[Greenbuilding] chainsaws (was sawdust for composters)

[Lawrence Lile]

Presumably this warning is from recent experience. Sorry to hear about
your chainsaw.    

NEC Table 9 tells us #12 copper is 1.7 ohms to neutral per 1000 ft, 2.7
for #14 ga.  

200/1000 * 2.7 *2 (both ways) is 1.08 ohms, at 14 amps gives a 15 volt
drop, 12.5% drop from 120 volts plus however much your inverter will
sag. This will definitely burn out a motor.

Same calc for #12 gives 9.5 volt sag, or almost 8%

Same calc for #10 at 1.1 ohms gives 6.16 volt sag, or 5%. 

Your friendly power company promises, usually, to hold their voltage to
+/- 10%.  Either the #12 or the #10 will stay within this, if your
inverter doesn't sag too.  But you are right the #10 wire is really a
good idea if you are 200' from a battery.  A #12 100 foot cord might be
a better idea than 200' of anything.  

I've used a 100' cord on an electric mower for many years without issue,
it's a 12 amp motor on a #12 cord.   

For any of these tools, a GFCI should be used in case you cut the cord
in two.   

Lawrence Lile, PE, LEED AP
Project Solutions Engineering

-----Original Message-----
From: jefro at mcn.org [mailto:jefro at mcn.org] 
Sent: Tuesday, October 30, 2007 6:05 PM
To: Lawrence Lile
Cc: GB REPP
Subject: Re: [Greenbuilding] chainsaws (was sawdust for composters)

Gah... I wish I had read this note YESTERDAY (literally).

BTW, beware that that 200' of cord should probably be 10ga or better if
you want to draw the 12-14 amps that a saw will require, and the
inverter
should be attached to a 2000+ watt generator (or battery array etc). 
Otherwise you'll burn out that non-wimpy motor very quickly, as my small
collection of dead drills and saws can attest.  The voltage drop across
200' of standard 12ga (or worse, 14ga) wire is quite hefty at large
amperage.

> I was just bucking up some 30" diameter oak logs with the electric
saw,
> they are NOT wimps as widely believed, they'll hold their own even in
> thick oak.