Circuit type transfer switch for feed through?

[ritelec]

I see all these circuit type transfer switches, where by the circuits in the original panel get spliced (and fed through the original panel) and fed from the new sub panel/transfer,circuit panel.

What makes this allowed?

Lets say for instance, there is a circuit that I want to add a switch to. From what I understand, I can NOT just add a nipple to the panel and splice that switch leg in the panel. That circuit would need to be pulled out of the panel and brought into the switch box. Is this correct? And if so, why would the transfer panel be allowed to splice through the panel?

Thank you.

 

[GoldDigger]

The problem most commonly cited with these installations is not providing separate neutrals for each of the transferred circuits, making a nightmare where AFCI or GFCI are involved.
The OCPD in the transfer panel replaces the branch breaker in the main panel when on the alternate power source.
I do not see any exemption in the NEC for mandatory AFCI or GFCI requirements just because you are on alternate power.

 

[suemarkp]

Lets say for instance, there is a circuit that I want to add a switch to. From what I understand, I can NOT just add a nipple to the panel and splice that switch leg in the panel. That circuit would need to be pulled out of the panel and brought into the switch box. Is this correct?

I think you could splice in a switch leg like that, although it is not the best design. There is no prohibition on splicing in a panel if you have sufficient gutter space.

A neutral doesn't have to be run with the ungrounded conductors if you have one coming and one going (e.g. a switch loop). In 2014 they did add some more rules about switches and neutrals, but if you can easily pull a neutal to the switch you don't have to run one.

AS GoldDigger said, the main problem with these transfer panels is when AFCI/GFCI breakers are involved. And that is becoming a majority of circuits.

 

[ritelec]

Thank you for the responses.

There's the feed the sub panel (with neutral also) then back feed the existing circuits in the existing panel.

That doesn't seam right either. I'm pretty sure if I were installing a regular sub panel I wouldn't be able to do this.

 

[GoldDigger]

Thank you for the responses.

There's the feed the sub panel (with neutral also) then back feed the existing circuits in the existing panel.

That doesn't seam right either. I'm pretty sure if I were installing a regular sub panel I wouldn't be able to do this.

In a regular sub panel, there would be a single independent power feed to the panel, so this issue would not come up in the first place. The transfer panel is simply a convenient place to put all of the individual circuit transfer switches. It does not have provision for a main lug or breaker connection, a bus structure, or any of the other things we usually associate with a sub panel, so don't be too concerned about other differences.
Since there are now wires in the main panel which can be energized by source(s) outside that panel, you do have some labeling to do there.

When the alternate power source is not in use, the wiring leaves each main panel breaker and then comes back into the panel enclosure to get to the branch circuit wires.
Not that much different from putting in a switch leg, which I do not think is prohibited, as long as fill requirements are met.
You also have to be very careful about handle ties in the transfer panel for any MWBCs that you are going to transfer.

 

[ritelec]

The transfer panel is simply a convenient place to put all of the individual circuit transfer switches. It does not have provision for a main lug or breaker connection, a bus structure, or any of the other things we usually associate with a sub panel, so don't be too concerned about other differences.

sorry???

are we looking at the same picture?

Thanks GoldDigger

 

[GoldDigger]

I went by the title of the thread, not the picture.
The picture is not what I would ever call a circuit type transfer switch. It is just a subpanel with main breaker interlock that happens to access the branch circuit wires through the other panel. I do not see anything unusual about it except maybe 1. problems fitting AFCI or GFCI breakers and the 2. NEC restriction that the neutral HSS to originate from the same panel as the hot. That can be desktop with by rewiring the neutral.

 

[ritelec]

It is just a subpanel with main breaker interlock that happens to access the branch circuit wires through the other panel.

That's a great thing.

Now I know that I can just install a sub panel next to a main panel and refeed the existing circuits through that main panel without removing the circs from the main panel and putting them into the sub panel.

Very cool is I can do the same thing switches/timeclocks/contactors/jboxes etc..

Thank you

Now I Know

 

[kwired]

That's a great thing.

Now I know that I can just install a sub panel next to a main panel and refeed the existing circuits through that main panel without removing the circs from the main panel and putting them into the sub panel.

Very cool is I can do the same thing switches/timeclocks/contactors/jboxes etc..

Thank you

Now I Know

Outside of some local restrictions, it was always possible to run circuits through a cabinet containing a panelboard.

How the neutrals are run may be somewhat of an issue - but maybe this assembly has a listing that covers that issue.

As mentioned one current dilemma with such transfer panels is the need for AFCI's on many of the circuits in dwellings in the more recent editions of NEC.