What is the purpose of the concentric neutral on SE cable?

[ericsarratt]

Why is it beneficial to have the neutral (concentric neutral) on SE cable wrapping around the other cables?

Safety feature?

Decreases electromagnetic interference?

 

[masterinbama]

My guess would be ease of manufacturing

 

[LarryFine]

I believe it is/was so a conductive object cutting the cable would contact the grounded conductor first.

 

[infinity]

Decreases electromagnetic interference?

No. It's likely the cheapest way to manufacture the cable.

 

[LarryFine]

No. It's likely the cheapest way to manufacture the cable.

Wouldn't a parallel round conductor like in SER be less labor-intensive than spiral-wrapping?

 

[infinity]

Wouldn't a parallel round conductor like in SER be less labor-intensive than spiral-wrapping?

I don't know, the bare concentric neutral does save money due to the lack of insulation.

 

[LarryFine]

I don't know, the bare concentric neutral does save money due to the lack of insulation.

Same with the bare round conductor in SER cable.

 

[ericsarratt]

I do realize that there is a PVC coating over the concentric neutral, but wouldn't it be safety to have three independent cables?

Doesn't the neutral carrying electricity and complete the circuit back to the utility.

 

[Little Bill]

I do realize that there is a PVC coating over the concentric neutral, but wouldn't it be safety to have three independent cables?

Doesn't the neutral carrying electricity and complete the circuit back to the utility.

You ever look at the utility's neutral?

 

[LarryFine]

I do realize that there is a PVC coating over the concentric neutral, but wouldn't it be safety to have three independent cables?

Doesn't the neutral carrying electricity and complete the circuit back to the utility.

It does, and touching it is no different from touching the meter base, etc.

 

[jaggedben]

I believe it is/was so a conductive object cutting the cable would contact the grounded conductor first.

I'm trying to understand why exactly that would help. Seems like a ground fault would not be detected in most cases and whatever is doing the cutting keeps on going. At which point why does it matter?

I guess it makes it much more likely that a conductive object cutting the cable causes a short, and therefore gets noticed before it shocks someone. As opposed to energizing the cutting object and creating a shock hazard if only partially cut through or punctured in a way that only hits the hot.

I suppose it also makes it less likely that the cutting object creates a completely open neutral.

 

[LarryFine]

I'm trying to understand why exactly that would help. Seems like a ground fault would not be detected in most cases and whatever is doing the cutting keeps on going. At which point why does it matter?

Same reason the grounding pin of a plug is longer: so it makes contact first, to trip the OCPD.

I guess it makes it much more likely that a conductive object cutting the cable causes a short, and therefore gets noticed before it shocks someone. As opposed to energizing the cutting object and creating a shock hazard if only partially cut through or punctured in a way that only hits the hot.

Yes, just like the EGC: so a line-to-enclosure fault mimics a line-to-neutral or -line fault.

I suppose it also makes it less likely that the cutting object creates a completely open neutral.

As Sheldon and Amy say on The Big Bang Theory: "A happy accident!"

 

[Sberry]

Its something to do with electromagnetic field stuff which is over my head mostly, keeps the conductors incl the fault path tightly bound together most of the way. Just like putting it in a pipe.

 

[jim dungar]

Its something to do with electromagnetic field stuff which is over my head mostly, keeps the conductors incl the fault path tightly bound together most of the way. Just like putting it in a pipe.

Pipes and race ways are not required to be magnetic, therefore their intended purpose is not to control EMF during faults.
Concentric neutrals are used as part of the cable shielding in MV and HV cables.

Its use in LV cables, like SEU, is most likely due to cable handling issues and the ability for the external covering to be thinner and smooth. Why else would we have such physical differences between SEU and SER?

 

[Sberry]

I didnt say they were magnetic. I probably worded that wrong but the closer those wires are the faster the fault. Cant get any closer than wrapping them.

 

[Sberry]

(B) With Circuit Conductors. By an equipment grounding conductor contained within the same raceway, cable, or otherwise run with the circuit conductors.
NEC HANDBOOK COMMENTARY;
One of the functions of an equipment grounding conductor is to provide a low-impedance ground-fault path between a ground fault and the electrical source. This path allows the overcurrent protective device to actuate, interrupting the current. To keep the impedance at a minimum, it is necessary to run the equipment grounding conductor within the same raceway or cable as the circuit conductor(s). This practice allows the magnetic field developed by the circuit conductor and the equipment grounding conductor to cancel, reducing their impedance.
Magnetic flux strength is inversely proportional to the square of the distance between the two conductors. By placing an equipment grounding conductor away from the conductor delivering the fault current, the magnetic flux cancellation decreases. This increases the impedance of the fault path and delays operation of the protective device.

 

[jim dungar]

I didnt say they were magnetic. I probably worded that wrong but the closer those wires are the faster the fault. Cant get any closer than wrapping them.

I do know about faults, but I am not sure what you mean about the "faster the fault". I assume you mean they will be cleared faster.

My point was if a concentric neutral is as desirable as you imply, why is SEU the only <1000V general use cable built this way?

The flat construction of SEU allows it to be installed more closely following the surface of a structure than a round cable.

 

[electrofelon]

The flat construction of SEU allows it to be installed more closely following the surface of a structure than a round cable.

Yeah, I think that's it. IMO, seu is the least aesthetically unappealing surface wiring method on a house due to its low profile. We SEU in new York!