Derating conductors

[ActionDave]

When you meet the conditions of 310.15 B(4).
Basically when the neutral only carries the imbalance of the circuit and the majority of the loads are nonlinear.

 

[eager2learn]

non linear meaning? Please excuse my ignorance i'm just trying to keep up

 

[Smart $]

non linear meaning? Please excuse my ignorance i'm just trying to keep up

Linear loads are ones which the current waveform is close to sinusoidal.

Non-linear loads have either harmonic currents which add together to cause neutral current on a 4-wire wye-powered mwbc, even when the loads are balanced, or non-sinusoidal loads, such as SCR powered, where the load currents combine at different timings to cause balanced loads to have neutral current on a 4-wire wye-powered mwbc. In simpler terms, linear loads when balanced have no neutral current. Non-linear loads when balanced do have neutral current.

 

[ActionDave]

The way I understand it is this- Remember the picture you always see of an AC sine wave? That is a picture of voltage and current together in harmony, like you and your first girlfriend.

When you have a lot of nonlinear loads the wave gets all messy because the voltage and the current get out of sync, like when your girlfriend finds you at her hot friend's house Saturday morning when she drops by.

Fluorescent lights with electronic ballasts, computers, VFD's cause that kind of messiness.

 

[mbeatty]

The way I understand it is this- Remember the picture you always see of an AC sine wave? That is a picture of voltage and current together in harmony, like you and your first girlfriend.

When you have a lot of nonlinear loads the wave gets all messy because the voltage and the current get out of sync, like when your girlfriend finds you at her hot friend's house Saturday morning when she drops by.

Fluorescent lights with electronic ballasts, computers, VFD's cause that kind of messiness.

Great analogy Dave.

 

[15michael15]

I had a similar situation with an underfloor metal raceway (walkercell). You can get some help here applying FPN No. 1 of Table 310.15(B)(2)(a), which applies load diversity. Helped me a lot. Check Annex B, Table B.310.11.

 

[George Stolz]

I had a similar situation with an underfloor metal raceway (walkercell). You can get some help here applying FPN No. 1 of Table 310.15(B)(2)(a), which applies load diversity. Helped me a lot. Check Annex B, Table B.310.11.

That is a steep hill, and difficult to sell an AHJ on - but if you succeeded, that's a feather in your cap.