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6210
Appendix T1 Ground-Fault
Protection |
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1.0
Introduction
An important
part of ensuring the safety of electrical equipment is maintaining appropriate
insulation and a reliable ground.
This
appendix discusses the purposes of good insulation and proper grounding. It also outlines the appropriate use and
maintenance of ground-fault
circuit-interrupters (GFCIs).
2.0
Grounding and
Insulation
All
electrically-powered tools and appliances that meet the safety criteria of a
Nationally Recognized Testing Laboratory (NRTL) – and these are the only devices
we should purchase – have built-in provisions for safeguarding against
electrical shock in normal use, for the intended purpose and application. NRTL listing for residential use is
meaningless, for example, if the device is used for more severe commercial or
industrial purposes. Use a “household”
appliance in a manner consistent with home uses. Information about NRTL approval limitations
is found on the approval label.
·
Electrical
insulation is a non-conductive layer of material between you and the
energized components. Its composition
and thickness are selected for that particular application. It cannot be modified without invalidating
the NRTL listing or approval. Double-insulated
tools and appliances have two, independent layers of insulations, one of which
may be the exterior case. Insulation is
reliable unless it is damaged by impact damage, heat, chemicals, or tampering. Most insulation will not prevent an electric
shock if the device gets wet.
If you detect any deterioration of outer jackets, cases or
cabinets, or you suspect that the insulation or
barriers have been impaired, immediately take the device out of service. Inform your supervisor and area safety warden
or ESH&Q staff.
·
Grounding an
appliance or tool provides a safe path for stray currents that may result from
an internal fault. It requires a third
conductor in the appliance cord and in any extension cord and branch circuit
into which it is plugged. Ground prongs
on plugs lead a hard life. They are the
longest blade, and they often get damaged by chronic physical abuse, including
“whipping” the plug out of the receptacle.
Since ground conductors are not needed for the device to operate, there
may be an undetected open ground in an appliance, its cord, or in a branch
circuit. For this reason, it is
important to test grounded appliances, and circuits periodically for ground continuity. Your supervisor or ESH&Q staff can
perform or arrange for this test
Never ignore any indication – slight
tingling during use, for example – that a ground is not intact. Cease the work, and get help. Never use a cord that has a missing ground
prong, and never use a “cheater plug” (as shown below) adapter at Jefferson Lab. As a safety feature, extension cords and most
appliances have polarized plugs (one blade wider than the other). These special plugs are designed to prevent
electric shock by properly aligning circuit conductors. Additionally if the ground prong connection
from a portable GFCI
in series with an extension cord is faulty, the GFCI protection is
ineffective. Extension cords should be
inspected and tested periodically. See ES&H
Manual Chapter 6120 Hand and Power Tools for
more information on cords.
Figure 1. Cheater Plug
3.0
Ground-Fault Circuit
Interrupters (GFCIs)
A GFCI is one of the
most effective means available for preventing electrical shock. These devices are specially constructed
circuit breakers or receptacles, and they open the circuit when they detect a
very small imbalance in the current between the two active conductors. This imbalance means that current is leaking
to an unwanted ground connection – perhaps through your body. Unlike conventional circuit breakers and line
fuses; individual branch-circuit GFCIs open the circuit at currents well below those capable of
causing electrical injury: about 5mA. Be
aware, however, that you may be sufficiently startled by contact with a GFCI-protected circuit
that you may react reflexively; you can fall from a ladder, for example.
National Electrical Code
(NEC) requires permanent GFCI
protection for many potentially hazardous locations. Occupational Safety and
Health Administration (OSHA) requires GFCI protection for
electrical service in construction environments. Jefferson Lab requires GFCIs in all new
installations where they are required by code and standards. These include the following:
·
Restrooms, kitchenettes,
laboratories, and other locations where receptacles are within six feet of
sinks or showers
·
Exterior and rooftop
receptacles
·
Electrical heating
equipment on pipes and vessels (heat tapes, for example)
Temporary
ground-fault protection shall be provided whenever appropriate by using
portable GFCIs and
cord sets with built-in GFCI
devices.
