As I posted earlier, I'm setting up an old Craftsman 10" bench saw I
inherited. This will be a big improvement over the $100 Delta table
top saw I've been using.
This saw has a 1 HP capacitor motor. It was hard wired but I'm not
sure if it was set up for 115 or 240 volts?
I would like to attach a cord to the saw.
What I have now is a junction box attached to the saw frame. Amored
cable runs from this box to the bottom of a switch bolted under the
table top. The switch has two buttons for on and off. Armored cable
comes out of the top of the switch, and runs along the saw to the
motor. Ive never used this armored cable and I see a wire (ground?)
that looks like aluminum? that runs through it and is grounded on a
screw at each box. There are 3 wires, Red, Black and White. The white
is grounded at each box just like the "aluminum wire".
Here is what I'm not sure of. The red and the black wires are attached
to screws on the bottom of the switch. Red and black wires are
atteched to thetop of the switch and they continue on to the motor.
I would have though only one wire would be attached to the switch and
the other wire would continue straight through to the motor.
Does this indicate it was set up for 240 volts?
Should I reuse what was there and just wire an extension cord to the
junction box? What size cord for about 6 - 8 feet.
Or should I replace everything? What would I use instead of the armor
I know this should be basic stuff but I have limited electrical
experience but with a little help I can do this.
*PROBABLY*. But not "absolutely 100% guaranteed".
The switch and wiring set-up is designed for 240V use. It is _possible_
that the motor is capable of running on either 120 or 240, *and* that
it has been set up (via where the wires actually connect _at_the_motor_)
to run on 120V, Or that several different motors were available as "options"
on that saw, some of which were 240V operation.
OTOH, a '1 hp' motor is a bit on the small side for 120/240 operation.
It's most common on units in the 1.5-3.0 hp range.
There are only a few ways to tell 'for sure' --
1) Find the owners manual, read it -carefully-, making *sure* that the
motor on the saw matches what is described in the manual.
*IF* the manual mentions 120/240 operation, there will be a wiring
diagram, on how to connect things for each voltage. Match those
diagrams against the actual saw wiring.
2) Find the manufacturer model/part number on the motor, See if you
can find the 'specifications' for that motor somewhere -- it may
take a phone call to the manufacturer, if they're still in business.
3) Consult a _professional_ in the field of electric motor repair.
That's what _I would do. *After* establishing what the voltage requirement
is, obviously. Needless to say, you've gotta have the right plug on the
end of the cord, and the right kind of an outlet to plug it into,
For 120V, 12 ga is recommended. although for 1hp, you could get away with 14.
For 240V, 14 ga is definitely adequate, and with only 1HP you could get away
with 16 ga.
No reason to replace the existing stuff that is 'perfectly good'. :)
The 'mechanics' of doing it _is_ simple/straightforward, Figuring out _what_
_exactly_ needs to be done is the hard part.
I'm not an electrician but the plug and socket for a 110 volt line and
a 220 volt line are quite different. It seems to me that if you have
the usual 2 parallel slots and a round hole below, then you have 110
volts. If you have three curved slots in a circle, then you have 220.
On 15 May 2005 15:57:11 -0700, firstname.lastname@example.org wrote:
It was hardwired to an old fusebox and I didnt have much time to get
it out. The black wire ran to one 15 amp screw in fuse and the red
wire ran to another 15 amp screw in fuse. My stepfather didnt like
The motor will run 120 or 240. I dint know if you could tell by what
I've discribed what voltage it was set up for.
What you just described is definitely 220, two 15 amp hot leads.
220 does not need a neutral. The best thing to do would be to
create a 220 v extension cord and create or share (you may have
something else using a 15 or 20 amp 220 circuit) the proper
amperage 220 circuit. It would be best to establish a green
ground to this system to meet current codes. Most machines seem
to do a little better when wired for 220. Get an electrician if
you need to.
