Moving Circuits to Subpanel - 300.3B Debate

[wwhitney]

I can say in response to the feeder neutral being used for the purpose of the branch circuits is not compliant in this case.

200.6

I think you mean 200.4(A), as that is the section you quoted.

But in the arrangement in the OP, what neutral conductor is being used for more than one branch circuit? I think you'll find there isn't one.

Cheers, Wayne

 

[Tulsa Electrician]

Why would that be a problem? There is a neutral feeder conductor in the new panel connected to it's neutral bus.

I read it he did not install a netural with the feeder. If he did than yes, not an issue.

I should have ask first.

 

[hitehm]

I read it he did not install a netural with the feeder. If he did than yes, not an issue.

I should have ask first.

Yes, We did install a neutral with the feeder. All the circuits we moved were 120V circuits over so we had to.

 

[hitehm]

I've always interpreted where used to mean if the circuit actually has a neutral, like a 120 volt circuit. For a 208 or 240 volt 2-wire circuit it is not used.

Agreed, although again, the wording is ambiguous and should be changed or updated.

 

[hitehm]

AFAIK the rule was primarily written to prevent inductive heating, but maybe not worded well enough to indicate that. Some the conditions in the following subsections however do indicate this is the main reason for the rule.

This was most of the point of my original post. 300.3B forced us BY CODE to make a mess of the main panel by splicing ALL 3 (H,N,G) conductors from sub back to the main onto the original Romex cables. After that I really wanted to know what my fellow electrical tradesmen thought of this from a PRACTICAL point of view. And like I asked in post 23 (and still haven't seen a response) - What if we JUST USED PVC! If the entire point of the rule is to prevent inductive heat then why isn't there an exception for ALL nonmetallic raceways?

 

[hitehm]

All the language in 300.20? Word for word.

Where do you see any inductive heating being caused if the feeder current negates the branch circuit current?

So would you have also relocated the EGCs to originate from the sub or left them in the main?

 

[winnie]

This was most of the point of my original post. 300.3B forced us BY CODE to make a mess of the main panel by splicing ALL 3 (H,N,G) conductors from sub back to the main onto the original Romex cables. After that I really wanted to know what my fellow electrical tradesmen thought of this from a PRACTICAL point of view. And like I asked in post 23 (and still haven't seen a response) - What if we JUST USED PVC! If the entire point of the rule is to prevent inductive heat then why isn't there an exception for ALL nonmetallic raceways?

The code in the US for preventing induction issues covers both NM raceways _and_ penetrations into metallic enclosures.

My understanding is that the corresponding code in Canada has a lower limit for circuit size below which one doesn't need to worry about induction. However this is vague recollection on my part.

-Jon

 

[LarryFine]

As I alluded to earlier, I would run a feeder neutral and relocate the load neutrals.

The EGCs could stay, because we can use any combination of wires and conduits.

 

[hitehm]

And for those who were concerned with the conduit fill, our total conductor area with feeders and branch splices including all H,N and Gs was .4401 sq.in. We used FMC between the main and sub and at 60% (less than 24in) allows for 1" FMC but even better, we used 1.25".

 

[RWC/NC.]

In your original posting hitehm, you denoted feeder & five (5) branch circuits. If the possibility exists, that these 5 circuits were 120volt circuits, how many grounded conductors (neutrals) were present, for the denoted circuits.

Reasoning in asking, were any of the (5) denoted branch circuits set up as multiwire branch circuits, more than one circuit on same neutral. (?) Or 5 individual neutrals. ..Curious..

210.4 (A)

 

[kwired]

This was most of the point of my original post. 300.3B forced us BY CODE to make a mess of the main panel by splicing ALL 3 (H,N,G) conductors from sub back to the main onto the original Romex cables. After that I really wanted to know what my fellow electrical tradesmen thought of this from a PRACTICAL point of view. And like I asked in post 23 (and still haven't seen a response) - What if we JUST USED PVC! If the entire point of the rule is to prevent inductive heat then why isn't there an exception for ALL nonmetallic raceways?

There is in subsection (3), and it includes all non ferrous wiring methods not just PVC. If you had two or more raceways that together would balance out on the magnetic effects, you would need to cut slots between them in any entries to ferrous enclosures - this to effectively make one hole in the enclosure.

 

[hitehm]

The code in the US for preventing induction issues covers both NM raceways _and_ penetrations into metallic enclosures.

Where does it specifically cover all NM raceways for induction issues? I know 300.3B.3 says raceways with NM and non-magnetic "sheath" will follow the rules of 300.20B but I'm not sure if that's what you mean.

