Tapping a parallel feeder

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tnoble406

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New to the forum, so I ask for your patience in advance. Hope I am in the right place, and that this question falls within the TOS guidelines.
We have a 600 amp MDP with ancient breakers, and are adding a 200 amp panel for some mini-split A/C units. My intent is to install a 200 amp disconnect within 10 feet of the MDP, and use it to supply a w/p panel on the roof where the condensers will be located. The MDP is fed from a 600 amp main disconnect, in parallel. My question is, can this be accomplished by tapping one set of those parallel feeders in the MDP, or do the taps need to be in parallel as well? I hope my explanation is clear enough to be understood, and thank you in advance for your help.
 
tnoble406 said:
My question is, can this be accomplished by tapping one set of those parallel feeders in the MDP, or do the taps need to be in parallel as well? I hope my explanation is clear enough to be understood, and thank you in advance for your help.
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Welcome, it is, you're welcome, and yes, the taps must include all conductors (per phase, of course).
 
tnoble406 said:
So, I must feed the new 200 amp switch in parallel? May I assume the load side feeders going from the disconnect to my new rooftop panel can be one set of 3/0s? And thank you again for your clarification!!
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Yes you can use a single set of #3/0 for the 200 amp tap. Since the 200 amp conductor is 1/3 of the 600 amp feeder ampacity you can up to 25' with the 25' tap rule.

Welcome to the Forum. :)
 
ggunn said:
Just to further clarify, the code does not explicitly say that.
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It must say that; we've always done it that way! :p


Added: From: https://www.ecmag.com/section/systems/conductors-connected-parallel

Any taps made to the paralleled sets of conductors must be made to all the conductors in the set, not just one. Tapping only one of the conductors in the set could result in an imbalance with one of the conductors carrying more current than the other, resulting in heating of that one conductor and possible insulation damage or failure.

For example, if three 500 kcmil conductors are run per phase, a tap from that particular phase must be a tap from all of the 500 kcmil conductors, not just one of the set. This would require a common terminal point for all three parallel conductors with a tap conductor connection to the common terminal.
 
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LarryFine said:
It must say that; we've always done it that way! :p


Added: From: https://www.ecmag.com/section/systems/conductors-connected-parallel

Any taps made to the paralleled sets of conductors must be made to all the conductors in the set, not just one. Tapping only one of the conductors in the set could result in an imbalance with one of the conductors carrying more current than the other, resulting in heating of that one conductor and possible insulation damage or failure.

For example, if three 500 kcmil conductors are run per phase, a tap from that particular phase must be a tap from all of the 500 kcmil conductors, not just one of the set. This would require a common terminal point for all three parallel conductors with a tap conductor connection to the common terminal.
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I'm not arguing that point, only that if you consult the NEC to find where it says that, you won't find it.
 
I'm guessing there is a problem sourcing the breaker or is the mdp full? U can find breakers for pretty much any enclosure no matter how old , at least here in NYC . If u have time and can get me some information on the breaker I can probably get one for you

Sent from my SM-G950U using Tapatalk
 
ggunn said:
I'm not arguing that point, only that if you consult the NEC to find where it says that, you won't find it.
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I feel you can use the rules of 310.10(H) as the reason. To "tap" only one conductor would violate "be terminated in the same manner" portion of that Section.
 
augie47 said:
I feel you can use the rules of 310.10(H) as the reason. To "tap" only one conductor would violate "be terminated in the same manner" portion of that Section.
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But that's what I mean; it requires interpretation and interpretations differ. For example, if you are using IPC's to make the connection are you terminating the conductor you are tapping? Would it be so hard for the NEC to state explicitly that all conductors in a parallel set be tapped? Would such a statement cause other ambiguities to arise?
 
ggunn said:
But that's what I mean; it requires interpretation and interpretations differ. For example, if you are using IPC's to make the connection are you terminating the conductor you are tapping? Would it be so hard for the NEC to state explicitly that all conductors in a parallel set be tapped? Would such a statement cause other ambiguities to arise?
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What about 300.3(B)(1)? It doesn't tell you why but basically tells us properties of each conductor of a parallel set must have same properties - this so resistance of each path will be as close to same as possible and result in equal distribution of current between conductors of the set. Tapping one in the middle disrupts this "equalness", involving all conductors of the set in the tap maintains that "equalness".
 
ggunn said:
I'm not arguing that point, only that if you consult the NEC to find where it says that, you won't find it.
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Well, I'm sticking with "that's how we've always done it," Regis. :D

It can be argued that the idea of "similar characteristics" applies here.
 
Beyond the code argument, I believe this is one where safety and common sense needs to reign. If only one set is tapped, that set can see an overcurrent that won't trip an overcurrent. This is on a par with violating 300.20 in terms of creating a dangerous situation that won't be caught by any protection device.
 
ggunn said:
Just to further clarify, the code does not explicitly say that.
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So if one is an inspector, what basis would one have for citing a violation, if an installer used an insulation piercing connector to just tap one set? One could claim that the parallel conductors are still "terminated in the same manner", since piercing a tap through the insulation is not a termination by strict definition.

There also is the issue of whether you can independently tap the parallel sets, as long as you maintain the symmetry. For instance, 2 parallel sets in the tap circuit, tapped onto any even number of sets on the feeder. Does one necessarily need to bring them all together? Or just group half the wires for the feeder to tap the first wire in the tap circuit, and the other half of the wires of the feeder to tap the second wire? I get that since it is impossible to get everything identical, it's probably better from an electrical theory point of view (NEC aside) to bring everything together at the tap point.
 
Carultch said:
So if one is an inspector, what basis would one have for citing a violation, if an installer used an insulation piercing connector to just tap one set? One could claim that the parallel conductors are still "terminated in the same manner", since piercing a tap through the insulation is not a termination by strict definition.

There also is the issue of whether you can independently tap the parallel sets, as long as you maintain the symmetry. For instance, 2 parallel sets in the tap circuit, tapped onto any even number of sets on the feeder. Does one necessarily need to bring them all together? Or just group half the wires for the feeder to tap the first wire in the tap circuit, and the other half of the wires of the feeder to tap the second wire? I get that since it is impossible to get everything identical, it's probably better from an electrical theory point of view (NEC aside) to bring everything together at the tap point.
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I believe there is more justification to what you suggested in the second paragraph than in the first as being acceptable. Note I didn't say it is acceptable just has more justification.
 
kwired said:
I believe there is more justification to what you suggested in the second paragraph than in the first as being acceptable. Note I didn't say it is acceptable just has more justification.
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All of which illustrates my point. If it is such a bad idea to tap single conductors in multiconductor sets, why doesn't the code explicitly proscribe it?
 
A "what if":

Say I have a feeder that feeds a panel with three parallel sets of conductors and I want to connect a PV system with a single set of conductors on the line side of the panel. What if I used a four port Polaris block to split the PV output three ways and I connect each port to an IPC on a feeder conductor? All the feeder conductors would still look the same as each other.
 
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ggunn said:
A "what if":

Say I have a feeder that feeds a panel with three parallel sets of conductors and I want to connect a PV system with a single set of conductors on the line side of the panel. What if I used a four port Polaris block to split the PV output three ways and I connect each port to an IPC on a feeder conductor? All the feeder conductors would still look the same as each other.
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I meant, of course, a four port Polaris block for each conductor from the PV system.
 
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