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I am looking to see if the NEC has any guidance on where you can cut a hole into your outdoor electrical panel. (To add a cable clamp). The existing pre-marked knockouts are either used or require running conduit and additional penetrations through the outer walls.

Is there guidance or rules for distance between holes/knockouts? Or from breakers or busbars to the holes? I know that code dictates some limitations about what angles/bends wires can make, so obviously there is a relationship between distance to a circuit breaker.

also i wouldn’t want to have an entry into the box too close to the hot busbars(?) as it would probably require turning off the whole panel to work safely and avoid accidental death or injury.

I’m thinking of going below the breakers/ busbars but want to know if I need to maintain any kind of distance or distance between other penetrations.

this question was similar but the question is more about conduit, Adding a new "knockout" to side of main electrical panel

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  • It’s an outdoor panel, hence why I’m trying to add additional holes to the back of the panel where the holes already exist.
    – bwp8nt
    Sep 1 at 14:13
  • Is where you're trying to add holes to above or below the bottom of the busbars?
    – ThreePhaseEel
    Sep 1 at 23:24
  • @ThreePhaseEel Yes. I am explicitly looking at adding them below, but didn’t want to place them too close, also I was curious if there is anything in code that prohibits coming alongside the busbars besides perhaps the common sense piece of working room and making it harder to position wires within the panel if you have random entries into the box.
    – bwp8nt
    Sep 2 at 15:01

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You can add additional holes...

It is permissible to add extra knockout holes to a cabinet or junction box; in fact, many commercial panelboard cabinets and some pull boxes ship without any knockouts, expecting the user to make their own.

...however, there are some caveats with outdoor boxes

However, if you have an outdoor-rated box, such as a NEMA 3R loadcenter cabinet, then you have to be careful to maintain that box's NEMA rating. For a NEMA 3R, in particular, you have to use a watertight hub fitting to enter the box anywhere above the lowest live part in the box.

In your case, since this is a loadcenter, the lowest live part is the bottom end of the busbars, so if you're coming in anywhere above that with a hole of your own, you have to use a Myers hub or equivalent watertight fitting instead of an ordinary cable clamp or conduit connector.

As far as hole proximity goes, on the other hand, the main constraint is physical installability as you'll need a bit of space to ensure the locknuts on the various fittings and conduits entering the box don't collide with each other.

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  • Thanks, this makes sense from a gravity perspective, water really should only flow down, thus holes above hot portions of the panel require different protections!
    – bwp8nt
    Sep 2 at 18:41

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