grounding and bonding

[sparklet569]

greetings forum,
I was recently in a class and a test question was posed as such. "bonding plays a far more important role in protecting people from shock than grounding." The astute teacher said the answer was true. I contended, unsuccessfully, that one is not effective without the other. There must be something I am not understanding as I still believe an effective bonded system must also be grounded(i.e. grounding electrode). Help me understand. Thank you

 

[roger]

The teacher is correct. Even though a system may be grounded (earthed) it plays very little if no part of personnel safety at voltage levels below 1000V. Bonding the systems parts with a low impedance path back to the source is what opens OCPD's


Roger

 

[GoldDigger]

greetings forum,
I was recently in a class and a test question was posed as such. "bonding plays a far more important role in protecting people from shock than grounding." The astute teacher said the answer was true. I contended, unsuccessfully, that one is not effective without the other. There must be something I am not understanding as I still believe an effective bonded system must also be grounded(i.e. grounding electrode). Help me understand. Thank you

A totally ungrounded circuit can be perfectly safe, since no point on that circuit can source current to ground as a result of a single fault. Bonding of mental that is not connected to any circuit point will not make a difference except when two faults are present at the same time. In that case bonding is a second level safety precaution, and it does not hurt to ground the bonded mesh.
If you have a grounded circuit, on the other hand, with one conductor of the supply tied (bonded) to ground, then everything that is not normally energized should be bonded AND tied to ground to prevent a hazardous voltage from appearing as the result of a fault.

 

[augie47]

A swimming pool is a good example. To assure than any surface with which one has contact is at the same potential, all conductive elements of the pool, including the water, are bonded together. The bond is present even if no components are intentionally grounded. Stray voltages from power transmission elements can be present and pose a hazard unless proper bonding is assured.

 

[electrofelon]

A totally ungrounded circuit can be perfectly safe

Yes, Many people see the word "ground" or other forms of the word and think "safety" or "safer". I like to say that system grounding is just a system topology and not about safety. Both have advantages and disadvantages.