Voltage Regulators, Voltage Drop, and NEC

liverpool

Member
I am working on a project where we have multiple branch circuits with long runs in the thousands of feet sometimes. The electrical sub-contractor on the project was suggesting using a voltage regulators to cut down the coast of over sized conductors. However, the client's representative reviewer thinks that this will not be in line with the intent of the code especially the part that talks about not having voltage drop less than 5% total (2% feeder and 3% branch circuits). TBH, I first thought it was a no brainer to use voltage regulators, but now this reviewer is making me rethink it again. Are you aware of any issues with using voltage regulators for long runs as it relates to the NEC?:huh:
 
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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
what kind of voltage regulator are you thinking of using?

the code does not specify any particular level of voltage drop as acceptable. that is solely a design decision.

personally, I am a fan of moving the transformers as close to the load as one can to cut down on the large conductors needed to reduce VD. for some reason this is not a popular option in most facilities.
 

charlie b

Moderator
Staff member
Location
Seattle, WA
"Voltage drop" is not really the issue. The code does speak of getting "reasonable efficiency" if the total voltage drop along the feeders and branch circuit wiring does not exceed 5%. But the intent is to keep the voltage at the load above 95% of the system's nominal value. How you achieve this is not important. You can use large conductors, combinations of step-up and step-down transformers, voltage regulators, or any other method you like.
 

JDBrown

Senior Member
Location
California
I agree with Bob and Charlie. I will just add that the whole voltage drop thing depends on your AHJ. As far as the NEC is concerned, the suggestion to limit the voltage drop to 5% is in a couple of "Fine Print Notes" or "Informational Notes", and is not part of the enforceable language of the Code. However, the City of Los Angeles, for example, enforces it as though it were part of the actual Code language. You can argue with the Building Department all you want, you can show them in the Code book where it says that it's just a suggestion (not a requirement) you can file appeals, but at the end of the day you will lose.

They're strict about it, too -- less than 5% voltage drop from the service to the last outlet. Doesn't matter how large the building is. (Airport terminal with only one service? That last receptacle on the far side of the terminal had better not have a voltage drop over 5%!) "But can't we just make adjustments to the transformer taps to bring the voltage back up?" Nope. The rule says less than 5% voltage drop from the service to the last outlet. No exceptions.

On the other hand, none of the other jurisdictions I work in even ask for voltage drop calculations. I believe that's set to change next year, though -- last I checked, the new California Title 24 Energy Efficiency Standards make it an official requirement statewide.

SECTION 130.5 ?ELECTRICAL POWER DISTRIBUTION SYSTEMS
(c) Voltage Drop
1. Feeders. Feeder conductors shall be sized for a maximum voltage drop of 2 percent at design load.
2. Branch Circuits. Branch circuit conductors shall be sized for a maximum voltage drop of 3 percent at design load.
I checked your profile and wasn't able to find your location, so I apologize if the above is irrelevant for you.
 

JDBrown

Senior Member
Location
California
From the OP's log in name, I might have guessed London. :lol: But the zip code points to Arlington, VA.

Well, he was asking about the NEC, so I figured he wasn't actually in jolly ole England. As a Mod you must be able to see more information than I can (or you just know how to use the site better than I do), because I don't see a zip code in his profile.

Either way, watch for other states to follow CA's example on all this energy efficiency stuff. It seems like most of the rest of the country ends up copying our energy efficiency standards after 5-10 years, no matter how wacky or Draconian they are. Of course, by the time everybody else adopts them they don't seem so wacky or Draconian, because we've got a whole new set of (even stricter) regulations.

But I'm not bitter... :D
 

liverpool

Member
Thank you all for the feed back. We'll see how the argument that FPNs are not enforceable by the NEC goes by this reviewer.

BTW, I live in the Washington-DC Northern Virginia area. My username is because I support only one sport team :D

Thanks again.
 

GoldDigger

Moderator
Staff member
"Voltage drop" is not really the issue. The code does speak of getting "reasonable efficiency" if the total voltage drop along the feeders and branch circuit wiring does not exceed 5%. But the intent is to keep the voltage at the load above 95% of the system's nominal value. How you achieve this is not important. You can use large conductors, combinations of step-up and step-down transformers, voltage regulators, or any other method you like.
:thumbsup:The NEC is concerned with the performance of the utilization equipment, and so cares at most about the voltage at the outlets.
But an energy code is, whatever language it may use, fundamentally concerned with efficiency and so for a provision in such a code, the voltage regulator should not be an acceptable solution.
How this is enforced by any given AHJ is another question.
And since the OP mentions branch circuits rather than feeders, the voltage drops involved may correspond to a very small fraction of the energy used at the facility or even of the potential energy savings for the cost.
 
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