The Sandwich Board: September 2013

Tuesday, September 10, 2013

Electrical Phases

I walked in to a problem at one of our business locations today - one of the electrical phases was out. This is referred to as "losing a leg". When you lose a leg, all the big breakers stop working correctly, and some of the regular sized breakers stop working, It has to so with which power bar the breakers are attached to in the panel, because the "leg" is one of those power bars.

Basically, half the lights and outlets stop working, and it seems random.

This location has three phase electric, which is a little confusing. I looked it up on Wikipeda and learned this: "There is nothing magical about three-phase power. It is simply three single phases synchronized and offset by 120 degrees."

I don't really understand what all that means, but in a 3 phase panel, you have three big power wires coming in from the top, powering the breakers. You can see those in the panel here. They are the three big black wires coming in from the top. (from http://en.wikipedia.org/wiki/Electrical_wiring_in_North_America)

In our restaurant, some of the breakers went off, and all the triple size breakers were turned off by the responding electrician as a precaution. Evidently if a piece of 3 phase equipment, like an air conditioner, is running on one too few phases, it will burn up the motors. There are two triples on the right of this photo below.

The electrician said we should go out to the pole outside, and see if we could find a blown fuse laying on the ground, or a dead squirel who caused the short. We went outside. The 3 phases are the parallel wires on the top of the poles. In this situation, each one of the power wires has a little connector attached, to the right of the pole, that has a power wire going down to fuses. In this photo, you can see three clamps on the top three wires that each go down through fuses, and feed in to the conduit beside the pole so they can be buried underground.

The electrician said all the fuses looked intact upon a visual inspection (no wires hanging down like in a broken light bulb filament,) so one of them probably burned up internally. We searched the ground, and immediately found a dead hawk. It was a fresh death with no flies or maggots, so we think this guy caused the short, and got zapped.

The power company took it from there to identify and replace the bad fuse.

Around my house, the 3 phases are often wired vertically, not horizontally. In the photo below, there are three phases, but the power connection is to one house with a single phase (the top wire). The doohickey at the bottom hanging out on the left of the pole is the fuse (the bucket thing is the transformer, which is another story).

We also have single phase out at some of the farms where I jog. This photo below shows single phase (one wire on the top). The other wires are phone and structural.

Here is another triple phase pole, below, powering a single phase house. This time with the middle wire. Are you getting it?

My house has single phase. Here is my pole. Squirrels shorted this out several times, until the power company put in squirrel proof equipment. Or all the dumb squirrel died and the smart ones reproduced. Not sure.