Sizing extension cords

Retiredguy2 · Sep 17, 2016

I have never really thought about this issue prior to today...just purchased a new electric chain saw that draws 12 amps. I have almost never used any extension cord over 25 feet long to power a tool that uses 12-plus amps but it appears that to use my new saw I will need to use much more cord length. My household wiring uses 12 gauge that is about 45' long to supply the GFCI outdoor outlet I want to use to power the saw. Do I need to allow for that 45' distance within the house itself to determine the maximum extension cord length I can use? Thanks for any advice.

4570Man · Sep 17, 2016

I've got 10 gauge cord in my shop that I use to power the heavy draw stuff. My shop panel is powered by about 50 feet of 6 gauge. All of my 110 volt is wiring is 12 gauge and all of my 220 volt wiring is 10 gauge. The 10 gauge cord is 110 volt. If needed I've made cords for my 220 volt stuff. If you don't need something elegant making a cord will be your cheapest option. How far do you need to run. If it's more than 50 feet I'd scrap that idea and get a gas saw. The chainsaw will likely trip the GFIC breaker. You may need to run the cord through a door and plug into a non GFIC protected breaker.

Retiredguy2 · Sep 17, 2016

4570Man said:
I've got 10 gauge cord in my shop that I use to power the heavy draw stuff. My shop panel is powered by about 50 feet of 6 gauge. All of my 110 volt is wiring is 12 gauge and all of my 220 volt wiring is 10 gauge.

Glad you planned ahead but how does your illustration help answer my query?

4570Man · Sep 17, 2016

Retiredguy2 said:
Glad you planned ahead but how does your illustration help answer my query?

We'll I've edited my post about 3 times, but I don't factor in household wiring for a cord size.

GregbkH · Sep 17, 2016

Use a 12 or 14 gauge extension cord and you'll be fine.

4570Man · Sep 17, 2016

GregbkH said:
Use a 12 or 14 gauge extension cord and you'll be fine.

Unless he needs to go more than about 5 feet a 14 gauge is definitely too small. He didn't say how long he needs, but a 12 gauge is likely too small. My circular saw doesn't operate properly with a 50 foot 12 gauge cord.

EarPlug · Sep 17, 2016

16 Gauge Cords Any 16 gauge cord between 0 and 100 feet long will adequately handle tool loads up to 10 amps.
14 Gauge Cords Any 14 gauge cord between 0 and 50 feet long will adequately handle loads between 10 and 15 amps.
12 Gauge Cords If your tool load is between 10 and 15 amps and the length of the cord is 50 to 100 feet, you need a 12 gauge cord to safely power any tool.

Retiredguy2 · Sep 17, 2016

GregbkH said:
Use a 12 or 14 gauge extension cord and you'll be fine.[/QUOTE

Total distance to plug in my saw will be about 130-140 feet from the outlet which is 45 feet from the service panel itself. 12 amps draw on a 12 gauge cord for 175 feet? Would never try to use a 14 gauge cord for that purpose. I am sorry for not giving more clarification in the OP.

4570Man · Sep 17, 2016

You're going to need a minimum 10 gauge cord. I still wouldn't attempt it. The cost of such a cord alone makes it impractical. I would get a generator or a battery or gas powered saw.

2458n · Sep 17, 2016

Should have asked question first. 175 feet is way to far. Gas powered is made for this use.

Redneck in training · Sep 17, 2016

The saw will take 12 A at rated (highest safe load before it start smoking) load. Depending how hard you push on it or how big logs you will be cutting the current might be less than 12A. 12 AWG would drop about 12 v at 225 ft and 120 VAC/18A.
Online Wire Size Calculators & Tables

ultrarunner · Sep 17, 2016

There was a cabin in the mountains at the very end of a dirt road and voltage was low... so low it affected function.

This was in the 1960's and the owner mentioned it to one of his telephone company co-worker who sugested a buck-boost transformer... made all the difference going from 97 to 127 volts.

I picked up a small boost-buck portable transformer that has 10, 15 and 20% boost terminals... I have never tried it but thought it could be just the ticket in a low voltage situation...

97 volts boosted 20% would provide 116 volts.

We have our own transformers at work... the typical voltage in the hospital is 124 volts... the old line voltage clocks run fast.

4570Man · Sep 17, 2016

You can't get enough amperage to do that.

ultrarunner · Sep 17, 2016

If you had a circuit at the the panel or the existing circuit is 12ga with a 20 amp breaker and the saw requires 12 amps it would seem boosting low voltage would help... just thinking out loud.

I do agree you would hit a wall if the load was higher... but 12 amps of load on a 20 amp circuit?

4570Man · Sep 17, 2016

I thought the transformer went at the end of the cord? This project doesn't make much sense anyway. He could buy a gas saw for what that much cord will cost. If there's some reason he's against gas he could get a battery powered saw.

ultrarunner · Sep 17, 2016

Mine can be hardwired to the panel or use a 24" 10 ga cord to the transformer...

Transformer has a single 20 amp receptacle.

Wonder if a voltage reading has been taken to see what Retiredguy2 has to work with?

I bought a Stihl electric 170 saw thinking my brother could use for the freshcut at the Christmas tree farm.. right now he uses gas Stihl saws and on a busy day the saw will be started maybe a 150 times... and each cut is a few seconds.

Electric just seemed to make more sense but so far has been no sale as he has 3 gas saws at the cashier booth.

prichard · Sep 17, 2016

The problem with buck boost is hi are increasing the current as much as you are the voltage. So if you boost voltage 20% you will increase current through the cord by 20%. Now the 12 amps that the voltage drop was calculated based on is 14.4 so your drop is higher and you're no longer at 116v. You end up chasing your tail.

prichard · Sep 17, 2016

So retired guy, what prompted you to buy an electric chainsaw for remote work? Not trying to give you a hard time I'm actually curious.

ultrarunner · Sep 17, 2016

prichard said:
The problem with buck boost is hi are increasing the current as much as you are the voltage. So if you boost voltage 20% you will increase current through the cord by 20%. Now the 12 amps that the voltage drop was calculated based on is 14.4 so your drop is higher and you're no longer at 116v. You end up chasing your tail.

Outside of boosting 208 to 240 for equipment... what would be the purpose of single phase 120V buck boost transformers?

Last year at the Christmas Tree farm they brought in a center drill machine for spotting and drilling the taper hole in the base of the trunk... it is about 150 from the meter... every time the drill was turned on the LED light string went dark for a moment... the 20 amp breaker never tripped.

I explained it was an effect of voltage drop and certainly not good for the LED lamps...

The solution was having a expensive 150' extension cord made up.