Old sub panel landing 3 wire 240V branch for dryer

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Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
Just curious, working on a house that the range and dryer each only had 3-wire cables landing in a subpanel. The subpanel was wired with 4 conductors (as a subpanel in same building should be). Where would you have landed say the bare ground of the 10/2 NM of the dryer, on neutral or ground bus?
The existing wireing of the range and dryer landed differently, one of them on the neutral, the other on the ground. Based on the wire it could have been that way for more than 30 years.
Could have landing the wire on one vs the other caused or contributed to the breaker of the dryer becoming fused to the bus of the A side of Single-Phase? (Cant separate the breaker from the bus.) Found similar fusing on the 100 Amp main breaker of the same phase in sub panel (set screw welded). Heat damage on the 100A wire all the way back to main panel on that same phase.
Fyi, Panel is being replaced as well as feed wire back to main panel, upgrading range and dryer to 4 wire as part of a planned kitchen rewire and upgrade.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
A 2-conductor cable could never have been used; you'd have needed either an SE cable or a 3-conductor with insulated neutral.

The neutral would have been the correct connection, as the neutral was permitted to do grounding, not the other way around.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
A 2-conductor cable could never have been used; you'd have needed either an SE cable or a 3-conductor with insulated neutral.

The neutral would have been the correct connection, as the neutral was permitted to do grounding, not the other way around.
(y)
Took the words right out of my fingers!;)
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
A 2-conductor cable could never have been used; you'd have needed either an SE cable or a 3-conductor with insulated neutral.

The neutral would have been the correct connection, as the neutral was permitted to do grounding, not the other way around.
I'm not sure where you got a 2 conductor cable from, a 10/2? Unless you miss interpreted my reference specifically regarding the landing of the bare conductors of the 2 appliances.
The existing wireing of the range and dryer landed differently, one of them on the neutral, the other on the ground.
I've seen 10/2 used many time for 240V appliances or equipment, use the white conductors as a current carrying one along with the black with the bare conductor for neutral/ground.

I was looking for thoughts as to whether inappropriate ground/neutral landing of a 3 wire (ie 10/2) of a 240V circuit would have a direct, or indirect yet causative, effect contributing to the catastrophic failure of the subpanel over time that carried thru to the main panel 100 amp feed breaker? Or would it be a curiosity but unrelated coincidence?
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
10/2 NM is considered '2 conductor plus ground' and has never been acceptable for loads requiring a neutral. Perfectly fine for a straight 240V load (2 hots plus ground).

SE cable is 3 conductors without a separate ground, and was previously acceptable for loads requiring a neutral. In this case the neutral served to bond the frame.

With modern cable this seems a silly distinction but '3 wire' installs are no longer permitted anyway.

Jon
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
10/2 NM is considered '2 conductor plus ground' and has never been acceptable for loads requiring a neutral. Perfectly fine for a straight 240V load (2 hots plus ground).

SE cable is 3 conductors without a separate ground, and was previously acceptable for loads requiring a neutral. In this case the neutral served to bond the frame.

With modern cable this seems a silly distinction but '3 wire' installs are no longer permitted anyway.

Jon
So what you say is almost every old dryer hookup has been in violation that I've seen, I know when I do new hookups I use a 4 wire receptacle but most old ones were wired with a 3 wire 30A receptacle. My understanding is a 4 wire was not a requirement before 1996, this house was constructed in late 60's and it appears based on wiring types used was last wiring changes would have been in the late 60's early 70's, well before the requirements. My main concern is whether landing the bare conductor on the ground bus rather than the neutral would have caused the problem.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
So what you say is almost every old dryer hookup has been in violation that I've seen, I know when I do new hookups I use a 4 wire receptacle but most old ones were wired with a 3 wire 30A receptacle. My understanding is a 4 wire was not a requirement before 1996, this house was constructed in late 60's and it appears based on wiring types used was last wiring changes would have been in the late 60's early 70's, well before the requirements. My main concern is whether landing the bare conductor on the ground bus rather than the neutral would have caused the problem.
No, it would not have caused a problem.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
So what you say is almost every old dryer hookup has been in violation that I've seen, I know when I do new hookups I use a 4 wire receptacle but most old ones were wired with a 3 wire 30A receptacle. My understanding is a 4 wire was not a requirement before 1996, this house was constructed in late 60's and it appears based on wiring types used was last wiring changes would have been in the late 60's early 70's, well before the requirements. My main concern is whether landing the bare conductor on the ground bus rather than the neutral would have caused the problem.
Electrically speaking, the feeder EGC should be capable of carrying the dryer's neutral current.

Legally and safety speaking, load current should never, ever be intentionally carried by an EGC.


As for the 3-wire major-appliance circuits, the neutral had to be either insulated or in an SE cable.

In either of those instances, the circuit was supposed to originate in the panel where the MBJ was.
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
Electrically speaking, the feeder EGC should be capable of carrying the dryer's neutral current.

Legally and safety speaking, load current should never, ever be intentionally carried by an EGC.


As for the 3-wire major-appliance circuits, the neutral had to be either insulated or in an SE cable.

In either of those instances, the circuit was supposed to originate in the panel where the MBJ was.
So it should never have been in a subpanel? Is that correct?
Now if a rewire and having a 4 wire branch feed for dryer and range can it land in a subpanel? Or would it still be required to be in main panel?
Can you give a code reference that states such if so, so that I can justify it with GC and homeowner? We are on 2017 NEC.
It seems a never ending battle with GC's over code requirements and "Can't you just" response from them.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
A three wire should never have been in a sub.
A four wire can originate from either but the neutral and EG can both land on the neutral bar at the SE. They must be separated in the sub as would any other circuit EGs and neutrals.
You need to be a bit more assertive. Have that code book in your truck. The first I can think of is 250.6.
 

packersparky

Senior Member
Location
Wisconsin
Occupation
Inspector
So it should never have been in a subpanel? Is that correct?
Now if a rewire and having a 4 wire branch feed for dryer and range can it land in a subpanel? Or would it still be required to be in main panel?
Can you give a code reference that states such if so, so that I can justify it with GC and homeowner? We are on 2017 NEC.
It seems a never ending battle with GC's over code requirements and "Can't you just" response from them.

