voltage drop

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hotrodnhra

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i have a 30amp service to an airplane hanger with a 30 amp main. the inspector wants me to upsize to #6 for voltage drop ok but he wants the grounded conductor to be upsized to a # 6 also. can anyone clarify this for me. thanks
 
Grounded conductor or grounding conductor?

For what it is worth the NEC has no section requiring up sizing the feeder for voltage drop so unless there is a local amendment you should be able to say no.
 
hotrodnhra said:
i have a 30amp service to an airplane hanger with a 30 amp main. the inspector wants me to upsize to #6 for voltage drop ok but he wants the grounded conductor to be upsized to a # 6 also. can anyone clarify this for me. thanks
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Read art. 250.122(B) if you do decide to upsize but better still upsize to #6 conductors and a #10 ground and put a 60 amp breaker on it. Bet that'll make him/her mad
 
iwire said:
Grounded conductor or grounding conductor?

For what it is worth the NEC has no section requiring up sizing the feeder for voltage drop so unless there is a local amendment you should be able to say no.
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no section ? 647? 695 ?:D
 
Hotrod,
As referenced, you are in an area where Code requirements and good engineering practices don't necessarily agree. If the situation (not saying Code ) requires you to upsize your power conductors, then 250.122 would indicate your Equip. Ground must be upsize porportionaly, which in this case would take you to a #6 also.

Welcome to the Forum by the way.
 
I tried a PM asking him to calrify perhaps we will see

it being post #1, I was shooting in the dark thinking he might not know of 250.122.... he would not be alone
 
Dennis Alwon said:
Read art. 250.122(B) if you do decide to upsize but better still upsize to #6 conductors and a #10 ground and put a 60 amp breaker on it. Bet that'll make him/her mad
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According to 250.24(C)(1) the smallest neutral he could have is a #8, if he used #6 service entrance conductors.

Something isn't right with all this...
 
augie47 said:
I tried a PM asking him to calrify perhaps we will see

it being post #1, I was shooting in the dark thinking he might not know of 250.122.... he would not be alone
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Another one many overlook or are unaware of is that grounded conductors need not be sized at 125% of continuous plus 100% non-continuous. They can simply be sized at 100%. It is however stipulated the grounded conductor not be connected to an overcurrent device.

Ref: 210.19(A)(1) Exception No. 2
215.2(A)(1) Exception No. 2
 
Last edited:
I received a PM from Hotrod. It is a 30 amp feeder and he was told to increase the grounding conductor to match his phase and neutral conductor.
 
Voltage drop clarification

Voltage drop clarification

The code requires oversizing for voltage drop so that the total voltage drop, that is feeder + branch circuit does not exceed 5%.

Article 215.2(A)(3) FPN No.2 is for branch circuits and article 210.19 FPN No.4 is for branch circuits.

It should be emphasized:

1) Feeder is from POE to the last overcurrent protection. Most of the times, the distance between the POE and the main switchboard or distribution board is overlooked.

2) The distance for branch voltage drop calculation should be to the farthest outlet (not to be confused with receptacle).

3) The calculation shown in the code for voltage drop is a modified DC formula . The AC formula should be used or alternatively as shown on example 1 (page 1184 of the 2005 NEC handbook)

Per 250.122 (b), the equipment ground must be adjusted accordingly.

Service ground is oversized automatically when due to voltage drop either service feeders are increased in quantity (same size) or decreased in quantity, but increased the size (service ground per table 250.66). For cases in which the leg size does not increase to the next step in table 250.66, I utilize the same method as for the equipment ground.

For the question in this post, #10 is good for 30A (table 310.16). If voltage drop calculation dictates that #6 should be utilized, then refer to chapter 9, table 8 for conductor properties; #10 - 10380 cmils, #6 26249 cmils. Adjust the equipment ground conductor (table 250.122) by the same ratio, that is, 26249/10380 = 2.53. Thus, #6 ground in required.
 
Twinman,
I can see only 1 small problem. FPNs are not Code enforcable.:)
 
twinman said:
The code requires oversizing for voltage drop so that the total voltage drop, that is feeder + branch circuit does not exceed 5%.
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I agree with Gus, there is no requirement for VD. It is a good idea and an FPN but not a code requirement.

I agree if you do upsize for VD from #10 to #6 then you would need a #6 EGC however putting the feeder on a 60 amp breaker would only require a #10 EGC.
 
twinman said:
The code requires oversizing for voltage drop so that the total voltage drop, that is feeder + branch circuit does not exceed 5%.
Click to expand...

That is incorrect.

twinman said:
Article 215.2(A)(3) FPN No.2 is for branch circuits and article 210.19 FPN No.4 is for branch circuits.
Click to expand...

FPNs are just suggestions or pointers to other references.

See 90.5(C)

'Fine print notes are informational only and are not enforceable as requirements of this code'
 
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