Roof Top A/C Compressor
- Thread starter Scott T.
- Start date
- Status
- Location
- Massachusetts
No, not normally.
Check out 725.55(A)
Check out 725.55(A)
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
725.55(J)(1) seems to allow this if a cable (I guess UF in this case) is used for the power conductors, although (J) doesn't really specify what kind of enclosures/raceways are included or excluded. It seems to be a miscellaneous section.
- Location
- Illinois
- Occupation
- retired electrician
Larry,
I don't see how 725.55(J) applies to raceways. The general rule in (A) for raceways is not modified by any of the other sections, so you can't mix the control and power conductors in the same raceway.
Don
I don't see how 725.55(J) applies to raceways. The general rule in (A) for raceways is not modified by any of the other sections, so you can't mix the control and power conductors in the same raceway.
Don
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Most of the power supplies that I have seen for HVAC equipment are rated as Class 2. How can these be reclassified as Class 1?
Under 725.52(A) you are reclassifying the circuits, not the power source. Please read the FPN.infinity said:
725.55(A) specifies "Cables and conductors of Class 2 and Class 3 circuits..." When these circuits are installed using a Class 1 method by way of 725.52(A) they not bound to this requirement because they are not Class 2 or Class 3 circuits.
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- Location
- Illinois
- Occupation
- retired electrician
When you reclassify the circuits they become Class 1 circuits. How can you connect this Class 1 circuit to a control device like a thermostat that is only listed for use with Class 2 circuits?
Don
Don
Listed for use with Class 2 power or Class 2 circuits? Perhaps a mild distinction, but nevertheless one which matters in this instance.don_resqcapt19 said:
I did a random search for a thermostat which was listed for Class 2 circuits and did not find any. I did find thermostats with a Class 2 power requirement. For example:
Johnson Controls T600xxx-3 Series Thermostats
Power Requirements 19 to 30 VAC, 50/60 Hz, 2 VA (Terminals 4 and 5) at 24 VAC Nominal, Class 2 or Safety Extra-Low Voltage (SELV)...
...Compliance United States UL Listed, File E27734, CCN XAPX,
Under UL 873, Temperature Indicating and Regulating Equipment
I ran into a dead end looking for UL 873.
- Location
- Illinois
- Occupation
- retired electrician
Smart,
Don
Where do you find that these are different in the NEC?
Don
- Location
- New Jersey
- Occupation
- Journeyman Electrician
don_resqcapt19 said:
That was my question too. We typically use one of these for boiler controls.
Printed on the outside of the transformer is CLASS 2. How can this be made into a Class 1 installation?
Only by inference where the the Code states Class ? circuits and Class ? power sources... as I said a mild distinction :wink:don_resqcapt19 said:
Anyway, going back to listed thermostats, if they are listed under UL 873: Temperature-Indicating and -Regulating Equipment, I don't see any part of the listing standard that limits thermostats to Class 2 circuits.
Whatever the case may be, if the thermostat manufacturer's spec's say Class 2 circuit only, then you can't use it on a Class 1 circuit.
- Location
- Illinois
- Occupation
- retired electrician
Smart,
It appears to me that UL 873 does not apply to Class 2 thermostats. From the scope document that you linked to:
I would expect that the instructions for the standard heating and AC control thermostats do specify for use on Class 2 circuits only, but I don't have one to check.
Don
http://forums.mikeholt.com/editpost.php?do=editpost&p=761453
It appears to me that UL 873 does not apply to Class 2 thermostats. From the scope document that you linked to:
I would expect that the instructions for the standard heating and AC control thermostats do specify for use on Class 2 circuits only, but I don't have one to check.
Don
http://forums.mikeholt.com/editpost.php?do=editpost&p=761453
Well I don't have one either :wink:don_resqcapt19 said:
In that UL 873 doesn't cover Class 2 thermostats says to me that Class 1 thermostats exist. The series I mentioned above from Johnson Controls is apparently an example. Note it is listed under UL 873 but yet it spec's a "low voltage" power requirement.
All in all, running control circuits with power is not something I would do... "not normally" :grin: ... but the question was asked and not completely answered... so I expanded on the subject a bit. In summation, it can be NEC-compliant to run A/C control circuits with power, but doing so does present this snag.
- Location
- Massachusetts
Smart $ said:
I think I head that somewhere before.....
'Normally' the snags outweigh the benefits.
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HVAC control
HVAC control
Try 300.11(B)(2),
Finding Code and UL references on HVAC equipment is most unlikely. A/C and heatpump secondary control 24VAc is located in the equipment and has a grommet for messenger wiring (Thermostat cabling types per Ashrae) at the control box. This is consistent with up to 6 ton units on commercial down to 1 ton on residential systems. (In all the energy management systems I have observed or worked on, roof unit LV control wiring is not included in feeder conduit raceways.) rbj
HVAC control
Try 300.11(B)(2),
Finding Code and UL references on HVAC equipment is most unlikely. A/C and heatpump secondary control 24VAc is located in the equipment and has a grommet for messenger wiring (Thermostat cabling types per Ashrae) at the control box. This is consistent with up to 6 ton units on commercial down to 1 ton on residential systems. (In all the energy management systems I have observed or worked on, roof unit LV control wiring is not included in feeder conduit raceways.) rbj
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