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    By Jim Knapp

    Jim K

    If there is one thing we can count on from this time of year it’s that the New Year brings lots and lots of lists; best, oldest, newest, things to expect, things to eat - you name it. With that in mind, here is a list of fun answers to questions you never asked:

    1. How quick is a ground fault circuit interrupter (GFCI)?

    GFCIs trip in as little as 1/40th of a second (.025). That’s about the equivalent of one frame of a motion picture. Also known as RCDs (residual current device) GFCIs measure the current difference between “hot” and “neutral” and trip if there is more than a 5 milliamp difference (.005 amps). You can die from as little as .030 amps.

    2. Does solder or braze really flow towards the torch flame?

    Yes! Thermo-capillary convection (Bénard–Marangoni convection) is a transfer of mass caused by a gradient difference. That means that because the surface tension of hot solder is less than cooler solder it’s mass moves toward the heat. A  similar effect is observed when you see whiskey or wine climbing up the side of a glass, but this is caused by the interface of water and alcohol instead of different temperatures.

    3. Why don’t hot surface ignitors crack like they used to?

    Three reasons. First, many newer ignitors are made from silicon nitride which is much less brittle. Secondly, if a furnace receives higher voltage (say 130v instead of 120v) the HSI will heat to a much higher temperature, causing more wear. Many furnace controls now limit the voltage applied to the ignitor automatically.  Lastly, equipment with atmospheric venting is at the mercy of the chimney - a slow chimney means poor air flow around the ignitor, making it hotter. Draft inducers have eliminated that problem by regulating air movement.

    4. What was the first plastic insulator?

    In the early 1900s Leo Baekeland was trying to find a substitute for shellac, a very expensive natural insulator made from beetle excretions. In 1907 he branded Bakelite, the first fully synthetic plastic polymer. Bakelite is designated a National Historic Chemical Landmark and is still used today.

    5. Where did the word plumbing come from?

    Plumb comes from the latin word for lead, plumbum. Roman piping was often made of lead. Plumb-bob has a similar origin - heavy lead weights used to measure a plumb line. It may sound  like a surfer-dude expression, but plumbum is not a contractor on vacation.

    6. What is the difference between Schedule 40 and Schedule 80?

    Pipes are sized in North America using nominal pipe size (NPS) so that pipes from different sources will fit together. By this standard the outside diameter of a pipe size is always the same and indicates a “nominal” volume can be carried on the inside. Making pipes of differing strengths requires different pipe wall thicknesses. That is what the Schedule indicates. You can couple a 1” thinner walled schedule 40 pipe with a thicker walled 1” schedule 80 pipe because the NPS calls for them to be the exact same outer diameter. That means that a higher schedule has a smaller inside diameter. There are 11 schedule designations between 5 and 160, with 40 and 80 being very common. 

    7. What is the difference between variable speed and constant torque?

    Both are terms for electronically commutated motors (ECM). They both convert alternating current to 3-phase direct current to power themselves, making them about 30% more efficient than a PSC motor. What is different is the logic that controls their operation. A constant torque (X-13) motor has a range of speed/torque selections that are fixed, much like any multi-tap motor. A variable speed motor uses input from equipment software to attempt to deliver a specific airflow/torque. The motor ramps up or down to meet the needs of the system, so there aren’t any fixed speeds.

    8. Does natural gas always burn?

    Like any other fuel, natural gas needs two conditions to begin combustion - air (oxygen) and temperature. Natural gas must be between 5% and 15% of the total air/gas mixture; any more or less than that and it won’t ignite (propane is 2-10%). Natural gas has an  ignition temperature of 1163F. Below that temperature combustion doesn’t occur (Propane is 920F-1020F, 2150F for oil, and coal is 2200F).

    9. Who invented the electrical transformer?

    The alternating current transformer was invented in Hungary by Ottó Bláthy, Miksa Déri and Károly Zipernowsky. Because Bláthy created the name “transformer” he gets most of the attention. Bláthy also invented the watt-hour meter, motor capacitor and the tension regulator.

    10. Why is it called a Hartford Loop?

    Back before forced air or hydronic heat, central heating for large buildings was all about steam boilers. It could be distributed throughout a building by using only gravity. The boiler operator had to feed and maintain the coal fire and he had to keep an eye on the water level. Without automatic safety controls steam boilers were very dangerous and a whole new insurance industry built itself around insuring (underwriting) steam systems. One of those companies was the Hartford Steam Boiler Insurance and Inspection Company. It was very common for the water return piping, which often sat on corrosive concrete flooring to rot or crack and let out the boiler water. This would empty the boiler and allow it to overheat, either cracking it or making it explode. In the early 20th century Hartford decided they wouldn’t underwrite a boiler system unless the system had a specific pipe configuration at the boiler. It created a sort of backwards trap that would prevent all the water from draining from the boiler if the return cracked. It became known as the Hartford loop and is still used today in steam systems.


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