- Record Type:
Interpretation
- Standard Number: 1910.147
- Subject: Motor starter circuits
and energy isolation devices
- Information Date:1991
August 5, 1991
MEMORANDUM FOR: MICHAEL G.CONNORS
REGIONAL ADMINISTRATOR
FROM: PATRICIA K. CLARK, DIRECTOR
DIRECTORATE OF COMPLIANCE PROGRAMS
SUBJECT: Interpretation of "Energy Isolation Device" Application
of 1910.147 to Conveyors
This is in response to your memorandum
of February 12, requesting answers to three questions concerning
the relationship of motor starter circuits and energy isolation
devices as defined in the Lockout/Tagout Standard, 1910.147.
Please accept our apologies for the delay in responding. Your
questions and our answers are listed below.
1. Question: It is
recognized that a motor starter is a control circuit device.
Did the writers of these standards intend that assured control
of the motor starter in the "off" condition be accepted as
an energy isolation device?
Answer: The intent
of the standard was not to include motor starter circuits
within the scope of the definition of energy isolation devices.
For further clarification,
the definitions of certain terms that have application to
the 1910.147 (Lockout/Tagout) standard can be found in the
complementary electrical OSHA standard, Subpart S of 1910.
Three appropriate definitions are as follows:
1910.399(a)(31) Controller.
A device or group of devices that serves to govern, in some
predetermined manner, the electric power delivered to the
apparatus to which it is connected.
1910.399(a)(40) Disconnecting
Means. A device, or group of devices, or other means by which
the conductors of a circuit can be disconnected from their
source of supply.
1910.399(a)(124) Isolating
Switch. A switch intended for isolating an electric circuit
from the source of power. It has no interrupting rating, and
it is intended to be operated only after the circuit has been
opened by some other means.
2. Question: It is
our understanding that the electric motor, once it is stopped
using the motor-controller "stop" button and is spun down
to a full stop, cannot restart without being activated by
the motor-controlled starter and its control circuit. It is
further our belief that deactivation of the motor-starter
device, using two independent keyed energy isolation devices
properly wired and installed, can be effective in preventing
the motor from starting and energization of its control circuit.
Does the standard prohibit the use of this type of control
circuit device as an energy isolation device for lockout purposes?
Answer: The intent
of the standard was not to accept motor-controlled stop buttons
or motor-controlled starter circuits as energy isolation devices.
Thus during the servicing and/or maintenance of equipment,
such mechanisms will not be sufficient to provide the protection
envisioned by the standard. On the other hand, for normal
production operations, such as during routine, repetitive
package clearing operations on conveyor belts, mechanisms
that permit work to be performed by using alternative measures
which provide effective protection would be acceptable. Further
clarification on this issue is provided in OSHA Instruction
STD 1-7.3, Appendix C, Paragraphs A.1. through 4. Also, please
see the note under Paragraph 1910.147(a)(2)(ii)(B) of the
Lockout/Tagout Standard.
90) that "...
A diagram from the 1990 NEC Handbook, which tends to support
the company's proposed application of control energy isolation,
has been provided as Attachment B." We have not seen Attachment
B. However, from our knowledge of the 1990 NEC Handbook, we
are not familiar where this support is given. It might be
that reference is being made to Article 430-111 of the NEC
which states the conditions under which a switch or circuit
breaker is permitted as both controller and disconnecting
means. This requirement, taken from the 1990 NEC, is repeated
here for convenience as follows:
430-111. Switch or
Circuit Breaker as Both Controller and Disconnecting Means.
A switch or circuit breaker complying with Section 430-83
shall be permitted to serve as both controller and disconnecting
means if it opens all ungrounded conductors to the motor,
if it is protected by an overcurrent device (which shall be
permitted to be the branch-circuit fuses) that opens all ungrounded
conductors to the switch or circuit breaker, and if it is
of one of the types specified in (a), (b), (c) below:
(a) Air-Break Switch.
An air-break switch, operable directly by applying the hand
to a lever or handle.
(b) Inverse Time Circuit
Breaker. An inverse time circuit breaker operable directly
by applying the hand to a lever or handle.
(c) Oil Switch. An
oil switch used on a circuit whose rating does not exceed
600 volts or 100 amperes, or by special permission on a circuit
exceeding this capacity where under expert supervision.
