Sizing extension cords

teejk · Sep 18, 2016

Retiredguy2 said:
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.

I'm not a "sparky" but have read through this entire post where you asked the time of day and have been instructed how to take your watch apart and put it back together. Here's my take...most electrical tools now come with a manual that will specify extension cord lengths for various wire gauges. I'm guessing those tables are assuming that your source (your GFCI outlet) is delivering 110-120v (a long standing argument about proper terminology on 110/120 and 220/240). A quick check with a voltage meter at your GFCI will tell you line loss inside your building before it gets to the outlet so if you are getting 110/120v at that point, use the tables provided with your tool.

Redneck in training · Sep 18, 2016

Quick check with volt meter will tell the voltage loss only when the load is attached. If there is no load there is no loss. Once you know the voltage before you attach a load you can calculate voltage loss for various loads.

ultrarunner · Sep 18, 2016

I have one of those simple testers that imposes a load... plug and play.

It has alerted me to problems a few times... one was a lose set screw on a circuit breaker and another one was more dubious... someone had spliced romex in the attic by twisting the conductors together and electric tape and no box... it was my brother's home starting out...

teejk · Sep 19, 2016

Redneck in training said:
Quick check with volt meter will tell the voltage loss only when the load is attached. If there is no load there is no loss. Once you know the voltage before you attach a load you can calculate voltage loss for various loads.

I think the OP was asking about having to include the internal wiring distance. I have a lot of woodworking stuff and they all come with power tables. Never seen one yet that said anything about plugging into an outlet delivering 110/120v (or 220/240v). From there they get into "extension cords"...lengths and wire gauges. Again I'm not a "sparky" but I think there might be a little difference between pure "line-loss" (a function of distance from source regardless of load but rather related to heat loss...conservation of energy theory) and "load loss" (which will include the former but will add in the power required by the tool). Near as I can figure it all comes down to "total loss" and that is a function of capacity of the wire. I've run some stuff on 14ga and can say that while everything ran well, the cord was hot. I tend to stick to 12 ga because I know my outlets will deliver 120v (actually a bit higher than that like 121v or so) but also have a long pricey 10 ga cord just in case...it is a beast and it is collecting dust at the moment...don't need it).

Opti-Mist · Sep 19, 2016

Here is a bit of a different approach. I use a 2000W generator as an extension cord for such uses. No angst and no long cords.

RPW · Sep 21, 2016

Another thought. Get yourself a 2000 watt inverter attach appropriate battery cables and clips. Drive your vehicle to the spot. Open hood leave motor running and clip to battery. Even the cheap inverters from HF will power a chainsaw. I do that a lot around the property. I've even U
used a small 800 watt inverter with my small chainsaw on the tractor but the only problem I've experienced is the tractor doesn't have much of a charging current.