THE BEST LOCATION TO MEASURE CURRENT 1

[garciaf]

WHERE IS THE BEST LOCATION (PLACE) TO MEASURE THE CURRENT OF A TRIPHASE MOTOR, IN MCC (MOTOR CONTROL CENTERS) OR IN FIELD (MOTOR TERMINALS/TERMINAL BOX).
THANKS FOR YOUR HELP.

 

[ScottyUK]

The current will be the same at both locations, so in one sense it doesn't matter. Which is the easiest location to fit a current probe / clampmeter? Generally I'd prefer the MCC because it's usually easier to control access to the location if there are exposed live terminals.

 

[waross]

If there are power factor correction caps connected at the motor you must access the motor leads past the capacitor connection.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

Both good answers.
But in these days of increased awareness of Arc Flash dangers, measuring current in the MCC bucket may come with some added procedural requirements for opening the door when live ("Hot Work Permits), as well as added PPE based on the "incident energy" in the MCC as a whole and the fact that an arc blast could start in some area other than where you are working yet still put you in danger. I've heard it argued that opening the motor terminal box while energized does not present the same risk of arc flash danger. I'm not sure I agree 100%, but I do think it is slightly less risky, depending on how the terminations are made up (i.e. bolted connections fully wrapped or covered).


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[krisys]

Technically speaking opening the live terminal box is more dangerous than opening the MCC cable alley. In the cable alley normally you are not directly exposed the shock hazard, as the live terminals are normally shrouded.

When you open the motor terminal box, you are exposing to the shock hazard as well.

Additionally:
Please note that the MCCs are normally located in an environmentally better location than the motor. Will be conditioned and clean, with better clearance for working.

The motor locations are generally not conducive to take the current measurements.

 

[jraef]

The best practice now is to use “intelligent motor control” devices that can communicate to remote systems and allow you to monitor motor current without ever opening the door of anything. That’s all I specify any more. People whine about the up front cost, but once it’s installed and they realize the time savings of not having to suit up in PPE just to monitor current, change OL settings or check to see if a contactor is closing, they never regret that decision.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden