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6240
Appendix T1 Electronic
Equipment – Best Practices |
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1.0
Purpose
Often Jefferson Lab has need of
unusual electronic
equipment which does not meet the standards and listing requirements set forth
for industrial applications. In order to ensure that such equipment is safe in
accordance with Jefferson Lab’s acceptable safety standards, best design and
construction practices are provided within this appendix. These are to be reviewed
and incorporated as applicable into department procedures.
2.0
Scope
This
appendix provides best work practices for safely constructing, modifying, and
maintaining electronic equipment. The extent to which these
practices are applied is determined by the person responsible for the design,
construction, and commissioning of the equipment.
Items that have not been altered, and are certified by a Nationally Recognized Testing Laboratories (NRTL) (e.g.: those that are UL listed), meet the requirements of this document.
Modification to
NRTL listed equipment invalidates the listing. If certification needs to be
restored, a recertification inspection is required.
3.0
Responsibilities
NOTE: Management authority may be delegated to a task qualified Jefferson Lab employee at the discretion of the responsible manager.
3.1
Supervisor/Subcontracting
Officer’s Technical Representative (SOTR)/Sponsor
·
Ensure that only
qualified workers design or modify electronic equipment and the work is accomplished as specified in ES&H Manual Chapter 6230 Electronic Equipment Safe
Work Program.
·
Ensure appropriate
level of review, construction, and modification is performed as needed.
· Ensure inspection of final product.
3.2
Designers
·
Obtain
appropriate authorization to design or modify equipment.
·
Comply
with appropriate standards or guidance.
·
Reduce
hazards by incorporating engineering safeguards, and reducing mode or class
levels.
·
Create
and maintain proper documentation of design in accordance with department
procedures. For example:
o
Specifications
o
Design
analysis and calculations
o
Drawings
o
Schematics
o
Software
o
Pressure
system procedures
o
Wiring
diagrams
o
Safety
Analysis
·
Schedule,
perform, and document appropriate design reviews.
3.3
Technicians
- Make no modifications to any
equipment without appropriate authorization.
- Prior to modifying any
equipment analyze the hazards to equipment users.
- Incorporate risk-reduction techniques during work subject
to appropriate review.
- Follow established quality procedures. For example:
- Control of Nonconforming Material or Products Procedure
- Graded
Approach Procedure
- Material
Identification and Traceability Procedure
- Pressure
Systems Quality Procedure
- Receiving
Inspection and Acceptance Testing Procedure
- Suspect/Counterfeit
Items (S/CI) Identification Procedure
- Visual
Examination Procedure for Examiners
- Build equipment in accordance with design drawings,
including specified materials and components.
- Perform visual inspection and peer review prior to
completion of work
- Document or otherwise communicate “as-built” changes to the
Designer per departmental procedures.
4.0
Expectations
4.1
Minimum Expectations
Any work activity at Jefferson Lab follows the same minimum over-reaching
safety procedures. These include:
·
Performed tasks in accordance with principles recognized by the industry
as good practice, consistent with consumer safety.
·
Provide for an equivalent level of protection if recognized or harmonized
standards cannot be strictly followed.
·
Meeting the intent of applicable
electrical safety standards.
4.2
General Electronic
Safety
It is Jefferson Lab’s preference to use NRTL listed
electronic equipment for all equipment needs. When this is not possible, the
following considerations comprise a non-exhaustive guide:
·
Voltage Verification Units (VVU)
Incorporate wherever possible as a means to mitigate
Mode 2 to Mode 1 on Class 2 or above equipment. VVUs greatly reduce the
exposure to electrical energy during Lock, Tag, and Try;
and assist with the standardization of the procedures for de-energizing
electrical equipment.
o
The
VVU operation must meet the requirements of the VVU equivalency.
·
Appropriate Connections to Electrical Distribution
Equipment
This includes proper grounding,
respect of polarity, insulation, and the reduction of Mode and Class, wherever
possible.
- Design
Reviews
Implement as necessary commensurate with level of complexity and
hazards.
Reduce whenever possible.
- Status
Indicator Lights
Use to indicate the status of the circuit.
Design and construct appropriate personnel protection to prevent
unintended access to energized circuits.
- Mechanical-Strain-Relief
Device
Use as suitable for any wire or cable penetrating an enclosure.
Grommets or similar devices are unacceptable for use as strain relief.
- Area Lighting
Consider area lighting required for larger pieces of equipment.
o
Incorporated lighting into the design, or
o
Provide for a means for temporary illumination.
- Color Code Convention for
Wiring Main AC Power
Per National Electrical Code (NEC), or consistent
with existing wiring (e.g. modifications to imported products) (avoid confusion
whenever possible).
- Minimize the use of Flammable
or Toxic Materials
Consider the design, construction, and proximity of other
electrical components. If unavoidable, use an appropriate method of
containment.
4.3
Disconnects
·
Provide for overload protection and maximum fault current
interruption.
·
Incorporate local “off” controls particularly on remote-controlled
equipment.
·
Incorporate power switches on chassis so power can be removed without
unplugging the device, wherever feasible.
·
Clearly label loads and associated controls. When 50VAC or above is used as a
control voltage, the control voltage must be clearly marked.
·
Design for Lock, Tag, and Try.
4.4
Overload protection
·
Utilizes appropriate over-current-protection on inputs and outputs.
·
Employs only approved fuse holders or circuit breakers.
·
Is properly rated and devices are labeled.
