Just ordered one. Reading through the owners manual I was struck by the
electrical diagrams calling for 10Ga wire and a 30Amp (220V) circuit for the
3hp 1phase motor. Years ago (in anticipation of ordering the saw) I
installed a 20A 220V line to my saw -- it was my understanding that a 20A
220V circuit was plenty of power for a 3HP motor. Is the 30A designation in
the manual just a typo ?
It doesn't matter what the cord is. The internal wiring on my 23a water
heater is #12.
#12 can handle more than 20a, but anything over 20a requires a 30a breaker,
and a 30a breaker requires #10.
Then there is the issue of voltage drop; cords are shorter than your house
It is best to follow their recommendation. Perhaps the voltage drop is
excessive on #12 when starting, leading to shorter life. Or maybe they have
a reason I haven't thought of.
(Now, the circuit to my water heater had been #12 on a 30a breaker for 35
years until I noticed and replaced it last year; and the house didn't burn
down. But that doesn't make it safe or legal. And it is not a motor; a
water heater doesn't really care about voltage drop.)
I would have to agree with Woody. I always think of voltage drop as the run
gets longer. I think this every time I wire up a machine straight from the
panel with say 10gauge to say a welder and then connect it to the 14gauge
wire inside the welder. I always say to myself "I spent three times more
for 10ga because of the voltage drop???"
Never fully understood why, but I always think that the electrical code and
UL approval have two different ideas on electricity (i.e. electrical code
says you need 10ga to the machine, UL says you need to run 14ga in the
On the other hand I think the cooper manufactures "influence" the
electrical code in a mafia like style, and maybe, just maybe that have not
infiltrated the UL yet.
Of course I am wrong on all fronts.
What's the actual motor plate rating and starting inrush?
If it's a dedicated circuit or only one item is run on the circuit at
one time it will undoubtedly serve as I'd assume you have a pretty short
I wired the shop w/ 10AWG and 30A breakers just on general principles.
The PM66 I have is nearly 30 yrs since I bought it so I have no
recollection any more of what was suggested but I'd have run 10AWG
irregardless just on general principles...
I would absolutely contact their customer support people before spending
money on breakers or wiring.
I purchased a 54A jointer a year or so ago. While setting it up I noticed
some areas where the manual and the jointer were at odds. After setup I
walked through the book and compared it with the features the manual
described. There were problems - some glaring. Powermatic finally admitted
they had some problems with the 54A manual.
If it can happen once it will happen again.
Just got off the phone with Powermatic Tech support -- they acknowledge that
a 20 Amp should do but that the saw draws 17A when running and can double
that at startup. Given this they _recommend_ the 30Amp breaker to avoid
problems in the future. Evidently if the current fails to support the motor
at startup it can damage the motor.
Now to knock the rust out of my brain I was under the impression that a
single phase 20Amp circuit could supply 20Amp but that a 220V circuit could
source 20Amp on each phase -- thus providing an effective 40 Amp rating --
was I dreaming ?
Guess I know what I have been saving that coil of 10Ga Cable for..........
I got the same story (more or less) from Powermatic when considering
their saw. I ended up with a Unisaw 3HP. It runs off of a 220 line I
installed with 20 amp breakers. It shares the line with a compressor.
It has NEVER kicked off the breaker (3+ years usage). AND, I don't
believe that Delta even suggests that a 30A breaker is needed to use
their 3HP Unisaw. Someone correct me if that's wrong.
240V is <still> a single phase...only thing different is the second leg
isn't at neutral, it's at the opposite polarity of the other. The total
current still flows through the two conductors so they're rated same as
You can still most likely get by, the recommendation is surely
conservative, but what do you expect from the vendor? They've got to
consider any installation where there may be a long run (hence, voltage
drop) from the supply panel....
17A would be full load current, which is rarely ever reached unless you are
ripping 3" very hard wood. I would venture to say you won't even get to
half load ripping anything less than 5/4. The initial current (starting
inrush is for a very, very short time on a table saw, because you are only
have the inertia of spinning up the blade to overcome. The circuit breaker
characteristics are such that it tolerates short term high current without
tripping. Voltage drop is not really a factor for short runs.
But this is all academic. There's nothing wrong with the conservative
approach of going with the 10 ga.
I have my 1ph-5hp-PM66 on a 20 amp dedicated w/ 10ga wire to the
IIRC after getting the saw setup, I checked the amp draw at startup and
18amp reading. Also, IIRC I saw 15amp while running.
I've not had any problem with this setup. I was comfortable with the
service to the saw after doing some study and research on the same
while I was waiting for my saw to arrive.
However, this is your baby (and your home or shop). You would
on the safe side with 30amp. I would not scrimp on the wiring ... do
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