 

[hitehm]

There is in subsection (3), and it includes all non ferrous wiring methods not just PVC. If you had two or more raceways that together would balance out on the magnetic effects, you would need to cut slots between them in any entries to ferrous enclosures - this to effectively make one hole in the enclosure.

exception 3 I believe is only if you run each phase of the same circuit in different nm raceways. But I'm still not sure why running in the same raceway only your Hots with no neutrals (return path) would be able to induce anything in a PVC or any other nm raceway for that matter.

 

[Dennis Alwon]

The code does not say that the purpose is for inductive heating but perhaps that is the reason, however as Charlie Beck says, the code says what it says not what you want it say or what you think it says.

 

[wwhitney]

Seems like the debate just boils down to whether "where used" means "where used anywhere in the branch circuit" vs "where used between the two points between which the ungrounded conductors are running."

I think we can all agree that when a grounded conductor and an ungrounded both run from box A to box B, then the various sections cited give the rules for whether the two conductors must be in the same raceway or not.

However, if the ungrounded conductor runs from box A to box B and back to box A, I don't see those rules as generically requiring the the grounded conductor to detour to box B if it is not used in box B. The one case that was brought up so far is when box B has the OCPD for an MWBC, as then the grounded conductor must "originate" in box B.

Cheers, Wayne

 

[kwired]

exception 3 I believe is only if you run each phase of the same circuit in different nm raceways. But I'm still not sure why running in the same raceway only your Hots with no neutrals (return path) would be able to induce anything in a PVC or any other nm raceway for that matter.

it is subsection 3 (300.3(B)(3)) not an exception and it deals with not just non metallic but all non ferrous wiring methods.

Example where I most often use this permission is with type NM cable. Say you have a bath exhaust fan with light and heater - I may run power to the switch location, then two two wire cables to the unit. One cable has the grounded conductor and the heater lead, the other cable has the light and fan leads and both those use the grounded conductor in the other cable. Most the time the switch box is non metallic so no problems with induction there, to comply with 300.20(B) at the unit which is usually ferrous they need to enter the same KO entry or have slot cut between entries, which from the magnetic effects essentially makes it same as one hole.

Ever notice for some old metallic device boxes that were original to K&T wiring will have a slot between the entry holes? They knew about this inductive effect way back then.

 

[LarryFine]

As long as all conductors between enclosures are within the same conduit, the induction conversation is irrelevant.

The main debate here is whether the feeder should include a neutral and the load neutrals should be relocated.

In the case of switch loops, it's not required, but general breaker-panel rules say that it should be done that way.

Electrically speaking, it's not necessary to include the neutrals, but code says it is required for breaker panels.

In my opinion, existing EGCs need not be relocated, as the can generally be landed almost anywhere that qualifies.

 

[petersonra]

Electrically speaking, it's not necessary to include the neutrals, but code says it is required for breaker panels.

Just where is this in the code?

 

[hitehm]

it is subsection 3 (300.3(B)(3)) not an exception and it deals with not just non metallic but all non ferrous wiring methods.

Example where I most often use this permission is with type NM cable. Say you have a bath exhaust fan with light and heater - I may run power to the switch location, then two two wire cables to the unit. One cable has the grounded conductor and the heater lead, the other cable has the light and fan leads and both those use the grounded conductor in the other cable. Most the time the switch box is non metallic so no problems with induction there, to comply with 300.20(B) at the unit which is usually ferrous they need to enter the same KO entry or have slot cut between entries, which from the magnetic effects essentially makes it same as one hole.

Ever notice for some old metallic device boxes that were original to K&T wiring will have a slot between the entry holes? They knew about this inductive effect way back then.

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.

 

[hitehm]

As long as all conductors between enclosures are within the same conduit, the induction conversation is irrelevant.

By all conductors I assume you mean the neutrals as well since the neutral on the other side of the load provide the cancelling effect that minimizes the induction?

The main debate here is whether the feeder should include a neutral and the load neutrals should be relocated.

Agreed. That is what this boils down to. Although strict code would have us all moving the grounds as well so there comes a point we need to use common sense.

In the case of switch loops, it's not required, but general breaker-panel rules say that it should be done that way.

Isn't a breaker just a switch with OCPD protection? I don't see how it differs electrically in this case. And as several have pointed out, multi-breaker transfer switches get away with this, it's even in their own wiring diagrams. And if not mistaken, the only reason the feeder to the transfer switch includes a neutral is for the generator itself and provides no return path for any of the emergency circuits.

Electrically speaking, it's not necessary to include the neutrals, but code says it is required for breaker panels.

In my opinion, existing EGCs need not be relocated, as the can generally be landed almost anywhere that qualifies.