Remote panel as J-box

[Marc M]

Jerry,
I thought I read in the NEC where a remote panel cannot be used as a junction box.

[Jerry Peck - Codeman]

Hi Marc,

'Are not supposed to be' ... is different than 'are not' ...

From the 2008 NEC. (underlining and bold are mine)
- 312.8 Enclosures for Switches or Overcurrent Devices.
- - Enclosures for switches or overcurrent devices shall not be used as junction boxes, auxiliary gutters, or raceways for conductors feeding through or tapping off to other switches or overcurrent devices, unless adequate space for this purpose is provided. The conductors shall not fill the wiring space at any cross section to more than 40 percent of the cross-sectional area of the space, and the conductors, splices, and taps shall not fill the wiring space at any cross section to more than 75 percent of the cross-sectional area of that space.

This part is the key to that section: "unless adequate space for this purpose is provided"

The UL standard to which those are listed and labeled 'does not provide space for that purpose'.

Only after "adequate space for this purpose is provided" is the last sentence about how much space is allowed 'for that purpose'.

The last sentence states two things: 1) "The conductors shall not fill the wiring space at any cross section to more than 40 percent of the cross-sectional area of the space, and"; 2) "the conductors, splices, and taps shall not fill the wiring space at any cross section to more than 75 percent of the cross-sectional area of that space."

That means that the conductors terminating in those enclosures are not allowed to fill more than 40 percent of the cross-sectional area, and that if those conductors fill that 40 percent, then the "splices, and taps" are only allowed to fill 35 percent. However, if the conductors fill less than 40 percent, then the splices and taps can fill the difference up to the 70 percent maximum fill.

Many electricians try to apply the last sentence without regard to the limitations placed by the first sentence, which is incorrect.

In my discussions with UL on this very subject, they stated that they would be more than happy to work with any manufacturer and develop a standard to test to for allowing those enclosures to be used as "junction boxes, auxiliary gutters, or raceways for conductors feeding through", but to date no manufacturer has expressed an interest in developing any such standard or listing for such use.

[Marc M]

Thanks Jerry-merry christmas

[Bill Kriegh]

There is a line of panels manufactured specifically for pass through applications (Cutler Hammer, I think. I need to find my correspondence.) Anyway, when I checked the catalog the cabinet size was the same as the standard rated panel for the Amperage, as was the number of available circuits. When I contacted the customer service about this they indicated the only difference in the panels was that the breaker buss bar assembly is offset to one side to allow a straight wire feed for the pass through wire. No extra space is alloted for the purpose.

[Jerry Peck - Codeman]

There is a line of panels manufactured specifically for pass through applications (Cutler Hammer, I think. I need to find my correspondence.)

Hi Bill,

If you find that, would you please post it?

Panelboards are listed to UL Standard 67 and that standard does not test for pass through conductors.

When I contacted the customer service about this they indicated the only difference in the panels was that the breaker buss bar assembly is offset to one side to allow a straight wire feed for the pass through wire. No extra space is alloted for the purpose.

The problem is not the lack of extra space, but the lack of extra space provided specifically for that purpose. The reason is not fill as there is usually sufficient fill space to accommodate additional conductors, the main reason is "pass through current" in that current not originating in that enclosure at those breakers will add heat and temperature rise to the panel, and that zero pass through current is what is being tested.

Additionally, if they were to allow for pass through conductors, the secondary reason is that the space provided for those conductors would need to be isolated from the other conductors by a suitable (i.e., listed, labeled, and provided by the manufacturer of the panelboard and enclosure) grounded metal separator shield to make sure that the pass through conductors could not come in contact with conductors originating at the overcurrent devices (breakers) - one would not want to turn all breakers to 'off' only to have an energized pass through conductor accidentally contact and energize a conductor with its overcurrent protection in the 'off' position, both for worker safety from electrical shocks and for fire safety and overcurrent protection of the conductors.

Testing for pass through conductors would need to be established to establish the minimum conductor size and its maximum pass through current allowed, and, the maximum conductor size and the maximum pass through current allowed, and the full tests would need to be run with the newly established allowances. The listing and labeling would need to state the maximum number and size combinations of cables and the fully loaded current condition acceptable.

It's a lot more complicated than just 'is there enough space' and 'is there enough wire bending space'.