TL;DR

A stuck racking mechanism is almost always dry rails or bent guide rails. Lubricate with a dry or silicone-based lubricant, inspect the rails, and straighten any bent sections. Never force the racking handle with excess torque.

What you might see

racking handle requires excessive force to turn
bucket stops midway between CONNECT and TEST positions
racking key will not insert or turn
visible binding or scraping when moving the bucket

Likely causes

Tap to mark as ruled out

Dry or corroded racking rail surfaces with insufficient lubrication
Bent or deformed guide rail from a previous mechanical impact or forced racking
Debris or foreign object on the rail or in the stab socket
Stab tips damaged or misaligned causing the bucket to bind on the bus

Required tools

Racking key (correct size for the bucket)
Dry lubricant spray or silicone-based lubricant (no petroleum grease)
Rubber mallet
Dry cloth
LOTO kit

Safety first

Never rack a bucket while the bus is energized unless the bucket has an approved safety interlock in place. If in doubt, de-energize the section first.
Do not apply excessive torque to a stuck racking mechanism. Forcing it can damage the bus stabs and create a short-circuit hazard on re-energization.

Procedure

8 steps · ~30 min

1
Attempt to move the bucket to the DISCONNECT or TEST position using normal racking key torque. Do not apply excessive force.
Warning: Forcing a stuck rack can damage the bus stabs, the bucket structure, or the MCC rail. Stop if movement is not smooth.
2
De-energize the section: open the breaker and verify the stabs are not in the CONNECT position if the bucket is partially racked.
3
Inspect the guide rails inside the section for obvious obstruction, debris, or deformation. Clean the rails with a dry cloth.[1]
4
Apply a thin coat of dry lubricant or silicone-based lubricant to the rails. Do not use petroleum-based grease, it attracts conductive dust.[1]
5
Check the bucket frame for bent edges or deformed corners that could be catching on the rail. Straighten minor bends with a rubber mallet.
6
Inspect the stab tips on the bucket for damage or misalignment. Bent stabs must be replaced before the bucket is returned to service.
7
After lubrication and inspection, rack the bucket through the full travel from DISCONNECT to TEST and back. Movement should be smooth.
8
If the mechanism is still stuck after lubrication and visual inspection, remove the bucket from the MCC for a bench inspection. Do not force it.

Sources

Square D Model 6 Motor Control Center Instruction Bulletin, Square D (Schneider Electric)
Square D Model 6 MCC installation and maintenance instructions, bucket racking and lubrication procedures (general)
View source

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