Class 2 Circuit - max power to keep class 2 designation

[saxman2u]

Hi,
We are in the design phase of a control system that uses a switching power supply that is UL listed. Primary output voltage is 24VDC and input voltage is 85 - 132 VAC or 170 - 264 VAC. Product detail located here.

Questions:
1. If our output power is kept under 100 watts or 4.17 amps with an overcurrent protection device like a fuse, does a class 2 designation still apply to this power supply?
2. If this device is housed in a UL listed NEMA box that is NEMA rated 1,2,4, 4X and is IP65 & 66 rated, can this specific power supply be housed in this specific NEMA box?

Thanks for your help!
-S

 

[Jraef]

1. Yes, but there must be more than just a fuse. There are electronic circuit protectors that limit the output to 4A, where you can put it downstream of a larger power supply and it has up to 6 outputs, each one limited to 4A. Allen Bradley has them for sure (link), there are others available. In the A-B units you might see that they have higher amp ratings, but if you specify that you want the Class 2 option, it limits you to 4A. The key point is, however that each individual output is a listed Class 2 circuit power source even though they are fed by a larger power supply that would NOT be listed for Class 2.

2. Yes, provided you account for the heat trapped in the box, meaning with no ventilation (if NEMA 4), you must size the box to be able to dissipate all of the internal heat created by the power supply out through the sides. That can be tricky in hot areas, direct sunlight, etc. in that the box size can get ridiculous. There are NEMA 4 rated power supplies that have external heat sinks though, I would recommend going that route.

 

[tom baker]

Will your power supply enclosure have a UL. listing? You will need terminal blocks, circuit breakers, DIN rail, etc? Without listing some jurisdictions won’t allow

 

[jaggedben]

Maybe I'm missing a detail but I don't believe you can use that power source as a Class 2 source under the NEC unless it is part of a larger assembly where the output is listed and/or marked as such. I'm used to power supplies for 'control systems' being listed or marked as Class 2. That's largely how we and the NEC know they are Class 2. I wonder if you wouldn't be better off starting with a power supply that already has a Class 2 listing.

 

[petersonra]

Hi,
We are in the design phase of a control system that uses a switching power supply that is UL listed. Primary output voltage is 24VDC and input voltage is 85 - 132 VAC or 170 - 264 VAC. Product detail located here.

Questions:
1. If our output power is kept under 100 watts or 4.17 amps with an overcurrent protection device like a fuse, does a class 2 designation still apply to this power supply?
2. If this device is housed in a UL listed NEMA box that is NEMA rated 1,2,4, 4X and is IP65 & 66 rated, can this specific power supply be housed in this specific NEMA box?

Thanks for your help!
-S

The brochure you linked doesnt say it is UL listed. Only UL recognized.

To use it to power a class 2 circuit it is required to be listed as a class 2 power supply.

You can put the power supply in any kind of box you want to. I am not sure the box is actually listed. NEMA does not list anything. The way the information is worded is a little goofy. I didn't look real close but it appears to be saying it is made of UL approved polymer, not that it is UL listed. My brief look could have led me down the wrong path though.