250.140 Frames of Ranges and Clothes Dryers. 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 connected to the equipment grounding conductor in the manner specified by 250.134 or 250.138.

Exception: For existing branch-circuit installations only where an equipment grounding conductor is not present in the outlet or junction box, the 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 permitted to be connected 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.
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
A three wire should never have been in a sub.
A four wire can originate from either but the neutral and EG can both land on the neutral bar at the SE. They must be separated in the sub as would any other circuit EGs and neutrals.
You need to be a bit more assertive. Have that code book in your truck. The first I can think of is 250.6.
250.140 Frames of Ranges and Clothes Dryers. 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 connected to the equipment grounding conductor in the manner specified by 250.134 or 250.138.

Exception: For existing branch-circuit installations only where an equipment grounding conductor is not present in the outlet or junction box, the 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 permitted to be connected 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.

Thank you both, so to be clear, with my plan to rewire with a 4 wire, the dryer branch circuit can be legally landed in the subpanel. And when I find other dryers, regardless of when they were wired, if they are wire with 10/2 NM they were and are not "legal" no matter if it is terminated in a main panel or subpanel?
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Thank you both, so to be clear, with my plan to rewire with a 4 wire, the dryer branch circuit can be legally landed in the subpanel. And when I find other dryers, regardless of when they were wired, if they are wire with 10/2 NM they were and are not "legal" no matter if it is terminated in a main panel or subpanel?
They were not legal. Are they likely to cause a fire? I doubt it.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Thank you both, so to be clear, with my plan to rewire with a 4 wire, the dryer branch circuit can be legally landed in the subpanel. And when I find other dryers, regardless of when they were wired, if they are wire with 10/2 NM they were and are not "legal" no matter if it is terminated in a main panel or subpanel?
Correct and correct.

Mobile homes have always required 4-wire major-appliance circuits, by the way.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
Electrically speaking, the feeder EGC should be capable of carrying the dryer's neutral current.

Legally and safety speaking, load current should never, ever be intentionally carried by an EGC.


As for the 3-wire major-appliance circuits, the neutral had to be either insulated or in an SE cable.

In either of those instances, the circuit was supposed to originate in the panel where the MBJ was.
You could run from a subpanel if the grounded conductor was insulated. We've had this discussion before. Only the SE cable with uninsulated grounded conductor had to originate in the main panel.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
You could run from a subpanel if the grounded conductor was insulated. We've had this discussion before. Only the SE cable with uninsulated grounded conductor had to originate in the main panel.
Right, because of the bare conductor. My bad.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
You could run from a subpanel if the grounded conductor was insulated. We've had this discussion before. Only the SE cable with uninsulated grounded conductor had to originate in the main panel.

We've had this discussion before and IMHO there are reasonable conflicting interpretations.

I've always understood that a 3 wire circuit could never originate at a subpanel. However the interpretation depends on how you group the clauses of part 3 of the exception. Either it is (cable with insulated neutral or SE cable) and not from a subpanel [my understanding] or it is cable with insulated neutral or (SE cable and not from a subpanel)

In both cases, 10/2 NM with a bare EGC does not meet the requirement. Old school 10/3 with an insulated neutral but without an EGC would meet the requirement. SE cable with a bare neutral would meet the requirement.

Jon
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
We've had this discussion before and IMHO there are reasonable conflicting interpretations.

I've always understood that a 3 wire circuit could never originate at a subpanel. However the interpretation depends on how you group the clauses of part 3 of the exception. Either it is (cable with insulated neutral or SE cable) and not from a subpanel [my understanding] or it is cable with insulated neutral or (SE cable and not from a subpanel)

In both cases, 10/2 NM with a bare EGC does not meet the requirement. Old school 10/3 with an insulated neutral but without an EGC would meet the requirement. SE cable with a bare neutral would meet the requirement.

Jon
I wish I had the explanation that a CMP made on this but I can't find it. But the explanation was that the bare/uninsulated grounded conductor had to originate from the main service panel and not a subpanel because of the possibility of the bare conductor touching something conductive that shouldn't be used as current carrying, or inducing current where it shouldn't.
If you look at the exception in the code stated above, it's clear that a insulated grounded conductor can be run from a subpanel. Notice the "comma" after the word insulated, that distinguishes that part of the sentence from the rest. And the rest says "is uninsulated and ......and". No further "commas" separating the last part. So only the last part of the sentence is saying it has to originate from service equipment, not the first part.

(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.
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
I wish I had the explanation that a CMP made on this but I can't find it. But the explanation was that the bare/uninsulated grounded conductor had to originate from the main service panel and not a subpanel because of the possibility of the bare conductor touching something conductive that shouldn't be used as current carrying, or inducing current where it shouldn't.
If you look at the exception in the code stated above, it's clear that a insulated grounded conductor can be run from a subpanel. Notice the "comma" after the word insulated, that distinguishes that part of the sentence from the rest. And the rest says "is uninsulated and ......and". No further "commas" separating the last part. So only the last part of the sentence is saying it has to originate from service equipment, not the first part.
The explanation makes sense as to point of origin, but why type SE and not a 10/2 NM if both have an uninsulated ground?
 
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