How to create a class 2 circuit?

Status
Not open for further replies.
D

darekelec

Senior Member
Location
nyc
hey, professionals!
I have a question on how to create class 2 circuit to energize for example incandescent 24V light fixtures - cove light strips or individual LV lights.
How to protect the transformer? How to distribute power from lets say 300W transformer to multiple light fixtures.
Do I have to install any additional breaker for transformer or driver if it says class 2 on it?
what kind of wires can I use on class 2 circuit?
this knowledge will be usefull for me to apply in installation of LEDs as well.
I am asking all this because in my area inspectors don't pay attention to low voltage installation but they are becoming more strict and I believe they will start inspecting LV soon.
Thank you in advance :)
 
darekelec said:
hey, professionals!
I have a question on how to create class 2 circuit to energize for example incandescent 24V light fixtures - cove light strips or individual LV lights.
How to protect the transformer? How to distribute power from lets say 300W transformer to multiple light fixtures.
Do I have to install any additional breaker for transformer or driver if it says class 2 on it?
what kind of wires can I use on class 2 circuit?
this knowledge will be usefull for me to apply in installation of LEDs as well.
I am asking all this because in my area inspectors don't pay attention to low voltage installation but they are becoming more strict and I believe they will start inspecting LV soon.
Thank you in advance :)
Click to expand...

Class 2 Transformers are thermally protected and do not require over current protection but make sure it's listed and LABELED as Class 2 from the manufacture.
Also bare in mind NEC states Chapter 9 11B (2008) a 24VDC power supply class 2 max power is 100W. Wiring for class 2 is CL2, CL2P, and CL2X
ON THE LOAD SIDE of the transformer and in fire alarm and control signaling circuits it would be FPLP, FPL etc..
I have NY license as well as CT and inspectors are very particular in most counties with burg alarm and especially fire alarm. What parts of NY are you talking about?
 
You don't "create" a class 2 circuit any more than you create, say, a 20 amp circuit. For a 20 amp circuit you feed it from a 20 amp breaker. For a class 2 circuit you feed it from a transformer or power source that says CLASS 2 on it. Not big enough for all the stuff you need to power? Install more transformers and circuits. That's really all you need to know.

For wiring CL2, CL2R, CL2P, CL2X, CL3, CL3R, CL3P, CL3X, CM, CMR, CMP, CMX. Where:

R= riser
P= plenum
X= sunlight resistant outdoor
nothing= regular PVC

You need to look at the chart in Art 725.

-Hal
 
darekelec said:
hey, professionals!
I have a question on how to create class 2 circuit to energize for example incandescent 24V light fixtures - cove light strips or individual LV lights.
How to protect the transformer? How to distribute power from lets say 300W transformer to multiple light fixtures.
Click to expand...

You buy the right equipment, you don't cobble it together.


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 sys-tem shall be listed for the use as part of the same identified lighting system.

(B) Assembly of Listed Parts. A lighting system as-sembled 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.
Click to expand...
 
I dont think it says class 2 transformer on 300W 120/24V xfmr from technomagnet that i installed recently. if i need multiple class 2 circuits can I just install 4 Amp breakers on secondary? did I read somewhere that those breakers have to be accessible from outside (not in box) and resettable?
what if my 24V festoon cove light strip is more than 100W?
Is DC any different from AC in terms of wire sizing?
i'm in NYC working on hi end res and i have never heard about a violation on LV but inspectors are getting more and more strict so i would like to learn before they start to write tickets for LV installation
 
Iwire just posted the applicable section. I just posted same section in your other thread covering similar topic with low voltage LED's.

300 watt supply is too big to be a class 2 supply, there is no way around that.

About the only class 2 systems you will find, you will buy as a set most cases.

Remember that 300 watts @ 12 volts is 25 amps. You will be running 10 AWG minimum conductors. Don't be fooled by the fact it is only 12 volts, 25 amps will still heat up conductors if they are too small. I think the largest class 2 supply you will find will be about 60 watts, which is only 5 amps @ 12 volts.
 
darekelec said:
I dont think it says class 2 transformer on 300W 120/24V xfmr from technomagnet that i installed recently. if i need multiple class 2 circuits can I just install 4 Amp breakers on secondary? did I read somewhere that those breakers have to be accessible from outside (not in box) and resettable?
what if my 24V festoon cove light strip is more than 100W?
Is DC any different from AC in terms of wire sizing?
i'm in NYC working on hi end res and i have never heard about a violation on LV but inspectors are getting more and more strict so i would like to learn before they start to write tickets for LV installation
Click to expand...

