Moving Circuits to Subpanel - 300.3B Debate

[LarryFine]

Just where is this in the code?

Still looking.

 

[roger]

Isn't a breaker just a switch with OCPD protection?

Yes it is.

 

[RWC/NC.]

Wow.. This is one -LONG AZZ- thread w/82 (eighty-two) posting.. Now noticing, when I posted 210.4(A) that someone "w.whitney" having already posted same before hand.. (sorry about that).

 

[roger]

Wow.. This is one -LONG AZZ- thread w/82 (eighty-two) posting.. Now noticing, when I posted 210.4(A) that someone "w.whitney" having already posted same before hand.. (sorry about that).

Aren't you glad we don't allow ground up / ground down threads?

 

[LarryFine]

Okay, I can not find anything that says that grounded conductors must land in the panel that contains the breakers.

Also, there is no requirement to provide a neutral with a feeder to a panel that supplies no line-to-neutral loads.

However, it seems that a panel that does supply line-to-neutral loads should have a neutral bus for an added loads.

I'm on the fence on this one. I think I would include a neutral even if I left the existing whites in the existing panel.

 

[jap]

I'm still trying to figure out what was gained by all of this.

If you installed a 6 circuit subpanel with 5 circuits spliced to the subpanel to free up space in the main panel for the additional circuits, why weren't piggy backs used to free up space in the main panel for the 80 amp feeder breaker and the new circuits simply brought directly to the subpanel to begin with?



JAP>

 

[petersonra]

I think I would include a neutral even if I left the existing whites in the existing panel.

I am inclined to agree. However, that is a design decision and not a code requirement.

 

[hitehm]

I'm still trying to figure out what was gained by all of this.

If you installed a 6 circuit subpanel with 5 circuits spliced to the subpanel to free up space in the main panel for the additional circuits, why weren't piggy backs used to free up space in the main panel for the 80 amp feeder breaker and the new circuits simply brought directly to the subpanel to begin with?



JAP>

1) It's a square D main that has only 10 spaces which allow tandems (3040 model if you know Square D part #s) and they were full.
2) there was a physical limitation where we could place the subpanel and we couldn't pull back the branch circuits out of the main to bring them whole into the sub, so they had to be spliced.

 

[kwired]

Hey Kwired - Thanks for the explanation. Sounds to me you need to get some 12/4 or 12/2/2 on the truck!

Also, I should be more careful to be strict to the actual "exceptions" in the book, but when something reads "unless otherwise permitted" I tend to call it an exception as well...bad habit. The subsection 3 wording is what I'm really stuck on as it reads: "Conductors in wiring methods with a nonmetallic or other nonmagnetic sheath, etc." . which grammatically seems to imply it's only including "sheathed" wiring methods like nm cable and not conduit, tray, or other nm wiring methods. Am I reading this wrong? I'm really just hoping I can run PVC next time and be covered by code and be safe.

For no more than I do this, not worth it to me. Only would use 10-15 feet here and there and a 250 foot coil would probably last me a year or two, or even longer. Sure hope today's prices aren't still in effect in a couple years, and if they do go down don't want to be sitting on very much of something I paid double what it is currently selling at either.

 

[kwired]

Okay, I can not find anything that says that grounded conductors must land in the panel that contains the breakers.

Also, there is no requirement to provide a neutral with a feeder to a panel that supplies no line-to-neutral loads.

However, it seems that a panel that does supply line-to-neutral loads should have a neutral bus for an added loads.

I'm on the fence on this one. I think I would include a neutral even if I left the existing whites in the existing panel.

If filling all the slots (no room to add anything) I'd have little issue myself in a situation of a nipple from adjacent panel where the feeder and branches all are and not bring individual neutrals or even a feeder neutral to the sub panel. If there is space to add more circuits, I think might be good design to include a feeder neutral but not necessarily required until a new circuit would be added.

 

[kwired]

I'm still trying to figure out what was gained by all of this.

If you installed a 6 circuit subpanel with 5 circuits spliced to the subpanel to free up space in the main panel for the additional circuits, why weren't piggy backs used to free up space in the main panel for the 80 amp feeder breaker and the new circuits simply brought directly to the subpanel to begin with?



JAP>

I have a house where sometime in near future I am to be adding a 50 amp circuit for a hot tub, a couple 5 kW heaters for the garage and an electric fire place. Two unused spaces in the panel right now. I intend to add a subpanel and move general use lighting and receptacle circuits to it and add these heavy loads to the main panel. In fact I intend to add a 125 amp sub in the garage, install the heaters and hot tub from there, and still possibly add a 200 amp panel next to the existing 200 amp panel - it likely will end up being more than 200 amp load calc when done, but at same time I am willing to bet it seldom sees enough load to be an issue. The garage panel would be around 70 feet of conductor away from the service plus some those loads are on far end of what is 3 car garage. But want to be set up to be able to convert rather easily to 2-200 amp supplies for service if needed. If we end up upgrading service - likely will involve directional boring for majority of the run, no room for much of any equipment between this house and back property line and a big fence on the line as well, let alone disturbing what is there for landscaping and such.

