I just bought a saw and dust collector and they both run on 220. The
question I have is, would it be OK for me to use 10/3 and a 30 amp double
breaker and put both devices on the same circuit and be able to run both of
them at the same time? I would not turn them on at the same time. I would
let one get up to speed and then turn the other one on. I want to save the
other 5 spaces in my 100 amp sub panel (in which my electric stove is also
connected to) I have for lights and other outlets for tools. I am in the
process of building a shop in my basement. I just moved into a new home.
Thank you all for your opinions.
One word: subpanel.
Okay, two words, if you spell it: sub panel.
Solves all of your problems. Since your shop is in your basement and
your load center almost assuredly is too, it'll be duck soup.
Master Woodbutcher and seasoned termite
Shamelessly whoring my website since 1999
Grizzly states the following in the manual for their G1029Z Dust Collector:
Circuit Breaker: The 2 H.P. motor will draw roughly 12 amps @ 220V. We
recommend using a 20 amp circuit breaker. Circuit breakers rated higher will
not adequately protect the motor.
I suppose this is true with any 220 amp motor.
Awright Greg, let's see if an extreme example will clear this up for you.
Let's say you could find a 1000 amp breaker and installed it on the circuit
in question. Now let's say that something goes horribly wrong with the
motor and it starts drawing 200 amps ("cause it found a wrong ground or
something) The wiring starts to catch fire along with the surrounding
structure, but the 1000 amp breaker (or even the unrecommended 30 amp
breaker) thinks everything is just dandy, so it keeps that (or some other
excessive) current supplied to the fault in progress. Now if you had minded
the warning that 20 amp protection would be correct and proper, it would
have tripped and the fire department wouldn't be on the way.
Hope this helps
I said earlier, it is clear that article 430 may simply be too complicated for
most folks but I will try again.
Start with the nameplate (FLA) rating of the motor. (for example 16a)
Multiply this number by 1.25. That is the ampacity requred for the wire. You
can use table 310.16 for this (14ga is OK for 20a at 60c)
Now take the FLA and multiply it by 2.5, that is the maximum size of the branch
circuit overcurrent device. (40a)
Some motors can have higher O/C devices, up to 11 times the FLA but you folks
are confused enough.
You have only sized the wire and the branch circuit O/C device at this point
NOW you need an "overload" device sized to the motor and some kind of thermal
protection (may be the same thing)
This is what protects the motor from burning up. Usually that is built into the
motor or the equipment the motor is in.
It may also be part of the motor starter assembly.
You also need a disconnect.
In your case the motor would have to have a 400a FLA to allow a 1000a breaker
and you would need 1500Kcmil wire although most folks would just parallel two
I'm certain your description above is well intended; however, what it truly
illustrates is your lack of the NEC and it's intended purpose.
The motor you describe could turn into burned toast, the NEC could care less
as long as the insulation on the conductors feeding the motor is not
Circuit protective devices are designed to protect insulation on conductors,
not the loads such as a motor, that consume the power.
Overload devices provide that function.
S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland)
Lew - your point is well taken and it has never been disputed in any of the
recent threads on this topic. However - the discussions have not been about
what NEC is intending to do. The electricians (or seemingly so) in the
group keep referencing NEC and the fact that NEC intends to protect the wire
not the device. The points that have been made about protecting the motors
represent the *owner's* concerns. Not everything in the world of
electricity is covered by NEC's interest. Owners have other interests
besides their house wire. To date, I've not heard any of the electricians
argue that the statements about properly sizing a circuit to the load is
improper. The owner is concerned for his saw motor. It appears from the
Griz literature that he should be. Maybe there is an error in the Griz
literature, but to repeat that NEC only cares about wire insulation really
does nothing to further understandings in these threads.
I addressed that and pointed out 2 12a motors on one 30a circuit will actually
provide MORE protection than one on a 20a.
The reality is the NEC does talk about protecting the motor. That is the
overLOAD protection that should be integral to the equipment.
If your overloaded motor is tripping the wall breaker you either have the
circuit overcurrent device sized TOO SMALL or the overload protection is not
working. The overload should trip first if things are sized "properly".
I am confused after reading all the replies.
So folks what should I do for my Grizzly 12 amp saw & 12 amp DC, go with (2)
220 separate 20 amp breakers 1 for each device using 12/3 for each, or go
with 1 220 30 amp breaker using 10/3 cable and putting them both on the same
I msut have missed the earlier messages but I would use two 20 amp
circuits. Two 12 amp motors starting at the same time would probably
trip a 30 amp breaker. Thats assuming the 12 amps is running amps as
oppossed to starting amps. See NEC 430 for code requirements for
I'd go with the 10/3 and 30 amp. One point is that neither of these
devices is of the kind you leave to operate unattended. If you're saw
is overloaded and its built in protection fails to intervene, hopefully
you're paying enough attention to notice "something's not quite right"
and not be depending on the branch circuit protection to come into play.
Aha - my apologies Greg - I missed that when you first posted it. I've been
following the threads on this pretty closely but then again sometimes
earthlink (sometimes...???) drops posts along the way.
There is no harm to running 10/3 rather than 10/2, but unless your machines
actually require a neutral you don't have to.
You have not mentioned what the machines draw, but unless they are huge 30a
should be plenty; I run both of mine on 20a.
You will have to use receptacles rated for 30a, but other than that it seems
pretty straight forward.(though I would rather see two 20a circuits..)
He didnt mention with ground, It needs a ground of course.
I would check on the distance and current draw with a meter. I use all
12/3 with a ground. All my tools are within 30 feet of the panel.
A cheap amp-probe can be a real eye opener on some of these 5 HP
motors. It can also be used to tell if the start capacitor is bad on a
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