't know what the intention was at the time but that is how I read what was quoted.
 
To me it is clear. If the neutral is insulated it could have been run from a subpanel prior to 1996. There are millions done like this and as I recall this was the way virtually AHJ's saw it in my experience.
 
iwire said:
May not ... very likely could be.


I am willing to read it the other way if someone could explain why the concern of a difference of potential is greater when the conductors are buried in a wall or a box .... is greater than where a person actually comes into contact with the items?

It is my belief that goal is to keep the grounded conductor as close to ground potential as possible by mandating it go back to the bonding point.
Click to expand...

That, IMO, is why they required the neutral to be insulated if ran from a sub panel. It would be very easy for the uninsulated neutral in SE cable to contact the metal can or even the ground bar, depending on how it was routed in the sub.

It would not matter in the main panel as it's already bonded.

If you think about it, there would have been no need in even mentioning the SE cable if all 3-wire runs had to originate in the main panel. They could have just said that any wiring method that uses the grounded (neutral) conductor as also the ground, would have to originate from the main panel.
That is why the stipulation of having to originate from the main panel was put in. It's only for the uninsulated neutral in the SE cable.
 
Little Bill said:
That, IMO, is why they required the neutral to be insulated if ran from a sub panel. It would be very easy for the uninsulated neutral in SE cable to contact the metal can or even the ground bar, depending on how it was routed in the sub.

It would not matter in the main panel as it's already bonded.

If you think about it, there would have been no need in even mentioning the SE cable if all 3-wire runs had to originate in the main panel. They could have just said that any wiring method that uses the grounded (neutral) conductor as also the ground, would have to originate from the main panel.
That is why the stipulation of having to originate from the main panel was put in. It's only for the uninsulated neutral in the SE cable.
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The neutral was required to be insulated whether it was from a sub panel or not. They just allowed SE cable with a bare grounded conductor to be be one exception - but only if run to a service panel.
 
kwired said:
The neutral was required to be insulated whether it was from a sub panel or not. They just allowed SE cable with a bare grounded conductor to be be one exception - but only if run to a service panel.
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That was my point, the only reason they added the part about coming from the main or service panel was for the SE cable. If the exception for the SE cable wasn't there they wouldn't have mentioned having to originate at the service panel.
 
iwire said:
May not ... very likely could be.


I am willing to read it the other way if someone could explain why the concern of a difference of potential is greater when the conductors are buried in a wall or a box .... is greater than where a person actually comes into contact with the items?

It is my belief that goal is to keep the grounded conductor as close to ground potential as possible by mandating it go back to the bonding point.
Click to expand...
Are you willing to read what is a actually written no matter what it is that makes a better install?
 
iwire said:
The oldest code book I own is the 1990 NEC here is the wording from the section at the time.

I will do my best to copy it perfectly.



In my opinion it is very clear that they list two allowed wiring methods but either one used must originate from the service panel.
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The semi colon IMO splits it into 2 separate parts. Id guess 2 parts exists since the only time the NEC allows for a bare current carrying conductor is SEU cable, however SEU can break neutral to ground isolation in a sub hence for disallowing it. An insulated wouldn't matter in that stance.







iwire said:
OK, can you explain to me why reading that makes sense from an electrical safety standpoint? :)
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The truth is nothing makes sense with the whole article in terms of safety. Using the neutral as a ground is a poor idea no matter its origin. Its the boot leg equivalent of grounding a major split phase appliance. Canada if Im not mistaken never had this problem, they have always required 4 wires.







GoldDigger said:
To which I counter that I do not see any particular reason why running an insulated neutral from a subpanel is any worse than running it from the main.
The additional voltage drop (and hence neutral ground offset) from the feeder wire length may not be any worse than the VD from running the SE all the way back to the main.

Tapatalk!
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Id agree with that. If it couldn't reach a local sub panel near by the builder would just run it to the main.






mjf said:
It's such a shame that one needs to be an English major with a law degree to decipher parts of the code.
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I agree with you on that:(






iwire said:
May not ... very likely could be.


I am willing to read it the other way if someone could explain why the concern of a difference of potential is greater when the conductors are buried in a wall or a box .... is greater than where a person actually comes into contact with the items?

It is my belief that goal is to keep the grounded conductor as close to ground potential as possible by mandating it go back to the bonding point.
Click to expand...


The code doesn't state anywhere the neutral must be kept as close to ground potential as possible. However, when its also doing duty as a ground, from a safety standpoint it is a better choice.

But, the voltage rise from a sub panel might actually end up being less in most scenarios (most but not all). Think of condo with a second floor subpanel and laundry or a restaurant with a sub-panel in the kitchen and a main else where. Option one is just run the load from the sub panel fed via say a #2 AL for the sub in the condo or a 3/0cu for the restaurant. The sub is 20 feet away. The main is 150ft away. The other option is run 10/3 200 ft to the main. A single #10 carrying 6 amps 180 to 200 feet will have more voltage drop than say #10 only traveling 20 feet then going to a #2AL or 3/0cu. The #2 AL will of course also be carrying imbalance from 120 volt loads, but unless we are talking over 60 amps worth over the typical 10 or 15, the voltage rise will actually be less when compared to ground. In this case relative to the washer. (Think of sub panels being used to limit voltage drop) So in theory if one took a voltage meter to a fully isolated (not in contact with anything grounded) running dryer the frame would read a higher voltage to the washer with the 200ft run back to the main as appose to the dryer being fed via sub panel. This problem could be theoretically verified via voltage drop calculations.

In both cases we are talking only about a few volts potential on the dryer frame at most. The real driver however for the codes reason from 3 wire to 4 wire comes from energized frames stemming from compromised neutral connections. An open connection can easily put 120 volts on the frame of the dryer. Not fun when transferring laundry between a grounded washer with damp hands and the dryer's drum light is making its frame perky:eek::eek:
 
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