natfuelbill
Senior Member
Is there a difference in safety between manual and automatic bus shutters inside MCC equipment?
Why would you specify one versus another?
Why would you specify one versus another?
MCC (square d) Manual Shutters or Automatic Shutters
- Thread starter natfuelbill
- Start date
- Status
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Hope somebody tells me what bus shutters do, too. 
natfuelbill
Senior Member
They serve as a barrier bewtween the energized bus and your fingers.
masterinbama
Senior Member
- Location
- Huntsville Alabama
Pretty sure he means the shutters that cover where the bucket plugs in.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
When you pull a bucket from an MCC, the vertical bus insulation cover will have a hole in it over each bus bar where the bucket stabs made contact. If you were to leave that unit empty, you cannot lock the door because the door interlock goes with the bucket. Technically you are supposed to cover those holes, and MCC mfrs provide bus insulation cover plugs to do this, or they have covers that are on a single hinged rivet that require someone to reach in and move them over the holes.
But people tend to ignore that, and in the new age of Arc Flash protection requirements, doing it manually would mean serious PPE. So when Johnny Doofus comes along later and opens the cubicle door, sees the shiny bus bars and says to himself "I wonder what happens if I stick my finger in here?", he gets seriously injured or killed.
Automatic shutters are spring loaded so that as soon as you pull a bucket out, they close over the opening. So no added PPE to reach in where the live bus is to close it off.
Now it means Johnny D must extend his curiosity to say "I wonder what's behind those shutter looking things? OOOOH Look! Shiny bus bar! I wonder what happens if..."
But people tend to ignore that, and in the new age of Arc Flash protection requirements, doing it manually would mean serious PPE. So when Johnny Doofus comes along later and opens the cubicle door, sees the shiny bus bars and says to himself "I wonder what happens if I stick my finger in here?", he gets seriously injured or killed.
Automatic shutters are spring loaded so that as soon as you pull a bucket out, they close over the opening. So no added PPE to reach in where the live bus is to close it off.
Now it means Johnny D must extend his curiosity to say "I wonder what's behind those shutter looking things? OOOOH Look! Shiny bus bar! I wonder what happens if..."
- Status