·
Adequate accessibility for maintenance.
4.5
Remote Control Devices
·
If failure could create a hazardous condition then a “fail-safe”
is designed into the initial configuration.
·
In the event of a fault in a main system containing breakers,
fuses, interlocks or momentary on-off switches, the control circuit seals or
latches to prevent the release of energy or re-energization and aid in fault
identification and manual reset.
·
Control power is isolated from higher-power circuits by
transformers, contactors, or other means.
·
Control power is limited to no more than 120 volts, AC or DC
except on previously installed equipment.[1]
|
The standard
Jefferson Lab control voltage for the accelerator is +24 VDC. |
·
Hazardous additive voltages are not produced between control
circuits derived from line power having different phase or polarity.
·
Control-circuit currents do not exceed 5-amperes, and are limited
by fast-acting fusing, circuit breakers, or power-supply rating.
4.6
Chassis/Enclosure
Construction
·
Chassis components are specified in accordance with their intended
environment. They are designed to be sturdy enough to withstand an appropriate
qualification test. Chassis materials
are non-combustible, and/or non-flammable. They do not result in toxic or
poisonous fumes. Internal power supplies are secured, such that they will
survive the appropriate qualification testing.
·
Direct contact of Class 2 and Class 3 hazards
are prevented by the use of covers and/or enclosures, so as to isolate the
source.
o
Class 2 enclosures may consist of voltage rated plastic
barriers or covers.
o
Class 3 enclosures and chassis systems must
include in their source isolation:
§
Screw-on panels, possessing a minimum of four
screws or bolts, or
§
Locked and/or electrically interlocked doors or
panels
·
The frame or chassis of an enclosure is connected to a good
electrical ground with a conductor capable of handling any potential fault
current. An enclosure may be a room, a barricaded area, or an equipment
cabinet.
·
Easy open doors, panels, etc., that permit access to exposed
hazardous circuits, are interlocked so that the act of opening de-energizes and
automatically discharges the stored energy.
·
Enclosures physically prevent contact with live circuits.
Enclosures can be constructed of conductive or nonconductive material. If
conductive, the material must be electrically interconnected and connected to a
good electrical ground. Connections must be rated to carry all potential fault
currents.
·
Enclosures are designed to contain flying debris caused by
explosive component failure.
·
Ventilation is sufficient to prevent overheating of equipment and
to purge noxious toxic fumes produced by an electrical fault.
·
Ventilation openings are designed to minimize the risk of
accidental contact through the openings, e.g., use of small mesh grille.
·
Enclosures large enough to be occupied by personnel allow for
exterior observation of equipment and personnel working inside the enclosure.
·
Appropriate signage and labeling is applied to identify hazards,
functions, and operations.
·
A keyed switch can be used in each interlock chain involving
personnel hazards, or major equipment hazards to assure power removal before
anyone enters the enclosure. This same key is also used to gain access to the
controlled equipment. This does not replace the requirement for the Lock, Tag, and Try
Procedure.
|
Although not strictly required at the time of this writing, the use of NEMA (Association of Electrical and Medical Imaging Manufacturers; formerly National Electrical Manufactures Association) approved enclosures are strongly encouraged for Class 3 source isolation systems. See: www.NEMA.org or http://www.nema.org/prod/be/enclosures/upload/NEMA_Enclosure_Types.pdf |
4.7
Class 2 & 3
Equipment
·
Use self-contained power supplies to protect personnel from
line-level voltage when equipment is energized.
·
Any hazardous voltage present in electronic equipment is protected, such
that individuals are not exposed to live conductors. Conductors carrying
hazardous voltages are not accessible, without the use of tools and proper Personal Protective Equipment (PPE).
·
Heat-generating components, such as resistors, are mounted so that
heat is safely dissipated and does not affect adjacent components.
·
All conductors, switches, resistors, etc., are operated within
their design tolerances. Pulsed equipment does not exceed the average, the Root Mean Square (RMS), or the peak rating of components.
The equipment is de-rated as necessary for the environment and the application
of the components. Exceptions are clearly described in relevant documentation.
·
Equipment having an Emergency-OFF switch is clearly identified.
The switch is within easy reach and resetting it is not automated.
·
Distinctively color and/or label components that are commonly
non-hazardous if they could become hazardous when used in a unique application
(e.g.: a copper pipe carrying high voltage or high current).
·
NFPA
70E - Standards for Electrical Safety in the Workplace
·
NFPA 70 - National Electric Code
·
OSHA Regulation 29 CFR 1910 and
29
CFR 1926
·
DOE Electrical Safety Handbook
· MIL-HDBK-781A (01-April-1996) Department of Defense Handbook for Reliability Test Methods, Plans, and Environments for Engineering, Development, Qualification, and Production
6.0
Revision
Summary
Revision 1.3 – 11/14/18 – Periodic
Review; Deleted reference to NFPA-70E (2004 edition) per CATS#
STR-2017-12-06-04
Revision 1.2 – 11/12/15 – Periodic Review; no
substantive changes
Revision 1.1 – 05/20/12 – Periodic Review; updated format with no substantive changes
Revision 1.0 – 05/20/09 – Update to reflect current
laboratory operations
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ISSUING AUTHORITY |
TECHNICAL POINT-OF-CONTACT |
APPROVAL DATE |
REVIEW DATE |
REV. |
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ES&H Division |
11/14/18 |
11/14/21 |
1.3 |
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