Are LED lighting considered linear or nonlinear loads?

John P79

New member
Location
Houston, Texas
Im reviewing a print that the feeder suppling a 100A panel has four conductors, a 3 phase 4 wire wye connected system, connected with #3 copper. According to Table 310.16(B)(16) #3 can carry 100 amps at 75 degree, however that table is based on no more than 3 current carying conductors and this panel has four including the neutral. The majority of the load of the panel is lighting consisting of LED fixtures. Is there a case that because LED fixtures are the majority of the load, that the neutral shouldn't be counted and Table 310.15(B)(3)(a) should be used to de-rate the conductors? Are LEDs considered linear or nonlinear?
 

GoldDigger

Moderator
Staff member
LEDs themselves are non Ohmic and therefore non-linear.
The combination of LED and driver can be power factor corrected to any degree you want to pay for, just as with fluorescent luminaires.
But if you are talking run of the mill, off the shelf, I would call them non-linear in terms of neutral sizing and CCC status.

Tapatalk!
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
So what kind of havoc are these and other electronic ballasted fixtures causing to 3phase electrical systems?

Seems like we are saving power but creating other issues.
 

Besoeker

Senior Member
Location
UK
LEDs themselves are non Ohmic and therefore non-linear.
The combination of LED and driver can be power factor corrected to any degree you want to pay for, just as with fluorescent luminaires.
But if you are talking run of the mill, off the shelf, I would call them non-linear in terms of neutral sizing and CCC status.

Tapatalk!
Power factor correction and and non-linear loads is a tricky business.
The LED driver circuits I've seen have a bridge rectifier input which would usually have good displacement power factor but very poor distortion power factor. And that's not so easy to correct.
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
So what happens in Existing older buildings?
It's not like you can just add a larger neutral or install an oversized neutral bussing.

What are power companies doing to deal with this.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
So what happens in Existing older buildings?
It's not like you can just add a larger neutral or install an oversized neutral bussing.

What are power companies doing to deal with this.
The marketing department is high-fiving all their customers for going green. The engineering department is quietly tearing their hair out.:eek:hmy:
 

Besoeker

Senior Member
Location
UK
So what kind of havoc are these and other electronic ballasted fixtures causing to 3phase electrical systems?

Seems like we are saving power but creating other issues.
Yes, that's probably the case. And not just lighting. A lot of single of single phase electronic loads produce third harmonic. A single appliance isn't a problem in itself. Just the sheer number of them in aggregate. The third harmonics add in the neutral of a three phase supply - three times the supply frequency means they coincide so add arithmetically. This can overload the neutral. I've been involved with cases where it has.
 

GoldDigger

Moderator
Staff member
The classic case has been the neutrals in wiring harnesses for older modular office (cubicle) gear.
Got burned out by load profile of desktop computers and servers.

Tapatalk!
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
This is going to be a real interesting with more implementation of electronic lighting.
In july new buildings of a certain size will have to have load shedding. and maybe seperate panels just for lighting loads.

going to be a problem when harmonics are not taken into account.
 

dfmischler

Senior Member
Location
Western NY
Cree customer service told me by email today that their 1100 lumen 2700K (75W equivalent) 13.5W bulb has an "official" power factor of 0.976. They said they do not yet have "official" numbers for the 1600 lumen (100W equivalent) bulb.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety

Besoeker

Senior Member
Location
UK
Some things your are better off not knowing the gruesome details of, like sausage making, politics...and now, resi power waveforms.
Indeed, you have a point.
I like to know what's in what I'm eating.

There was a serious point to my measurements of my current. It was for the evaluation of an energy saving device I was asked to test.
 

Electric-Light

Senior Member
It depends on each lamp. The amount of displacement power factor is negligible for all types, but the distortion power factor can range from about 0.5 to near unity. Dimmable ones usually have less THD. If you understand how standard dimmers work, you'll see that a common peak-drawing type front end wouldn't work. It does not car about how far you delay the power on is, because rectified power factors naturally have a turn-on delay pretty close to 90 degrees.

It works like an extremely fast clutch. Imagine you're rowing a boat. A resistive loads load it evenly across the entire stroke. A dimmer adjusts the power by always starting unloaded as you row, then decides when to load the oars. A rectified load don't load at all at the beginning, then loads the oars VERY heavily during a short range abruptly, then drops the load very abruptly.

For a dimmer to work it has to be similar to linear load or it will just ignore the power and use its own "clutch" to notch load.
 
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