Circuit Breaker Lockout Devices
Benjamin D. Miller, P.E.
Original issue October 2, 2001
Revised April 16, 2005
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.
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
Each device was installed on four different
types of single-pole, 20 amp circuit breakers:
- Square D Q0
- Cutler-Hammer CH
- Siemens QP
- GE THQL
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
- 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
- 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 firstname.lastname@example.org.