Exam prep question

[Sparkyrob]

I'm having some trouble with an exam prep question and I'm hoping someone can clarify for me. It's a voltage drop question regarding finding the max load allowable on a conductor so as to not exceed the NEC recommendations for voltage drop. My question is do I calculate at 2%, or 3%. These seem like they are feeders to me, so wouldn't a 2% calculation apply?

1/0 AWG copper conductors in a nonmetallic raceway to a panelboard located 200 ft. from a 240V, single phase power source. What's the maximum load that can placed on the panelboard without exceeding the NEC recommendation for voltage drop?

I wasn't sure, so I worked out for 2% & 3%, both answers possible options on the test.

 

[LEO2854]

I'm having some trouble with an exam prep question and I'm hoping someone can clarify for me. It's a voltage drop question regarding finding the max load allowable on a conductor so as to not exceed the NEC recommendations for voltage drop. My question is do I calculate at 2%, or 3%. These seem like they are feeders to me, so wouldn't a 2% calculation apply?

1/0 AWG copper conductors in a nonmetallic raceway to a panelboard located 200 ft. from a 240V, single phase power source. What's the maximum load that can placed on the panelboard without exceeding the NEC recommendation for voltage drop?

I wasn't sure, so I worked out for 2% & 3%, both answers possible options on the test.

Read this,,,, http://www.mikeholt.com/nec-voltage-drop.php

.

 

[jumper]

1/0 AWG copper conductors in a nonmetallic raceway to a panelboard located 200 ft. from a 240V, single phase power source. What's the maximum load that can placed on the panelboard without exceeding the NEC recommendation for voltage drop?

Look at these definitions from Article 100.

Which one would apply to your question and why?

Branch Circuit. The circuit conductors between the final
overcurrent device protecting the circuit and the outlet(s).

Feeder. All circuit conductors between the service equipment,
the source of a separately derived system, or other
power supply source and the final branch-circuit overcurrent
device.

 

[Sparkyrob]

Look at these definitions from Article 100.

Which one would apply to your question and why?

I would say a feeder would apply to my question because don't feeders supply a panelboard? A panelboard would house the OCPD of the furthest branch circuit. And that's why I was thinking I would be needing to figure 2% voltage drop at the panelboard, allowing for the remaining 3% at the furthest branch circuit fed by this panelboard. The answer on the test key says 3%, and I'm not sure why.

I hope I'm getting the terminology correct here, but doesn't a feeder provide the source to another OCPD(or a cabinet full of them) and a branch circuit generally provides power to the utilization equipment or a receptacle? Is this where I'm making my error? Could a panelboard be fed by a branch circuit?

 

[GoldDigger]

A panelboard could only be fed by a branch circuit if that panelboard did not contain any OCPD and there was at least one load with no downstream OCPD either.
One of the oddities of the definitions is that you can argue that some wires are both feeders and branch circuit conductors at the same time.
But I think that the test prep answer is flat out wrong.

 

[Pharon]

I would say a feeder would apply to my question because don't feeders supply a panelboard? A panelboard would house the OCPD of the furthest branch circuit. And that's why I was thinking I would be needing to figure 2% voltage drop at the panelboard, allowing for the remaining 3% at the furthest branch circuit fed by this panelboard. The answer on the test key says 3%, and I'm not sure why.

Read the 215.2 informational note again. It says nothing about 2%. Only 3% for feeders or branch circuits individually, or 5% for feeders and branch circuits combined.

One of the oddities of the definitions is that you can argue that some wires are both feeders and branch circuit conductors at the same time.

Care to share an example? I can't think of any.

 

[Smart $]

Read the 215.2 informational note again. It says nothing about 2%. Only 3% for feeders or branch circuits individually, or 5% for feeders and branch circuits combined.

I agree. It only mentions 3% on feeders or branch circuits. People misinterpret it as a recommendation of 2% on feeders, thinking 5% total minus 3% for branch circuits... but quite often branch circuits are substantially less than 3%, which allows for greater than 2% voltage drop on feeders.

Care to share an example? I can't think of any.

Can't think of any specific, but see allowed branch circuit taps under 210.19 exceptions. Any such tap that has an additional OCPD on the tap would technically be a feeder and a branch circuit. Granted, any such installation would be atypical.

Edit to add: Just thought of one of the most common feeder/branch circuit scenarios... a two motor situation where the OCPD doesn't protect the smallest motor, and tap has a secondary OCPD for the smaller motor.

 

[GoldDigger]

Edit to add: Just thought of one of the most common feeder/branch circuit scenarios... a two motor situation where the OCPD doesn't protect the smallest motor, and tap has a secondary OCPD for the smaller motor.

That is the sort of circuit layout that I was thinking of, I just did not have any concrete example that would justify actually wiring something that way.
Thanks!

 

[Sparkyrob]

Read the 215.2 informational note again. It says nothing about 2%. Only 3% for feeders or branch circuits individually, or 5% for feeders and branch circuits combined.

Okay, I was actually looking at 210.19(A) (1) I.N. I didn't realize it was noted for feeders in 215 as well. Basically the same but the wording was tripping me up.

I'm sure I was taught this correctly in the apprenticeship program, but apparently (obviously),I need to clear out the cobwebs. Studying for this exam has been difficult, but I love it. The more I learn, the more I realize how little I know. I take my Theory portion tomorrow, I feel good about it.

I appreciate All the feedback and comments, I think this forum is Great for this industry. Thanks guys!

 

[Pharon]

The more I learn, the more I realize how little I know.

Join the club. I've been in this industry for over 20 years and am shocked sometimes at the stuff I should know but don't.

And you're right -- this place is an excellent resource. Good luck on your test.

 

[Sparkyrob]

Join the club. I've been in this industry for over 20 years and am shocked sometimes at the stuff I should know but don't.

And you're right -- this place is an excellent resource. Good luck on your test.

Passed my Theory. That's two down, one to go. I'll retake that Code portion next month & be good to go.