Matt Mckenzie
Member
- Location
- United States
Does non linear mean multiply by 125%? Fluorescent is non linear? Means multiply by 125%?
does non linear mean multiply by 125%?
- Thread starter Matt Mckenzie
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
No. The reason we often have 125% on fluorescents is because they are continuous- Continuous according to the NEC means that they are on for 3 hours or longer
In general, non-linear loads only affect whether a neutral conductor is counted as a current-carrying conductor for derating purposes.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
For a long time designers used a factor of 1.73 when designing neutrals for non-linear loads. Whether they do anything or not to this day we still install some 200% neutrals for this purpose.
Carultch
Senior Member
- Location
- Massachusetts
The 125% factor is due to it being a continuous load. I.e. operates at its full ampacity continuously for 3 hours or more.
You might think that another 125% factor might apply, because when you count the neutral of a 3-phase circuit as a "current-carrying conductor", that your ampacity adjustment becomes 0.8. The reciprocal of 125%. This is only true for instances when the neutral affects the ampacity adjustment factor.
I'm not familiar with nonlinear loads, so I'm not sure if other correction factors apply. If there are multiples of the 3rd harmonic, these currents add up instead of cancel, when applied to the neutral conductor. This is why the neutral might be larger than the phase wiring.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Amount of extra capacity for non linear loads depends on details of the non linear load(s). Also at the branch circuit level it may be high but at same installation it may be low at the feeder or service level of distribution if there is a lot of linear load on other circuits.
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