Archive for November, 2011

Changing Lighting Bulbs

Wednesday, November 30th, 2011

This comic attempts to answer the age-old question, “How many ninjas does it take to change a light bulb?” Credit for this idea goes to Dharmesh Patel of Phoenix, Arizona, who wrote in several suggestions for MEP Ninja scripts. This one especially caught my fancy. More ideas are welcome, and as you can see, we publish the good ones.

P.S. One of our avid MEP Ninja followers commented that the unrealistic part of this cartoon is not that the ninjas would use their swords to change the light bulb, but that ninjas are creatures of the night and would not need light to study by! My bad.

Mark Robison, PE

Beer Conduit

Wednesday, November 16th, 2011

You recall the famous Pee-wee Herman bar scene from Pee-wee’s Big Adventure, right? That’s my favorite scene from my favorite movie. (You can watch it on Youtube if you’ve never seen it or want a refresher).

In this comic, we find the ninja in the basement of the US Green Building Council headquarters below the bar. The ninja sees a 4″ electrical conduit which he assumes must be the main power feed for the building. Instead, it turns out it is the conduit that carries the beer lines from the beer cooler in the basement to the beer taps in the bar!

Every electrical engineer knows that one of their duties as the engineer is to provide the 4″ electrical conduit for running the beer lines. It really is a conduit, and it really is installed by the electrician! But as the ninja learns, there are no wires in the conduit, just beer lines. And nothing angers a mob of LEED accredited drinkers more than cutting off their beer!

For once, the ninja is able to dance his way out of his situation, rather than being killed or captured. Don’t expect this to happen regularly!

Mark Robison, PE

Centrifugal Fan

Wednesday, November 2nd, 2011

The ninja almost, but not completely, understood what he was trying to do here.

The exhaust fan has a three phase motor. Three phase motors run in one direction or another depending upon the phase rotation of the power. The phase rotation is easily changed by reversing two of the three wires connected to it, which the ninja did.

Unfortunately, he assumed that reversing the direction of the motor would reverse the direction of airflow when the fan was on. For propeller or turbine fans, this assumption is true. But centrifugal fans blow air in the same direction no matter which direction they turn.

Instead of the gas being sucked into the building and killing the occupants, it was blown back at the ninja and he dies instead. Victory to our heroes at the Green Building Council!

Side note: what if the fan had a single phase motor? In that case, reversing the wires would have made no difference. The motor always turns in the same directions. But for three phase motors, the connection sequence of wires is critical to the performance of the fan. I can hardly count the number of times I have “fixed” a design problem by reversing the direction of the fan. It is one of my favorite fixes.

Mark Robison, PE