allowable voltage drop

Status
Not open for further replies.
K

Ken 6789

Senior Member
What is the allowable voltage drop? I've always thought it was 10% max. from trans. to last device on a circuit and 5% max. on motors. Is this correct?
 
allowable voltage drop

Dear All,

Voltage drop for lighting system is 2 % to 3 % of Lighting System,3 % for power Feeder And 5 % Percent For Motors.

rgrs,

Budhi Rahardjo
 
Ken 6789 said:
What is the allowable voltage drop? I've always thought it was 10% max. from trans. to last device on a circuit and 5% max. on motors. Is this correct?
Click to expand...

Basically the NEC does not limit voltage drop except for a couple of places.

The ANSI standard is roughly 10% total, 5% on the utility side and 5% on the customer side.
 
Check your local building code.

Here in Florida, the Energy Efficiency Code requires a maximum of 2% on feeders and 3% on branch circuits for all non-dwelling occupancies.
 
bphgravity said:
Check your local building code.

Here in Florida, the Energy Efficiency Code requires a maximum of 2% on feeders and 3% on branch circuits for all non-dwelling occupancies.
Click to expand...

Which lines right up with the ANSI standard of 5% in the premise wiring sytem along with 5% on the utility side. :)
 
NEC allows up to 3% on feeders, and up to 3% on branch ckts., but not more than 5% total. It's most practical to keep the feeder VD down to 2% (larger conductor/less impedance), and 3% on branch ckts. (smaller conductor/higher impedance).
 
hdpeng said:
NEC allows up to 3% on feeders, and up to 3% on branch ckts., but not more than 5% total. It's most practical to keep the feeder VD down to 2% (larger conductor/less impedance), and 3% on branch ckts. (smaller conductor/higher impedance).
Click to expand...

The NEC does not restrict voltage drop other then for fire pumps 695.7 and sensitive electronic equipment 647.4(D).

For all other circuits the NEC suggests a maximum allowable voltage drop.

You can find that suggestion in the non-enforceable FPNs after 210.19(A)(1) FPN No. 4 and after 215.2(A)(3) FPN No. 2.

FPNs (Fine Print Notes) are just explanatory material and are not part of the NEC. See 90.5(C)
 
Last edited:
iwire said:
Which lines right up with the ANSI standard of 5% in the premise wiring system along with 5% on the utility side. :)
Click to expand...
Good comment about the electric utility side Bob. Most of the public service commissions permit 5% voltage drop in urban areas and 6% in rural areas.
 
While it is nice to say that the utility should stay within 5%, the Illinois Commerece Commission says the standard voltage is 113 to 127, but goes no to permit a ?10% variation for services that are supplied at other than the standard voltage. I don't know if the utilities take advantage of this or not.
Section 410.300 Voltage Regulation

a) Standard voltage. Each entity supplying electrical energy for general use shall adopt a standard service voltage of 120 volts (when measured phase to neutral) and shall maintain the service voltage within the allowable variations from that value at all times.

b) Allowable voltage variations. For service rendered at the standard service voltage, voltage variations as measured at any customer's point of delivery shall not exceed a maximum of 127 volts nor fall below a minimum of 113 volts for periods longer than two minutes in each instance. For service rendered at voltages other than the standard voltage value, voltage variations as measured at any customer's point of delivery shall not exceed 10% above or below the service voltage for a longer period than two minutes in each instance.
Click to expand...
 
don_resqcapt19 said:
While it is nice to say that the utility should stay within 5% . . .
Click to expand...

Don, the 113 to 127 volts is very close to 5%. Every state is different and Indiana actually has 5%, 6%, and 8% depending on the size of the city or if the service is in a rural area. What I was saying is most of the public service commissions . . ., not all. I believe Bob was indicating an average of what most of the public service commissions permit as well. :)
 
Charlie,
Yes the 113 to 127 is ~5%, but that only applies to services supplied at 120...for all others Illinios permits the ?10%. I guess I am just trying to say you need to check your state's rules as they are all not the same. With ?10% a 480 volt service would be permitted to range from 432 to 528 and be with in the state specs.
 
Status
Not open for further replies.
Top