Maximum wattage on a circuit

[jeff1166]

We prewired a building with one switch for three hanging fixtures in the entrance. We put this switch on a seperate 20 amp circuit. We did not know what type of fixtures they may purchase so we based our calculation on three fixtures @ 600 watts each. We were wrong...they have a total of 15-40 watt and 5-25 watt total 725 each or 2175 watts total. Am I correct in reading the code that this is a continious load so the maximum wattage I can have on this switch is 1920 watts? (120volts X 20 amps X 80%= 1920 watts)

I am trying to get them to change the 40 watt lamps to 25 watt but no luck.

Thanks for your help

 

[peter d]

Re: Maximum wattage on a circuit

Well, are these lights turned on for more than 3 hours? If so, then it's a continuous load.

 

[arkiesparky]

Re: Maximum wattage on a circuit

You are correct in that 1920 Watts is the maximum you can put on a 20Amp circuit.

Are these lights going to be dimmed?

 

[jeff1166]

Re: Maximum wattage on a circuit

The lights will be on for more than three hours with no dimmer.

 

[arkiesparky]

Re: Maximum wattage on a circuit

With that being the case, you will need to split the load.

Unless, the light sockets are rated "Heavy-Duty", in which case you could replace the breaker with a 30Amp and pull #10 wire to feed the circuit.

 

[jeff1166]

Re: Maximum wattage on a circuit

No such luck on the rating. I guess I know what needs to be done. Thanks for your help.

 

[peter d]

Re: Maximum wattage on a circuit

Originally posted by arkiesparky:
You are correct in that 1920 Watts is the maximum you can put on a 20Amp circuit.

You're not talking about all branch circuits, are you? Yes, that is the maximum you can put on a continuously loaded circuit, but there is no blanket provision that limits all branch circuits to 80% loading.

In fact, you can load a 20 amp circuit to 20 amps for 2 hours, 59 minutes and 59 seconds. As long as the load is turned off once every 3 hours, there is no code violation.

[ August 23, 2005, 04:50 PM: Message edited by: peter d ]

 

[plate]

Re: Maximum wattage on a circuit

In the text of the post you say ?maximum wattage on a switch?, although the title of the post is ?maximum wattage on circuit.? I assume you meant max wattage on ckt

210.20(A) (NEC2003) has an exception ?where the assembly, including the overcurrent devices protecting the branch circuit is listed for 100 percent of its rating, the ampere rating of the overcurrent device shall be permitted to be not less than the sum of continuous load and noncontinuous load?

If I am missing something here, I know I hear about it soon.

 

[steve66]

Re: Maximum wattage on a circuit

am trying to get them to change the 40 watt lamps to 25 watt but no luck.

That wouldn't help anyway. You have to base the load on the maximum wattage lamp that can be placed in the fixture per its label. If the fixtures say you can use 100W lamps, you would need (4) branch circuits. (3 X 20 X 100 = 6000 watts)

Steve

 

[petersonra]

Re: Maximum wattage on a circuit

Originally posted by steve66:

am trying to get them to change the 40 watt lamps to 25 watt but no luck.

That wouldn't help anyway. You have to base the load on the maximum wattage lamp that can be placed in the fixture per its label. If the fixtures say you can use 100W lamps, you would need (4) branch circuits. (3 X 20 X 100 = 6000 watts)

Steve

where does it say that???

 

[redfish]

Re: Maximum wattage on a circuit

We prewired a building with one switch for three hanging fixtures in the entrance. We put this switch on a seperate 20 amp circuit. We did not know what type of fixtures they may purchase so we based our calculation on three fixtures @ 600 watts each. We were wrong...they have a total of 15-40 watt and 5-25 watt total 725 each or 2175 watts total. Am I correct in reading the code that this is a continious load so the maximum wattage I can have on this switch is 1920 watts? (120volts X 20 amps X 80%= 1920 watts)

What type of wire did you use for yor branch circuit? #12 NM is allowed 25A and THHN is allowed 30A. You can install a 25A breaker and a contactor for a switch. Your continuos load is 2175VA x 125%= 2719VA or 23A. Please feel free to correct me if I'm wrong.

 

[paul]

Re: Maximum wattage on a circuit

Originally posted by redfish:
What type of wire did you use for yor branch circuit? #12 NM is allowed 25A and THHN is allowed 30A. You can install a 25A breaker and a contactor for a switch. Your continuos load is 2175VA x 125%= 2719VA or 23A. Please feel free to correct me if I'm wrong.

240.4(D)

 

[steve66]

Re: Maximum wattage on a circuit

Posted by petersonra:

where does it say that???

220.3(B)(4) of the 2002 NEC. Although now that I read it again, it says it applies only to recessed luminaires? I wonder why that only apply to recessed fixtures?

Steve

 

[charlie b]

Re: Maximum wattage on a circuit

I would say that 220.3(B)(1) covers the other luminaires, Steve.

We use the "VA per square foot" method for general lighting loads, but that is for the lighting load of an entire building. If you are discussing a single lighting circuit, then I think you need to go with the sum of the ratings of all the luminaires powered by that circuit.

 

[steve66]

Re: Maximum wattage on a circuit

Posted by Charlie B:

I would say that 220.3(B)(1) covers the other luminaires, Steve.

The same thing had crossed my mind, but I wasn't sure. So if a light fixture says it is suitable for use with a 100W lamp, one should use that for the branch circuit load calculation, even if we only install a 60W lamp.

Does that sound right? It sounds reasonable to me since anyone can buy larger lamps and install them themselves.

 

[charlie b]

Re: Maximum wattage on a circuit

Since we have to keep safety in mind, I would approach it that way.

 

[cselectric]

Re: Maximum wattage on a circuit

Originally posted by steve66:
Posted by petersonra:

where does it say that???

220.3(B)(4) of the 2002 NEC. Although now that I read it again, it says it applies only to recessed luminaires? I wonder why that only apply to recessed fixtures?

Steve

Not sure if this was meant to clarify the issue, but it seems to:

2005 NEC, art.220.14(D)
An outlet supplying luminaires shall be calculated based on the maximum volt-ampre rating of the equipment and lamps for which the luminaire is rated.

 

[LarryFine]

Re: Maximum wattage on a circuit

Originally posted by paul:

Originally posted by redfish:
What type of wire did you use for yor branch circuit? #12 NM is allowed 25A and THHN is allowed 30A. You can install a 25A breaker and a contactor for a switch. Your continuos load is 2175VA x 125%= 2719VA or 23A. Please feel free to correct me if I'm wrong.

240.4(D)

Paul, consider yourself corrected.

Yes, you may use these higher figures for derating purposes, but not for protection.

 

[steve66]

Re: Maximum wattage on a circuit

Posted by Cselectric:

2005 NEC, art.220.14(D)
An outlet supplying luminaires shall be calculated based on the maximum volt-ampre rating of the equipment and lamps for which the luminaire is rated.

If the NEC keeps clarifying all the grey areas, (just for the sake of safety), were not going to have anything fun left to debate

Steve