How do I wire up my drum switch? (220V, single phase)
I've finally gotten around to wiring up the South Bend 13" lathe that I bought this summer, and I would really appreciate some advice on wiring the drum switch.
I put a Baldor 220V, Single phase motor in the lathe (model #L1322T) which is a drop in replacement having very similar specs to the original 3 phase motor. The wiring diagram on the motor is shown here. Note that there are 7 different wires coming out of the motor.
I have a 3 pole Allen-Bradley drum switch (model #350-TAV32) whose internal switching is shown here.
The only way that I can think to wire it up is shown below. Motor leads #2 and #3 would be connected together right at the motor. The rest of the motor leadss (5 conductors in total) would run the 5 foot distance up to the switch. That seems kind of complicated, but I've never wired this sort of switch before. I AM NERVOUS ABOUT LEAVING THE #4 TERMINAL "HOT" EVEN IN THE "OFF" SWITCH POSITION. Any advice that you could give would be appreciated.
(I should probably say that I plan to connect the bare, uninsulated ground wire to the case of the motor and switch, just in case someone else reads this in the future. This is a wire which doesn't normally carry current, but it there to provide a good path to ground incase something breaks.)
This is the diagram that was inside my drum switch. I had to reproduce it as it was badly deteriorated when I cleaned things up. It may or may not help, but it has several different kinds of hookups.
I've seen similar drawings elsewhere. Unfortunately, since I don't know how they relate to my motor they don't tell me too much.
Let me ask, is this a "Thermally Protected" motor?
Is this an "Instant Reversing" motor? Is this a dual
The reason I ask is that your motor has one more
lead than the usual 6 lead dual voltage reversible
motor. If your motor is thermally protected, then
some of the leads are coming off of the thermal
protection device and would account for the "extra"
The NEMA standard dual voltage single phase induction
motor has 6 leads (T1 through T5 plus T8). These
could be the same as your motor's #1 to #5 and #8
but the #9 lead is the problem. without knowing more
info, it is hard to give advice.
"I AM NERVOUS ABOUT LEAVING THE #4 TERMINAL "HOT" EVEN IN THE "OFF" SWITCH POSITION."
What I did on my lathe was to have a master power switch which then fed the motor and drum switch. The drum switch is just too easy to bump when you are setting things up in the lathe and I like the added safety of that. So it may be an option for you. The wiring diagram for your switch looks ok and I wouldn't have any trouble trying it...but that's just me. After you have the switch mounted and stuff sometimes you have it wired where it is running opposite from the handle position so all you would have to do is swap your 5 and 8 wires to get it to run in the direction it's comfortable with the direction of the handle.
Here's a spec for you Webb, see page 8
I believe this is the correct CD diag.
Thanks Steve, I had seen all of that document except the final page with the internal motor wiring diagram. (Love your website by the way, I've used it many times.) Here's that final page...
I'm still not sure what to make of wiring up my switch though, unless my diagram in the original post (above) is permissable. It makes me nervous leaving motor lead #4 connected to Line #2 (hot) at all times. It would probably work properly, but is it dangerous from "safe wiring practice" standpoint?
My motor is not thermally protected (i.e. not stamped "thermally protected" on the nameplate, and doesn't have the 2 extra wires.) I'm not sure, but I believe that it is not "instant reversing".
Steve, I found that document shortly after posting
my response. After looking at the diagram on page 8,
The only way I see to safely wire this switch with
the motor is to add a contactor or motor starter to
circuit. The A-B-C-D terminals in the drum switch
can be used to swap leads 5 and 8 between 4 and
9. The E-F terminals can be used to control the con-
tactor. The contactor is used to switch L1 and L2
on/off with leads 1 and 4.
Will my wiring diagram work? What exactly is unsafe about leaving the #4 lead hot?
In my garage I plan to have a mill, lathe, bandsaw and air compressor running off a circuit breaker subpanel. That entire panel is shut off by a large manual disconnect switch (a separate switch, not a circuit breaker). When I'm not out there working I plan to leave this main switch off. Essentially this is a manual disconnect switch to the four machines.
Thanks for the kind words,
I concure with Webb,
Review this and see if it works with the 350 switch:
lead 9 = A
lead 8 = B
lead 5 = C
lead 4 = D & lead from contactor L2
lead 1 = lead from contactor L1
E & F to contactor signal switch
I really appreciate your help. I think that I understand the basic idea of the external contactor switch, but then I look at Mcmaster-Carr and I'm baffled as to what to buy. Do you have a particular model in mind that would work in my situation?
Compositesguy, the diagram you posted will
work but as noted, it allows part of the motor's
wiring to be energized (hot) all the time. This
is not a safe way to wire equipment. Even if
you put a disconnect box between the panel
and the drum switch, the main control for the
lathe is still the drum switch. On the surface,
this doesn't seem much of a problem but consider
Some metal chips work their way into the motor
cabinet and into the electrical system (or a screw
is too long in the conduit box) and pushes against
some of the wires. Eventually, it works through the
insulation and a short develops. You smell smoke.
