Combo Starter, control system power and Motor power issu

[copper123]

I am trying to find some code references.
Here is the Challenge:

460 volt, 3 phase saw.
Wired with a combination starter. Fused and overloads included. Coil voltage for contactor is 120 volts. In this situation, they have suggested that you can run the two different system voltages into the enclosure. No transformer needed in the combo to create a 120 volt ckt. 480 3 phase, 3 wire for the motor, and then a 120 volt circuit for the controls. I am trying to find out if this is legal. Power is from two separate panels. To do any deenergized maintance, you need to disconnect power from two sources, ect. I am finding a lot of info in 430.74. and if you go to 300.3C it talks about the dif. voltages in the same enclosure. My experience with combo starters have been that they all have had a transformer feeding off the motor voltage with fuses wired in line. The disconnect means of the starter also disconnects the the?control circuit.
Thanks in advance!

[ June 17, 2005, 07:40 PM: Message edited by: copper123 ]

 

[iwire]

Re: Combo Starter, control system power and Motor power issu

It is perfectly fine and not that uncommon.

 

[kiloamp7]

Re: Combo Starter, control system power and Motor power issu

copper123 - using a separate 120V. control source for the combo starter is generally not the preferred way to do it. A 480-120 control power xfmr is the first choice for the vast majority of motor control ckts.

Sure, NEC allows it, but the NEC is not a design manual.

One must be sure & abide by the control ckt. disc. means requirements of 430.74, when using the separate control source.

 

[don_resqcapt19]

Re: Combo Starter, control system power and Motor power issu

I have worked on starters in MCCs that used a "outside" 120 volt circuit for the control power. Auxiliary contact kits were added to the 480 volt breaker to disconnect to control power at that same time as the 480 was disconnected.
Don

 

[templdl]

Re: Combo Starter, control system power and Motor power issu

Besides the aux sw. we also have added a yellow warning label to the outside door which indicated separate source control power.

 

[l_zabel]

Re: Combo Starter, control system power and Motor power issu

I would agree that the not generally acceptable is incorrect. In industrial wiring using a seperate control source is not uncommon, we see it all the time with equipment that is run together ie. saws, furnaces etc. it saves on control transformers and also wiring, also by having a common voltage source on your motor starters and solenoids you can install an emergency stop circuit for equipment that is grouped together. I've also seen seperate control voltage sources on PLC's about 50/50 of the time.

 

[friebel]

Re: Combo Starter, control system power and Motor power issu

Yes, it is not against the NEC to have a foreign voltage in your Combination starter. I will give you a good example.
On large motors, they sometimes have a calrod heater in the base of the motor to keep the motor windings dry, especially in areas where you may have excessive humidity.
We would always feed the electric calrod heater from an outside source. Generally a 120/208, three-phase panel. The heater could be either 120 or 208 volts, single-phase.
If you open the disconnect switch on the combination starter for maintenance repairs to the motor, etc., you would still have the heater energized from the 120/208 panel.
We would put an engraved RED plastic tag on the Combination starter, stating the foreign voltage that is present at the motor, and the panel voltage and circuit number. I am a great believer in proper identification on all equipment, stating the voltage, and where it is fed from.

 

[copper123]

Re: Combo Starter, control system power and Motor power issu

Hey guys, thanks for the information!
As far as the placard or sign, is that a NEC code requirement? Do you have to have a sign that says this equipment has a duel voltage feed going to it like when you have duel voltages in a building? I can see how you would save on control transformers ect. but it still seems dangerous. However, if you are working on the systems, you should be qualified. I too am a firm believer in notification and identification.

 

[iwire]

Re: Combo Starter, control system power and Motor power issu

I am not sure if 430.113 requires the markings at controllers or just at the motor but it would be a good idea regardless.

 

[friebel]

Re: Combo Starter, control system power and Motor power issu

To: copper123, you ask the question is it a NEC ruling that you must identify if you have more than one voltage source in your switch, that if the switch is opened, would not de-energized all of the voltage sources.
There are sections in the NEC addressing identification, and the Sections are:
110.22 Disconnecting Means Identification
408.4 Circuit Directory Identification
700.9(A)Emergency Systems Identification
230.70(B)Service Disconnect Identification

copper123, does the NEC need to tell you to identify a switch that has a foreign voltage in it.
If I was the electrician that was not familar with the equipment, I certainly would be appreciative of some identification on the switch or starter informing me of the voltage and where it fed from. It seems to me that this is just common sense and good electrical safety. I certainly hope that you agree and would identify all foreign voltage sources.