 

[kwired]

1) It's a square D main that has only 10 spaces which allow tandems (3040 model if you know Square D part #s) and they were full.
2) there was a physical limitation where we could place the subpanel and we couldn't pull back the branch circuits out of the main to bring them whole into the sub, so they had to be spliced.

That be thirty spaces total, 20 of them will not accept tandems, 10 of them will. That gets you to possibly having 40 ungrounded conductors on OCPD's but unlike say GE and their 1/2 size breakers that do go to combinations up to 50 or 60 amps and in single or double pole, the QO tandems are mostly limited to 15 and 20 amps. "Quad breakers" that some other lines have are pretty much non existent in the QO line.

And with the AFCI requirements anymore - tandems and 1/2 size breakers are sort of useless anymore, for dwellings anyway.

 

[jaggedben]

Suppose someone comes along an installs a solar inverter output circuit in the subpanel.

Is there still not an inductive heating issue?

 

[winnie]

Suppose someone comes along an installs a solar inverter output circuit in the subpanel.

Is there still not an inductive heating issue?

Still no problem.

(I am only discussing the point of inductive heating here, not other code requirements related to the subpanel branch neutrals. )

No matter what the combination of subpanel load and PV input the _net_ current in the nipple with the subpanel feed and the 'switch loop hots' of the subpanel branch breakers will remain zero.

Without the PV input you would have the situation where the branch 'hot' currents are balanced by feed 'hot' currents.

Throw the PV in and now the feed 'hot' current might drop to zero because everything is coming from the PV source. But in this case one of the other feed conductors will be carrying the necessary balance current because the supply from the PV system is balanced in terms of current flow.

This even works if the PV is connected 120V to the subpanel. If you have a situation where current is flowing 'out' on the branch hots is supplied by the PV, then the necessary balancing current would be flowing 'out' on the feed neutral. No net current and no induction heating.

Jon

 

[kwired]

Suppose someone comes along an installs a solar inverter output circuit in the subpanel.

Is there still not an inductive heating issue?

Current coming in on one conductor from the inverter is equal to current returning on the other conductor(s) from the inverter. Only way inductive heating occurs is if you bring conductors from the inverter to the panel via separate ferrous entry methods, or in our installation that this thread is related to if you brought the ungrounded conductors into the subpanel but brought a neutral to the main panel via separate cables/raceways. If you bring all three into the sub panel via same cable/raceway but have no neutral in the subpanel to connect to and continue with that neutral to the main panel via the nipple in question in this thread, magnetic fields would still cancel out.

 

[tthh]

It seems to me that the easiet route would have been to pull the relocated circuits out of the main panel [creating room in the main panel which seems to be part of the problem] and splice them in a big box or two boxes and run that over to the subpanel and wire the subpanel normally and not worry about all this other stuff.

 

[hitehm]

Suppose someone comes along an installs a solar inverter output circuit in the subpanel.

Is there still not an inductive heating issue?

This whole discussion is because of a solar install. The solar breaker is what we needed to make room for. The solar breaker went in the main panel where we made room so that will not be happening at this job. However, I'm not sure how installing a solar breaker in the sub would matter to inductive heating since all it's wiring (L1,L2,N,G) from the inverter (and disconnect if mandatory in with your AHJ) would be in it's own conduit.

...and I just read others explaining similar.

 

[hitehm]

It seems to me that the easiet route would have been to pull the relocated circuits out of the main panel [creating room in the main panel which seems to be part of the problem] and splice them in a big box or two boxes and run that over to the subpanel and wire the subpanel normally and not worry about all this other stuff.

See my post #88 , #2 reason. We couldn't.

 

[wwhitney]

This whole discussion is because of a solar install. The solar breaker is what we needed to make room for. The solar breaker went in the main panel where we made room so that will not be happening at this job.

You could have put the subpanel feeder breaker in the main panel where you put the solar breaker, and then put the solar breaker in the subpanel opposite its supply. That would have required clearing up 2 fewer positions in the main panel.

Cheers, Wayne

 

[hitehm]

You could have put the subpanel feeder breaker in the main panel where you put the solar breaker, and then put the solar breaker in the subpanel opposite its supply. That would have required clearing up 2 fewer positions in the main panel.

Cheers, Wayne

The subpanel feeder breaker IS in the main. However we didn't want to land the solar breaker in the sub since it would've required a larger diameter conduit or more than 1 conduit for both feeders and solar and branch circuits, so we didn't want to deal with that or future load issues. Plus, we really thought it to be a cleaner install to have the solar breaker land in the main. And even though we would've been ok, we didn't want NEC 705 rules dictating our subpanel and breaker selection with the solar breaker in the sub.