Magnetic starters

[87bob]

I am in the process of hooking up a milling machine. I am using a rotary phase convertor as the mill is 3 phase but my shop only has two phase. Should I use a mag switch on the 220 two phase or on the 3 phase side of the convertors? I believe it should be in the two phase to protect if there is a power outage.can anyone confirm this? Thanks!

 

[Techie1961]

It should be on the 3P as far as I know. Make sure that you use the generated leg though for one side of the contactor coil. Roto phase units like to be shut down properly, not dropped out all of a sudden. Put a fused disconnect box on the 2P circuit.

 

[miner]

Switch goes on the three phase side. Also, you have a single phase supply, not two phase.

 

[wyliesdiesels]

The OP is right. He needs a way for the unit to not restart after the power comes back on following a power outage!

I will see if i can find a diagram...

 

[MN4x4]

This may be stating the obvious, but the primary purpose of a magnetic starter is a safety one - to make sure the machine can't RESTART by itself if power is lost and then restored.

Functionally, the magnetic starter could go on either side of the rotary phase convertor. Traditionally, however, magnetic starters are also used as the primary on-off control for the device, so they're typically mounted at the point of use - i.e. at the specific machine.

Local code may require one location over the other, depending on whether you are in a commercial, industrial, or home situation. Since you're converting single phase to 3 phase, I'm guessing this is a home shop situation.

If you haven't already purchased the Rotary Convertor and maybe even if you have - look into one of the new electronic Variable Frequency Drive (VFD) phase convertors. They are digital, lightweight, have no moving parts, and offer additional features like variable speed, over/under speed capability, and remote control. They also eliminate the need for a magnetic starter, since they provide the same function at no additional charge.

 

[miner]

He needs a way for the unit to be shut off when theres a loss of power.

??? If there is a loss of power, then all machines will be shut off.

Putting a magnetic starter on the single phase side of a rotary converter does nothing but add a switch to the RPC itself, which makes no sense since the RPC should have its own magnetic switch.

Most Bridgeport-type milling machines do not have magnetic switches, just a fused disconnect straight to the manual reversing switch.

 

[JoeFin]

They also eliminate the need for a magnetic starter, since they provide the same function at no additional charge.

They eliminate the need for "Overload Protection" but from a liability/engineering stand point but NO they do not provide a "mechanical means of disconnection" - (air gap)


If you have ever been involved in design/start-up of large rotating machinery automation projects you would know exactly why there is this requirement. Machinery with multiple motors/VFDs can induce voltages that will make the VFDs that are not currently running toggle back and forth.

So the design test is this - "Are there moving parts that can be touched by humans" - if 'yes' you need a mechanical means of disconnection.

OK - enough of the code Nazi ****

In all practicality I run multiple machines simultaneously off of an RPC. Yes I realize there is a dedicated section of the NEC pertaining to RPCs and I used it in selecting my feeder and breaker size. Surprising enough, they required I size the feeders and breaker at 175% of load. Which doesn't provide any real protection for overheating of the windings of the RPC itself.

So at the RPC itself I use a 'Safety Switch' fused with 'Slow-Blow' fuses sized at 95% of the rated load of the RPC.

So as I first started to read this thread I tried to think of any machines I have that are not protected by a Mag-Starter. I don't have any except for a fractional Hp 3 ph Block Grinder. So I use the 'Safety Switch' to start my RPC (which runs all day when I'm out in my shop) and then the machines dedicated Mag-Starters to run the machines.

As far as using VFDs to provide your 3 phase conversion - I haven't had good experiences with that.

You will need to pay very close attention to the Kw rating of the VFD in 3 phase and then derate it 40% to figure its capability using a single phase input. Additionally those attractively priced made in China VFDs on Eboner have done for VFDs and Kw ratings what the made in China electric motors have done with Hp ratings - essentially its way less then rated if you want to use all the features

OK - I've been rambling way too long here guys - take care now

 

[Norcal]

They eliminate the need for "Overload Protection" but from a liability/engineering stand point but NO they do not provide a "mechanical means of disconnection" - (air gap)


If you have ever been involved in design/start-up of large rotating machinery automation projects you would know exactly why there is this requirement. Machinery with multiple motors/VFDs can induce voltages that will make the VFDs that are not currently running toggle back and forth.

So the design test is this - "Are there moving parts that can be touched by humans" - if 'yes' you need a mechanical means of disconnection.

OK - enough of the code Nazi ****

In all practicality I run multiple machines simultaneously off of an RPC. Yes I realize there is a dedicated section of the NEC pertaining to RPCs and I used it in selecting my feeder and breaker size. Surprising enough, they required I size the feeders and breaker at 175% of load. Which doesn't provide any real protection for overheating of the windings of the RPC itself.

So at the RPC itself I use a 'Safety Switch' fused with 'Slow-Blow' fuses sized at 95% of the rated load of the RPC.

So as I first started to read this thread I tried to think of any machines I have that are not protected by a Mag-Starter. I don't have any except for a fractional Hp 3 ph Block Grinder. So I use the 'Safety Switch' to start my RPC (which runs all day when I'm out in my shop) and then the machines dedicated Mag-Starters to run the machines.

As far as using VFDs to provide your 3 phase conversion - I haven't had good experiences with that.

You will need to pay very close attention to the Kw rating of the VFD in 3 phase and then derate it 40% to figure its capability using a single phase input. Additionally those attractively priced made in China VFDs on Eboner have done for VFDs and Kw ratings what the made in China electric motors have done with Hp ratings - essentially its way less then rated if you want to use all the features

OK - I've been rambling way too long here guys - take care now

The single phase input 3 HP & smaller VFD's do not need to be derated.

 

[Charles (in GA)]

Installed the RPC and use it to drive a small three phase circuit breaker panel, then distribute from the panel to the various equipment with disconnects at the equipment.

As Joe does, go into the shop, throw the switch to power up the RPC, wait till it gets running and all the lights/meters etc look normal and go to work.

Charles

 

[wyliesdiesels]

??? If there is a loss of power, then all machines will be shut off.

Putting a magnetic starter on the single phase side of a rotary converter does nothing but add a switch to the RPC itself, which makes no sense since the RPC should have its own magnetic switch.

Most Bridgeport-type milling machines do not have magnetic switches, just a fused disconnect straight to the manual reversing switch.

I miss typed what I was trying to say....MN4x4 said what i was trying to say...