grounded conductor

[iwire]

he's using 3 phase 120/208 panel

Would you like me to post the handbook 3 phase example that was right beside the single phase example? :smile:

Either way the concept is the same, the shared neutral would have to be sized for the maximum possible imbalanced neutral current.

 

[steelersman]

Would you like me to post the handbook 3 phase example that was right beside the single phase example? :smile:

No that won't be necessary. I was just being technical, that's all. But if the 3 phase example was right next to the single phase one then why didn't you post it instead, since he's using 3 phase?

Either way the concept is the same, the shared neutral would have to be sized for the maximum possible imbalanced neutral current.

unbalanced

 

[Strahan]

Would you like me to post the handbook 3 phase example that was right beside the single phase example? :smile:

Either way the concept is the same, the shared neutral would have to be sized for the maximum possible imbalanced neutral current.

Yes you are exactly right and that is what I have been referencing it is in the basic electricity book by the man himself that I have been writing the formula for! I'm not sure if I'm missing something or not the neutral will certaintly need upsized I gave the formula for doing this what more is there. Another thing if the choice is given 6 circuits should be broken down to 2 ungrounded conductors per phase for balancing issue's.

 

[Strahan]

3 phase 120/208 panel

Thanks! By the way what do you think of a Giants Steelers super bowl?

 

[steelersman]

if the choice is given 6 circuits should be broken down to 2 ungrounded conductors per phase for balancing issue's.

yes if it's a single phase panel. But since it's a 3 phase panel then if 6 circuits then I would pull 2 grounded conductors. In the OP's case he has 5 circuits. So I would pull 2 grounded conductors and neither one needs upsizing.

 

[steelersman]

Thanks! By the way what do you think of a Giants Steelers super bowl?

Sure! I'd be happy with Steelers-anyteam superbowl. But I don't think the Giants will make it to the big game. Probably not the Steelers either unfortunately. Watch out for the Dolphins, Colts, or Ravens. The AFC really is a tossup this year. NFC lookout for the Panthers.

 

[Strahan]

Sure! I'd be happy with Steelers-anyteam superbowl. But I don't think the Giants will make it to the big game. Probably not the Steelers either unfortunately.

I'm with you but as last season proves anything can happen keep hoping! As for the topic I don't follow you I was refering to a 3 phase system 2 ungrounde conductors per phase one neutral. I have not ran the numbers so I don't know if this is the best possible way. I just went over this last night at work so I'm curious maybe I'm missing something?

 

[quogueelectric]

sure you could use circuit 1 and 7 without upsizing the neutral, 1 and 7 would be on seperate legs, you just couldn't use a handle tie or a 2 pole breaker. But keep in mind he's on a 3 phase panel not a single phase.

That is why I used 1 and 7 They are both a phase and the current is additive so you would need a 40 a neutral.

 

[steelersman]

That is why I used 1 and 7 They are both a phase and the current is additive so you would need a 40 a neutral.

I thought you were referring to a single phase panel. Then 1 and 7 would be seperate legs and then you wouldn't need to upsize the neutral.

 

[Strahan]

Good luck but is anyone going to answer this guys question? Iwire I believe this is a 3phase panel maybe same calcs but show him how you did it ok its not a show me how site.

 

[don_resqcapt19]

Yes you are exactly right and that is what I have been referencing it is in the basic electricity book by the man himself that I have been writing the formula for! I'm not sure if I'm missing something or not the neutral will certaintly need upsized I gave the formula for doing this what more is there. Another thing if the choice is given 6 circuits should be broken down to 2 ungrounded conductors per phase for balancing issue's.

The formula has nothing to do with the size of the grounded conductor when it is used with more than one ungrounded conductor of the same phase. The size of the grounded conductor must be equal to the sum of the OCPDs for all of the ungrounded conductors that are on the same phase.

 

[eager2learn]

so when i do the calculation and get the total amperage per phase per ungrounded conductors on that same phase - i take that total and size accordingly for the grounded conductor for all phases and circuits to be shared

 

[Dennis Alwon]

so when i do the calculation and get the total amperage per phase per ungrounded conductors on that same phase - i take that total and size accordingly for the grounded conductor for all phases and circuits to be shared

No calculation. You would use the breaker size. Thus if you had 2-20 amp breakers on the same phase then the grounded conductor must be 40 amps. If you had 2- 15 amp conductors on 2- 15 amp breakers on the same phase then you would need a 30 amp grounded conductor.

 

[eager2learn]

where can this be found in the codebook ?

 

[Strahan]

The formula has nothing to do with the size of the grounded conductor when it is used with more than one ungrounded conductor of the same phase. The size of the grounded conductor must be equal to the sum of the OCPDs for all of the ungrounded conductors that are on the same phase.

I was under the assumption that the ungrounded conductors were not all on the same phase.

 

[eager2learn]

there not all on the same phase - i would say that there will be 2 on " A " phase, 2 on " B " phase and 1 on " C " phase

 

[hillbilly1]

as someone stated, you might need a transformer, (ie buck boost) to get past this voltage drop if this is such an issue. Thats the only less EXPENSIVE way I can see this working.

A buck/boost would work, but I'm not fond of doing this if there is more than one load connected to the circuit, if part of the load was turned off or quit working, you have a potential of too much voltage to the load as the voltage drop would be reduced increasing the available voltage at the end possibly exceding the loads rating if the boost is high enough.

 

[Strahan]

The formula has nothing to do with the size of the grounded conductor when it is used with more than one ungrounded conductor of the same phase. The size of the grounded conductor must be equal to the sum of the OCPDs for all of the ungrounded conductors that are on the same phase.

I agree if there is a grounded conductor per phase. If a MWBC is being used I don't think the same applies with a 4-wire 3phase system. Atleast from what I have read in this case you just can't add the OCPDs. Correct me if I'm wrong which it won't be the first and certainly not the last.

 

[don_resqcapt19]

where can this be found in the codebook ?

240.4 applies to all conductors, including the grounded conductor. The real issue is if the code permits the use of a common grounded conductor outside of the two specific permissions in Articles 215 and 225. It is my opinion that there is no code rule that prohibits the use of common grounded conductors for other applications, but the code making panel does not agree.

 

[don_resqcapt19]

I agree if there is a grounded conductor per phase. If a MWBC is being used I don't think the same applies with a 4-wire 3phase system. Atleast from what I have read in this case you just can't add the OCPDs. Correct me if I'm wrong which it won't be the first and certainly not the last.

If it is a multiwire branch circuit then the grounded conductor size is based on the largest device that protects any one of the phases as that is the maximum unbalanced current. Again no calculations are required to size this conductor.