I have a 300' run to a 1/2 horse water well pump to be fed with 240v single phase. With voltage drop I need #6CU conductors. Problem is, #6's will not go under the lugs of the 1/2 HP Franklin motor control which is at the start of the run, nor will they go under the 20A lugs of the 2pole breaker at the panel where the circuit originates. Can I start the circuit at the panel with #12's (20A) for 20' to the Franklin control, go out of the control with 3/#12 +1 ground (for capacitor start), then another 4' to a JB where the #6's start to go underground to the well head? I've wondered before if I can feed larger conductors necessary due to voltage drop on a longer run with smaller conductors starting the circuit, for the same reason each time.
Voltage drop
- Thread starter hconant
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charlie
Senior Member
- Location
- Indianapolis
Re: Voltage drop
No problem at all as long as the OC protection is set for the smallest conductors in the circuit. I am assuming the Vd calcs are correct, I did not check your math.
No problem at all as long as the OC protection is set for the smallest conductors in the circuit. I am assuming the Vd calcs are correct, I did not check your math.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: Voltage drop
hconant
You also need to consider the VD due to the drop cable feeding the submersible pump. Start at the motor, allow 5% VD from there to the source.
Its a 230 V rated motor, you want no less than 230-11.5 volts (5%) at the motor. You can use a smaller drop cable and make up the voltage drop on the run from the pump controller to the source.
The motor is designed to run +/- 10% voltage, so going with -5% gives you a bit of a fudge factor.
hconant
You also need to consider the VD due to the drop cable feeding the submersible pump. Start at the motor, allow 5% VD from there to the source.
Its a 230 V rated motor, you want no less than 230-11.5 volts (5%) at the motor. You can use a smaller drop cable and make up the voltage drop on the run from the pump controller to the source.
The motor is designed to run +/- 10% voltage, so going with -5% gives you a bit of a fudge factor.
Re: Voltage drop
My calculator indicates that #14 cu will give a terminal voltage of 230 volts from a 240 volt supply, with a load of 5 amps.
Check out this: http://www.stanselectric.com/vdrop.html
Bennie R. Palmer
[ November 28, 2003, 02:18 PM: Message edited by: bennie ]
My calculator indicates that #14 cu will give a terminal voltage of 230 volts from a 240 volt supply, with a load of 5 amps.
Check out this: http://www.stanselectric.com/vdrop.html
Bennie R. Palmer
[ November 28, 2003, 02:18 PM: Message edited by: bennie ]
Re: Voltage drop
Bennie,
That is interesting. However, according to the plate ratings, I need 15 amps. Even so, your calculator shows #10 is fine for 15A. Here is the link for the calculator I have been using which is where I came up with the #6. What do you think?
http://www.elec-toolbox.com/calculators/voltdrop.htm
Bennie,
That is interesting. However, according to the plate ratings, I need 15 amps. Even so, your calculator shows #10 is fine for 15A. Here is the link for the calculator I have been using which is where I came up with the #6. What do you think?
http://www.elec-toolbox.com/calculators/voltdrop.htm
- Location
- Massachusetts
Re: Voltage drop
15 amps is interesting, Table 430.148 lists a 1/2 hp 240 motor at 4.9 amps, according to the table 15 amps is about a 2 or 3 hp motor.
Are you sure of the HP?
Disconnects, conductor size and short circuit ground fault protection are to be selected by use of the tables in 430.
430.6(A)
15 amps is interesting, Table 430.148 lists a 1/2 hp 240 motor at 4.9 amps, according to the table 15 amps is about a 2 or 3 hp motor.
Are you sure of the HP?
Disconnects, conductor size and short circuit ground fault protection are to be selected by use of the tables in 430.
430.6(A)
Re: Voltage drop
hconant: I don't understand the 15 amp load.
3 percent is not required for a pump motor. 10 percent will work. 10 percent drop from 240 volts is 216 volts at the terminals.
#14 cu is still within the parameters. Of course 10 or 12 would be sensible. #6 cu is overkill.
hconant: I don't understand the 15 amp load.
3 percent is not required for a pump motor. 10 percent will work. 10 percent drop from 240 volts is 216 volts at the terminals.
#14 cu is still within the parameters. Of course 10 or 12 would be sensible. #6 cu is overkill.
frenchelectrican
Senior Member
- Location
- Nord'est Wisconsin et Paris France
Re: Voltage drop
i have calauator for wire size (made by calcaulated industries)
and i came up with wire size for 300 feet in lengh then i clicked on 240 volts then clicked on 5 amp ( typical for 240v 1/2 hp motor) and then clicked on wire size it came up 12 gauage wire size and voltage drop is 5.9 vd and at 2.5% volt drop and you can use the 12 or 10 gauage wire it will be plenty fine for this appaction and btw some 240 volts pump motors will be rated for 208 also so check the nameplate too .
i did read the other post about this and why need a full 15 amp curcuit ???
is this pump is two or three wire system it can make some diffrence there.
most pump are 2 wire but few have 3 rd wire for starting only .
please let us know what is your inted so we can steer you right
merci , marc
i have calauator for wire size (made by calcaulated industries)
and i came up with wire size for 300 feet in lengh then i clicked on 240 volts then clicked on 5 amp ( typical for 240v 1/2 hp motor) and then clicked on wire size it came up 12 gauage wire size and voltage drop is 5.9 vd and at 2.5% volt drop and you can use the 12 or 10 gauage wire it will be plenty fine for this appaction and btw some 240 volts pump motors will be rated for 208 also so check the nameplate too .
i did read the other post about this and why need a full 15 amp curcuit ???
is this pump is two or three wire system it can make some diffrence there.
most pump are 2 wire but few have 3 rd wire for starting only .
please let us know what is your inted so we can steer you right
merci , marc
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Voltage drop
What about startup current stalling the motor. The motor might only pull 4.8 amps running but can pull as much as 28.8 amps starting. this also has be accounted for. or this motor will be very sluggish in starting up if a high power factor cap isn't installed.
Just a thought.
What about startup current stalling the motor. The motor might only pull 4.8 amps running but can pull as much as 28.8 amps starting. this also has be accounted for. or this motor will be very sluggish in starting up if a high power factor cap isn't installed.
Just a thought.
charlie
Senior Member
- Location
- Indianapolis
Re: Voltage drop
Whenever you are doing Vd calculations, be aware of what voltage the local electric utility is supplying to the service. We pump out the voltage at the substation at about 4% overvoltage so we can go for a longer distance before we need to install voltage regulators. If you are on the end of the line, you may already have a 5% or more Vd before you even start your calculations. This is especially true in rural areas where the public service commissions will typically permit more Vd.
Whenever you are doing Vd calculations, be aware of what voltage the local electric utility is supplying to the service. We pump out the voltage at the substation at about 4% overvoltage so we can go for a longer distance before we need to install voltage regulators. If you are on the end of the line, you may already have a 5% or more Vd before you even start your calculations. This is especially true in rural areas where the public service commissions will typically permit more Vd.
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