acceptable voltage drop for power tools

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Cleveland Apprentice

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Cleveland, Oh
What would you consider the maximum voltage drop for power tools using long extension cords? I plan on using a 10 amp sawzall at a distance of approximately 200 feet. I knew someone using a circular saw at a distance like this and it burned up the cord in saw. I plan on use a #14 cord. Is a 5% max drop a good rule of thumb? Thanks
 
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K8MHZ

K8MHZ

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Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
Cleveland Apprentice said:
What would you consider the maximum voltage drop for power tools using long extension cords? I plan on using a 10 amp sawzall at a distance of approximately 120 to 150 feet. I knew someone using a circular saw at a distance like this and it burned up the cord in saw. I plan on use a #14 cord. Is a 5% max drop a good rule of thumb? Thanks
Click to expand...

10 amps on 150 feet of #14 gives you a 7.6 percent drop. If you start with a full 120 you will have 111 at the saw.

The #14 should handle the current fine. I would be more concerned about the saw.
 
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Cleveland Apprentice

Senior Member
Location
Cleveland, Oh
I'm sorry, correction on the distance. It's approx 200'. I was just wondering what is max % of VD is acceptable. I'm thinking 5%, but someone I know said 10% max. I'm not sure if 10% is ok. Thanks
 
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broadgage

Senior Member
Location
London, England
As above, a thicker cord is probably desirable.
A lot depends on what the actual voltage is at the outlet into which the cord is plugged, this can be measured but is liable to variation.

Most appliances, including power tools should tolerate a voltage range of from 90% up to 110% of nominal or nameplate voltage.

The proposed cord would therefore be probably just acceptable IF the voltage at the outlet was a full 120 volts.
But what if the voltage from the utilty was 5% low at 114 volts, and with another 5% lost in the wiring between the service and the outlet, giving only about 108 volts at the outlet.
That would be under 100 volts at the tool and probably unaceptable.
And remember that the draw and therefore the voltage drop will be greater under starting conditions.
 
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suemarkp

Senior Member
Location
Kent, WA
Occupation
Retired Engineer
I know one electrician who has a little buck-boost transformer setp to kick the voltage up a bit. Even with a short cord, the boost doesn't seem to hurt the motor. Heavy loads and low voltages will have the motors suck a lot of current and get too hot.
 
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hurk27

Senior Member
Location
Portage, Indiana NEC: 2008
Universal motors are immune to voltage drop, I have used variac transformers to control the speed of non variable drills many times, the only problem is if you stall them which is more likely in a voltage drop case, a universal motor is a DC motor.
 
kwired

kwired

Electron manager
Location
NE Nebraska
Just because the equipment is rated 10 amps doesn't mean you will load it to 10 amps. But if you do you will have some voltage drop to contend with,

Buck/boost is not a very good solution for voltage drop problems, especially when load is not constant.
 
kwired

kwired

Electron manager
Location
NE Nebraska
wiigelec said:
For the cost of the 200' 12awg extension cord you can buy a battery operated sawzall and never have this issue again...
Click to expand...

And you can go much more than 200 feet from power supply if you wish. You can then take the battery out of the recip saw and use it in another cordless tool same distance from power suppluy:thumbsup:
 
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
wiigelec said:
For the cost of the 200' 12awg extension cord you can buy a battery operated sawzall and never have this issue again...
Click to expand...

and then when one battery dies you can plug in the other to find out you forgot to charge that one Sunday afternoon just prior to settling in to watch that all important golf game with a 2 yr old holding you in place for a couple hours. :)

Good sharp blades and not forcing the tool at the end of 200' of cord will help considerably.
 
G

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
120404-0936 EDT

What is an electric tool with a universal motor and a variable speed control other than a universal motor with adjustable applied voltage?

So you can tolerate a very large voltage drop to one of these tools, but with reduced power output. As the motor RPM gets low you may also have to accept lower torque (not load the motor as much) to avoid overheating the motor because there is less air cooling.

.
 
T

templdl

Senior Member
Location
Wisconsin
I always never viewed it as a voltage drop but the actual voltage available at the tool location regardless of the drop. What this amounts to is what voltage the tool can operate satisfactory at.
Most tool instruction books will include a section on allowable cord length which assume a given source voltage with a given length of extension cord that way be used to maintain tool performance. If your source voltage is marginal at best to begin with it?s down hill from there when extension cords are added.

In most cases heat is an issue. When voltage does down it takes more current to do the same amount of work. More current equates to increased heating and the potential for tool burn out. As one of the other guys pointed out the available torque can be severely reduced with low voltage.
 
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