I think for some reason you are getting hung up on CL2. There is no such thing as a CL2 load, the load does not determine the type of circuit, only the power source does that.

You absolutely cannot install breakers after a transformer and call them CL2 circuits. The reason that transformer doesn't say class 2 on it is because it isn't a class 2 transformer. Likely it doesn't say anything and that makes it a class 1 requiring class 1 wiring methods. Class 1 wiring methods are the same Chapter 3 methods as for line voltage power and lighting- Romex, AC, conduit, etc.


We get questions about this every so often from those looking to install undercabinet and indoor wiring for landscape LV lighting. If it isn't fed from a class 2 power source you have to use Romex or whatever other Chapter 3 wiring method works for you just like it was line voltage.

Your only other alternative is a number of small class 2 transformers if it is possible to split up the lighting into groups.

-Hal
 
Class 2 circuits do have a current limitation Chapter 9 tables 11(A) &(B). The circuit that exceed the current limitations cannot be considered Class 2. Yes, by fusing the load side -- as a Q tran 12v 300w transformer with intregal 5 amp resets -- will produce 5 - class 2 circuits. Are you having an issue with the connections not within a j box?
 
Last edited:
mwm1752 said:
Class 2 circuits do have a current limitation Chapter 9 tables 11(A) &(B). The circuit that exceed the current limitations cannot be considered Class 2. Yes, by fusing the load side -- as a Q tran 12v 300w transformer with intregal 5 amp resets -- will produce 5 - class 2 circuits. Are you having an issue with the connections not within a j box?
Click to expand...

First off I have always taken exception with the inclusion of those tables in Chapter 9. It's not for us to design power sources, that is up to the manufacturer and the listing agency who will do the testing for compliance. That's why we now have the system in place where a class 2, class 3 or class 1 power source will be listed and have a label affixed attesting to what it is.

If a transformer has multiple class 2 outputs fed through integral breakers it is a listed assembly. You cannot take a transformer and wire breakers on it's output and expect it to be code compliant.

-Hal
 
To back up what Hal said.


III. Class 2 and Class 3 Circuits

725.121 Power Sources for Class 2 and Class 3 Circuits.
(A) Power Source. The power source for a Class 2 or a
Class 3 circuit shall be as specified in 725.121(A)(1), (A)(2),
(A)(3), (A)(4), or (A)(5):


(1) A listed Class 2 or Class 3 transformer

(2) A listed Class 2 or Class 3 power supply

(3) Other listed equipment marked to identify the Class 2
or Class 3 power source

Exception No. 1 to (3): Thermocouples shall not require
listing as a Class 2 power source

Exception No. 2 to (3): Limited power circuits of listed
equipment where these circuits have energy levels rated at
or below the limits established in Chapter 9, Table 11(A)
and Table 11(B).


(4) Listed information technology (computer) equipment
limited-power circuits.


(5) A dry cell battery shall be considered an inherently limited
Class 2 power source, provided the voltage is 30 volts or
less and the capacity is equal to or less than that available
from series connected No. 6 carbon zinc cells.
Click to expand...
 
Mucho inteligente.
I am learning here. thank you for your knowledge and input.
if i do not want to use class 1 wiring but class 2 can I install a driver like this

http://www.amazon.com/MEANWELL-Comp...265966&sr=8-2&keywords=class+2+led+driver+24V

in for example 12x12 enclosure with power conductor for input and on output go with class 2 wiring to led light strips?
how about the rule that cl1 and cl2 cannot be mixed in enclosure without a barrier?
could I use thermostat wire if my led strips dont use much power?
 
darekelec said:
Mucho inteligente.
I am learning here. thank you for your knowledge and input.
if i do not want to use class 1 wiring but class 2 can I install a driver like this

http://www.amazon.com/MEANWELL-Comp...265966&sr=8-2&keywords=class+2+led+driver+24V

in for example 12x12 enclosure with power conductor for input and on output go with class 2 wiring to led light strips?
how about the rule that cl1 and cl2 cannot be mixed in enclosure without a barrier?
could I use thermostat wire if my led strips dont use much power?
Click to expand...

Again go to 411.3 here is the last sentence in that section:

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.
Click to expand...

There is likely luminaires identified as same system that go with the unit you posted a link to. You need to find the driver that goes with the luminaires you wish to install.
 
Well, that is a class 2 power supply. Says so right on it like it should.

As for the line voltage and the LV being in the same enclosure without a partition, that is allowable in this case- see 725.137(D)

51HmgoxtRuL.jpg
 
Status
Not open for further replies.
Top