single phase panel in a 3 phase system?

[wwhitney]

I tend to side with @jap that connecting a wire at the supply end only doesn't change this, but IMHO there is no realistic scenario where you get the heat production of 4 conductors.

Thanks for your response, you have a nice way of summarizing things clearly, although I don't agree with the above.

Connecting the 4th wire at the supply end ensures that there is nothing you can do at the load end to get the heat production of 4 conductors at full current (using linear loads), and therefore it becomes only 3 CCCs.

A conductor "capped at one end and energized at the other end" is more like a conductor that is "energized and landed on a bus with no loads connected to it" than it is like a conductor "capped at both ends".

Cheers, Wayne

 

[wwhitney]

What electrical magic happens by energizing a single spare conductor in a conduit that's not landed on the load end to make any difference as to whether or not de-rating should apply?

The same magic that happens whenever you have a conduit on a 3-phase wye system that contains all of L1, L2, L3, and N--any current from linear loads that could possibly occur on N would only be the unbalance of L1, L2, and L3.

Cheers, Wayne

 

[jap]

The same magic that happens whenever you have a conduit on a 3-phase wye system that contains all of L1, L2, L3, and N--any current from linear loads that could possibly occur on N would only be the unbalance of L1, L2, and L3.

Cheers, Wayne

That's a fact and not arguing that.

Where it get's cloudy for me is the assumption that the line side connection only determines the functionality of the feeder.

I say it takes the "line and load" connection to determine a circuit's functionality.

The "4th wire" to my knowledge is not a name given solely to the Neutral conductor.
The "4th" wire could be any one of the "4" phase conductors of a 3ph 4 wire system.

With that being said, if you connect all 4 wires at the line side feeder panel as you had suggested, but, only connect A,C and the Neutral conductor at the load end, leaving the 4th wire or B phase conductor disconnected at the load end, then, the Load end connection has now changed your 3ph 4wire Feeder configuration to a 1ph 3wire feeder.

JAP>

 

[wwhitney]

I say it takes the "line and load" connection to determine a circuit's functionality.

Certainly it takes a line and load connection to determine the actual current drawn. And the CCC rules consider the nature of the load as far as whether it's linear or not. But that's the only way I see them as considering the nature of the load. The cancellation is guaranteed as soon as you make the line side connections.

With that being said, if you connect all 4 wires at the line side feeder panel as you had suggested, but, only connect A,C and the Neutral conductor at the load end, leaving the 4th wire or B phase conductor disconnected at the load end, then, the Load end connection has now changed your 3ph 4wire Feeder configuration to a 1ph 3wire feeder.

I'm going to disagree, I see that as a 4W3P feeder with a 3W1P connected load. Entirely analogous to a 4W3P MWBC with loads only connected A-N and C-N.

Cheers, Wayne

 

[winnie]

Two 'pathalogical' situations to consider:

1) The single phase panel is replaced with a 3 phase panel. But loads are only connected on busses A and C. How is this different from the situation being discussed? How many CCCs?

2) The single phase panel is replaced with a 3 phase. Only linear, resistive loads are connected. Only L-N loads are connected on phase B. Only L-L loads are connected on phases A-C. Officially, how many CCCs are there?

IMHO we can play lots of what-if games. Realistically this feeder has 3 CCCs even if it is legally 4.

-Jon

 

[wwhitney]

2) The single phase panel is replaced with a 3 phase. Only linear, resistive loads are connected. Only L-N loads are connected on phase B. Only L-L loads are connected on phases A-C. Officially, how many CCCs are there?

Wow, I forgot about this scenario. Shouldn't 310.15(E) be amended to require the N to be counted as a CCC in the above scenario?

Cheers, Wayne

 

[jap]

I'm going to disagree, I see that as a 4W3P feeder with a 3W1P connected load. Entirely analogous to a 4W3P MWBC with loads only connected A-N and C-N.

Cheers, Wayne

I don't think we're that far apart.

I agree with this also.

Barring everything else, the only thing I don't agree with is that energizing an unused conductor on one end and it capped off on the other end,
somehower changes it from a spare conductor to "not a spare conductor".

Jap>

 

[wwhitney]

Ihe only thing I don't agree with is that energizing an unused conductor on one end and it capped off on the other end,
somehower changes it from a spare conductor to "not a spare conductor".

I don't think I ever claimed that it necessarily does. It counts as a CCC whether it is a spare conductor or not, so I'm agnostic on that.

All I claimed is that once you energize it you can consider it a circuit conductor for purposes of applying 310.15(E).

Cheers, Wayne

 

[jap]

I don't think I ever claimed that it necessarily does. It counts as a CCC whether it is a spare conductor or not, so I'm agnostic on that.

All I claimed is that once you energize it you can consider it a circuit conductor for purposes of applying 310.15(E).

Cheers, Wayne

So after all of this we're going to come full circle and agree on everything?

Sweet,,,,

Jap>

 

[wwhitney]

So after all of this we're going to come full circle and agree on everything?

So you agree that if the spare conductor is energized at the supply end by the 3rd phase but capped off at the load end, 310.15(E) says the neutral is not a CCC, so there's just 3 CCCs?

Cheers, Wayne

 

[jap]

So you agree that if the spare conductor is energized at the supply end by the 3rd phase but capped off at the load end, 310.15(E) says the neutral is not a CCC, so there's just 3 CCCs?

Cheers, Wayne

Let me rephrase.

I agree with everything but that.

