Watch Those Connections!

Some appliances such as stoves and dryers, do not come with line cords when the appliances are purchased.  As a result, consumers have to make separate purchases in order to use their new machines.  When attaching the cords to the appliance, pay close attention to the way the manufacturer requires that the line cords are connected.  For many do-it-your-selfers, this is no big deal.  It shouldn’t be a big deal for a professional electrician either.  However, we are all human and subject to making mistakes.  Case-in-point: the following dryer fire.  Although minor as residential fires go, the damage could have been much worse.  The photographs shown below illustrate how the manufacturer called for the installation of the line cord and the subsequent way, the cord was connected.

The manufacturer’s schematic drawing shows how the “hot” (red and black wires) lines of the line cord were to be attached to the L1 and L2 terminal block terminals.  The common line or white wire was to be connected to the N terminal on the terminal block.  Lastly, the green wire or earth ground, was to be connected directly to the appliance housing.  The photograph below shows how the white and black wires were reversed on the terminal block.

 

 

Since the common and earth ground points are electrically the same point, the dryer was, in effect, energized through the housing.  Anything in contact with the dryer housing, such as the exhaust duct, will also become energized.  Dryer ventilation ducts are usually coils of steel wire wrapped with a thin layer of vinyl or aluminum material.  As current flows through the steel wire, the external covering is heated.  If not stopped, the heat will cause the covering to melt and possibly ignite.

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Cut Those Tree Limbs!!!

I just completed an assignment where contact between a power line and a tree limb caused damage to several home appliances. We all know that power lines are sometimes routed through tree branches between the transformer and the weatherhead on a residential or commercial building roof.  It’s also no secret that electricity can travel through a tree.  In this particular case, contact with the limb came about as a result of rubbing so that when the wire insulation had worn off and the conductor was exposed, a short circuit to ground was created.  When this happens, current is going to go in all directions.  It is possible to energize the neutral side of a building’s electrical system so that current is fed into an appliance in the wrong way which causes damage.  Although electric utilities sometimes take on the responsibility for pruning tress, home and building owners should be proactive in helping to maintain the safety and reliability of power distribution.  As this article is being written, the northeast is being “slammed” with a huge winter snow storm.  It’s no stretch of the imagination to conceive of the number of power lines that will come down as result of broken tree limbs.  But, keeping tree limbs pruned and off power lines can mean the difference between staying warm and waiting several hours if not days for utility crews to make repairs.  Remember, unless you are in an extremely isolated area, the transformer that feeds you home or business, also feeds your neighbor’s homes and businesses.

Is Technology Changing Too Fast?

I just finished reading an article about how in the not to distant future we will have autonomous vehicles. That is to say that cars and trucks will drive themselves. The article, published by the Society of Automotive Engineers, went on to predict that autonomous vehicles would be available by the year 2020, only seven years from now. As a forensic engineer that investigates vehicular accidents, I can’t help but wonder what is going to fail that will cause these vehicles to crash. And something will FAIL. Will it be a software glitch or will some system that is supposed to detect danger miss a cue? History is littered with examples of engineering failures that have caused massive amounts of property damage as well as countless numbers of lives. Imagine traveling at some high speed and smashing into another vehicle because your vehicle, NOT YOU, failed to apply the brakes. The point to be made is that manufacturers, regardless of the industry, are all too eager to be the first to get a new product on the market. When the public starts buying the product, it’s not until then that we find out that the product has problems that have not been eliminated. What products am I talking about? Just think phones, computers, appliances, and yes, cars. I’m sure something will come to mind. Is technology changing too fast? Yes, I think so. As long as manufacturers rush to get their products to market before they are ready, we, the consumers, are going to be paying the price. As a result, I also think that those same manufacturers should be held responsible for property damage and personal injury if their products fail to perform as advertised.

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