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Old 03-13-2010, 08:32 AM
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Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 22,293
Pete VanderLaan is on a distinguished road
Pg 242 of the 4th edition of Glassnotes shows an interesting drawing of a simple wiring diamgram Fritz did about forty years ago, but it's not very good.

Think of it like this:
Power comes in in two hot legs that go into a switching mechanism called a relay. You put the two hot leads on one side of the relay and then the outbound power on the other side which gets hooked to both ends of your 240V element. The relay is controlled by a solenoid if it's mechanical. Mercury relays last longer than mechanicals but are getting harder to legally use. When power is applied to the solenoid on the relay, the circuit closes and power flows to the element you have. When power is withdrawn, the circuit opens and power to the element shuts off. The controller has a thermocouple input on it which measures milliamps from the thermocouple. Your controller has adjustable settings on it which when the milliamps are matched with the thermocouple, power goes from the controller to the solenoid on the relay. When the controller to the gets turned on, or off,that in turn powers or shuts off the element.

It's just a big assed light switch with some bells and whistles. That's actually true of a moly furnace as well. It just has a rectifier in line which breaks the sine wave up into manageable bite size chunks.

If you can, just go and look in someone's control panel and follow the wires. It's not hard if you are remotely mechanically inclined.
Where are we going and why am I in this basket?
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