2017 NEC 250.184(A)(1)

[VladChiefns830]

Hello I have a question:

Assume solidly grounded neutral system. Code is 2017 NEC 250.184(A)(1). Assume feeder to downstream equipment requires a neutral and a ground.

Exception number 1 states that bare conductor can be used for the neutral for direct-buried portions of feeders. But would this not create a bad situation if the equipment ground wire was bare - and the bare neutral and bare equipment ground wire were to accidentally make contact with each other in the trench?

Could this not impose some undesired current on the equipment grounding conductor and quite possibly - on a person touching the equipment?

Am I off base on this?

 

[dpc]

This only applies for systems over 1000 V. What voltage are you talking about?

 

[VladChiefns830]

Yes. Let's assume over 1000-volts. Code Article is 2017 NEC 250.184(A)(1).

Assume solidly grounded neutral system. Code is 2017 NEC 250.184(A)(1). Assume feeder to downstream equipment requires a neutral and a ground.

Exception number 1 states that bare conductor can be used for the neutral for direct-buried portions of feeders. But would this not create a bad situation if the equipment ground wire was bare - and the bare neutral and bare equipment ground wire were to accidentally make contact with each other in the trench?

Could this not impose some undesired current on the equipment grounding conductor and quite possibly - on a person touching the equipment?

Am I off base on this?

 

[dpc]

I'm guessing this exception was put there mainly for concentric neutral cable. The neutral is going to be grounded, at least at one end, and preferably both ends. It would not be common to have both a neutral and ground conductor at medium voltage. I've never seen that, that I can recall. But even if it happens, I'm still not seeing a safety issue. All metal equipment at each end has to be bonded.

Important to remember that the NEC is not a design guide. If you've got a specific application question, you'll get better answers than mine if you post more details.

Cheers,

Dave

 

[wroggent]

An uninsulated neutral would constitute a multigrounded neutral system - see 250.184(B)(7). If the rest of the system has not been design in this manner (for example, grounding the neutral all equipment locations), then the underground feeder neutral should instead be insulated to maintain a single point grounding system. If multigrounding is the goal however, I don't see why two separate conductors would be necessary in the underground portion as long as a single conductor is sized for both neutral and grounding conductor criteria since they both should be connected to a grounding electrode at your 'downstream equipment' anyway. You may however want a second conductor of the same size for redundancy. Note that 250.184(B)(1)(b) allows for a single point grounding system to be brought out from a multigrounded system - something you could do at your 'downstream equipment' and beyond.

 

[VladChiefns830]

Thank you everybody for helping me understand this code better. As stated, an uninsulated neutral would constitute a multigrounded neutral system, yet the NEC has this in the first section, as if it applies to all systems. I will bet that a change will be forthcoming. Thanks again.

 

[jghrist]

As stated, an uninsulated neutral would constitute a multigrounded neutral system, yet the NEC has this in the first section, as if it applies to all systems. I will bet that a change will be forthcoming.

250.184(B)(7)requires the neutral to be insulated for single-point grounded neutral systems.

 

[VladChiefns830]

Yes. Agree. So you see the issue with how 250.184 is structured.