I need to consider providing a low voltage (120/24 VAC) transformer with a 175VA to 300VA rating and fused outputs (8 total outputs). The output current is 3.5A per output. Since I am a temperature controls contractor, I am considering using 14AWG. plenum rated Class 2 twisted shielded wiring to power my field panels to be located above the ceiling. Can I do this?
class 2 power limitations
- Thread starter timaud
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Re: class 2 power limitations
According to the cutsheets of the 24VAC 8-output power supply, the outputs are PTC Protected Outputs (Class 2 power limited). But I admit, I do not know what the significance of "power limited". Also, just because it is over 100VA, so what? I would imagine each output is limited to a certain current level.
Can you shed some light on power limited vs. VA?
Thank you.
Tim
According to the cutsheets of the 24VAC 8-output power supply, the outputs are PTC Protected Outputs (Class 2 power limited). But I admit, I do not know what the significance of "power limited". Also, just because it is over 100VA, so what? I would imagine each output is limited to a certain current level.
Can you shed some light on power limited vs. VA?
Thank you.
Tim
- Location
- Illinois
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- retired electrician
Re: class 2 power limitations
A number of code cycles ago the code specified the maximum voltage and power permitted for a Class 2 power supply. At that time the maximum permitted power was 100va for a Class 2 power supply. Now the code just requires that the power supply be listed as a Class 2 power supply. If it is listed as such, then rules in Part III of Article 725 apply, if it is not listed as a Class 2 Power supply, then the rules in Part II apply.
Don
A number of code cycles ago the code specified the maximum voltage and power permitted for a Class 2 power supply. At that time the maximum permitted power was 100va for a Class 2 power supply. Now the code just requires that the power supply be listed as a Class 2 power supply. If it is listed as such, then rules in Part III of Article 725 apply, if it is not listed as a Class 2 Power supply, then the rules in Part II apply.
Don
Re: class 2 power limitations
Functional Devices, Inc. makes an enclosed 500VA power supply with five 100VA class II outputs. Model number PSH500A. Each output has a switch/circuit breaker rated for 4 amps. This and #14 TP jacketed wire can be used in a ceiling. If the ceiling is a plenum, make sure the wire is rated as such. Try: www.funtionaldevices.com
Functional Devices, Inc. makes an enclosed 500VA power supply with five 100VA class II outputs. Model number PSH500A. Each output has a switch/circuit breaker rated for 4 amps. This and #14 TP jacketed wire can be used in a ceiling. If the ceiling is a plenum, make sure the wire is rated as such. Try: www.funtionaldevices.com
Re: class 2 power limitations
Yes earlier NEC's had tables of power limitations right there in Art.725.
2002 NEC has in Tables 11(A) & 11(B) in Chapter 9.
It would be interesting to know if the #PSH500A is actually an xfmr with multiple windings rated 100VA each. As I have said before, Art.725 is one article that I am not real comfortable with. But I had to throw in my 2-cents worth.
Yes earlier NEC's had tables of power limitations right there in Art.725.
2002 NEC has in Tables 11(A) & 11(B) in Chapter 9.
It would be interesting to know if the #PSH500A is actually an xfmr with multiple windings rated 100VA each. As I have said before, Art.725 is one article that I am not real comfortable with. But I had to throw in my 2-cents worth.
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