Class 2 transformer

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I installed a small 150 watt electronic transformer in a box in a cabinet for Low voltage lighting, 12 volt. Inspector wants to make sure it is a class 2. What is the difference and where in the code book does it refer to this
 

nhfire77

Senior Member
Location
NH
I installed a small 150 watt electronic transformer in a box in a cabinet for Low voltage lighting, 12 volt. Inspector wants to make sure it is a class 2. What is the difference and where in the code book does it refer to this


Article 411 low voltage lighting systems


Class 2 power supplies is defined in Article 725. Read this section for definitions between power and light circuits and class 1,2,3.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Inspector wants to make sure it is a class 2.

Real simple. What does the transformer say on it? If it's class 2 it will say class 2. If it doesn't say anything it's class 1 and you're screwed if you used CL2 wiring. It's not up to you to determine what class a power source is, it must be printed on the device.

-Hal
 

kwired

Electron manager
Location
NE Nebraska
Transformer should be marked class 2 if it is class 2.

Also see ch 9 table 11 for limitations on class 2 and 3 power supply.

150 VA is too large to be class 2, for 12 VAC, 60VA is max for class 2.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Also see ch 9 table 11 for limitations on class 2 and 3 power supply... 150 VA is too large to be class 2, for 12 VAC, 60VA is max for class 2.

Ordinarily if this were a simple transformer I would agree however with electronic power supplies engineers have been known to do some very exotic things to get around the UL class limitations. That's why the last word is what is printed on the device and why the NEC tables are obsolete unless you are "rolling your own".

-Hal
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
What kind of transformer is it? A low voltage lighting system has to be made of listed parts, either as an entire system or individual listed parts. Your power supply must be a listed lighting system power supply or a class 2 power supply, not just any listed transformer.

411.3 Listing Required.
Lighting systems operating at 30 volts or less shall comply with 411.3(A) or 411.3(B).
(A) Listed System. Lighting systems operating at 30 volts or less shall be listed as a complete system. The luminaires, power supply, and luminaire fittings (including the exposed bare conductors) of an exposed bare conductor lighting system shall be listed for the use as part of the same identified lighting system.
(B) Assembly of Listed Parts. A lighting system assembled from the following listed parts shall be permitted:
(1) Low-voltage luminaires
(2) Low-voltage luminaire power supply
(3) Class 2 power supply
(4) Low-voltage luminaire fittings
(5) Cord (secondary circuit) for which the luminaires and power supply are listed for use
(6) Cable, conductors in conduit, or other fixed wiring method for the secondary circuit
The luminaires, power supply, and luminaire fittings (including the exposed bare conductors) of an exposed bare conductor lighting system shall be listed for use as part of the same identified lighting system.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
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Electrical Engineer
The definition of a Class 2 transformer per UL-1585 is limited to 100VA and under 30V. If it is 150VA then by definition it cannot be Class 2 regardless of the voltage. Your inspector probably knows that but can't tell you what to use, just that it has to be Class 2. You need to either find a smaller transformer or not use Class 2 wiring methods. Most likely your LV lighting system is designed around Class 2 wiring so you you are stuck with the other limitation, a smaller power supply. That may mean more than one if your total light wattage exceeds 100W, no way around it that I can think of.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
The definition of a Class 2 transformer per UL-1585 is limited to 100VA and under 30V. If it is 150VA then by definition it cannot be Class 2 regardless of the voltage. Your inspector probably knows that but can't tell you what to use, just that it has to be Class 2. You need to either find a smaller transformer or not use Class 2 wiring methods. Most likely your LV lighting system is designed around Class 2 wiring so you you are stuck with the other limitation, a smaller power supply. That may mean more than one if your total light wattage exceeds 100W, no way around it that I can think of.

He certainly can buy a listed low voltage lighting power supply. They can be good up to 300 Watts or 25 amps @ 12 volts.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
He certainly can buy a listed low voltage lighting power supply. They can be good up to 300 Watts or 25 amps @ 12 volts.
Yes, but he would need Chapter 3 wiring methods or cable that was listed for use with that system. Class 2 wiring methods are not permitted with that power supply.
 
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