Arc-Flash, Take 1

October 25, 2012

Arc-Flash, Take 1

An open electrical panel is a deceptively dangerous thing. The bus bars in the panel just sit there, doing nothing, giving no hint of their awesome power to instantly kill. If something causes a fault (or a short circuit to non-electrical engineers) between two bus bars, an incredible amount of energy is released. In fact, up close it rivals the power of a nuclear blast! What happened to the ninja occured in less time than his brain could even process it. In this case, he truly never knew what hit him.

Here are some videos of real arc-flash incidents to give you a sense of the danger.

Arc-flash demonstration. Watch the whole thing.

Arc-flash accident. Fast foward to 1:10.

Arc-flash accident. Fast forward to 1:10.

Mark Robison, PE

PS–curious about what the ninja discovered before his untimely death?

Current transformers are installed by utilities on large electrical services to avoid having gigantic electric meters. The current transformer converts the main building current to a lower value (between 0 and 5 amps) so that a standard meter can read the power. If the current transformers are bypassed, the current does not reach the meter and the electric bill is lower. Utilities have seal-locks on the meter section of the switchgear to alert them if cheaters have gained access.

In this case, the implication is that the current transformers are bypassed not to save money, but to give the appearance of using less power (and therefore appearing to be a more green building than it really is).

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