Calculating voltage drop, wire gauge ampacity over distance
 

I'm confused by a couple of online calculators I've found.

I'm trying to determine the proper gauge wire to carry 20A, 120VAC over a
distance of 300 ft. with an approx allowable 2% (per NEC) voltage drop.
This UF cable will be buried for most of it's length.

This calculator:
http://www.stealth316.com/2-wire-resistance.htm
advises a 6 ga. wire would be sufficient (voltage drop 2.414V)

However, this calculator seems much more conservative:
http://www.vihon.com/Vihon_Calculato...alculator.html
It says a 0 (zero) gauge wire is required !

Also would like some real world advice on the voltage drop recommendations
of the NEC. At what point does one see excessive/dangerous wire heating?
2% ? 5% ? 10% ? 20% ?

-- Paul

Calculating voltage drop, wire gauge ampacity over distance
 

"Paul" wrote in message
...
I'm confused by a couple of online calculators I've found.

I'm trying to determine the proper gauge wire to carry 20A, 120VAC over a
distance of 300 ft. with an approx allowable 2% (per NEC) voltage drop.
This UF cable will be buried for most of it's length.

This calculator:
http://www.stealth316.com/2-wire-resistance.htm
advises a 6 ga. wire would be sufficient (voltage drop 2.414V)

However, this calculator seems much more conservative:
http://www.vihon.com/Vihon_Calculato...alculator.html
It says a 0 (zero) gauge wire is required !

Use 600 feet and a maximum resistance of 0.12 Ohms ... and check out the
copper wire tables. Hope that helps.

Calculating voltage drop, wire gauge ampacity over distance
 

"Paul" wrote in message
...
I'm confused by a couple of online calculators I've found.

I'm trying to determine the proper gauge wire to carry 20A, 120VAC over a
distance of 300 ft. with an approx allowable 2% (per NEC) voltage drop.
This UF cable will be buried for most of it's length.

This calculator:
http://www.stealth316.com/2-wire-resistance.htm
advises a 6 ga. wire would be sufficient (voltage drop 2.414V)

However, this calculator seems much more conservative:
http://www.vihon.com/Vihon_Calculato...alculator.html
It says a 0 (zero) gauge wire is required !

Also would like some real world advice on the voltage drop recommendations
of the NEC. At what point does one see excessive/dangerous wire heating?
2% ? 5% ? 10% ? 20% ?

-- Paul


Heating is not a concern as long as the wire size is adequate for the
current. 12 gauge wire will generally cary 20 amperes over any distance with
acceptable heating. Long runs require heavier wire only because of voltage
drop under load, not because of heating. The extra heat generated is
distributed over the extra wire length. Twice the heat with twice the wire
length gives the same temperature along the wire. Two seperate, though
related, concerns.

Don Young

Calculating voltage drop, wire gauge ampacity over distance
 

"Paul" wrote in message
...
I'm confused by a couple of online calculators I've found.

I'm trying to determine the proper gauge wire to carry 20A, 120VAC over a
distance of 300 ft. with an approx allowable 2% (per NEC) voltage drop.
This UF cable will be buried for most of it's length.

your calculation is off @2% drop it calls for #0



This calculator:
http://www.stealth316.com/2-wire-resistance.htm
advises a 6 ga. wire would be sufficient (voltage drop 2.414V)

However, this calculator seems much more conservative:
http://www.vihon.com/Vihon_Calculato...alculator.html
It says a 0 (zero) gauge wire is required !

Also would like some real world advice on the voltage drop recommendations
of the NEC. At what point does one see excessive/dangerous wire heating?
2% ? 5% ? 10% ? 20% ?

-- Paul