single phase panel in a 3 phase system?

[wwhitney]

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

So any 4 wires MWBCs that happen to only be loaded L-N on 2 phases are now 4 CCCs? I think not.

Cheers, Wayne

 

[jap]

Not that I would but, what if I used 1 of the

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

In that scenario you've defined it's purpose and it would no longer be a spare.

JAP>

 

[jap]

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

No uncertainty is gone until you complete a potential circuit of some sort.

JAP>

 

[jap]

So any 4 wires MWBCs that happen to only be loaded L-N on 2 phases are now 4 CCCs? I think not.

Cheers, Wayne

I agree with you, but, there are no conductors that are not landed as to their intent.

Jap>

 

[jap]

Heck, some code violating ding dong might install a 1p 20a breaker in the load end panel and tie a #12 Thhn to the spare feeder conductor to turn on an indicator light back at the line side feeder panel for a proof positive indicator they had voltage on that particular buss bar at the load end panel.

Uh-oh,, our spare just became an actual current carrying conductor, and, that would make 4 wouldn't it?

Jap>

 

[wwhitney]

Heck, some code violating ding dong might install a 1p 20a breaker in the load end panel and tie a #12 Thhn to the spare feeder conductor to turn on an indicator light back at the line side feeder panel for a proof positive indicator they had voltage on that particular buss bar at the load end panel.

Uh-oh,, our spare just became an actual current carrying conductor, and, that would make 4 wouldn't it?

Yes, sure, for the case that the spare conductor starts off disconnected at both ends. That makes the counting of spare conductors as CCCs at least plausible.

But if the 4th conductor is energized at the supply end by the 3rd phase, they can't use it that way without rewiring the supply end. Once the 4th conductor is energized at the supply end in that way, the neutral now satisfies 310.15(B)(5)(a), so you only have 3 CCCs:

"A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted . . ."

Cheers, Wayne

 

[jap]

Yes, sure, for the case that the spare conductor starts off disconnected at both ends. That makes the counting of spare conductors as CCCs at least plausible.

But if the 4th conductor is energized at the supply end by the 3rd phase, they can't use it that way without rewiring the supply end. Once the 4th conductor is energized at the supply end in that way, the neutral now satisfies 310.15(B)(5)(a), so you only have 3 CCCs:

"A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted . . ."

Cheers, Wayne

Why do we keep falling back to talking about the Neutral conductor?

The de-rating is applied based on the number of CCC's. in the conduit regardless of what the neutral gets counted as.

Jap>

 

[wwhitney]

Why do we keep falling back to talking about the Neutral conductor?

Because, on a 3 phase system L1, L2, L3, N, if the conduit has:

(a) L1, L2, N, and spare, then N gets counted as a CCC. That was Jim's point in post #4. Now it's 4 CCCs, as the spare gets counted as well.
(b) L1, L2, L3, and N, then N does not count. So it's 3 CCCs. Regardless of the load on L1, L2, or L3.

Cheers, Wayne

 

[Joethemechanic]

Can you reidentify it as a ground, and connect it to the ground bar at each end?

 

[jap]

But if the 4th conductor is energized at the supply end by the 3rd phase, they can't use it that way without rewiring the supply end. Once the 4th conductor is energized at the supply end in that way, the neutral now satisfies 310.15(B)(5)(a), so you only have 3 CCCs:

"A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted . . ."

Cheers, Wayne

And they can't use that same spare conductor to satisfy the rule without rewiring the load end.

A spare is a spare until it's landed.

Jap>

 

[wwhitney]

A spare is a spare until it's landed.

You can still call the L3 conductor that is capped off at the load end a spare, but its presence means the neutral no longer counts as a CCC. Which was implicit in my original post #5; maybe I haven't stated it explicitly until recently.

