Unisaw Funny humming noise

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Forum topic by clarksound posted 06-22-2014 09:00 PM 908 views 0 times favorited 4 replies Add to Favorites Watch
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2 posts in 854 days

06-22-2014 09:00 PM

Topic tags/keywords: unisaw problem

I just recently bought a unisaw 34-461 3hp 1ph (1969 or 70) and noticed after I bought it that a lot of the insulation on the wiring was brittle and crumbing off the wires. I replaced the power cord with 12 ga, and the cord to the switch with 10 ga. Once completed, I plugged in the saw and noticed a quiet humming coming from the box. The saw runs fine but I am afraid to leave it plugged in. I am not an electrician but can someone tell me what the coiled parts ore in the power box? Are they rectifiers? Could this damage the motor? I believe this is what may be causing the noise. Thanks in advance!

4 replies so far

View TheFridge's profile


5676 posts in 905 days

#1 posted 06-22-2014 09:07 PM

Coil for a contactor? It would be the only thing besides the motor that would hum. Don’t know why it would him when it’s plugged in but not running. Unless it’s a fail close contactor. Which is possible but not probable.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

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Tommy Evans

137 posts in 1594 days

#2 posted 06-22-2014 10:12 PM

My Unisaw magnetic starter box has a quiet hum to it. I chalked it up to being 40 year old analog coils and transformers.
I could be wrong. It’s happened a couple of times before. ;)
But I keep it unplugged anyway when not in use, so haven’t worried about it in the 2 1/2 years I’ve had it.

View clarksound's profile


2 posts in 854 days

#3 posted 05-21-2015 02:40 AM

So after 1.5 years of using this saw the magnetic switch may be shot. The saw will not stay on when I push the on button. Is this a switch problem? The magnetic button just releases. Also. I thought about just buying a new switch but mine has 4 wires and everything I see out there is for 3 wires. It is a Rockwell unisaw model 34-461 3hp 1ph (1969 or 70) 220 volt. Any help would be much appreciated.

View Oughtsix's profile


42 posts in 594 days

#4 posted 05-21-2015 03:08 AM

The way a motor control works there should be no power to anything until the the start button is pressed. When the start button is pressed the coil in the contactor is energized closing the contacts on the contactor. An extra set of contacts closes and bypasses the start button causing the contactor coil to remain energized after the start button is released. The stop button is a normally closed button that is in the loop between the extra set of contacts and the coil. When the stop button is pressed the power to the contacor coil is interrupted and the contactor opens.

Modern code requires that the power to the contactor coil be reduced from line voltage of 220v to 24v to reduce the electrical hazard of 220v going through the start and stop buttons. In this case a 220v to 24v transformer is used. The primary side of the transformer is always energized but there is no current flowing through the secondary side of the transformer until the start button is pressed so the only current through the primary coil is a very small parasitic current.

I can understand a humming if 24v control is used but in the era of your saw 24v was not very common due to the extra expense of the transformer.

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