JAP>

 

[wwhitney]

I agree with everything but that.

The question of what counts as a circuit conductor is open to interpretation, since the term "circuit conductor" is not defined in the NEC. The way it appears in the NEC implies it doesn't cover EGCs, GECs, bonding jumpers, and the like. And clearly it doesn't cover a spare conductor in a conduit if both ends are capped off. Likewise, if it's carrying actual current to a load, it's clearly a circuit conductor.

But in between those two extremes are middle ground cases like Winnie's example #1 in post 45. To me the obvious threshold is that the conductor is energized at the source. I see no difference between Winnie's example #1 and the case where the unloaded ungrounded conductor is capped off at the load end panelboard rather than landed on a bus. So I see the ungrounded conductor as a circuit conductor in both cases, and so 310.15(E) applies to both cases.

If you consider that when the ungrounded conductor is capped off rather than landed on a bus, it is not a circuit conductor, then 310.15(E) wouldn't apply. But I would say that's an unwise choice of where to draw the line between circuit conductors and non-circuit conductors. Because of the various examples I've given previously, like the analogous configuration with a 4W3P MWBC and loads connected only L1-N and L2-N. "Landed as to their intent" is not a notion that appears anywhere in the NEC.

Cheers, Wayne

 

[jap]

So you agree that if the spare conductor is energized at the supply end by the 3rd phase but capped off at the load end, 310.15(E) says the neutral is not a CCC, so there's just 3 CCCs?

Cheers, Wayne

I think our differences lie in our individual opinions of what the definition of a 3ph 4 wire circuit actually is.

I'm gathering your opinion is that a 3ph 4 wire circuit is still a 3ph 4 wire circuit even if one of the phases is capped off on the load end as long as that phase conductor is terminated and energized on the line side.

My opinion is that a 3ph 4w circuit or feeder is only truly a 3ph 4w circuit or feeder if installed complete with all the conductors of the circuit or feeder terminated at both line and load ends.

Energized or not, the unused capped off phase has nowhere to be landed on the load end, and, doesn't change the fact that even though it's available that the available power in that panel is still 1ph.

JAP>

 

[wwhitney]

My opinion is that a 3ph 4w circuit or feeder is only truly a 3ph 4w circuit or feeder if installed complete with all the conductors of the circuit or feeder terminated at both line and load ends.

OK, consider a 4W MWBC originating at a 208Y/120V panelboard, going to a junction box where the home run splits into a balanced set of 3 separate 2-wire legs to 3 different 120V receptacle outlets. 310.15(B) clearly applies, so the home run has just 3 CCCs.

Now you remove one receptacle, cap the conductors, and blank off the box. Under the above interpretation, now you only have a 1P3W circuit, plus a spare. So if that spare is not a circuit conductor, 310.15(B) says to count the neutral as a CCC, and with the spare you have 4 CCCs in the homerun and need to do an 80% ampacity adjustment.

That's an unappealing result, so I don't think that's the above is the wisest interpretation. The spare should still count as a circuit conductor for 310.15(B).

Cheers, Wayne

 

[jap]

OK, consider a 4W MWBC originating at a 208Y/120V panelboard, going to a junction box where the home run splits into a balanced set of 3 separate 2-wire legs to 3 different 120V receptacle outlets. 310.15(B) clearly applies, so the home run has just 3 CCCs.

Now you remove one receptacle, cap the conductors, and blank off the box. Under the above interpretation, now you only have a 1P3W circuit, plus a spare. So if that spare is not a circuit conductor, 310.15(B) says to count the neutral as a CCC, and with the spare you have 4 CCCs in the homerun and need to do an 80% ampacity adjustment.

That's an unappealing result, so I don't think that's the above is the wisest interpretation. The spare should still count as a circuit conductor for 310.15(B).

Cheers, Wayne

I don't think it's an unappealing result, I just think that's the way it is.

The circuit has in fact changed.

Although correct in theory, you now have 2 phase conductors, 1 neutral and 1 spare which has caused a potential inbalance that now by the rules needs to be counted as 4 CCC's.

Energizing the spare conductor that doesn't attached to anything doesn't change this.


Jap.

 

[jap]

I think Winnie summed it up the best.

IMHO we can play lots of what-if games. Realistically this feeder has 3 CCCs even if it is legally 4.

-Jon


Jap>

 

[wwhitney]

I don't think it's an unappealing result, I just think that's the way it is.

OK, I think we've hashed out the root of our disagreement.

I expect most people would find unreasonable an interpretation that blanking off a receptacle could mean there are more CCCs on the supply. So I'll stick with the interpretation that "energization" is the threshold to be a circuit conductor.

Cheers, Wayne

 

[jap]

OK, I think we've hashed out the root of our disagreement.

I expect most people would find unreasonable an interpretation that blanking off a receptacle could mean there are more CCCs on the supply. So I'll stick with the interpretation that "energization" is the threshold to be a circuit conductor.

Cheers, Wayne

So you're saying that dropping 1 phase doesn't change the circuitry? or That we all wish that it didn't?


JAP>

 

[wwhitney]

So you're saying that dropping 1 phase doesn't change the circuitry?

I'm saying that disconnecting a load doesn't increase the maximum heating possible in the supply conductors.

Cheers, Wayne

 

[jap]

I'm saying that disconnecting a load doesn't increase the maximum heating possible in the supply conductors.

Cheers, Wayne

I agree, so, maybe the rule for the spare conductor needs to be rethought.

Until then it is what it is.

JAP>