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Voltage Drop

Merry Christmas
J

Jimmy7

Senior Member
Location
Boston, MA
Occupation
Electrician
Do you determine voltage drop by the actual load? Meaning, if I ran a 120 volt, 20-amp circuit I determine the voltage drop off the actual load, not the 20 amp ocpd correct? If this is the case, for design purposes how long can you run the following
1. 20-amp 120 volt circuit for receptacles (When you're not exactly sure what is going to be plugged in)?
2. 15-amp 120 volt for receptacles (When you're not exactly sure what is going to be plugged in)?
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Yes the voltage drop is directly correlated to the amount of load. For general purpose receptacle circuits there is no rule on what load amp number to use in a VD calculation so it's up to you. Any reason why you're doing VD calculations or compensation?
 
J

Jimmy7

Senior Member
Location
Boston, MA
Occupation
Electrician
infinity said:
Yes the voltage drop is directly correlated to the amount of load. For general purpose receptacle circuits there is no rule on what load amp number to use in a VD calculation so it's up to you. Any reason why you're doing VD calculations or compensation?
Click to expand...
No, I was just thought of it.
Do you have a rule of thumb on how long to run 120 volt 15 amp or 20 amp circuits?
 
kingpb

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
Jimmy7 said:
Do you determine voltage drop by the actual load? Meaning, if I ran a 120 volt, 20-amp circuit I determine the voltage drop off the actual load, not the 20 amp ocpd correct? If this is the case, for design purposes how long can you run the following
1. 20-amp 120 volt circuit for receptacles (When you're not exactly sure what is going to be plugged in)?
2. 15-amp 120 volt for receptacles (When you're not exactly sure what is going to be plugged in)?
Click to expand...
Us the maximum allowable load that can put on each as worst case.
 
tortuga

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
G

garbo

Senior Member
Mike Holt has a great place that you can input the voltage, ampere & if you are using single or three phase. Pre internet ( ya many years ago won a lunch when I proved my co-workers electrician dad wrong calculating wire for think it was 10 driveway pole luminares with a small wattage lamp ( maybe 75 watts @120 VAC. First luminare was 100' from the house then one every 100'. Co worker did not want the last luminare to have less then 106 volts. Anyway cheated and used Ohm's law like it was a DC circuit. Had him run #8 copper to first luminare then #10 to second to maybe 4th luminare then #12 copper rest of run. When he had exactly 120 volts at the circuit breaker he had 107 volts at last luminare. His dad said being the load was only around 6.5 amps to use #12 copper because that's good for 20 amps. At the large hospital/research centers that I retired from they had two smart rules. No shared grounded conductors ( ya neutrals ) and all receptacles were 20 amp Hospital grade TR type and #10 THWN to first pull box wired to 20 amp bolt on circuit breakers to keep voltage drop low. Money was no object so for general use office receptacles they never wired more them three on a 20 amp breaker.
 
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