The oil switch or circuit
breaker specified above shall be permitted to be both power
and manually operable.
The overcurrent device
protecting the controller shall be permitted to be part of
the controller assembly or shall be permitted to be separate.
An autotransformer-type
controller shall be provided with a separate disconnecting
means.
If this is the NEC Article referenced
by the Cincinnati Area Office as Attachment B, then it obviously
can be seen that it is not applicable to the proposed UPS
installation since neither the Air-Break Switch, the Inverse
Time Circuit Breaker nor the Oil Switch, as specified in 430-111(a),
(b) and (c), is used in the UPS design. It should be further
noted that both the Air-Break Switch and the Circuit Breaker
must be "operable directly by applying the hand to a lever
or handle." And again the UPS method would not satisfy this
requirement.
3. Question: It has
been proposed, since the motor starter includes control circuit
devices and is itself a control circuit device, that it would
not be acceptable as an "Energy Isolation Device," per the
1910.147 standard. In the event of control circuit or motor
starter failure it could cause the actual three- phase wires
feeding power to the motor, coils, armature, and the motor
starter circuit to become energized. Do you agree?
Answer: We agree.
The OSHA standard, 1910.147 (Lockout/Tagout),
clearly stipulates that in order not to be covered by the
standard while performing minor servicing activities during
normal production operations, the work must be performed using
alternative measures which provide effective protection (emphasis
provided). To provide effective protection, the isolation
from the source of power must be positive. A dependency on
automatically controlled circuits to provide this isolation,
even where all ungrounded conductors to the motor are opened,
is not positive.
With the proposed UPS method of conveyor
stoppage, one scenario may occur as follows:
An UPS package jams
on the conveyor and other packages quickly begin to pile up.
The attendant immediately actuates the stop button at one
of the keyed lockout (field station) devices. The conveyor
comes to a stop and the attendant climbs aboard the conveyor
to free the jammed packages. Lacking the direct control of
a manually operated switch or breaker to remove power by disconnecting
all power conductors, motor stoppage becomes dependent on
the proper functioning of the control circuits. In this case,
we assume that the automatic control circuitry in the motor
control center malfunctions such that only one phase of the
three phase source to the motor is opened (not an uncommon
occurrence especially where the overcurrent protection device
opens the third phase (L3) without disturbing the motor starter
circuit). Because of the additional load placed on the belt
by the jammed packages, the motor, now only operating on two
phases, has insufficient torque and stalls, and the belt stops.
The attendant, believing that the conveyor has been safely
stopped because the maintained stop button on the keyed lockout
device was actuated, climbs upon the belt in order to free
the jammed parcels. However, as the jam is removed, the resulting
load on the conveyor motor is reduced and the belt starts
again with sufficient start-up torque from the two remaining
phases which have not been disconnected. The attendant becomes
unbalanced by the moving conveyor, slips and falls, and is
injured.
Other scenarios can also be postulated
as a result of the lack of effective (positive) energy isolation.
Wiring Considerations. In accordance
with 29 CFR 1910, Subpart S, Electrical Standards, the UPS
conveyor motor control installation must comply with the 1910.305(j)(4)
requirements. The following table estimates UPS compliance
based on the UPS submitted schematic diagram:
OSHA Standard UPS Compliance
1910.305(j)(4)(ii)(a)
A disconnecting means shall be No
located in sight from the controller location (Refer to 1910.305(j)(4)(i)
for definition of "In sight from.")
1910.305(j)(4)(ii)(c)
If a motor and the driven machinery
are not in sight from the controller location, the installation
shall comply with one of the following conditions:
(1) The controller Unknown disconnecting
means shall be capable of being locked in the open position.
(2) A manually operable switch that
will No disconnect the motor from its source of supply shall
be placed in sight from the motor location.
1910.305(j)(4)(ii)(d)
This disconnecting means shall plainly
indicate whether it is Unknown in the open (off) or closed
(on) position.
1910.305(j)(4)(ii)(e)
The disconnecting means shall be
readily accessible. If No more than one disconnect is [Refer
to UPS compliance with provided for the same 1910.305(j)(4)(ii)(a)]
equipment, only one need be readily accessible.
