Lighting Load Calculations

[A/A Fuel GTX]

When laying out lighting circuits, how do you guys figure fixture totals when using LED's? For example, a standard 6" recessed can is usually rated for a 75W flood. For a 15 amp circuit, that would be roughly 23 cans per circuit. Now if LED's are used in place of the 75W floods ( 11W each in this case ) in the initial installation, can the circuit be designed with a greater number of cans to reflect the much lower LED power consumption?

 

[Smart $]

What is the fixture rated? That's what you use.

 

[Greg1707]

residential load

residential load

For residential I just figure 3 watts per square foot.

 

[A/A Fuel GTX]

What is the fixture rated? That's what you use.

Yeah, but lets get real here........Do you really think with the advent of LED lamps and the continuing drop in prices, consumers are going to install 75W lamps when 11W lamps of equal output are available for $10.00 each? So, if you figured the layout with LED lamps and the consumer opted for 75W lamps, what's the worst that could happen? Perhaps they'd trip a breaker? What's the difference between this scenario and someone using 8 microwaves on a SABC? The OCPD and properly sized wire trumps all poor decisions the homeowner may choose IMHO.

 

[A/A Fuel GTX]

For residential I just figure 3 watts per square foot.

Greg, I'm referring to actual loads on circuits. Not demand factors.

 

[Cow]

What is the fixture rated? That's what you use.

That's how we do it.

 

[A/A Fuel GTX]

That's how we do it.

OK, so you have a 15 amp circuit, 23, 75W recessed cans on the circuit. That's 1725W total load based on the fixture rating. If the same circuit was utilized with 11W floods, that's only 253W on a circuit capable of providing 1725W. Perhaps recessed cans need to come out with similar labeling like combination dimmers have, ie incandescent, CFL and LED ratings. Heck, it won't be long and LED's will be all that are available anyway. Love the technology, let's use it to our benefit.

 

[Smart $]

... Heck, it won't be long and LED's will be all that are available anyway. Love the technology, let's use it to our benefit.

Don't know what the 2017 NEC edition holds for us in this respect, but Code will adapt over time.

 

[mgookin]

When laying out lighting circuits, how do you guys figure fixture totals when using LED's? For example, a standard 6" recessed can is usually rated for a 75W flood. For a 15 amp circuit, that would be roughly 23 cans per circuit. Now if LED's are used in place of the 75W floods ( 11W each in this case ) in the initial installation, can the circuit be designed with a greater number of cans to reflect the much lower LED power consumption?

Answer to that was whatever the fixture is rated at.

Yeah, but lets get real here........Do you really think with the advent of LED lamps and the continuing drop in prices, consumers are going to install 75W lamps when 11W lamps of equal output are available for $10.00 each? So, if you figured the layout with LED lamps and the consumer opted for 75W lamps, what's the worst that could happen? Perhaps they'd trip a breaker? What's the difference between this scenario and someone using 8 microwaves on a SABC? The OCPD and properly sized wire trumps all poor decisions the homeowner may choose IMHO.

Are you saying the consumer is using the fixture outside of its rating, like is done with the old 60W max and they screw in 100W?

Greg, I'm referring to actual loads on circuits. Not demand factors.

You clarified what you were asking as the thread progressed. Are you saying you are installing LED fixtures which can also accept a 75W lamp? What's the fixture rated at? If you do your circuit per the rating of the fixture, you have done your job.

You can't stop someone from plugging in 50 daisy chained power strips and you can't stop them from exceeding the rating of a fixture.

 

[A/A Fuel GTX]

This is regarding standard, 6" recessed cans that have a rating of up to 75 W incandescent based on trim choice. The design here was to use 11W LED lamps throughout. Light output for the 11W LED's are equal to the 75W Halogens.

 

[Greg1707]

actual vs rated

actual vs rated

Does the NEC address this issue? I would think the load would be calculated on the actual load not the possible load?

 

[Dennis Alwon]

Does the NEC address this issue? I would think the load would be calculated on the actual load not the possible load?

Yes it does and Smart answered it.

220.14(D) Luminaires. An outlet supplying luminaire(s) shall be
calculated based on the maximum volt-ampere rating of the
equipment and lamps for which the luminaire(s) is rated.

 

[A/A Fuel GTX]

Does the NEC address this issue? I would think the load would be calculated on the actual load not the possible load?

I agree. If the system was designed for 11W per can, why would the max wattage of 75 be a factor?

 

[Dennis Alwon]

I agree. If the system was designed for 11W per can, why would the max wattage of 75 be a factor?

Because someone may not like led and they may use the full wattage of the can. Perhaps the incandescent bulbs will disappear one day and the nec will have to play catch up

 

[Smart $]

I agree. If the system was designed for 11W per can, why would the max wattage of 75 be a factor?

Because someone may not like led and they may use the full wattage of the can. Perhaps the incandescent bulbs will disappear one day and the nec will have to play catch up

There are already LED fixtures available that you can use the LED driver input rating for the load calculation. No catch up necessary.

Of course, the downside is reverting to incandescent is not an 'unplug-n-play' option. :happyno:

Make certain the customer has compared and chosen the desired CRI index (among other attributes) before purchasing. :happyyes:

 

[Greg1707]

220.12

220.12

I don't understand the relationship between 220.12 and 220.14D.

 

[Smart $]

I don't understand the relationship between 220.12 and 220.14D.

There is no relationship. 220.12 is general lighting. 220.14(D) being other loads is not.

 

[A/A Fuel GTX]

Because someone may not like led and they may use the full wattage of the can. Perhaps the incandescent bulbs will disappear one day and the nec will have to play catch up

How is having 13, 15 Amp receptacles on a 15 Amp circuit any different? Someone may plug in 13 space heaters..........

The OCPD will do its job forcing the end user to use the circuit effectively.

 

[Smart $]

How is having 13, 15 Amp receptacles on a 15 Amp circuit any different? Someone may plug in 13 space heaters..........

The OCPD will do its job forcing the end user to use the circuit effectively.

In the sense that you present it, it is no different. In the Code sense of our responses, it is different simply because Code says so.

As a lawyer once told me, you are trying to apply logic where logic does not apply.

 

[mgookin]

This is regarding standard, 6" recessed cans that have a rating of up to 75 W incandescent based on trim choice. The design here was to use 11W LED lamps throughout. Light output for the 11W LED's are equal to the 75W Halogens.

There is no "up to". They are rated 75W.
Ratings are max load.
You have to go by the rating of 75W per.
The light output "equal to" ... is moot.