Honeywell's published documentation for their R182C switching relay
contains the following warning:
IMPORTANT: The transformer [120VAC primary, 24VAC secondary] on the
R182C may overheat when used with a series 20 thermostat if the total
resistance of the thermostat circuit exceeds 2.5 ohms. If the measured
resistance of the thermostat (including thermostat wire and thermostat
contact resistance) exceeds 2.5 ohms, add a 100 ohm, 10 watt resistor
between the W and R terminals.
I don't understand that -- if the total resistance is, say, 10 ohms,
clearly the current drawn will be *lower*
than it would be at 2.5 ohms,
or at 1 ohm.
How is the transformer in danger of overheating at a *lower*
Seems to me that the greatest danger of overheating would occur with a
circuit resistance of near zero ohms, i.e. a dead short across the
transformer secondaries. Someone please explain this to me.
[Please note that I *do*
understand the purpose of the 100 ohm 10W shunt
resistor, in reducing the total resistance of the connected load. What I
understand is how a *lower*
resistance avoids overheating the