I'm working on a 60 kW project and we're installing a 400 A fused disconnect with 400 A fuses for our utility disconnect of the PV array. The service voltage is 208/120 Three phase so either a general or a heavy duty disconnect meets my voltage and current requirements. Is there any reason to use the heavy duty disconnect? I don't imagine the disconnect will be switched more than a couple times a year if that so I don't see a reason to use the heavy duty disconnect to allow for more switching actions over the lifetime of the system. Is there any other reason I should use heavy duty instead of general duty for my disconnect? The project is for a facilities maintenance building...
General or Heavy Duty Disconnect
- Thread starter SunFish
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petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
I don't know much about PV systems but I do not care one way or the other about disconnect switches. They are not generally rated to make or break current anyway.
However, there is not enough difference in price for the stuff I use to make buying a lighter duty unit worthwhile.
However, there is not enough difference in price for the stuff I use to make buying a lighter duty unit worthwhile.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
You know how marketing terms can be: in 1958, Square D said general duty safety switches "are designed for residential and light commercial applications where pricing is limiting and service factor is not great..." and heavy duty were "designed for heavy duty and/or mass production industries were price is secondary to maximum safety and continued performance...".
Carultch
Senior Member
- Location
- Massachusetts
There's gotta be a more objective specification on what "General Duty" and "Heavy Duty" mean. What would you look for in an application, to determine that general duty is insufficient? We all know what volts, poles, amperes, and NEMA enclosure ratings mean, but unless there is a more objective definition, it seems as if it could be that a particular Square D general duty switch could be equivalent to a particular GE heavy duty switch, and you'd never know for sure.
I think in most solar applications, we're talking about a knife blade switch that the utilitys require as a "belt-and-suspenders" means of being able to make sure your system doesn't backfeed the grid. Even though the UL standard of grid tied inverters already does this. In otherwords, we're talking about a switch that would likely remain in the on position for the whole service life.
Unless it doubles as a switch you use for maintenance purposes, it is simply there because the utility requires it to be there.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Typically, General Duty devices are rated at 240V max, and are available in NEMA1 and NEMA3R enclosures only. Rarely do they include interlocks that prevent the door from being opened, without tools, when the switch is on.
In contrast, Heavy Duty devices are rated up to 600V, they have many types of enclosure choices, the doors are interlocked with the mechanism, and there are options, like aux contacts, available.
Other than when used for 'Across the Line' motor starting, the performance of heavy duty devices is rarely compared to general duty ones.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Electrical Engineer - Photovoltaic Systems
Very generally, we use GD switches in residential applications and HD switches on commercial systems.
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
What he said.
I think the only important thing here is whether the specs on the switch are sufficient for the application.
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