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Circuit Breaker Lockout Devices
Benjamin D. Miller, P.E.

Original issue October 2, 2001

Revised April 16, 2005

New:      Field lockout incidents

This report is copyright B. MILLER ENGINEERING, but may be freely distributed in it's entirety as long as the correct author is indicated. The only official copy resides at http://www.bmillerengineering.com/lockout.htm.

This report evaluates several lockout devices intended for use on single and multi-pole miniature panelboard circuit breakers to determine their effectiveness and compliance with OSHA 29CFR1910.147(c)(5)(ii)(C)(1) which states: "Lockout devices shall be substantial enough to prevent removal without the use of excessive force or unusual techniques, such as with the use of bolt cutters or other metal cutting tools."

It is not the intent of this report to provide a thorough evaluation of all such devices, or to single out any particular manufacturer. The devices evaluated were selected based on their widespread availability, and were purchased new through normal retail channels. None of the manufacturers provided any samples, assistance or funding.

Devices Tested:

North Safety Products (Marketed by a number of different companies under various names)

    CB01 Single pole, non-adjustable device that uses the handle holes
    CB02 Multi-pole, non-adjustable tie-bar device
    CB03 Single pole, adjustable clamping set-screw device

Brady USA, Inc. (Marketed by a number of different companies under various names)

    Cat #65688 "Single pole Breaker Locking device", non-adjustable, uses the handle holes
    Cat#65965 "No hole" circuit breaker lockout
    Cat #66320 Multi-pole breaker lockout


    Cat #PSL-CB "Universal circuit breaker lockout", adjustable set-screw type for single or multiple breakers

Each device was installed on four different types of single-pole, 20 amp circuit breakers:

  • Square D Q0
  • Cutler-Hammer CH
  • Siemens QP

The tie-bar devices were tested on dual versions of the Cutler-Hammer, Siemens, and GE breakers. The dual Square D breaker does not use a tie bar, but can be locked with a single-pole locking device. While all of these breakers contain holes on each side of the handle, the size, shape, depth, and location of these holes differ considerably (Fig 1).


  • The Brady 65965 & North Safety CB03 single-pole devices and the Brady 66320 multi-pole device use adjustable clamping action to lock them to the breaker handles, and worked well on these breakers. They clamped tightly, prevented operation of the breaker, and were not removable with any reasonable amount of force (Fig.2). An exception occured on Square D single-pole breakers, which have a taper on the end of the handle. The Brady device did not work on this breaker, as the set screw position was too high on the taper, and it slid off. This was not a problem on the dual Square D breaker, due to its mushroomed handle.
  • It is possible to remove the Brady 65688 & North Safety CB01 non-adjustable handle hole devices with the lock installed, using only moderate hand pressure. This is because of flexing of the body in the case of Brady (Fig. 3), and flexing of the pin in the case of North Safety Products (Fig. 4). Even if the devices are strengthened to prevent flexing, they allowed some of the breakers to operate while installed, due to the clearances inherent in their design.
  • The North Safety CB02 non-adjustable multi-pole device allowed operation of the Siemens & GE breakers while it was installed due to the large amount of handle clearance (Fig. 5). It worked properly on the Cutler-Hammer, which has a larger handle.
  • The Panduit PSL-CB device was easily removed from all of the single-pole breakers by twisting it sideways, as there is no side retaining wall, the handle cavity is very large, and the clamping force is marginal due to the minimal contact area (Fig. 6). It worked well, however, on the tie-bar dual breakers (Fig.2), and also on the SquareD dual breaker with the mushroomed handle.


  • Several of these molded plastic lockout devices are too flimsy or do not clamp the breaker handles adequately, and can be easily removed with much less than the "excessive" force required by OSHA. As such, they fail to perform their intended function.
  • Non-adjustable "universal" devices that utilize the handle holes are ineffective. The holes provide a pivot point which imparts a sliding action to the lockout device as the handle is moved. The cavity walls that surround the handles have excessive clearance which allows significant movement and in some cases operation of the breaker. In addition, these holes are highly variable between breaker types, and it does not appear that any molded plastic pin of that size could have the strength necessary to comply with the OSHA requirements for "substantial" devices. For these reasons, the use of side handle holes for lockout purposes should be abandoned.
  • Multi-pole devices that capture the tie-bar without clamping, or single pole devices with large "universal" handle cavities, contain excessive handle clearances that can allow operation of breakers with the device installed.
  • Adjustable clamping designs work well in general, although specific combinations are not acceptable. Because the lockout device is clamped to the handle, it attempts a rocking motion that causes interference with the breaker body and prevents handle operation. Overtightening of these devices can cause damage to the breaker handle.
  • The Brady & Panduit instructions contain warnings for the user to verify the lack of handle operation after installation, or not use the device on that breaker. They also state that "Appropriate use... is the sole responsibility of the user". There is no discussion about checking for easy removal of the device. These warnings are of little value, however, to a person who 1) may not be qualified to investigate the device to the extent needed, and 2) needs to lock out a machine or electrical system, and has only one lockout device available. The choice will be between improper lockout or none at all.
  • The circuit breaker and lockout device manufacturers must work together to insure compatability between their products. For example, tapered breaker handles make the only viable means of locking extremely difficult, and should be redesigned. A mushroomed handle allows more effective clamping. A more worthwhile "standard" than the current side holes might be grooves or depressions on the front and back of the handle to insure good clamping action of the locking device set-screws and cleats, with less torque on the screws.
  • As of this revision date, all of the devices in this report are still on the market and have not undergone any design changes. Additional devices are also available, in the form of permanent bracket systems mounted to the panel covers, which appear to be far more effective.

For more information regarding this report, you may contact B. MILLER ENGINEERING at information@bmillerengineering.com.


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