lady sparks lover
Senior Member
Re: Roof Top HVAC Units
That's right, and it wouldn't be...
Roof Top HVAC Units
- Thread starter maggmick
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Re: Roof Top HVAC Units
Personra,
You must be unfamiliar with 210.21 or210.24.
Also, a dedicated 2,000 VA transformer has a lot of voltage drop. A typical dry transformer has an impendance of around 5.4% at a power factor similar to the locked rotor current of a motor. A 5.4% impendance transformer needs to be able to supply at least 3 times the full load current of the largest motor to be able to start the largest motor.
Therefore, you are usually better off to get the 20 ampere branch circuit from the nearest 120/whatever panelboard as the panelboard will have a stiffer source. Almost nobody uses 15 amp wiring for commercial receptacles anymore.
Personra,
You must be unfamiliar with 210.21 or210.24.
Also, a dedicated 2,000 VA transformer has a lot of voltage drop. A typical dry transformer has an impendance of around 5.4% at a power factor similar to the locked rotor current of a motor. A 5.4% impendance transformer needs to be able to supply at least 3 times the full load current of the largest motor to be able to start the largest motor.
Therefore, you are usually better off to get the 20 ampere branch circuit from the nearest 120/whatever panelboard as the panelboard will have a stiffer source. Almost nobody uses 15 amp wiring for commercial receptacles anymore.
gmreynol
Member
Re: Roof Top HVAC Units
In use cover not needed, Disconnects with the gfci receptacle installed within it needs its own power, how ever you get it. And if you can talk the hvac co. into supplying internal receptacles, why not get them to supply the factory disconnects too lol. I cant even get a cut sheet from them.
In use cover not needed, Disconnects with the gfci receptacle installed within it needs its own power, how ever you get it. And if you can talk the hvac co. into supplying internal receptacles, why not get them to supply the factory disconnects too lol. I cant even get a cut sheet from them.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: Roof Top HVAC Units
As sceepe mentioned, there is no flexibility about the intended duration or interval of use.
If it's wet, an in-use it gets.
I'd say a roof top sounds like a wet location, IMO.
As sceepe mentioned, there is no flexibility about the intended duration or interval of use.
If it's wet, an in-use it gets.
gmreynol
Member
Re: Roof Top HVAC Units
Yes George you are correct, I misread article 406.8(b)(2)(b). All you transformer people might check out 210.9 branch circuits shall not be derived from autotranformers unless the circuit supplied has a grounded conductor of the system supplying the autotransformer. Also 210.63 is intended to prevent makeshift methods of obtaining 120 volt power for service receptacle
Yes George you are correct, I misread article 406.8(b)(2)(b). All you transformer people might check out 210.9 branch circuits shall not be derived from autotranformers unless the circuit supplied has a grounded conductor of the system supplying the autotransformer. Also 210.63 is intended to prevent makeshift methods of obtaining 120 volt power for service receptacle
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: Roof Top HVAC Units
I am in agreement that it would be "better" to just run a 20A branch circuit. I don't see how anything you have cited requires it. The outlet has to be put an a branch ciruit with OCPD that does not exceed the outlet rating, but nothing prohibits you from putting it on a circuit with an OCPD with a lower rating.
sandsnow
Senior Member
- Location
- Southern California
Re: Roof Top HVAC Units
Trane makes a unit with integral disconnect and xfmr/recep off the line side of that. All you have to do is run power to the unit and you're done.
Trane makes a unit with integral disconnect and xfmr/recep off the line side of that. All you have to do is run power to the unit and you're done.
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