derating for neutral

[greenawaltmark4]

When to use your nuetral wire as a ccc's for derating. I understand that it is when you have a non linear load, like motors . What are some other non linear load to look out for?

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[GoldDigger]

Motors are *not* non linear. They are not resistive though.
Old computer power supplies and some fluorescent or LED lighting can be non linear.
You also count the neutral if you have MWBC using only two of three phase conductors plus neutral for line to neutral loads. Or if you have a simple 120V only circuit with just hot and neutral.

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[infinity]

This may help:

Neutral Conductors:

Here's some examples of when to count and not count the neutral as a current carrying conductor or CCC:

3Ø- 208Y/120 or 480Y/277 volt system-different circuit types:
A) 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
B) 3 wire circuit w/ 2 ungrounded, 1 neutral = 3 CCC's
C) 4 wire circuit w/ 3 ungrounded, 1 neutral = 3 CCC's*


Notes:
A) A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
B) In this circuit the neutral current will be nearly equal to the current in the ungrounded conductors so the neutral counts as a CCC
C) In this circuit the neutral will only carry the imbalance of the current between the three ungrounded conductors so it is not counted as a CCC, with an exception,
*if the current is more than 50% nonlinear (see below for NEC article 100 definition) then the neutral would count as a CCC.


1Ø- 120/240 volt system-different circuit types:
D) 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
E) 3 wire circuit w/ 2 ungrounded, 1 neutral = 2 CCC's
Notes:
D) A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
E) In this circuit the neutral will only carry the imbalance between the two ungrounded conductors so the neutral is not counted as a CCC.
Nonlinear Load. A load where the wave shape of the steady-state current does not follow the wave shape of the applied voltage.
Informational Note: Electronic equipment, electronic/electric-discharge lighting, adjustable-speed drive systems, and similar equipment may be nonlinear loads.

 

[Smart $]

...
Old computer power supplies ... can be non linear.
...

Even new computer power supplies can be nonlinear. Without doing extensive research, it is fair to say that any equipment with a front-end power supply converting AC to DC or to another AC frequency is nonlinear.

 

[greenawaltmark4]

This may help:

The exception for 50% of non linear loads using 3 phases, how would the over 50% be determined?

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[infinity]

The exception for 50% of non linear loads using 3 phases, how would the over 50% be determined?

You would to add up the non-linear load and compare that to the linear load. If the non-linear total exceeds 50% then the neutral would count as a CCC.

 

[greenawaltmark4]

You would to add up the non-linear load and compare that to the linear load. If the non-linear total exceeds 50% then the neutral would count as a CCC.

Very informative , much appreciated

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