generator transfer panel neutral wiring.

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stew

Senior Member
Hope this isnt a dumb question but it came up in conversation. When you set a subpanel/generator transfer panel for resdential portable generator applications is it required that when you rerun the circuits over and back to the subpanel that you include a neutral for each of the circuits or does the Main neutral that you run to the sub suffice? Say you have 12 circuits you want to put on the generator sub. All 12 neutrals run with the circuit conductors? A single large neutral in each raceway? Or if yopu are running in a short 2" niple between panels ???? I have always run neuts for all but the conversation we had a few folks seem to think its not needed? I have always been of the opinion that the code always requires the neutrals to be run in the same raceway etc as the circuit conductors and one for each circuit. yes? No? Code ref?
 

Smart $

Esteemed Member
Location
Ohio
Why would you run circuit conductors over and back...???

If you are adding a transfer panel, you supply the panel with utility power feeder from the main panel (assumption) and power feeder from the generator. The built-in transfer switch takes care of which source is utilized at any particular time. The panel's branch circuits get wired just like any other panel... all circuit conductors originate in that panel: ungrounded, grounded neutral, and EGC's. If splicing in the original panel, you take all those branch circuit conductors to the other panel. Note you cannot have MWBC's originating in two different panels... i.e. no shared branch circuit neutral conductors between panels.
 

6sunset6

Member
Location
United States
I am in the middle of an install that is a little ugly. The transfer panel is 50 ft from the generator and 15 ft from the main panel. Essential services only. No question I run branch hot and neutral pairs Whoops excuse me ungrounded and grounded pairs from the main panel to the transfer panel. But it seems to me I can leave the EGC 's on the branches tied in at the main panel. As long there is an EGC , big enough, tying the two panels together.
 

ceb58

Senior Member
Location
Raeford, NC
Why would you run circuit conductors over and back...???

If you are adding a transfer panel, you supply the panel with utility power feeder from the main panel (assumption) and power feeder from the generator. The built-in transfer switch takes care of which source is utilized at any particular time. The panel's branch circuits get wired just like any other panel... all circuit conductors originate in that panel: ungrounded, grounded neutral, and EGC's. If splicing in the original panel, you take all those branch circuit conductors to the other panel. Note you cannot have MWBC's originating in two different panels... i.e. no shared branch circuit neutral conductors between panels.

I am in the middle of an install that is a little ugly. The transfer panel is 50 ft from the generator and 15 ft from the main panel. Essential services only. No question I run branch hot and neutral pairs Whoops excuse me ungrounded and grounded pairs from the main panel to the transfer panel. But it seems to me I can leave the EGC 's on the branches tied in at the main panel. As long there is an EGC , big enough, tying the two panels together.
300.3 Conductors.


(B) Conductors of the Same Circuit. All conductors of
the same circuit and, where used, the grounded conductor
and all equipment grounding conductors and bonding conductors
shall be contained within the same raceway, auxiliary
gutter, cable tray, cablebus assembly, trench, cable, or
cord, unless otherwise permitted in accordance with
300.3(B)(1) through (B)(4).
Look over this
 

6sunset6

Member
Location
United States
The transfer panel is UL listed and there is no ground buss. If I add one I am voiding the listing. IF I don't add one I am violating the NEC. I guess I will ask the AHJ what he wants.
Personally I would leave the EGCs in the main panel Just making sure I have a contiguous EGC from main panel to transfer panel to generator.
 

Smart $

Esteemed Member
Location
Ohio
The transfer panel is UL listed and there is no ground buss. If I add one I am voiding the listing. ...
I've never known a panel listing to be violated by [properly] adding a ground bus.

What is the make and model of the panel?
 

ceb58

Senior Member
Location
Raeford, NC
I've never known a panel listing to be violated by [properly] adding a ground bus.

What is the make and model of the panel?
I agree, I have added many ground bars to panels, that I was using as sub's, that did not have them. This is no different. It is a sub panel where the grounded conductors and equipment grounding conductors must be separate.
 

stevebea

Senior Member
Location
Southeastern PA
I am in the middle of an install that is a little ugly. The transfer panel is 50 ft from the generator and 15 ft from the main panel. Essential services only. No question I run branch hot and neutral pairs Whoops excuse me ungrounded and grounded pairs from the main panel to the transfer panel. But it seems to me I can leave the EGC 's on the branches tied in at the main panel. As long there is an EGC , big enough, tying the two panels together.

One of our guys did a generator install that failed because the branch circuit EGC's were not pulled to the loadcenter in the transfer switch. I'm going back tomorrow to pull them in.
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
300.3 Conductors.


