is voltage drop a requirement per nec?

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ramon1

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perris, ca,
I was just wandering if voltage drop is a requirement per the NEC because I cant find it but, I thought it was. Can someone please help? thanks
 

dereckbc

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Plano, TX
No, it is not an NEC requirement.
Not so fast there my friend. Take a look at 647.4 (D) limits voltage drop to 1.5%. Just poking some fun at you Roger.

Other than 647 applications I am not aware of any maximum voltage drop requirements. However you will see notes suggesting 5% max, but not required.
 

Fulthrotl

~Autocorrect is My Worst Enema.~
You guys are right, I was only thinking in terms of general wiring applications.

Roger

and calif. is now dealing with title 24, 2013 flavor, and i do
believe that voltage drop is now a part of *that*.

the ashrae 90.1 thing, as ron said.

my EE is having fits about it. the feeder calcs are killing him.

what used to be a 5% total voltage drop, 2% feeders, 3%
branch circuits, with the option of doing 3% feeders, 2%
branch circuit drops, is now 2% feeders, period.
 

roger

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Fl
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Electrician
and calif. is now dealing with title 24, 2013 flavor, and i do
believe that voltage drop is now a part of *that*.

the ashrae 90.1 thing, as ron said.

my EE is having fits about it. the feeder calcs are killing him.

what used to be a 5% total voltage drop, 2% feeders, 3%
branch circuits, with the option of doing 3% feeders, 2%
branch circuit drops, is now 2% feeders, period.

Yeah, there are requirements from other entities but we are only talking NEC here.

What I want to know is when we are dealing with these VD requirements what exact value do we start the VD calculation at and how is monitored to be sure it stays at that number continuously? How does equipment operating at a 5% VD on a service supplying 130 volts have no issues when operating at a 5% VD on a service supplying 120 volts.


My point is, why not just state a minimum voltage for each system voltage and be done with it? :cool:


Roger
 

roger

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220.5 says to use the nominal voltage to start.
220.5 is part of the NEC which doesn't mandate a VD limit, (besides the aformentioned article sections).

Now, if it were an NEC requirement and we are to use the nominal voltages per 220.5 we could simply set a number and be done with it.


Roger
 

kwired

Electron manager
Location
NE Nebraska
Until we figure out how to create a conductor that has no resistance whatsoever, voltage drop is going to happen no matter what NEC says:happyyes:

Now the NEC does not have any restrictions for voltage drop for general applications, but does have a few restrictions for specific applications as some have been mentioned.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
and calif. is now dealing with title 24, 2013 flavor, and i do
believe that voltage drop is now a part of *that*.

the ashrae 90.1 thing, as ron said.

my EE is having fits about it. the feeder calcs are killing him.

what used to be a 5% total voltage drop, 2% feeders, 3%
branch circuits, with the option of doing 3% feeders, 2%
branch circuit drops, is now 2% feeders, period.
This reminds me to buy some more Freeport McMoRan stock for the portfolio.
 

GoldDigger

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Placerville, CA, USA
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Retired PV System Designer
My point is, why not just state a minimum voltage for each system voltage and be done with it? :cool:


Roger
Well, one reason is that although the load causing the VD will work well with either spec, other loads seeing same VD will notice the difference. The voltage change will be noticeable in non- regulated lighting, some motor speeds, etc
This is also a reason for being more strict about service and feeder drop than branch drop.



Tapatalk!
 

roger

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Location
Fl
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Electrician
Well, one reason is that although the load causing the VD will work well with either spec, other loads seeing same VD will notice the difference. The voltage change will be noticeable in non- regulated lighting, some motor speeds, etc
This is also a reason for being more strict about service and feeder drop than branch drop.



Tapatalk!
My point is not about specific loads and their affects or what is the cause of the VD, my point is 5% is 5%, Start at any of the nominal voltages in 220.5 and do the math, now this number can be set in stone as a minimum for each system voltage.

A 5% VD on a nominal voltage of 120 is 114 volts, so if we have a service delivering 130 volts we can let it drop by 12.3% and be at the 114volts, there is no reason to worry about 3% and 2%, just call out the minimum voltage as far as allowable or recommended maximum VD and be done with it. ;)

Roger
 

GoldDigger

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Location
Placerville, CA, USA
Occupation
Retired PV System Designer
And I am saying that specifying the minimum load-end voltage will not do anything to limit the undesirable side effects of the non-constant VD as the loads are switched on and off.
If you are only dealing with a single load (pump motor 300' down a well, for example) then your point is well taken. But it does not generalize to all VD situations.

Tapatalk!
 
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