single phase panel in a 3 phase system?

[acrwc10]

We have an existing building that if supplied by a 3 phase service. Someone put a single phase panel in, where there is a 3phase 4 wire feeder, 120/208. Is there any reason we cannot leave it the way it is, with one leg capped off?

 

[ActionDave]

You can leave it. In the back of my mind is a fuzzy memory of someone mentioning a code section that says you have to cap it off with something other than tape.

 

[Joethemechanic]

Personally I would disconnect the other end and just consider it a spare

 

[jim dungar]

In this case the neutral wire becomes a current carrying conductor.

 

[wwhitney]

In this case the neutral wire becomes a current carrying conductor.

Then if the 4th conductor is unconnected at both ends, it's a spare conductor, and the Note to Table 310.15(C)(1) says that spare conductors are counted as current carrying conductors. So that means you have 4 current carrying conductors and would need to apply a 80% adjustment factor.

Which could be a problem for the ampacity, although it in this case a problem easily side stepped by just energizing the conductor at the supply end with the third phase. An odd outcome of the way the rules are written.

Cheers, Wayne

 

[jap]

Then if the 4th conductor is unconnected at both ends, it's a spare conductor, and the Note to Table 310.15(C)(1) says that spare conductors are counted as current carrying conductors. So that means you have 4 current carrying conductors and would need to apply a 80% adjustment factor.

Which could be a problem for the ampacity, although it in this case a problem easily side stepped by just energizing the conductor at the supply end with the third phase. An odd outcome of the way the rules are written.

Cheers, Wayne

How does terminating the conductor at the supply end and capping off the load end versus not terminating the conductor at either end change the definition of a spare conductor?

JAP>

 

[wwhitney]

How does terminating the conductor at the supply end and capping off the load end versus not terminating the conductor at either end change the definition of a spare conductor?

If the conductor is energized by the third phase at the supply then (a) I would no longer call it spare, even if it has no load and (b) you definitely have a 4-wire 3 phase feeder, which is definitely only 3 CCCs (assuming no majority of non-linear loads).

Cheers, Wayne

 

[jap]

If the conductor is energized by the third phase at the supply then (a) I would no longer call it spare, even if it has no load and (b) you definitely have a 4-wire 3 phase feeder, which is definitely only 3 CCCs (assuming no majority of non-linear loads).

Cheers, Wayne

How would you have a 3ph 4 wire feeder if one of the phase conductors is capped off on the load end and not terminated ?

To me the definition of a feeder is defined by what it's terminated as, not what it could be terminated as.

JAP>

 

[acrwc10]

Then if the 4th conductor is unconnected at both ends, it's a spare conductor, and the Note to Table 310.15(C)(1) says that spare conductors are counted as current carrying conductors. So that means you have 4 current carrying conductors and would need to apply a 80% adjustment factor.

Which could be a problem for the ampacity, although it in this case a problem easily side stepped by just energizing the conductor at the supply end with the third phase. An odd outcome of the way the rules are written.

Cheers, Wayne

maybe I will have them phase it to green and make it a full size EGC.

 

[jap]

maybe I will have them phase it to green and make it a full size EGC.

Why?

JAP>

 

[winnie]

I agree with @wwhitney that this 'spare' conductor counts as a CCC because of the way the code is written.

However I'd be inclined to ignore the violation.

I guess that spare conductors count as CCC because they might be energized in the future. But in this case if that spare conductor gets used, the neutral wouldn't be a CCC. So you never have 4 actual CCCs.

Jon

 

[wwhitney]

How would you have a 3ph 4 wire feeder if one of the phase conductors is capped off on the load end and not terminated ?

You raise a good point. But all 310.12(E) cares about is whether the neutral can only carry the unbalanced current from the ungrounded conductor. By energizing the spare conductor with the 3rd phase, you ensure that is true, so the neutral doesn't count. Even if the formerly spare conductor has no load on it.

But in this case if that spare conductor gets used, the neutral wouldn't be a CCC. So you never have 4 actual CCCs.

Only if you energize the spare with the 3rd phase. You could in theory energize it with, say L1, and then you'd have 4 CCCs, maybe 2 circuits, one L1-N and one L1-L2. So it's not so crazy to count the spare. If you energize it now as L3, then there's no issue.

Cheers, Wayne

 

[acrwc10]

Why?

JAP>

I meant that jokingly. I would not make them change it because there is no scenario where there would be 4 CCCs

 

[jap]

You raise a good point. But all 310.12(E) cares about is whether the neutral can only carry the unbalanced current from the ungrounded conductor. By energizing the spare conductor with the 3rd phase, you ensure that is true, so the neutral doesn't count. Even if the formerly spare conductor has no load on it.
Cheers, Wayne

A conductor can't simply be energized on the line side and not landed on the load end to make any difference because it lacks the capability to complete any circuit whatsoever.

It would still be considered a spare conductor.

The spare conductor in this scenario is not being used, and, it is not landed as an EGC so it's counted as (1) CCC to begin with.

The only thing that would make a difference in this scenario would be if that (1) CCC added to however many existing CCC's there are in the conduit would exceed the count of (3) CCC's and make the de-rating factors to kick in.

Seeing as this seems to have been a 3ph 4w feeder to begin with ( which would be a total of (3) H's (1) Neut. (1) EGC in the conduit) I doubt seriously we'd be talking about de-rating even if it is now being used as a 1ph Feed.

Jap>

 

[wwhitney]

A conductor can't simply be energized on the line side and not landed on the load end to make any difference because it lacks the capability to complete any circuit whatsoever.

Disagree. By energizing it on the line side, you dictate its behavior if any load were applied to it. The fact that no load is applied to it is immaterial.

Cheers, Wayne

 

[jap]

Disagree. By energizing it on the line side, you dictate its behavior if any load were applied to it. The fact that no load is applied to it is immaterial.

Cheers, Wayne

But there's no possibility of a load being applied to it seeing as how it wouldn't be landed on the load end.

JAP>

 

[kwired]

Then if the 4th conductor is unconnected at both ends, it's a spare conductor, and the Note to Table 310.15(C)(1) says that spare conductors are counted as current carrying conductors. So that means you have 4 current carrying conductors and would need to apply a 80% adjustment factor.

Which could be a problem for the ampacity, although it in this case a problem easily side stepped by just energizing the conductor at the supply end with the third phase. An odd outcome of the way the rules are written.

Cheers, Wayne

But at same time if and when you ever put it to use it likely turns the neutral back to a non CCC for adjustment purposes. So that makes it 3CCC's in the raceway whether utilizing as single phase 3 wire or utilizing as three phase 4 wire. IMO if that is not what they intended they need to clarify more in the wording.

 

[jap]

That's why I feel the spare is counted as a (1) CCC to begin with.

Because it hasn't been assigned yet as to what it's purpose is.

You don't define a conductors purpose until you land it on both the line and load end.

Jap>

 

[wwhitney]

But there's no possibility of a load being applied to it seeing as how it wouldn't be landed on the load end.

You could extend the conductor to a new enclosure and use it.

How is that situation materially different than running a 4W MWBC, originally for 3 separate L-N loads on 3 different phases, and then capping off one phase conductor when the plan changes and you only have 2 L-N loads? The issues involved are the same.

Cheers, Wayne

 

[wwhitney]

But at same time if and when you ever put it to use it likely turns the neutral back to a non CCC for adjustment purposes.

Likely, yes; definite no. But by energizing it on the line side, the uncertainty is gone--if the conductor is used on the load side, there will be only 3 CCCs.

Cheers, Wayne