Typical applications:
·
Outdoor use of power tools
where permanent GFCI
receptacles are unavailable
·
Garages and sheds
·
Other Locations where
personnel may contact electrical systems while in contact with water.
Portable GFCIs are a better
option for protection in areas that are infrequently occupied. Testing the portable device takes much less
time than visiting many locations to test seldom-used permanent GFCI receptacles or
breakers.
GFCI shall be used in
other locations where they would be beneficial.
This includes:
·
For any use of
120 VAC portable cords (extension cords) when cords are used in shops, in labs,
in service buildings, and in the experimental halls and tunnels. This protection may be provided by the use of
a GFCI-protected
outlet or by a portable GFCI-protected
cord or cord adapter plugged into a non-GFCI outlet.
This does not apply to portable cords or surge protector cords
used in an office environment or to provide temporary power to equipment in the
accelerator tunnel which would not be accessible to reset the GFCI during beam
operations.
- On 120
VAC outlets so located as to be routinely used to test or troubleshoot
electrical or electronic equipment or to plug in power tools. This includes outlets which are built
into or permanently attached to shop benches or shop carts.
Very large (≥ 1000A) circuit breakers are usually equipped with ground fault
features. The trip setting for these are
much too high for personnel protection, however. They are known as ground fault equipment
protection (GFEP) and are meant to protect equipment and cabling.
3.1
Selection,
installation, and identification of GFCIs
In order for GFCIs to be effective,
they must be selected correctly for the applications and installed properly by
qualified Jefferson Lab or subcontractor staff.
Receptacle GFCIs
are often preferable to circuit breaker types.
Circuit breaker trips “kill” the entire circuit; a GFCI receptacle can be
configured to protect only the devices plugged into it or those receptacles in
a longer branch circuit.
Additional receptacles protected by GFCIs should be
verified and marked accordingly by the installer. An acceptable method is to affix a small
decal to the cover plate with the message “GFCI Protected” or “GFCI.” This informs others that the receptacle
provides ground-fault protection when it is needed, and it cautions people from
plugging in equipment (such as a computer) that does not need the protection
and can be affected adversely by test and unplanned trips.
Circuit GFCIs
trip at 5mA. Substation GFEP are intended
for equipment protection, not people protection, and trip at much higher
currents.
A
GFCI Receptacle may
be reset once if it has tripped, anymore than one time requires troubleshooting
by a qualified individual.
3.2
GFCI testing
All GFCI
manufacturers recommend that their devices be tested at least monthly to ensure
they operate as designed. Using the
“Test” button to verify trip action and then resetting a GFCI fulfills the
testing requirement. The most effective
test method is via a special plug-in device that indicates if the receptacle is
wired correctly and that induces an actual fault when a test button is pressed. An improperly wired GFCI may not provide
any protection or may fail to trip under test.
An open ground, for example, prevents the tester from inducing the fault
condition. Always look first for proper
wiring as indicated by the device’s display lights. GFCIs usually, though
not always, fail in a mode that prevents them from carrying a load.
If the GFCI
fails to trip or if it cannot be reset, notify the area safety warden or
initiate a facilities management work request.
There is no special expertise
required for GFCI
testing. The occupants of the area or
the most frequent users of the GFCI are often the
best ones to test the device. Alternatively,
safety wardens and others who perform routine workplace inspections could
include GFCI
testing as part of their activities. It
is the responsibility of the owner division of a work area to ensure that the
test gets done.
Figure 2. GFCI Tester
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ISSUING
AUTHORITY |
APPENDIX
AUTHOR |
APPROVAL
DATE |
EFFECTIVE
DATE |
EXPIRATION
DATE |
REV. |
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ESH&Q Division |
12/09/03 |
12/09/03 |
12/09/06 |
0 |
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