no panel, grounded conductor

[russ]

Saw a panel today with no grounded conductor.
Three phase four wire 208 service, with three wire 200 amp "sub panel", no grounded conductor. Panel has only two pole breakers for air conditioning units. Just doesn't seem right. I fail to see where it is not allowed. Am I over looking something.

 

[iwire]

Re: no panel, grounded conductor

If you don't need it you don't have to run it.

 

[russ]

Re: no panel, grounded conductor

Hi Bob:

That's what I was thinking, but I asked just to check my self, thanks.

 

[hurk27]

Re: no panel, grounded conductor

Panel has only two pole breakers for air conditioning units

Russ This is a grounded "B" phase service not 208 but 240 volts. With the "B" phase as the grounded conductor it use to be allowed to just protect the ungrounded phases. This is why you only see two pole breakers. I'll bet you will read 240 volts from each ungrounded phase to ground?
I hope you weren't planing on using it for 120 volt loads?

 

[infinity]

Re: no panel, grounded conductor

Russ This is a grounded "B" phase service not 208 but 240 volts. With the "B" phase as the grounded conductor it use to be allowed to just protect the ungrounded phases. This is why you only see two pole breakers. I'll bet you will read 240 volts from each ungrounded phase to ground?
I hope you weren't planing on using it for 120 volt loads?

Why would you assume that it's a 3 wire Delta system when the original post mentioned a 208 volt wye system? For the B phase to be grounded it would have to be a 3 wire Delta system, not a 4 wire system as Russ mentioned in the original post.


Regarding the original post I would agree with Bob that since it's a subpanel, if you don't need the neutral at the subpanel than it's not required to be brought there.

[ August 03, 2005, 05:10 AM: Message edited by: infinity ]

 

[iwire]

Re: no panel, grounded conductor

Wayne I agree with Trevor, it sounds like the main panel has a 208Y/120 service. Including the required grounded conductor.

After that point the grounded conductor can be left behind if not needed.

 

[kevinware]

Re: no panel, grounded conductor

Ok, so what is the opinion of this form on the fault current path for this installation. Would you 100% depend on the conduit carrying the hot conductors as the low impedance path, or would you install an equipment grounding wire back to the 208Y/120 panel? Am I just being over cautious?

 

[wirenut1980]

Re: no panel, grounded conductor

kevinware, I believe in teh original post, there are 3 wires going to the "subpanel." I was envisioning those 3 wires to be 2 ungrounded conductors and an equipment grounding conductor, and no grounded conductor.

 

[kevinware]

Re: no panel, grounded conductor

Oooops!!!!!
I'm still working on my reading skills....

 

[charlie b]

Re: no panel, grounded conductor

Originally posted by wirenut1980: I was envisioning those 3 wires to be 2 ungrounded conductors and an equipment grounding conductor, and no grounded conductor.

I wasn't. The OP said there was a "three phase, four wire, 208 service." I read that as having A, B, C, and N, with the presumption that a ground bar existed in the main panel, and that the neutral and ground bars were bonded. Then when the subpanel feeder was described as "three wire," I read that as A, B, and C, with the presumption that the conduit would serve as the EGC.

So, Russ, which is it?

By the way, are the air conditioners rated for 208 volt operation? If not, then I think you were looking at a code violation.

 

[pattbaa]

Re: no panel, grounded conductor

2-pole C-B's protecting HVAC circuits implies the compressor-motors are sigle-phase ,split-phase motors.

Not the best design if 3-phase power is available.

 

[LarryFine]

Re: no panel, grounded conductor

Funny, I just ran this same scenario this week. From a single-phase 240/120 panel, I ran a #2 al. SE on a 100a. breaker to a sub-panel, with a 60a. breaker for the air handler w/10kw heat and a 30a. breaker for the AC compressor.

No neutral needed, none run, so I used the bonding screw to use the neutral bus as the EGC bus.

 

[augie47]

Re: no panel, grounded conductor

I ran a #2 al. SE on a 100a. breaker to a sub-panel,

this could lead back to the HVAC OCP thread, but I suspect you might raise the eyebrows on more than one inspector with a #2 AL on a 100 amp C/B

 

[LarryFine]

Re: no panel, grounded conductor

Originally posted by augie47:

I ran a #2 al. SE on a 100a. breaker to a sub-panel,

this could lead back to the HVAC OCP thread, but I suspect you might raise the eyebrows on more than one inspector with a #2 AL on a 100 amp C/B

This has always confused me. You can run a 100-amp service on a #2 al. feeder, so why not a sub-panel feeder?

 

[hurk27]

Re: no panel, grounded conductor

that's cuz table 310.16@75?al only allows 90 amps on #2Al.

table 310.15(B)(6) Is only allowed to be used for 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders.

From 310.15(B)(6) For application of this section, the main power feeder shall be the feeder(s) between the main disconnect and the lighting and appliance branch-circuit Panelboard(s).

So 3? is out.
Commercial is out.
garage feeds is out.
and sub panels is out.
They all have to use table 310.16@75?

Edited becuz I forgot to use spell check. :roll:

[ August 05, 2005, 12:35 AM: Message edited by: hurk27 ]

 

[magoo66]

Re: no panel, grounded conductor

And thats if all of your terminations are rated for 75C.

 

[russ]

Re: no panel, grounded conductor

Sorry I haven't gotten back to this, I figured the thread died.
The down stream panel was three phase 208 A,B,C just like Charlie said. Conduit ground with a redundant #4 ground wire. no grounded conductor was run to the breaker panel.
I just thought it was inviting trouble later on if someone tried to use the panel for 110 volt loads. As others have said it's legal.

[ August 05, 2005, 10:00 PM: Message edited by: russ ]

 

[grasfulls]

Re: no panel, grounded conductor

Hurk,
why would commercial be out? I have seen plenty of dedicated lighting panels, those do not count?
Gary

 

[hurk27]

Re: no panel, grounded conductor

By grasfulls:
Hurk,
why would commercial be out? I have seen plenty of dedicated lighting panels, those do not count?
Gary

Not in the application of 310.15(B)(6)

It is for dwelling's only!

As mentioned before: The diversities in the loading of a service for a dwelling is going to be much lower than for a commercial service where most circuits are installed "for a load" instead of "convenience" as in a dwelling. This is the very reason I'm making a proposal on the issue of derating for bundling in a dwelling, its not needed.

 

[George Stolz]

Re: no panel, grounded conductor

Originally posted by grasfulls:
Hurk,
why would commercial be out? I have seen plenty of dedicated lighting panels, those do not count?
Gary

See the title of the table, and read the section that refers to it.

If you fail to comply with a single variable mentioned, then you can't use that table.

So if you have a house that's somehow fed from two phases of a wye-configured transformer, you'd have a house supplied by a single phase, 120/208Y (derived from a 3?...), 3-wire system.

The table is for 120/240 services and feeders for dwelling units. So for this house, you can't use table 310.15(B)(6), it cannot be applied.

In your case, it's not for a dwelling unit, you can't use it.

As Wayne mentioned, houses have such load diversity that we can oversize the overcurrent protection for their conductors, since they probably won't endure a high load for very long.