Yes, I'm sure the motor can be swapped to 110. This will require
opening the little door on the motor and rearranging the
terminations on the studs inside the motor case. The proper
terminations should be printed on a metal tag on the outside of
the motor. Their reference to the hot wire(s) will be L1 and L2
(line one and line two). For 110 you will only have an L1 and a
neutral. In order to keep things simple, you would be best off
removing the existing switch. Buy a new 110V/20 amp switch to add
to the saw. This new switch will interrupt the black wire (L1 at
the saw), the white wire will be continuous to the motor, the
green wire should attach to the saw case, motor case, and switch
if it has a ground screw. You can junction the wires in the old
box. Use AWG 10 or 12 wire for your extension cord. I would use
(top posted for your convenience)
Keep the whole world singing . . . .
DanG (remove the sevens)
Why? By his description he has a DPST switch. It's perfectly adequate
for switching both 120V and 240V. Why complicate matters?
And what if he later wires the motor for 240V? Then he will have to
buy yet another switch when the existing one was suitable for both
120V and 240V.
Good lord, what for? He said it's a 1 HP motor. At most it's going to
draw something on the order of 10 Amps at 120V. 14 ga would be plenty
for an extension cord at 120V (so long as he doesn't go nuts on the
length), although I wouldn't hesitate to support the use of 12 ga. If
he's going to stay with 240V it'll only draw 5 Amps. Why in heaven's
name would you need/want 10 ga?
Answer to your earlier questions:
You can't tell from the wire, the switch, or the way the switch is
wired if the motor is 120V or 240V. Frankly, I wouldn't even count on
the plug, if there was one.
The switch is probably a DPST (double pole single throw) switch. That
way, when you change the motor from 120V to 240V operation (or vice
versa) you don't have to rewire the switch; just the motor and the
It shouldn't be, so long as it's a 120/240V motor.
Ah, that's another question. There is a lot of misunderstanding about
this issue. I'll try and simplify. From the standpoint of the motor
itself, it has two windings. When the motor is wired for 120V, the
windings are placed in parallel; when the motor is wired for 240V, the
windings are placed in series. Consequently, the windings always see
120V, no matter how the motor is wired.
The motor consumes the same amount of power (watts) regardless of
whether wired for 120V or 240V (check the label--it will show
something like Amps: 12/6, which means 12 Amps at 120V, 6 Amps at
240V). 12 Amps @ 120V is exactly the same power as 6 Amps at 240V.
Therefore, your motor will not save you a single penny on your
electric bill whichever voltage you wire it for.
Also note that because the watts are the same, the heat must be the
same. You will not improve the life of your motor by choosing one
voltage over the other.
Since the windings always see 120V, the input voltage has no relation
to efficiency. Efficiency is an aspect of motor performance, but only
in the overall view of the motor, irrespective of input voltage.
Now, most people will experience a little more snap on startup on
240V, and you may be able to hog that 16/4 hard maple a little faster
or longer on 240V, but that has another reason (be patient, I'm
getting to it).
If you are very close to your breaker panel, you should not see ANY
difference in performance (particularly if you're on a 20A circuit).
However, if you are 60 or 70' away, you need to be aware that although
power is the same (half the current at twice the voltage and vice
versa), voltage drop as a percentage of source voltage is lowered by a
factor of four when running on 240V.
One final thing: each motor briefly draws much more than its FLA
current on startup. All of the issues of voltage drop and resistance
come further into play at that higher current, which probably accounts
for the "snap" on startup on 240V.
So, the easy answers are:
Check the wiring diagram on the inside of the wiring cover plate on
your motor to see how it's wired. That'll resolve the 120V/240V Q.
You almost certainly don't need to rewire the switch, but check it out
with a meter (or continuity tester) while you have the jumpers on the
motor disconnected (the windings in the motor will show continuity and
throw off your cipherin').
Contrary to what someone else mentioned, there are several varieties
of plugs that might be attached and you may not know to differentiate
one from another. Moreover, are you willing to trust what someone else
might have put on there that didn't even have the internet to ask on?
If you have a 20A circuit you can easily and safely run the saw on
120V (properly jumpered). Eventually you may like it on 240V better,
but it's not a requirement.
The saw will be within 5 -10 feet of the breaker panel.
I'm hoping to plug it into an existing 20 amp outlet I installed.
