Personal Protective Grounding For Electrical Workers:"If It Isn't Grounded, It Isn't Dead"
- John J. Kolak (Praxis Corporation)
- Document ID
- American Society of Safety Engineers
- ASSE Professional Development Conference and Exhibition, 28 June-1 July, San Antonio, Texas
- Publication Date
- Document Type
- Conference Paper
- 2009. American Society of Safety Engineers
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- 35 since 2007
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Personal Protective Grounding /Bonding (PPGB) is one of the most important yet often misunderstood topics in High Voltage (>600 volts) electrical work (author’s opinion). PPGB refers to techniques used to provide shock protection for electrical workers by connecting de-energized equipment on which work is to be performed to the earth. PPGB is a paradox in that, if it is done correctly, it is by far the most effective means of protecting electrical workers from electrical shock. However, if PPGB is done incorrectly, it can precipitate arc-flash events of unimaginable magnitude. This technical paper will explain the purpose of PPGB and proper methods for installing PPGB on typical industrial equipment. Although every effort has been made to put this topic into layman’s terms, PPGB is a very technical topic and it will be best understood by readers who possess a good understanding of basic electrical concepts such as Ohm’s law and Series and Parallel circuitry.
Why PPGB Is Necessary
The techniques of PPGB were developed because High Voltage (HV) workers were being killed on lines and equipment that either were mistakenly thought to be de-energized or accidentally became energized through some external means1.The “external means” could include the following:
- Switching Errors- where equipment was energized remotely from the work location or a relay caused a switch to close after the circuit had been tested for voltage.
- Induction- HV circuits can “induce” voltage (measured in volts) and current (measured in Amperes) on conductive surfaces even several yards away from the energized conductors. The author has personally tested brand-new HV 13,200 volt switches that had been opened but not “racked-out” (physically separated from the energized bus bars to which they are connected) and a voltage of several hundred volts was present. This is the reason that HV switches must be racked-out AND grounded before workers touch them with any part of their bodies.
- Equipment Failure- Insulators within HV switchgear can either break allowing conductors to come into contact with each other or insulators contaminated with conductive residue can begin to “track” allowing voltage to flow over them.
- Backfeed- The proliferation of customer-owned generators provides an alternate feed for electricity that can present shock hazards to anyone working on the circuits to which the generators are connected.
- Bonding- Connected to establish electrical continuity and conductivity. The main purpose of bonding is to equalize any differences in potential (voltage) that might exist between conductive surfaces.
- Dead-Front Equipment- Without live parts exposed to a person on the operating side of the equipment. A common circuit breaker panel found in any home is an example of dead-front equipment. Opening the door of the panel reveals only a grounded metal panel cover and non-conductive circuit breakers. This is “dead-front”.
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