There is this high-rise residential building that was remodeled some time ago. I notice that the dryers, about 20 to 30, located in the utilities rooms of each floor, are with 3 prong, I opened one of then and notice that there is not a grounding jumper to the the neutral or if they are connected to sub panels or mains. I don't know exactly the building electrical configuration because it is the first time I have been in this type of facility as I worked only in residential service. Is this the norm on this type of building? The building was renovated in 1994 and is located in Seattle
3 prongs dryers
- Thread starter Esthy
- Start date
- Status
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
But the if the dryer requires a neutral, there would still have to be a ground to. neutral bond at the dryer, yes?
Tapatalk!
Tapatalk!
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
Unless these are 3? dryers, and if they require a neutral, you are suppose to bond the neutral to the dryer frame if there is only 3 wires run. They should be L-L-N.
kwired
Electron manager
- Location
- NE Nebraska
Look more carefully, many newer dryers don't have the removable link that the older ones had on the neutral terminal itself, you need to remove the green wire from under the green screw and insulate it when attaching a 4 wire cord, and of course land the green from the cord under the green screw.
Instructions on the dryer should indicate this, or you can verify continuity between neutral terminal and equipment case. Remove the green wire I mentioned above and you will lose continuity to the case if it is the design that I mentioned.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Can you use an ohmmeter to check for frame to neutral continuity with the cord unplugged?
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Tapatalk!
mjf
Senior Member
Did you open the receptacle or the back of the dryer?
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
The practice was allowed up until the 1996 NEC. Basically dryers and ranger were allowed to ground through the neutral. A "non grounding" type plug was used. NEMA 10-30 for dryers and NEMA 10-50 for ranges. These just had 2 hots and a neutral.
In your case if this was done prior to the 1996 NEC its ok. The thing to keep in mind these outlets were supposed to be fed via an insulated neutral. Exception was type SEU cable coming from a main panel only. I only bring this up because half the time I see 10-2 with bare ground feeding them or SEU but coming from a sub panel. Entire apartment complexes around here are like that:roll: I think the confusion came in that everyone thought these appliances were straight 240 and just assumed the 3rd pin to be a ground only.
If these are fed by conduit code wise it would be compliant to just toss a NEMA 14-30 and ground through the conduit.
- Location
- Massachusetts
But only if the feed came from the service disconect panel and this being a high rise that is very doubtful.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Or the neutral was insulated?
Tapatalk!
Tapatalk!
- Location
- Massachusetts
No, a three wire dryer or range feed was not allowed to originate in a subpanel at any time that I am awhere of.
Now that I give it more thought, I believe you are correct. In my earlier post I looked at a '93 McPartland Handbook I have and it failed to mention the circuit needed to originate from the service panel (it did reference 250.60 if anyone has a '93 Code).
Very astute of you, Bob.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
Bob may be astute, but he is not correct. We've had this discussion before and thought he finally got it. As the code is written, the part about originating from a sub panel is only for the uninsulated SE cable.
Notice the comma in red, everything before that comma is one part/item/phrase. Everything after that comma is the 2nd part/item/phrase. Also notice the two "ands".
So it is saying if uninsultated AND part of SE cable AND originates at the service equipment.
If they had meant all 3-wire connections had to originate from the service they would have used a second "comma" instead of the second "and".
If this was a typo, they would have caught and corrected it many code cycles ago.
- Location
- Massachusetts
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
Wrong again!
Let me add to what I said. Rather they should/would have added a comma then the "and".
I know the handbook isn't code, well the commentary part any way, but here is what it says and why.
Last edited:
- Location
- Massachusetts
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.
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.
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.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
Let's try this again.
This how it is written with a comma separating the two parts of the sentence.
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.
The first part being:
The grounded conductor is insulated,
The second part of the sentence which is everything after the comma.
Is:
or the grounded conductor is uninsulated and part of a Type SE service entrance cable and the branch circuit originates at the service equipment.
Now if it meant what you thought it meant it would be written this way with a comma added after "service entrance cable":
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.
There would be three parts to the sentence.
1st:
The grounded conductor is insulated,
2nd:
or the grounded conductor is uninsulated and part of a Type SE service entrance cable,
3rd:
and the branch circuit originates at the service equipment.
But since there is only one comma there can only be two parts to the sentence. The second part goes all together, which means they are describing how the uninsulated grounded conductor can only be used if it originates from the service equipment.
If it but had that one little extra comma, I would have to agree with you, but it doesn't!
I have changed out a few panels with sub panels with only a 3-wire feed to a stove. These had to be inspected and the inspector agreed that only the SE cable with uninsulated ground had to originate at the main panel.
- Occupation
- Licensed Electrician
I agree with Bill on this. Insulated neutral and SE cable are separate from each other .
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