Neutral sizing
- Thread starter Chong
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- Bremerton, Washington
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- Master Electrician
Re: Neutral sizing
There is a difference between table 250.66 and section 250.66. The table is full size, and the section allows smaller sizes for certain types of GE.
The size of the grounded conductor is the larger of table 250.66 or art 220 load calcs. The service grounded conductor should really be colored white and green, as it has two functions.
There is a difference between table 250.66 and section 250.66. The table is full size, and the section allows smaller sizes for certain types of GE.
The size of the grounded conductor is the larger of table 250.66 or art 220 load calcs. The service grounded conductor should really be colored white and green, as it has two functions.
Re: Neutral sizing
The reason for the 250.122 minimum is the popularity of autotransformers to run a 240 volt heater on 277 volts or to boost 120Y208 volts to 138Y240 volts. If a ground fault is downstream of the autotransformer the upstream neutral has to carry some of the fault current.
Somebody also pointed out that if there is a rarer phase to neutral short circuit then the neutral must have some fault withstand capability at least equal to the EGC.
The reason for the 250.122 minimum is the popularity of autotransformers to run a 240 volt heater on 277 volts or to boost 120Y208 volts to 138Y240 volts. If a ground fault is downstream of the autotransformer the upstream neutral has to carry some of the fault current.
Somebody also pointed out that if there is a rarer phase to neutral short circuit then the neutral must have some fault withstand capability at least equal to the EGC.
Re: Neutral sizing
You also may need a full size neutral from a voltage drop standpoint.
If there are nonlinear loads involved then a 3-phase neutral needs to be 200% capacity. For single phase loads such as dimmers you need in a movie studio you are required to have a 140% neutral read any substantial single phase dimmer installation.
You also may need a full size neutral from a voltage drop standpoint.
If there are nonlinear loads involved then a 3-phase neutral needs to be 200% capacity. For single phase loads such as dimmers you need in a movie studio you are required to have a 140% neutral read any substantial single phase dimmer installation.
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