Too late for this faulty one! Production losses: Over $1 million. Was only tested at install.


 Mandated or Recommended by:

NEC sect 230-95 (c) & 517-17 (c),   NETA, NFPA  70B ch. 11, 11


About 15% of all ground-fault protection systems installed at main or sub-main circuit breakers – as tested by NETA (Inter National Electrical Testing Association) in 2009-2010 – were found to be  improperly installed, contained defective components, did not operate correctly, had incorrect settings or had been disconnected illegally by electricians. They are a clear danger to their facilities.

8 WHY have GF Protection?    

image007 Even low-level arcing ground faults can destroy switchgear in fraction of seconds before main
service over-current protection can operate.
Today’s breakers and disconnects will
do little to protect life and equipment because their reaction time is simply
too slow. GFI special protective relays and CTs shorten the reaction time to limit damage. A 480/277V solidly grounded system has sufficient voltage to
maintain an arc between one phase and a ground, but not enough current to cause
a large main breaker or fuse to clear the fault quickly. The resulting ARC
FLASH is similar to an electric weld thus consuming large amounts of metal in
the seconds it takes for the breaker, disconnect/fuse to operate. 

A properly installed and operating ground fault protection system
will detect and clear the fault in milliseconds, fast enough to limit damage to very acceptable levels.
Ground fault protection is mandated by NEC on larger circuits and services of 480/277V 1000A and up, but increasingly these GFI systems are found on smaller downstream breakers as small as 100A, which increases the protection to the facility by limiting a shutdown due to a fault to specific areas rather than the entire operation.

  8 HOW do GFI Systems Work?  

 The several different types of GFI systems
all operate under the current balance principle. It monitors that the
current going out on any one phase is coming back on another phase or neutral.
If some current is going out on one phase but is coming back on the ground path
(conduit, piping, earth, building steel, etc.) then a ground fault has
occurred. GFI systems have (1) current transformer(s) [CT’s] to detect ground fault
current, (2) a relay or logic box to determine tripping current value and time, and (3) an
operating mechanism to trip the breaker or switch. (4) Some systems have a test panel
for simulating a ground fault signal to trip test the breaker and a monitor panel indicating system status, but these are not
a valid test of the ground fault true interruption functionality. It does not comply with the National Electrical
Code (NEC) requirements and does not detect many of the problems listed
above and does not comply with most manufacturers’ instructions, UL and NEMA recommendations.

8 WHICH Tests should be Performed?   

  • image009Field acceptance testing is REQUIRED by the NEC
  • Inspect neutral main bonding connection.
  • Verify proper sensors/grounding installation and connections.
  • Inject current through current sensor and verify pickup and timing characteristics of relay(s).
  • Test operation with control voltage reduced to 277V instead of 480V. One phase could be at 0 volts during a ground fault
  • Check operation of special features like zone interlocks, etc.

8 WHAT Problems are found?  

  • Neutral grounded downstream or bonded to G in
    wrong location. Causes false tripping.
  • Incorrect current sensor installation and wrong
    polarity. Causes false tripping.
  • Inadequate control power or connections. Causes
    lack of trip of the protective device.
  • Failure to trip within manufacturer’s tolerances.
    Causes inadequate protection.
  • Failure to trip entirely. Indicating
    damaged unit.

8 HOW often?              

 NEC and insurance companies believe GFI testing should be done as frequently as every (1)year and no less than three (3) years depending on usage.

8 WORTH the Cost? The alternative is TOO costly 

Cost will vary somewhat and whether done in conjunction with PM and other testing. Utilities charge a fee after hours. A functioning GFI saves lives and equipment. Primary injection is the preferred method. Bench testing of breaker is not a recommended method.


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