Pole Lighting EGC

Status
Not open for further replies.
If I'm running a single circuit to and thru pole lights on a parking lot and the last pole is at least 300' or more from the breaker, shouldn't I be installing a larger EGC than my circuit conductors to assist in clearing a fault. My thought is that a #8 will clear a fault faster than a #10 due to any increase in resistance with the length involved? Always thankful for your thoughts
 

iwire

Moderator
Staff member
Location
Massachusetts
Code wise you are required to upsize the EGC only if you upsize the circuit conductors.

What size breaker and what size conductors are you running.
 
I'm using #10 on a 30a breaker (277v) as instructed on the plans, but after taking a continuing education class I'm wondering if I'm thinking too hard or is there something to the reasoning behind what was described in class?
 

Jamar

Member
Location
Alaska
Short answer is found in 250.122(B)

#10 would probably do just fine, most Blueprints have general notes that do their own VD calculations. For ex. Note 1 might tell you for conductors #12-14 at runs more than 200ft. Should be sized #8-10.

Informational notes covering voltage drop are not mandatory. However of you want to learn how to do the calculation it's as follows.

VD =2 X L X R X I/1000

VD=2 X 300FT. X 1.21 X 30/1000

Resistance for a #10 can be found in Chapter 9 Table 8

VD=21.78V

Turn that into a percentage of 277V

%VD=(21. 78V)/(277V)

VD =. 078

%VD=7.8%

Which is more than the 5% or 12V Drop in Voltage

Answer. #8 phase conductor

The EGC is another formula based off the circular mils of the ungrounded. But a #8 would suffice



Sent from my SM-N915V using Tapatalk
 

Jamar

Member
Location
Alaska
He has a 30 amp circuit, that means the EGC has to be the same size as whatever ungrounded conductor size they chose.
Correct. A 30amp circuit requires the #10. If you apply the voltage drop it says you can upsize it to a #8. The voltage drop at 300 ft. For a 277 V circuit was at 8%

Sent from my SM-N915V using Tapatalk
 

iwire

Moderator
Staff member
Location
Massachusetts
Correct. A 30amp circuit requires the #10. If you apply the voltage drop it says you can upsize it to a #8. The voltage drop at 300 ft. For a 277 V circuit was at 8%

Sent from my SM-N915V using Tapatalk

My point was no formula is needed to deal with EGCs for 15, 20 and 30 amp circuits. :)

As the OP is working from plans it seems the engineer of record is fine with the potential voltage drop. The voltage drop will not be 8% as the load will not be 30 amps.
 

Jamar

Member
Location
Alaska
My point was no formula is needed to deal with EGCs for 15, 20 and 30 amp circuits. :)

As the OP is working from plans it seems the engineer of record is fine with the potential voltage drop. The voltage drop will not be 8% as the load will not be 30 amps.
You are correct since he is working "as instructed on the plans." Just giving him insight on how to correctly do the math in case he wanted some browny points.

Sent from my SM-N915V using Tapatalk
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
I'm using #10 on a 30a breaker (277v) as instructed on the plans, but after taking a continuing education class I'm wondering if I'm thinking too hard or is there something to the reasoning behind what was described in class?
There is no reason to up size your EGC unless you make the ungrounded conductors larger as well, in regards to code requirements or fault clearing ability.

You can make your EGC as big as you want but it will only carry fault current equal to what leaves the breaker on your #10 wire feeding the light.
 

iwire

Moderator
Staff member
Location
Massachusetts
You are correct since he is working "as instructed on the plans." Just giving him insight on how to correctly do the math in case he wanted some browny points.

Then we should explain that lighting circuit voltage drop calculations are typically based on the load not the breaker size and in the case of outdoor lighting will often be calculated individually using the point to point method or you will end up with ridiculously over sized conductors at the far end of circuit.

By the way, welcome to the forum. :)
 
Status
Not open for further replies.
Top