When do I consider nonlinear loads?

Status
Not open for further replies.
S

sgremmer

Member
I have a large condo/hotel building with a 120/208 volt 3 phase 3000 amp service. My concern on the matter is if I should count the neutral conductor [310.15 (B)(4)(c)]to derate the feeders from the MDC to the other disturbution centers.What is the red flag that should be thrown up for me to concider derating a 4-wire 3-phase feeder.
 
Last edited:
i would think this would be more an issue of unbalanced load vs nonlinear. The load will be unbalanced and the neutral will be a current carrying conductor.
 
wireguru said:
i would think this would be more an issue of unbalanced load vs nonlinear. The load will be unbalanced and the neutral will be a current carrying conductor.
Click to expand...
An unbalanced load does not make the neutral conductor a current carrying conductor for the purposes of derating. Derating is because of the heat produced when the current flows. The two worst cases for heat (maximum heat) are when all 3 phase conductors are fully loaded or when two of the phase conductors are fully loaded. All other combinations of loading, balanced or unbalanced produce less total heat.
 
Can anyone give a sold answer to the question given. Do I consider it when ever I see electronic lighting, or any place that has electronic equipment. How far do you take this?
 
sgremmer said:
Can anyone give a sold answer to the question given. Do I consider it when ever I see electronic lighting, or any place that has electronic equipment. How far do you take this?
Click to expand...


The NEC requires the neutral to be counted as a CCC when a major portion of the load is non-linear. That translates to more than 50% of the load. Given the fact that this is a condo/hotel building I don't see how you could ever come close to more than 50% of the load being non-linear. IMO it doesn't even require further consideration.
 
infinity said:
The NEC requires the neutral to be counted as a CCC when a major portion of the load is non-linear.
Click to expand...
All resistance loads like heat, incandescent light bulbs, electric ranges, all normal motor loads (not with VFDs), etc. are linear loads.

Most but not all electronic loads like some phone systems, VFDs, switch mode power supplies, electronic ballasts, computers, servers, etc. are non-linear loads.

The old ballasts produce triplen harmonics and will be additive on the neutral so the neutral on a wye circuit will have the same neutral current as is on the phase conductors. :D
 
charlie said:
All resistance loads like heat, incandescent light bulbs, electric ranges, all normal motor loads (not with DVDs), etc. are linear loads.

Most but not all electronic loads like some phone systems, DVDs, switch mode power supplies, electronic ballasts, computers, servers, etc. are non-linear loads.

The old ballasts produce triplen harmonics and will be additive on the neutral so the neutral on a wye circuit will have the same neutral current as is on the phase conductors. :D
Click to expand...


IMO it's safe to say that a Condo/Hotel will never have more than 50% of it's load that's non-linear, therefore the neutral would not have to be considered a CCC.
 
infinity said:
IMO it's safe to say that a Condo/Hotel will never have more than 50% of it's load that's non-linear, therefore the neutral would not have to be considered a CCC.
Click to expand...
I'm sorry, I did agree with you. It was my intent to just provide some additional information.
icon11.gif
 
Status
Not open for further replies.
Top