HVAC schematic

Delta prime

Joined Nov 15, 2019
576
it's a CURRENT spike on energizing a transformer, not a voltage spike, and it will only last a fraction of a second, usually too fast for fuses or circuit breakers to react to
 

MisterBill2

Joined Jan 23, 2018
7,306
It looks a bit like that is being used to indicate twisted pairs of wires. Really, though, it is a very poor symbol.
I determined that by observing that the 2 wires involved seemed to be "supply and return of the associated circuit.
What you are seeing is an artifact caused by a poor plotter driver routine.
There is a symbol for twisted pairs but that is not it. Instead, it is a very poor substitute.
 

MisterBill2

Joined Jan 23, 2018
7,306
They almost resemble thermal O/L's! ;)
Max.
Consider how many of them we see in the drawing and where in the circuit they are located and it becomes clear that they would not be thermal overload devices, neither the heater nor the contacts. They are a very poor attempt at a symbol that is rather obsolete.
 

MisterBill2

Joined Jan 23, 2018
7,306
If it is intended to show shielding then it is by far the worst rendering of a shield symbol that I have ever seen. ALSO, why would a 110 volts DC power circuit in an HVAC system be shielded? Twisted pair is common, and note that the return line is broken with a switch, which would never be done for a grounded shield. Twisted pairs are quite common in some arrangements of control wiring.
 
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