You hear sizzling-popping. You quickly shove the
drum switch to OFF but the short continues!
You have the lathe wired to your breaker panel but
it is hooked to a 30 Amp circuit. The chip (or what-
ever) may not draw enough to pull over 30 Amps
so, the breaker doesn't kick. Finally. you remember
to pull the disconnect box but by now, the oil has
caught fire and it is a real mess.
Remember, the breakers in the panel are there to
protect the wiring in the house and not specifically
to protect the device plugged into the circuit that
I see the safety issue there... thank you.
After some searching it looks like Mcmaster-Carr motor starter unit #7603K63 with a control voltage of 240 VAC might be what I want if I decide to wire up my switch as Steve has suggested. I've never used one of these devices before... am I on the right track?
CompositesGuy, I'm not sure whether the one
you picked is the best choice or not. I think
these are fine motor starters but the particular
model you chose is technically within specs of
the motor (I come up with 11.73 Amps) but
this unit is only rated for a 2 HP, 230 Volt single
phase motor. It may be better to step-up to
# 7603K65. I guess it will depend whether the
12.5 Amps listed is an absolute limit or a recom-
You could call McMaster-Carr and find out the
manufacturer and model number of the motor
starter and then call the manufacturer and get
their recommendations. This is probably the best
way to go.
I'm glad you are looking at motor starters. These
will give your motor protection from electrical over-
load (but you knew that).
And yes, 208-240 Volt control circuit is going to
make wiring much simpler. I'm glad you saw this.
Steve helpfully expanded upon an idea I suggested
and provided wiring connections for you. Follow them
and you should be okay. Of course, add a chassis
ground to all electrical enclosures. Use a green insu-
lated wire for ground and not a bear copper wire.
Just returning to thank you all for your input. I wired things up as suggested and it works!
The only odd bit is, as the motor starts up I have seen the occasional brilliant blue spark down around the motor. Upon closer inspection the spark jumps from the metal flex conduit (between the motor and the switch) to the iron casting of the lathe. I have no idea what's going on there. I brought an insulated ground wire from the main circuit breaker panel and connected it to the metal box containing the motor contactor, the metal switch and the chassis of the motor. Also, the entire system is rigid metal conduit up the lathe, and flex metal conduit from the wall to the switch, and from the switch to the motor. Basically there are good ground connections everywhere... so why the spark? I am talking this is a HUGE spark, not unlike an old-timey flashbulb... and it only happens occasionally.
First, check the wiring again and make sure there
aren't any mistakes. I don't think it is a static build
up discharging. If it is, you could try a ground wire
from the motor's frame to the cast iron pedestal.
Because the motor pivots to release belt tension,
the ground path through the mechanism is some-
what dubious. Dried oil and corrosion can interfere
with the ground continuity. Also, if you use isolation
mounts for the motor (or a resilient base motor),
you lose the ground path.
If you don't find any mistakes in the wiring, you might
check the capacitors in the motor for a short to ground.
Your description sound very much like a capacitor
discharge (probably the electrolytic start capacitor).
I suspect the capacitor. How long do these capacitors store charge (when is it safe to go poking around)?
The motor seems louder than I expected. I think the sound is the dull low 60Hz hum. (Much, much louder than my 3 phase bridgeport mill). Is that to be expected?
I can't say about the humming being too loud. It
might be an indication of a motor problem but then
again, maybe not. I haven't worked with many
capacitor start, capacitor run motors. Because the
"start/run" winding is thrown slightly out-of-phase
with the oil capacitor when in the "run" state, it will
cause some hum.
I don't think these capacitors are so large that you
can't "flash" them to remove the residual charge.
Disconnect the source power and flash across L1
and L2 on the motor's side of the contactor. If
you have a 150K Ohm 1/2 Watt resistor, you can
temporarily connect it across the motor's L1 and L2
to slowly bleed off the stored charge (it will take a
few minutes to fully discharge through the resistor).
If this is a new motor, It should have a manufacturer's
warranty on it but if you open the motor, they will
probably balk, claiming "tampering" and deny coverage.
So... I've finally solved the issue.
The start (electolitic) capacitor was out of spec, having too large of a capacitance value. The centrifugal switch which cuts out the start winding and this capacitor as the motor gets up to speed was of marginal quality for switching the necessary current. The extra current dumped by the extra large capacitor as the switch activated was too much for the switch. It caused arcing across the switch... which even jumped to the nearby frame of the motor (causing black charing marks on the frame)... hence the giant flash of light which sought the quickest past to ground through my lathe. After several starts the switch arc-welded itself and fused shut... causing the start winding to stay engaged during run... hence the horrible sound.
The fix was to replace the capacitor with a lower value one, and order a new centrifugal switch contactor from Baldor. $40 later it sounds and works great! :-)