Rooftop AC combining panel

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Z

Zee

Senior Member
Location
CA
Is there an AC load center that could be mounted:
1. at an angle
2. on rooftops (most AC breakers not listed for such high heat)
in order to combine the AC branch circuits of a micro-inverter system?

I don't want to do so, but I have very limited space at ground level.
In any case it seems like there would be a real need to mimic the usefulness of the DC CB's we use and love.
 
S

So Cal

Member
Location
Los Angeles, Ca
I don't Know about the angle, that may have more to do with the waterprof rating, but as to the heat; see SEC 93.0600. BASIC PROVISIONS, then Table 310.15(B)(2)(c) for temp adders for distance from the roof. Can the load center be placed on the north side of something like a chimney (shaded area) Can it be raised up off the roof? (lower temp adder) can a sunscreen be added? (shaded area)
 
kwired

kwired

Electron manager
Location
NE Nebraska
Dennis Alwon said:
Most cb cannot be mounted horizontally as the indication would not comply with 240.81
Click to expand...

You want to clarify what you mean? Most breakers in panelboards are mounted horizontally, indication works at any angle - the only thing to violate here is that handle up must be the ON position if the handle operates vertically.
 
Dennis Alwon

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
kwired said:
You want to clarify what you mean? Most breakers in panelboards are mounted horizontally, indication works at any angle - the only thing to violate here is that handle up must be the ON position if the handle operates vertically.
Click to expand...
There are other issues. How do you maintain WP with a panel turned sideways on a rooftop. Also unless the breakers were only on one side so the breakers would be up when on, it would be a violation-- I thought 240.81 clarifies that as I stated.
 
Z

Zee

Senior Member
Location
CA
So Cal said:
I don't Know about the angle, that may have more to do with the waterprof rating, but as to the heat; see SEC 93.0600. BASIC PROVISIONS, then Table 310.15(B)(2)(c) for temp adders for distance from the roof. Can the load center be placed on the north side of something like a chimney (shaded area) Can it be raised up off the roof? (lower temp adder) can a sunscreen be added? (shaded area)
Click to expand...
Thanks for the thoughts, SoCal.
No, no chimney to mount on. (good idea have used before for DC Comb. Box)
Yes, I can definitely, and would, raise it off roof.
Sunscreen difficult while maintaining accessibility and good appearance on residential sloped roof.
The point about shading a breaker panel is well taken: I will do what I can to mount it on wall.

BTW - I HAVE painted boxes white before, and it dramatically cooled them.
 
Z

Zee

Senior Member
Location
CA
Thanks guys for input! Yes, I will keep breakers in a position so that the handles are "up when on." (or sideways)

My primary concern is with the rooftop heat that I have heard will destroy - or trip AC breakers unnecessarily.
 
kwired

kwired

Electron manager
Location
NE Nebraska
Dennis Alwon said:
There are other issues. How do you maintain WP with a panel turned sideways on a rooftop. Also unless the breakers were only on one side so the breakers would be up when on, it would be a violation-- I thought 240.81 clarifies that as I stated.
Click to expand...

I think we have different interpretations of what OP is wanting to do.

I will also add:240.24(A) says "Overcurrent devices shall be readily accessible"
putting a panel on the roof may disqualify "readily accessible" unless there is permanent stairs or other access to the roof. 110.26 doesn't mention if a sloped surface (or how much slope) violates working space. Most people may agree 4/12 or less pitch maybe is ok. but 6/12 or greater is not that desirable to have to work on.
 
Z

Zee

Senior Member
Location
CA
Kwired,
a new and excellent consideration: accessibility. Thanks!

I decided I am placing the load center in the garage. Too much trouble on roof, given all the problems associated with it.
and yes, this roof pitch is at least 6/12, and "not desirable"......:sick:
 
S

SolarOH

Member
Location
SW Ohio
I don't believe the NEC covers this specifically. But many breaker manufacturers have derate tables for their breakers at various temperatures. If you used table 310.15 (3) (c) an applied that to your load center, taking into account your ambient temperatures. You could account for the temperature and derate your breakers. These tables are by the manufacturer, and some AHJ's may not accept the method in this situation.

informative link on breaker/temperature impact: click here

But there are two sides to this sword, in the summer, your breakers will have a lower trip value than is printed, and in the winter they will have a trip value HIGHER than listed. So you could end up with a system that does not adequately protect the equipment/wires.

I don't see this as a big issue with an outdoor load center mounted on a wall, where the temperature swings are mostly due to ambient temps, but on a shingle roof, where the differences between a snow covered winter roof, and blazing hot summer roof could vary by 78C or more (-20c winter, to 36C +22C = 58C for distance to roof in summer, as an example)

I know you've already installed you load center in the garage, but thought this might be a worthwhile point to add for future installations for you or others.
 
Z

Zee

Senior Member
Location
CA
Aha...I see it is the brkr. mnfctr.s that provide derate tables for temperature (and not NEC).
Yes , thanks. That is useful. I will remember this page for that link if needed.
The last place i want nuisance tripping is on a roof...................
 
kwired

kwired

Electron manager
Location
NE Nebraska
Remember a breaker for an AC unit is sized at least 200% and more likely closer to 250% of the compressor ampacity plus the blower FLA. It is not going to protect from overload - that is done by the overload device within the compressor and blower motors. A breaker protecting an AC unit should generally only trip in response to short circuit and ground faults, or abnormal conditions resulting in locked rotor current- but most of the time the motor overload cuts out before breaker trips during locked rotor conditions from my experiences.
 
J

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
kwired said:
Remember a breaker for an AC unit is sized at least 200% and more likely closer to 250% of the compressor ampacity plus the blower FLA. It is not going to protect from overload - that is done by the overload device within the compressor and blower motors. A breaker protecting an AC unit should generally only trip in response to short circuit and ground faults, or abnormal conditions resulting in locked rotor current- but most of the time the motor overload cuts out before breaker trips during locked rotor conditions from my experiences.
Click to expand...

This thread is not about air conditioning. AC refers to alternating current, and is being used to distinguish from DC because this is the PV forum.
 
kwired

kwired

Electron manager
Location
NE Nebraska
Sorry, I was not paying attention, and somehow got the AC embedded in my brain as air conditioning. I think early on I did realize this was about PV.

I don't generally pay too close attention to which forum category we are in, as I generally just search for either subscribed threads or new posts - and either of those will bring up mixed results.
 
S

SolarOH

Member
Location
SW Ohio
kwired brings a good point though.

An "AC" unit (air conditioner) is sized as kwired noted, and as such, their breaker will likely never trip purely from heat derating. With solar inverters, the "AC";) output is a relatively continuous current, that is the current used for the code calculation of breaker size, since the inverters have no real surge that requires special consideration. Meaning on a bight sunny day, then the solar is kicking out at capacity, you have your maximum AC current, continuously, at the same time you have you maximum roof top temperatures. (I know that if it's really hot, the PV array is less efficient, but a lot of installers, myself included, have more solar DC capacity than they do inverter AC capacity, so you'll certainly see this happen) So you are much more likely to run into issues with nuisance tripping.
 
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