Control wiring, way its done

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brother

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I know theres no 'code' issues here that I can think of, but I dont think this is common practice, at least I have not seen it done this way.

Theres this control cabinet (that controls 3 motors) that was not wired correctly, the 'run' indication lights are wired in parallel with each motors disco. Basically, you can turn off disco 1 and leave at least one other disco on (2 or 3) and turn the 'hand off auto' of motor 1 to the hand position and the run light will come on, showing that motor 1 is running, but in reality its not.

The controls are 120v (including the lights), which is normal, the motors run off of 3 phase 480. I suggested to a guy to correct this issue he just use some auxilary contacts on the each contactor and wire the indication lights off of them, so when that particular motor contactor is closed, the the lights will come on only at that time.

He wants to run '480 volt' to the indication lights off of the load side of the contactor (the t1, t2, t3 leads to the motor), basically just tapping off of them that way. He has to special order these '480' lights. Apparently he feels this will give 'true' indication. Would you wire it this way, or the way I suggested seeing that the 120 is already there from the transformer.???? 120 and below has always been for controls in my experience, including the lights.
 
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I am a little confused, is your control voltage a separate source from the motor circuits? A 120 volt indicator light connected across the coil of the motor starter would only light when the coil is energized. If you wish it to be more accurate of indicating the motor is running you would need current monitoring relay of some sort to drive the indicating light.

480 or 240 volt controls are not non existent. They are common on equipment consisting of a single motor or very few motors especially if there is only simple control methods. Start adding timers, counters, PLC's or other more complex controls and 120 volt or lower becomes very common as these devices become harder to find in 240 and 480 volt models.

If you are using a 480 volt indicator you may need overcurrent protection depending on the size of the motor circuit and where the indicator is located. See 430.72
 
IMO adding an auxiliary NO to each starter would be the more cost effective method to identify the motor that is running. Something about having 480 actually on the door seems off.
 
Brother, he is asking if it is a common control ckt ( tapped from the motor branch ckt) than NEC 430.72 applies. If it is a separate source such as a panel board, its called a separate branch ckt and NEC 725.41 applies.

In your case it is a common control ckt and 430.72 applies
 
The normal way is the use a NO contact on the starter and wire the starter's coil through the overload. So the NO contact will only close if there is a run command and the overload has not tripped. It is not normal to put 480VAC on a door of an enclosure.

The 480V indicator would show power is on at least one leg of the motor, but it still doesn't tell you the motor is running. You could drive an indicator off of a current switch to show there is a load on the circuit.

http://www.automationdirect.com/adc/Overview/Catalog/Sensors_-z-_Encoders/Current_Sensing_Switches
 
brother said:
No its not, its just a 480-120 volt transformer, so same source.. It is paralleled off the main feed comming in.
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So turning off the motor disconnect does not turn off the control voltage?

If so the motor contactor will still pull in if the control is closed and an aux contact will still close and the indicator will still be on, even though the motor circuit disconnect is open.

You need one of the following:

Control circuit transformer connected to load side of motor circuit disconnect.

Aux contact in motor circuit disconnect to disconnect the control circuit.

Current sensing relay to sense current of the motor to drive the indicator.

Other sensing device in the motor or driven load to sense that it is running.

480 volt indicator connected to load side of motor contactor (may need separate overcurrent device)

480 x 120 volt transformer connected to load side of motor contactor to drive your present 120 volt indicator.


It all depends on how critical indication is to actually proving the load is running. If it is very important to know the load is running then the current sensing relay is about the best way. You can set the current level so that it closes contact at a normal operating level. If a belt on the motor would break it could tell the operator that it is not running when the motor is in fact running but with less load than normal.

Depending on the process involved there may be other controls in place that verify operation of the load. Like a pressure switch to prove operation of a fan or pump before another load will operate. You could connect your indicator to this if that is available.
 
The way its wired now is more of a 'call to run' than actual feedback. We typically use an aux contact to give running feedback, although that too isn't true feedback. The best way would be to have some sort of current monitor, flow meter, tach return, etc. What you're proposing with using a 480VAC lamp would be only slighty better than an aux contact in my opinion and not worth the extra cost.
 
Actually, its really NOT that critical to see the 'LIGHT' running because the motor is right there not even 3 ft away LOL. I just wanted to be sure I wasn't thinking wrong on this. Basically a simple aux contact would be best here and quick and easy.

I dont like 480 on the doors either, but on VERY rare occansions on OLD systems Ive seen it, and most guys change it to 120 or less.
 
brother said:
I dont like 480 on the doors either, but on VERY rare occansions on OLD systems Ive seen it, and most guys change it to 120 or less.
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NFPA79 (the standard for industrial/machine control wiring) does not want anything more than 120V brought to an enclosure door.
 
Auxiliary contacts are just as good as phase wired lights. Unless you're talking a nuclear plant like Chernobyl. In that case I would recommend phase transformers on the load side and the light being on when all three phases have load, and an alarm when 2 phases or less have load and 1 or two don't have.

brother said:
I know theres no 'code' issues here that I can think of, but I dont think this is common practice, at least I have not seen it done this way.

Theres this control cabinet (that controls 3 motors) that was not wired correctly, the 'run' indication lights are wired in parallel with each motors disco. Basically, you can turn off disco 1 and leave at least one other disco on (2 or 3) and turn the 'hand off auto' of motor 1 to the hand position and the run light will come on, showing that motor 1 is running, but in reality its not.

The controls are 120v (including the lights), which is normal, the motors run off of 3 phase 480. I suggested to a guy to correct this issue he just use some auxilary contacts on the each contactor and wire the indication lights off of them, so when that particular motor contactor is closed, the the lights will come on only at that time.

He wants to run '480 volt' to the indication lights off of the load side of the contactor (the t1, t2, t3 leads to the motor), basically just tapping off of them that way. He has to special order these '480' lights. Apparently he feels this will give 'true' indication. Would you wire it this way, or the way I suggested seeing that the 120 is already there from the transformer.???? 120 and below has always been for controls in my experience, including the lights.
Click to expand...
 
Like everyone else said, I'd use an aux. contact. Sometimes that gets tough though on older starters with no accessory parts available...

jim dungar said:
NFPA79 (the standard for industrial/machine control wiring) does not want anything more than 120V brought to an enclosure door.
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I'll have to remember that.
 
Cow said:
Like everyone else said, I'd use an aux. contact. Sometimes that gets tough though on older starters with no accessory parts available...



I'll have to remember that.
Click to expand...

Ok, I found the code or standard I was looking for. IT was 2007 NFPA 79 Electrical Standards for Industrial Machinery like I had thought.

2007 NFPA 79 9.1.2.1 AC Control Voltages.
"The AC voltage for control circutis shall not exceed 120 volts, AC single phase. "

NFPA 79 9.1.4.1 Connection of Control circuit Devices

"All operating coils of electromagnetic devices and indicating lamps (or transformer winding of indicator lamps) shall be connected directly to same side of the control circuit."

NFPA 79 15.2.2.1" lighting circuits shall not exceed 150 volts between conductors"
 
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