Sounds like the motor was wired for 220 volts. I'll confirm tonight. I have
the manual for the saw and the motor.
I will rewire the saw for 110 volts.
I'll reuse the same switch.
A little confused here, Its ok on the DPST to have both wires run through
the switch? I haven't seen one before and I'm used to only running one wire
through the switch and the 2nd wire runs straight through to the motor. (I'm
sure my ignorance is showing here).
Also about the cord with a plug on it. Do I buy the correct cord and add a
plug to it or buy a 12 foot extension of the proper size (12 gauge) and cut
the outlet end off and wire that to the box?
Thanks for the help.
I'll reuse the same armored cable
You could comfortably use a 14 ga cord for that distance.
You shouldn't need to change a thing. Just verify the wiring with a
meter/continuity tester as I mentioned before.
Yes, in house wiring it's standard to only switch the hot side.
However, there's nothing wrong with switching both hot and neutral at
120V, and in fact doing so makes it possible to install one switch for
either 120V or 240V operation that doesn't need to be rewired when
changing over. You're fine with the switch as is.
Well, I don't think you'll be able to buy a 12 footer; probably 15
footer, but they're not always easy to find in 12 ga. In any event,
that's as good an idea as any (the extension with molded plug) and you
can cut it off to any convenient length.
What I did in my shop was buy a chunk of yellow 12 ga rubber coated (I
think it's SJ type cord) bulk cord and install my favorite plug on it.
I did that for two reasons, 1) I was going to put a 240V plug on and
premade cords with 240 plugs are rare as hen's teeth, and 2) I wanted
the visibility of the yellow for safety reasons (see it, don't trip
Don't _have_ to do it that way, but is *is* OK.
The reason _for_ doing it that way is simple -- "simplicity". <grin>
To change voltage, you only have to change the jumpering at the motor,
and use the right wall-plug. One less thing to futz with, at a later
date, if you (or someone else) decides to convert back to 240V operation.
It doesn't hurt anythiong to switch both hot and neutral wires.
Switching the hot leads is 'necessary for safety'.
Switching the neutral _alone_ is a *BIG* no-no.
Swithcing the neutral _with_the_hot_ is entirely acceptable, albeit 'optional'.
"Yes". Either one.
Price doing it either way, and go with whichever is the lower cost. :)
Your description of the fuse-box wiring in another post confirms that the
saw was set up for 240V.
There should be directions in the owner's manual, *or* on the underside
of the cover where the wires attach to the motor, that shows "what goes
where" for 120v and for 240v opertion.
I rewired the motor to 110.
Cut a 12 guage extension cord to about 12 feet and wired it to the
switch with white to a screw on the switch box.
Problem now with the thin ground wire that runs inside the armor.
It broke off around where the cable ends.
(how do you cut armored cable?) I used a dremel and checked with a
magnifier, I dont think I hit it. I think I flexed it to much trying
to get it attached inside the motor. Anyway, I assume this is bad!
This wire grounds the armor cable?
If I have to replace this cable, what are my options to get from the
switch to the motor?
On Mon, 16 May 2005 21:31:28 -0000, email@example.com
(Robert Bonomi) wrote:
Well, first of all, it doesn't have to be armored cable. Just use a
piece of stranded cord--a leftover piece of the cord you cut for the
extension will do.. It'll have three wires in it; black, white, green.
Black-to-black, white-to-white (or red), green-to-ground. It'll serve
you just fine, even if you wire back to 240V.
If the wire from the armored cable had terminals on it at the motor
end, you can get replacement terminals at the borg. You'll need a
crimping tool to install them, but you need one of those in your tool
box anyway. Get the kind of tool that'll shear machine screws--you
won't believe how many times you'll eventually use that feature. It'll
probably also include a wire stripper. You'll use that on this job.
Thanks for your help. I guess I overlooked the obvious.
I'll use the leftover extension.
I have all kinds of terminals I could crimp on the ends of the stranded wire
in the extension cord I cut.
Am I better off adding these connectors? The original wire was solid under
the screw connections. I now have stranded wire under the screw connections.
I dont like the way the strands flatten out under screw pressure.?????
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