w_tom wrote:
This debate will only produce more light than heat if we all refrain from personal attacks. The hallmark of someone who is confident in their position is that they find such tactics unnecessary. There is an old legal motto that goes "when you are strong on the facts you pound on the facts, when you are strong on the law you pound on the law, when you are strong on neither you pound on the table." Most people will recognize pounding on the table as an admission that you are not confident in your position. It weakens rather than strengthening ones case.
Let me ask some questions. If a protective device equalizes the voltage on all connections of the load to be protected will that not minimize destructive current flow?
Are we really trying to provide the destructive energy a path to ground or are we only interested in avoiding the use of the protected components as part of that path?
Are destructive transients only high voltage relative to the earth or are they sometimes high voltage relative to the normal supply?
Back when I was a trainee on large commercial work I had a more pugnacious attitude about many things. One day the tile crew brought in a boom box that literally had to be carried on dollys in an attempt to drowned out the country music that the carpenters preferred. Since the electrical work rules forbid having music playing on the job our gang was neutral in the dispute but by the first break I had enough of this mega boom box. I draped a piece of cable over the top of the service equipment and connected it to a double poled breaker in the service equipment. The other end was connected to one end of an old double pole, double through, switch from the junk bin of the gang box. The other end of the switch was connected to the single pole breaker and the neutral buss in the derived system panel that was supplying all of the temporary receptacles on that temporary circuit. I tied the center of the switch in parallel with the temporary circuits wires and then I cut the original temporary wires out of the circuit leaving only the switch as the receptacles supply. For those that will not know, that means with a flick of the switch I could apply 480 volts across the temporary receptacle circuit. I did nothing to disturb the temporary grounding which had been conscientiously installed and had passed it's quarterly OSHA inspection only two days before. Why then was I treated to the sight of the tile crew trying to beat out their burning boom box with a drop cloth after I through the switch? I believe it was because the voltage was more than high enough to burn up the power supply of the boom box the tile crew had been trying to deafen us all with for hours but no were near high enough relative to ground to damage the wiring itself. Brand new wiring in commercial installations is often tested by a testing company at one thousand volts to ground. Yet the stuff we plug into that wiring may fail at as little as two hundred volts. A plug in protector ahead of that boom box would have been a good investment for that tile crew. Not all transients are the same. I have seen with my own eyes the sacrificial failure of plug in surge protectors in saving copiers and computers from accidental over voltage connections. Grounding was not an issue in those cases because a surge cause by over voltage across the line may not give a rats patute about ground it is only trying to return to the source.
-- Tom H