(B) Conductors of the Same Circuit. All conductors of
the same circuit and, where used, the grounded conductor
and all equipment grounding conductors and bonding conductors
shall be contained within the same raceway, auxiliary
gutter, cable tray, cablebus assembly, trench, cable, or
cord, unless otherwise permitted in accordance with
300.3(B)(1) through (B)(4).
Look over this
I'm not trying to throw a wrench into things or derail this thread but assuming you are correct, under what conditions would you use either of these two types of panels:

This one (a manual type) switches the ungrounded conductors, has a common neutral and EGC landed on the neutral (and/or ground) bars of the adjoining breaker panel (not necessarily a MB panel) and neutrals originate in that breaker panel and not the transfer switch.

http://www.electricgeneratorsdirect.com/Images/Reliance-Controls-51410C/i1127.html

This one (although an automatic type but there are manual types like this available) is a sub-panel and the neutrals are spliced in the adjoining breaker panel and thus originate in this sub-panel.

http://www.electricgeneratorsdirect.com/Images/Reliance-Controls-51410C/i1127.html

Both are UL listed
 

JES2727

Senior Member
Location
NJ
300.3 Conductors.


(B) Conductors of the Same Circuit. All conductors of
the same circuit and, where used, the grounded conductor
and all equipment grounding conductors and bonding conductors
shall be contained within the same raceway, auxiliary
gutter, cable tray, cablebus assembly, trench, cable, or
cord, unless otherwise permitted in accordance with
300.3(B)(1) through (B)(4).


Look over this


This does not mean you need a separate EGC for each circuit. You need only one, provided it is sized properly.
 

Smart $

Esteemed Member
Location
Ohio
This does not mean you need a separate EGC for each circuit. You need only one, provided it is sized properly.
That depends on the wiring method. Need one per raceway or cable. If using one raceway, for both feeder and branch circuits, yes, one properly sized EGC would suffice... but then there'd likely be derating issues to deal with.
 

Smart $

Esteemed Member
Location
Ohio
I'm not trying to throw a wrench into things...
Trying or not, you've succeeded :p

From the start of the thread, I assumed the OP's reference to a transfer panel meant the type that functions like a typical panelboard with an integral automatic transfer switch and generator control. Your post brings to light that other transfer panel types exist.

In the case of the Reliance type you linked to, there would in fact be over and back circuit conductors, and branch circuit neutral conductors for generator power.

...under what conditions would you use either of these two types of panels
The Reliance type is better suited for portable generators, especially ones with marginal capacity to supply all the circuits.

The Generac is suited for permanently installed automated backup. For this type, the generator is required to have the capacity to power all the connected loads.
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
I guess what I was trying to determine was (with respect to the NEC and not necessarily to UL) under what conditions would it be Code compliant to have a larger neutral (like the one in the Reliance panel) bonded to the neutral in the breaker panel and merely manually switching the branch circuit conductors from line to generator in the transfer panel. In this case when the power is coming in from the POCO the branch circuit wires are being fed from the panel they originate in. However, when they are switched over to generator the ungrounded conductors originate through the individual transfer switches which do have fused protection, BTW.

Now in the case of the Generac essential circuits panel, all the branch circuit conductors originate in that panel. When you go onto generator those circuits are still being fed from that panel.

Electrically speaking, I don't see a difference but some inspectors have a problem with the Reliance type unit because the neutrals originate in a separate panel.
 

Smart $

Esteemed Member
Location
Ohio
...

Electrically speaking, I don't see a difference but some inspectors have a problem with the Reliance type unit because the neutrals originate in a separate panel.
If I understand the Reliance switching correctly, when on generator power, the circuit neutrals originate in the same panel where the ungrounded conductors do. On normal power, the neutrals are not used, so you just have ungrounded going over and back, just like a lighting switch leg.
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
If I understand the Reliance switching correctly, when on generator power, the circuit neutrals originate in the same panel where the ungrounded conductors do. On normal power, the neutrals are not used, so you just have ungrounded going over and back, just like a lighting switch leg.
That's true but the branch circuits are individually fused in generator mode. Aren't we doing the same thing as a sub-panel but only in emergency mode ? Am I making sense ?
 

Smart $

Esteemed Member
Location
Ohio
That's true but the branch circuits are individually fused in generator mode. Aren't we doing the same thing as a sub-panel but only in emergency mode ? Am I making sense ?
Sorta, kinda, but not ;)

(Oh! and yes you are making sense.)
 
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