Difference Between 3 wire and 4 wire Cables

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XylemMike

New member
Location
Auburn, New York
I have a label on a box containing a cord. The label says "10/3 21'." The cable has a black, white and green conductors.

The customer said they ordered a 3 wire cable for 3 phase. Which, I am assuming, has a 3 wires plus a ground.

Is this correct? Does the NEC define this?


Thanks,

Mike
 

iwire

Moderator
Staff member
Location
Massachusetts
What kind of cable?

NM (Romex) 12/3 will have bare, white, black and red.

On the other hand 12/3 rubber cord will only have green, white and black.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
What iwire said.

For most (all???) 'Building wire' type cable (NM, MC) the ground isn't counted when the cable is named, so 12-2 NM has 2 circuit conductors plus the egc.

For most (all???) 'flexible cord' type cables (SO, SOOW, etc) the ground _is_ counted when the cable is named, so 12-3 SOOW has 2 circuit conductors plus the egc.

-Jon
 

mwm1752

Senior Member
Location
Aspen, Colo
I have a label on a box containing a cord. The label says "10/3 21'." The cable has a black, white and green conductors.

The customer said they ordered a 3 wire cable for 3 phase. Which, I am assuming, has a 3 wires plus a ground.

Is this correct? Does the NEC define this?


Thanks,

Mike

a 3 phase motor cord (not used in concealed locations) would have 3 CCC & a ground usually -- branch circuits thay share a neutral fed by a cable gennerally have Bk,R.Bl.W,GR
 

GoldDigger

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Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
What iwire said.

For most (all???) 'Building wire' type cable (NM, MC) the ground isn't counted when the cable is named, so 12-2 NM has 2 circuit conductors plus the egc.

For most (all???) 'flexible cord' type cables (SO, SOOW, etc) the ground _is_ counted when the cable is named, so 12-3 SOOW has 2 circuit conductors plus the egc.

-Jon
Just to make it perfectly clear, the designation of NM on the box or reel, as well as on the jacket itself, often will read 12-2 w/g. The w/g indicates "with ground" which is additional to the normal CCCs counted in the 12-2 or 12-3 designation.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
a 3 phase motor cord (not used in concealed locations) would have 3 CCC & a ground usually -- branch circuits thay share a neutral fed by a cable gennerally have Bk,R.Bl.W,GR
Can you give us a part number for that cord? I have never seen a 3 conductor flexible cord that had a 4th conductor to be used as the EGC. In general if you need 3 circuit conductors and an EGC in a flexible cord, you buy a 4 conductor cord.
 

mwm1752

Senior Member
Location
Aspen, Colo
Can you give us a part number for that cord? I have never seen a 3 conductor flexible cord that had a 4th conductor to be used as the EGC. In general if you need 3 circuit conductors and an EGC in a flexible cord, you buy a 4 conductor cord.

Don, I did not note the colors of the 4 wire cord just that 3 were CCC with an equipment grd. most will color the white with blue marking. I personally would used a sharpie for the entire section of free conductor.
 

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
I have a label on a box containing a cord. The label says "10/3 21'." The cable has a black, white and green conductors.

The customer said they ordered a 3 wire cable for 3 phase. Which, I am assuming, has a 3 wires plus a ground.

Is this correct? Does the NEC define this?


Thanks,

Mike

A 10/3 "cord" is going to have a total of 3 conductors, a 10/4 "cord" is what you needed if you have a 3-phase application.
 

J.P.

Senior Member
Location
United States
In NM and MC the ground is not counted. Hence 12/2 has 3 wires in it.

In SO type cables 12/2 will only have 2 wires in it.

You have to watch that when ordering. Make sure you say the words with ground if you need one.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I think the convention is not universal.

some people automatically seem to assume there is a ground added so a 12/2 is really a 3 conductor cord.

I have ordered 12/3 SO cord and gotten 12/3 w/ground and ordered 12/2 and gotten 2 conductors and no ground.
 
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