Tap rules for parallel conductors

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mbrooke

mbrooke

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Can 240.21 (B) (1) be applied to parallel conductors? 600amp OCPD feeder from the main electrical room, 2 sets of 350 kcmil, 5 225 amp panels and two sets of 2 AWG taps into each 225 main breaker. Is this doable, or should 1,500 kcmil be used with a single set of 4/0s?



Also in terms of sizing the EGC, is 250.122 sufficient?
 
mbrooke said:
Can 240.21 (B) (1) be applied to parallel conductors? 600amp OCPD feeder from the main electrical room, 2 sets of 350 kcmil, 5 225 amp panels and two sets of 2 AWG taps into each 225 main breaker. Is this doable, or should 1,500 kcmil be used with a single set of 4/0s?



Also in terms of sizing the EGC, is 250.122 sufficient?
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Yes, you can tap parallel conductors...however, the tap should be connected to each of the parallel sets of 350 kcmil.
See 250.122(G) for the EGC sizing.
 
mbrooke said:
Each set- got it! :)





A bit of confusion on this one. Do I size based on the OCPD two #1 cu or do I split that in two #4?
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Sorry, I must not have been clear. The tap conductor should attach to both of the 350kcmil. Per 310.10(H), paralleled conductors should be electrically joined at both ends, and should be terminated in the same manner.
I don't believe that a #2 tapped separately from each of the 350kcmil meets that requirements.

Something like a 5 port polaris connector would be appropriate. (2) 350kcmil in, (2) 350 kcmil out, and (1) 4/0 AWG tap conductor to the panel.

I believe if you did have parallel sets of tap conductors, the EGC would be full size based on the upstream OCPD in each raceway.
 
david luchini said:
Sorry, I must not have been clear. The tap conductor should attach to both of the 350kcmil. Per 310.10(H), paralleled conductors should be electrically joined at both ends, and should be terminated in the same manner.
I don't believe that a #2 tapped separately from each of the 350kcmil meets that requirements.

Something like a 5 port polaris connector would be appropriate. (2) 350kcmil in, (2) 350 kcmil out, and (1) 4/0 AWG tap conductor to the panel.
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Let me look at that section. I never knew this.

When each set is tapped and the #2 connected to the 225 amp main in each panel, doesn't this qualify as electrically connected at both ends?
 
mbrooke said:
When each set is tapped and the #2 connected to the 225 amp main in each panel, doesn't this qualify as electrically connected at both ends?
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I don't believe what you described is electrically connected at both ends.

If it was, you would not be able run parallel sets of #2 to the panelboards. 310.10(H) permits paralleling of conductors #1/0AWG or larger.
 
david luchini said:
I don't believe what you described is electrically connected at both ends.

If it was, you would not be able run parallel sets of #2 to the panelboards. 310.10(H) permits paralleling of conductors #1/0AWG or larger.
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Oh! Duuh! :slaphead:


And it still would not be allowed even if it was 1/0, correct?
 
mbrooke said:
But I still need both those 350s going into a single Polaris?
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IMO when you have a parallel feeder and parallel tap both with the same number of sets, you can tap one-for-one as long as you keep distances the same. If the distance is offset, you have to 'tap' using an Fn x Tn matrix.

PS: I prefer gutter taps type connectors whenever possible... don't have to cut the feeder.
 
Smart $ said:
IMO when you have a parallel feeder and parallel tap both with the same number of sets, you can tap one-for-one as long as you keep distances the same. If the distance is offset, you have to 'tap' using an Fn x Tn matrix.

PS: I prefer gutter taps type connectors whenever possible... don't have to cut the feeder.
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Different people will give different answers to the basic question of whether putting a tap which does not break the original conductor (insulation piercing or split bolt) counts as terminating the conductor for the purpose of defining the extent of parallel wires. On the other hand, it arguably would still be the origin point of a new set of parallel tap connectors.
A larger number will say that cutting the original wire to make the tap connection does definitely terminate the original parallel run and requires bringing the parallel conductors back together in a Polaris connector, on a bus bar, or other means.
 
GoldDigger said:
Different people will give different answers to the basic question of whether putting a tap which does not break the original conductor (insulation piercing or split bolt) counts as terminating the conductor for the purpose of defining the extent of parallel wires. On the other hand, it arguably would still be the origin point of a new set of parallel tap connectors.
A larger number will say that cutting the original wire to make the tap connection does definitely terminate the original parallel run and requires bringing the parallel conductors back together in a Polaris connector, on a bus bar, or other means.
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So I guess its up to the inspector then?
 
Smart $ said:
IMO when you have a parallel feeder and parallel tap both with the same number of sets, you can tap one-for-one as long as you keep distances the same. If the distance is offset, you have to 'tap' using an Fn x Tn matrix.

PS: I prefer gutter taps type connectors whenever possible... don't have to cut the feeder.
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Gutter taps- yes- those make electrician's lives much easier! :happyyes:
 
mbrooke said:
Gutter taps- yes- those make electrician's lives much easier! :happyyes:
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I was googling for some two or more feeder with two or more tap conductors 'gutter tap' type connectors. Couldn't find any. I've run across them before but just can't seem to locate them anymore. Can anyone provide a link?
 
mbrooke said:
So I guess its up to the inspector then?
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Yes. I know of PV supply side connections that "tapped" single conductors of parallel service conductors via IPCs which passed inspections with no problems.
 
ggunn said:
Yes. I know of PV supply side connections that "tapped" single conductors of parallel service conductors via IPCs which passed inspections with no problems.
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I see no reason why it can't be done, unless the the 350s are slightly off in length where the #2s are carrying imbalance plus normal load current. For those who know electrical theory, is this possible?
 
mbrooke said:
I see no reason why it can't be done, unless the the 350s are slightly off in length where the #2s are carrying imbalance plus normal load current. For those who know electrical theory, is this possible?
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Don't think the taps will carry imbalance, but the currents may be slightly divergent per set. Matching distances is more to comply with Code and an inspector's interpretation thereof.

And no parallel #2's, as Don pointed out earlier.:happyyes:
 
Smart $ said:
Don't think the taps will carry imbalance, but the currents may be slightly divergent per set. Matching distances is more to comply with Code and an inspector's interpretation thereof.

And no parallel #2's, as Don pointed out earlier.:happyyes:
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I beg to differ. One set slightly longer or shorter will cause uneven current division between each pair. the shorter will see more current, the longer less current.
 
mbrooke said:
I beg to differ. One set slightly longer or shorter will cause uneven current division between each pair. the shorter will see more current, the longer less current.
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I agree... but how much difference in length are we talking. Code provides no tolerance and making certain each set has an exactly equal length is impossible.
 
Smart $ said:
I agree... but how much difference in length are we talking. Code provides no tolerance and making certain each set has an exactly equal length is impossible.
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For small percentage variations the % difference in current will be roughly equal and opposite to the % difference in length (assuming that we can ignore the termination resistance. For short runs of parallel wire the termination resistance and its variation may be more important than the actual wire resistance.) The impedance of the rest of the circuit has no effect on the current division.
 
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