Ground wire sizing considering the distance

[julianov]

Hello,

I have a question about determining the size of the ground wire. I know that we can use the 250.122 table, which depends on the end load current. However, what about voltage drop? How do we size the ground wire based also on the distance from the panel to the end load?

Best

 

[MasonF]

250.122 (B)

 

[augie47]

Note that 250.122 is not based on the "end load" current but on the overcurrent protective device and as pointed out in the above post, when you increase the size of the power conductors for voltage drop you must also increase the equipment ground.

What distances are you concerned with ?

 

[julianov]

Thanks for the responses. 250.122 (B) is:

Increased in Size. Where ungrounded conductors are increased in size, equipment grounding conductors, where installed, shall be increased in size proportionately accord-ing to the circular mil area of the ungrounded conductors.

Let's assume I have a single-phase load of 20 A, but since it's at a distance of 100 feet, I would need a 6 AWG conductor to have a voltage drop of less than 2%.

How would I then calculate the size of the ground conductor? If I refer to table 250.122, I should use a 10 AWG copper wire, but it doesn't take voltage drop into account. Because if the load were instead at 3 feet instead of 100 feet, I could use a 20 AWG wire and a ground conductor also of 10 AWG.

 

[augie47]

If you based it solely on Table 122 with a circuit protected by a 20 amp breaker you would use a #12 equipment ground.
250.122(B) however would require you to increase the size of the equipment ground proportionally IF you increase the size of the power conductors over what is required by the overcurrent device.
In your case if you had a 20 amp breaker and you used a #6 conductor to address voltage drop, your equipment ground would also be a #6.

Your wire sizes are determined by load but, in general, have to be sized with the overcurrent device in mind.