Cheers, Wayne

 

[jap]

Because, on a 3 phase system L1, L2, L3, N, if the conduit has:

(a) L1, L2, N, and spare, then N gets counted as a CCC. That was Jim's point in post #4. Now it's 4 CCCs, as the spare gets counted as well.
(b) L1, L2, L3, and N, then N does not count. So it's 3 CCCs. Regardless of the load on L1, L2, or L3.

Cheers, Wayne

Most all of us are aware of all that already.

Point is "All" the conductors are affected by deration depending on the number of CCC's in the conduit.

Not just the Neutral.

Jap>

 

[wwhitney]

Most all of us are aware of all that already.

So what are we arguing about? The only thing I said in post #5 was what was more explicitly stated in post #28.

Cheers, Wayne

 

[jap]

You can still call the L3 conductor that is capped off at the load end a spare, but its presence means the neutral no longer counts as a CCC. Which was implicit in my original post #5; maybe I haven't stated it explicitly until recently.

Cheers, Wayne

What?

We've changed the 3ph 4wire feed (in which the neutral was "not" originally counted as a CCC) to a 3wire 1ph Feeder in which the neutral "is" now counted as a CCC.

Jap>

 

[wwhitney]

We've changed the 3ph 4wire feed (in which the neutral was "not" originally counted as a CCC) to a 3wire 1ph Feeder in which the neutral "is" now counted as a CCC.

If the 4th conductor is capped at both ends, yes.

If the 4th conductor is still connected to L3 at the supply end, no. If L1, L2, and L3 are in the conduit with the neutral, the neutral is not a CCC, even if one or more of L1, L2, or L3 is capped off at the load end.

Cheers, Wayne

 

[jap]

If the 4th conductor is capped at both ends, yes.

If the 4th conductor is still connected to L3 at the supply end, no. If L1, L2, and L3 are in the conduit with the neutral, the neutral is not a CCC, even if one of L1, L2, or L3 is capped off at the load end.

Cheers, Wayne

I give up.

To me there is a difference between a conductor that is energized on one end that is capped of and serves no purpose on the other end, vs. a conductor that's terminated on both ends for a purpose but doesn't happen to have a load on it.

At least a conductor landed on both ends has the potential.

Jap>

 

[wwhitney]

I give up.

I suggest looking at it this way:

The supply end configuration of the wires determines the number of CCCs; the load end configuration is immaterial. When you have 4 conductors connected at the supply end as L1, L2, L3, and N (on a 3 phase wye system), then for all the possible ways to wire the load end, the worst case conductor heating with linear loads is what you get from 3 conductors carrying full current and 1 conductor carrying zero current. So it's 3 CCCs.

Cheers, Wayne

 

[jap]

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?

Jap>

 

[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?

See my previous post (#37).

How is a conductor capped off at the load end any different in terms of circuit analysis from a conductor that is landed on a breaker that is off, or is landed on a bus with no other connections? It isn't.

Cheers, Wayne

 

[winnie]

We agree that in the system as used (single phase panel on a wye system) the neutral (and all 3 loaded wires) counts as a CCC.

We agree that if the same system were built using a three phase panel, the neutral would not count as a CCC and you would still have 3 CCC.

Because the 4th wire is present in the conduit, per a strict reading of the code, all 4 wires must count as CCCs, even though one of those wires carries absolutely _zero_ current, because _spare_ conductors count a CCCs.

I think @jap is saying that this will always be the case; doesn't matter if the 4th wire is capped off at both ends or connected at 1 end, it still counts and you have 4 CCCs.

I think @wwhitney is saying that if that 4th wire is energized, even if not connected at the load end, then the system counts as a 4 wire wye feeder and suddenly there are officially 3 CCCs.

Personally: I am going to call this 3 CCCs and if someone wants to fight me about it they should come to Western Mass and I'll buy them a beer.

I absolutely agree that by a strict reading of the code it counts as 4 CCCs. 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. If someone replaces the panel with a single L-L load and a single L-N load (truly 4 CCCs) then it is up to them to recalculate the ampacity of the feeder they are re-using.

-Jon