3 phase motor starts automagically on 1 phase power??

[rogerrabbit]

Hi everyone,

I finally got my Burke #2 back together and was going to setup an RPC to run the gear motor on it.

When I purchased the burke, the seller threw in another 3 phase telling me that I could build a RPC from it. (did a google search on how to wire)

I wanted to test the whole RPC setup and figure out what size run capacitors I would need..

I hooked up the extra motor as follows:
L1 (as indicated on the wire) -- 1 leg of the 220 Circuit out of the wall and to 2 capacitors wired in parallel, 40 mf and 15 mf (I bought a whole assortment as I wasnt sure what i needed).
L2 -- 2nd leg of the 220 circuit out of the wall
L3 -- to a momentary switch which then goes to the other side of the caps.

ground to the frame of the motor.

turned off the circuit breaker, plugged the wire in.. turned on the circuit breaker expecting to have to hit the switch to get it started.. low and behold the motor started spinning w/o me touching the switch (i checked the switch to make sure it was infinite resistance as is and 0 resistance when the button was pressed).

thought maybe the caps were in the circuit somehow so I pulled the wires to take them out of the circuit completely.. the motor still starts??

questions:
1. is it possible this was converted to 1 phase (i doubt it since the wires say l1, l2, and l3)?
2. it the motor going to burn out ( i only ran a few seconds each try since I was not expecting this)? if so what should I be looking at/testing?
3. if not, do i still need start (and run capacitors)?

thank you,
Roger


some info on the label of the motor:
Rockwell 1 hp motor, manufactured by baldor. 1725 rpm, 4.4 amps, 3 phase. rockwell no 66-018

 

[Hawkeye]

I take it you were testing it with no load on the motor. I'm wondering if a load would make it operate more like you expected (needing a boost to start). The in-rush current may be causing enough of a jolt to make it twitch. The twitch may be enough to get it to ramp up when there's no resistance. Does it start in the same direction each time?

 

[Kevinb71]

Many 3ph motors will start with no load on single phase. They will also continue to run on 1ph. The problem is that they do not have the power they should and will burn out. The large 3ph motors are equipped with "single phase/under voltage" detection for this purpose. It detects a 1ph condition and shuts down the motor to protect it from burnout. You will still need the RPC in order to load the motor and keep it running. Just a short bit of running as you explained should have no detrimental effects on the motor.
If you have wires labeled L1, L2 L3 it is a 3ph motor.
Continue on with the RPC!

 

[Accelo]

Is the motor turning at the rated speed?
It may be running slow. It will make a lot of noise and get hot fast if it is single phasing.
If not this is an interesting case.
Rick

 

[Rbeckett]

Roger Rabbit, and others Thia is a reply I recieved regarding 3 pahes power. I would suggest we all pay heed to this gents suggestions in the interest of personal safety and fire prevention. Thanks to Mr Froneck for such a great explanation.

Here is his reply to a question I posed to him:
Hi Ron Years ago when color was written into the electrical code White was Neutral or grounded line. When 3 phase was connected with the 4 wire cord White was always used as the ground as Green or 5th connection wasn't in the code. Later when Ground and Neutral were defined White was considered current carrying ground and green non current carrying. Neutral has no application in 3 phase. You will find many old machines with White connected to the ground of the plug and socket not the green. White even today is considered to be current carrying Neutral. To get technical if your wiring your machine 208VAC 3 phase and have a 120VAC single phase device such as a light bulb using the Neutral to get low voltage not a transformer you should have a 5 wire plug because you have a current carrying Neutral. A 5 wire twist lock connector has a round post in the middle of the 4 blades. Your ground should never be current carrying though ground and Neutral are connected to the same terminal in the disconnect box. Reason for this it that if for what ever reason the white wire were to be disconnected from the circuit at some point and at your machine white is used for a light or pump motor and is also connected to the frame of the machine you will get a shock if your grounded.Furthermore all other equipment with the white connected to the frame that are on the same side of the disconnected Neutral will be hot to ground! Newer code does not define color but states color code should be established in the facility. Most continue using White as current carrying Neutral and Green non current carrying. For future reference get blue electrical tape and tape the ends on both sides of your cord's White wire Blue so you know what you did! Use green as ground.
Your doing this not to prevent smoke from the machine but from your ears!

Let's all pay special attention to wiring and consult a qualified electrician for new stuff we aren't well versed in. It could be a difference between living and dieing.
Bob

 

[Rbeckett]

Zackly!!!!

Bob

 

[burnrider]

Rbekett Eeehh, but there is a stupid qustion!! It's the one you don't ask!

Good spot for an opening.

What's the principle for some of the old timers running a 3 phase motor on 110 to properly use an installed 3 phase motor on a lathe. I saw an old timer start the 'pony' motor, kick the shaft to turn it one way, and use the lathe. Worked, but didn't look real convincing to me.

 

[Wade8A]

The 3 phase pony motor provides a generated 3rd leg for the 3 phase machine motor, although I have never heard of, or aware of a 3 phase motor that will start/run on 120V.

Using a pony motor works, but not the best solution by itself as there is no way to balance the voltages for the 3 legs.

A properly constructed RPC would include start and run caps for the RPC motor, a motor starter, overload protection, and a potential relay to take the start caps out of the circuit once the RPC motor is running.

 

[rogerrabbit]

just a quick "no" update.. I have read all your suggestions and will hopefully try them next weekend.. a little thing of a lathe kinda got in the way of work on this machine.

big thank you to all!

Roger

 

[rdhem2]

Roger Rabbit, and others Thia is a reply I recieved regarding 3 phase power. I would suggest we all pay heed to this gents suggestions in the interest of personal safety and fire prevention. Thanks to Mr Froneck for such a great explanation.

Let's all pay special attention to wiring and consult a qualified electrician for new stuff we aren't well versed in. It could be a difference between living and dieing.
Bob

We should all give thanks for this man's wisdom.

Technically, the green and white wires should never make contact unless in the main distribution disconnect. (Main Service Panel) The Green wire is the isolated equipment ground and is only present to carry fault current should the situation arise. The white wire is the electrical ground and is the return path for current flow to the source. The blue coloring is actually a phase conductor color(C) in a 3 phase 208/120 volt system but either way an electrician seeing it would be forewarned not to come into contact with it which is what its coloring is present for anyway.

Be safe, if unsure find someone who is.