Load diversity

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Mr.electric

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Ok, I was on a job and the electrician running it was filling up lighting pipes to the point were you can no longer put a 80% load on them.he justified his actions with the b.310.15 table in annex b. Just wondering if anyone could shed some light on this table what it even means and were it would apply. I'm pretty sure this was a illegal instal, and he was using it as a excuse because he was to lazy to run more pipe.
 
Mr.electric said:
Ok, I was on a job and the electrician running it was filling up lighting pipes to the point were you can no longer put a 80% load on them.he justified his actions with the b.310.15 table in annex b. Just wondering if anyone could shed some light on this table what it even means and were it would apply. I'm pretty sure this was a illegal instal, and he was using it as a excuse because he was to lazy to run more pipe.
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Will need to know what type/size conduit is installed and what type and size conductors are installed.
 
Mr.electric said:
3/4 emt with 12 #12 thhn conductors used for general purpose power and lighting in a retail store.


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Still more info needed. 120/240 or 208Y120 supply. Shared neutrals, OCPD size, etc. Depending on these details it may very well be compliant.
 
Are some of those wires EGCs?
Are some shared neutrals for MWBCs?
In both cases you will not count them for ampacity adjustment, but do need to count them for mechanical fill limits.
 
Lighting and power both 120 volt wye with shared neutrals on a 20 amp OCPD. All conductors had roughly 16 amps of load. Not sure what this load diversity is and if it even apply a to this situation?


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It was my understanding any circuit supplying fluorescent lighting loads the neutral was counted as current carrying. It was also my understanding that over 9 conductors in a raceway that conductor could only carry 50% the total ampacity.


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Mr.electric said:
It was my understanding any circuit supplying fluorescent lighting loads the neutral was counted as current carrying. It was also my understanding that over 9 conductors in a raceway that conductor could only carry 50% the total ampacity.


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The distinction is made for nonlinear loads, but the extent to which a particular fluorescent ballast acts as a nonlinear load will vary.

If the Code feels that any degree of nonlinearity triggers the exception, then you would have to count it. If the actual harmonic content of the particular luminaires is low enough, it should not be a practical problem.
If the nonlinearity is bad enough, triplen harmonics in particular, you might have to provide an oversized neutral and it would definitely be current carrying.
From definitions, Article 100, Nonlinear Loads:
Informational Note: Electronic equipment, electronic/electric- discharge lighting, adjustable-speed drive systems, and similar equipment may be nonlinear loads.
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But from 300.15(B)(5)(c):

(c) On a 4-wire, 3-phase wye circuit where the major portion of the load consists of nonlinear loads, harmonic currents are present in the neutral conductor; the neutral conductor shall therefore be considered a current-carrying conductor.
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Which does not seem to allow as much leeway for interpretation IF you automatically consider fluorescents to be non-linear.
 
As far as his basing his install on Annex B, I think I would have to ask him to show you his Professional Engineering License. Annex B is informational only and for jobs under engineering supervision.
As others have noted, it's no a simple resolve to determine if such a circuit is linear or nonlinear. I would think he would have to have some documentation to have an inspector pass the job as is.
 
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