Class 1, 2 and 3

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Dennis Alwon

Dennis Alwon

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For years this classification has been bugging me since I really don't get it. I understand class 2 and 3 will be written on the transformer or the power source that supplies the cir. What I don't get is Class 1.

Are there power systems that are class 1 that will give low voltage--24v on down?

Is not the line side wiring we do everday in homes etc considered class1?

If someone knows what makes something class 1, 2 or 3 I would be interested to get that knowledge.

This all came about because of discussions of art 300.3 (C). Is it every possible to have an hvac unit control circuit (24V) installed with the line voltage. I am told almost all hvac tranies are class 2.

Can someone give a compliant real life scenario when 300.3(C) can be used?
 
Does 725.41 help ?
(It's a bit lengthy for posting)

As far as 300.3(C), the most common application I would think is 480v and 208/120 circuits occupying the same raceway.
 
augie47 said:
Does 725.41 help ?
(It's a bit lengthy for posting)

As far as 300.3(C), the most common application I would think is 480v and 208/120 circuits occupying the same raceway.
Click to expand...

Yes that I knew but is there a situation where say 120v and 24V can be in the same raceway.
 
I have installed a sound system in a church where the amps for the speakers actually said class 1 for speaker wiring. I don't remember the specs, but something like 1500 watts each. Had to run 3/4 emt with #6 thhn because the inspector didn't like the speaker wire with no markings that came with the unit. :roll:

I was told long ago, if there was no bang and sparks by shorting the wires together, you have a class 2 or 3 circuit. (I know, not the WHOLE truth.)
 
defears said:
I have installed a sound system in a church where the amps for the speakers actually said class 1 for speaker wiring. I don't remember the specs, but something like 1500 watts each. Had to run 3/4 emt with #6 thhn because the inspector didn't like the speaker wire with no markings that came with the unit. :roll:
Click to expand...

So speakers are class one but you probably wouldn't want them in with the power conductors and was the insulation the same voltage rating as the thhn?

I was told long ago, if there was no bang and sparks by shorting the wires together, you have a class 2 or 3 circuit. (I know, not the WHOLE truth.)
Click to expand...
That is what I was thinking, but it ain't totally right.

Class 1 Circuit. The portion of the wiring system between the load side of the overcurrent device or power-limited supply and the connected equipment.
Click to expand...


And as Gus noted 725.41 shows class 1 transformers exist and are limited to 30 volts. So it seems that there are class 1 circuits that are low voltage-- just never been aware of them.
 
jumper said:
It seems to fit the definition at 1500w.

(A) Class 1 Power-Limited Circuits. These circuits shall
be supplied from a source that has a rated output of not
more than 30 volts and 1000 volt-amperes
Click to expand...

1500 watt is more than 1000VA, I presume. So how is it class 1
 
It's class1, just not power limited. So you need to use UF on that trans even if it's 12v. Not home depot cheapo cord.

I need to learn to quote messages.
 
defears said:
It's class1, just not power limited. So you need to use UF on that trans even if it's 12v. Not home depot cheapo cord.

I need to learn to quote messages.
Click to expand...

Bottom right of posts says reply with quote.

Now how do you know that trany is class 1
 
725.46 Class 1 Circuit Wiring Methods. Class 1 circuits shall be installed in accordance with Part I of Article 300 and with the wiring methods from the appropriate articles in Chapter 3.

Exception No. 1: The provisions of 725.48 through 725.51 shall be permitted to apply in installations of Class 1 circuits.

Exception No. 2: Methods permitted or required by other articles of this Code shall apply to installations of Class 1 circuits.
 
This is from nec plus.

Often, remote-control and signaling circuits that do not meet the requirements of Class 2 or Class 3 circuits are classed as Class 1 circuits by default. For example, a listed nurse call system may contain a power supply with an output of 500 watts at 24 volts. Because this power supply exceeds the maximum permitted output of a Class 2 power supply and the output terminals are not marked to indicate the equipment as suitable for a Class 2 power supply, the output circuit wiring is classified as Class 1 and subject to all the Class 1 circuit requirements.
 
Your welcome.

Every time you look up something that you've been doing forever, it's always harder to find it.
 
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