2

I'm running very short on space in my main panel. And I'm adding a second mini split air conditioner right now that needs another 240v breaker, and would eat the last space in my panel.

Rather than perpetuate the issue, I'd like to add a feeder panel and move both mini splits to it. The main panel and both the AC units are wall mounted on the same side of the house. Add a couple windows and a slope and I'm really tight on space.

Either I need to squeeze the feeder in between the main and a radon exhaust tube or take it out to the far side of the house where there's a fairly aggressive slope.

I couldn't find anything in wiring simplified that specifies a minimum distance between the main and a feeder. Did I miss it or is there really no minimum?

If I go the other way, and take it over the slope, I assume there is a maximum height from the ground, and I would measure that directly down to where the ground is below the feeder panel?

Either way it's a really short run, thinking 125 amp breaker with 1 awg copper to allow for future growth. I also imagine this might be close enough to the panel that I don't need a main breaker at the feeder panel? But I'll probably just choose a panel with one anyway, so I didn't look into whether it's necessary.

1
  • For very short runs I'm fine with copper wire since the cost will be negligible. (as in $30 instead of $10). However, keep in mind the subpanel's main lugs will be aluminum. Note the "$30 instead of $10".... $20 will buy you a whole bunch of breaker spaces, and breaker spaces are a great deal more useful than loyalty to a metal type. I like to see people get lots and lots of breaker spaces so they never need to do this again! Dec 9 '20 at 18:14
8

You can butt panels together as long as the doors open 90°

The absolute minimum distance between loadcenter cabinets, enclosed switches, or similar distribution enclosures is set by the 90° door-opening rule in NEC 110.26(A)(2):

(2) Width of Working Space. The width of the working space in front of the electrical equipment shall be the width of the equipment or 762 mm (30 in.), whichever is greater. In all cases, the work space shall permit at least a 90 degree opening of equipment doors or hinged panels.

However, you generally don't hit that save for corner cases; what will determine the actual minimum is loadcenter covers (combination covers tend to overhang their respective loadcenter boxes) and nipple sizing (you can't get any shorter than a close nipple) for surface mount installs, or the width of studs (1.5") for flush mount panels.

And yes, there is a maximum height for panels, measured straight down

The issue with the steep slope in your alternative location is twofold. First, a steep enough slope may simply not permit "ready and safe operation and maintenance" of the equipment in question, but that's an AHJ call. More importantly, though, the NEC sets a hard limit of 6'7" from the floor or ground level to the operating handle of the highest overcurrent device in the panel in NEC 240.24(A), as the exceptions to that rule don't apply to your situation. (This is so that you can get at your breakers in case you need to reset a tripped breaker or shut a faulty circuit off in a pinch, even if you aren't the Jolly Green Giant.)

Ditching the main breaker is actually a good idea

Since you were wondering, no, you won't need a main breaker in the subpanel provided that your subpanel is in or on the same building as the panel you're running the feeder from (and that you aren't invoking the feeder tap rules, but that's neither here nor there for you most likely). In fact, choosing a main lug panel here gives you an advantage, as many main lug panels ship with separate ground bars fitted at the factory, which saves you the work of having to fit them in the field. Just remember that neutrals go on neutral bars and grounds on grounding bars, in addition to pulling the green bonding screw or strap out of the new panel and running all four conductors (hot, hot, neutral, ground) to your new subpanel.

GO BIG OR GO HOME

Last but not least, there is no reason to pinch pennies on a tiny subpanel here. I would recommend a 40-space or 42-space, 200 or 225A, main lug panel in your situation as a minimum, since you're already starving for panel spaces. If you can, you might as well go bigger: the 2008 NEC allowed panels to have more than 42 spaces generally, so 54-space and 60-space panels have become available, if a bit pricier than their 42-space counterparts.

1

there is no minimum distance for the feeder.

you do not need a Main breaker in the sub panel. (at least where i live). but its a great idea if the sub panel is not in the same location as the main panel.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.