Archive for October, 2012

Arc-Flash, Take 1

Thursday, October 25th, 2012

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).

Motel 6

Wednesday, October 10th, 2012

If you are old enough to recall the voice of Tom Bodett saying, “We’ll leave the light on for you” as the signature end to all the Motel 6 ads, then you caught the attempt at humor. But even if the reference passed over your head, the message remains the same.

As a true believer in the Green movement, I applaud the work being done to reduce energy consumption, including lighting energy savings. But as with all regulations intended for the greater good, unintended consequences can occur for specific situations.

One area where I see too many restrictions is in regard to commercial lighting where the lighting is really part of the product, and not just an arbitrary element. To the credit of the USGBC and other regulatory agencies such as T-24 in California, the code is including more subtlety to allow commercial establishments to maximize their business plan.

Meanwhile, our MEP Ninja has gotten caught in the cross fire, and is having a bad day, as he always seem to have.

Mark D. Robison, PE