UNITED STATES DEPARTMENT OF LABOR
Occupational Safety and Health Administration
230 S. Dearborn Street, Room 3244
312-353-2220
DATE: August 8, 1991
MEMORANDUM FOR: Assistant regional Administrators
Area Directors District Supervisors
FROM: William Q. Wiehrdt
Assistant Regional Administrator
Technical Support
SUBJECT: Interpretation of "Energy Isolation Device" Application
Of 1910.147 To Conveyors
Enclosed is a recent interpretation from
the National Office on the Lockout/Tagout Standard. The memo
discusses several issues related to conveyor usage. Please share
this information with your staff.
Enclosure
U.S. DEPARTMENT OF LABOR
OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION
REGION V
.....................................................................
DATE: January 31, 1991
REPLY TO: William M. Murphy Facsimile Transmittal
Area Director
REGARDING; INTERPRETATION OF "ENERGY ISOLATION DEVICES"
IN ACCORDANCE WITH 1910.147
TO: William Wiehrdt
ARA-Technical Support
THROUGH: Michael G. Connors
Regional Administrator
In memos previously sent to the Regional
Office on December 10, 1990 (copy attached, less original attachments),
December 10, 1990 (copy attached), January 7, 1991, and January
24, 1991, the Cincinnati Area Office requested an official interpretation
of the term "energy isolation devices" as applied under OSHA's
lock out standard (1910.147). This request was in regard to
a proposed abatement method submitted by United Parcel Service
(UPS) for the deenergizing of conveyor belts to protect workers
when they climb onto the conveyors to clear jams and/or locate
missing parcels. Included in the information submitted was an
electrical schematic of the locking device to be used.
In the memorandum from the regional
Office which this office received on January 26, 1991 it appears
that the response to our inquiry is that an energy isolating
device is "designed to positively disconnect power..." and
that the device in question is an acceptable device.
Despite your response, there are
still unanswered questions in this matter. It appears from
our discussion with the company and review of the information
supplied that the locking switch involved is a switch on a
control circuit which controls a motor starter. The lock out
standard defines an energy isolation device as one which "physically
prevents the transmission or release of energy". It also indicates
that the term "does not include a push button, selector switch,
and other control circuit type device".
We believe that the schematic submitted
by UPS reflects that the keyed lockout switch is merely a
selector switch which is a control circuit that stops the
motor through a motor starter. In our view, this would not
meet the "energy isolation device" definition based upon the
switch being a control circuit device.
If this device would be considered
an unacceptable control type circuit, then we would request
some further clarification of the acceptability of devices.
Specifically we would need additional information as to why
this method does comply and what types of control circuit
methods and devices would comply.
Our purpose in raising this issue
was not simply based on a concern for this particular facility,
but on the possible ramifications at UPS facilities throughout
the United States. It is important to ensure that modifications
instituted by UPS are consistent with agency policy and in
accordance with the standard. Based upon the nationwide implications
we recommend having this issue forwarded to the National Office
for their review and response.
Finally, time is of the essence in
this matter. As I have pointed out in my previous memos on
this subject, the formal settlement of two contested cases
with UPS rests in part on the agency's interpretation of "energy
isolation devices". We would appreciate a thorough but expedient
review of this information in order to conclude the case.
If any further information is needed
regarding this matter, please contact our office.
Attachments
U.S. Department of Labor
Occupational Safety and Health Administration
Washington, D.C. 20210
Reply to the attention of:
December 14, 1990
MEMORANDUM FOR: William M. Murphy
Area Director
Cincinnati Area Office
FROM: W. O. Wiehrdt
Assistant Regional Administrator
Technical Support
SUBJECT: United Parcel Service: Lock Out Proposal
As discussed between you and James Kontos,
the correct interpretation of "Energy Isolation Devices" is:
"A mechanism, tool, or other piece of equipment designed to
positively disconnect the power capable of doing work. This
mechanism will release energy only by the person who locked
the energy, no one else."
The electrical schematic supplied
to us with your second memorandum depicts this type of device;
however it does not show that the lock out control is on the
"off" position. As shown in the drawing now it is a close
circuit "on position."
We have marked the schematic for your information.
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