I've noticed that in many/most modern furnaces the thermostat cable
enters and connects to the control module in the same compartment
with various line-voltage wiring. In fact, much of the line-voltage
wiring terminates on the same control module. There is no partition to
keep the low-voltage and line-voltage wiring separate. This would seem
to violate the frequently quoted rule about separation of low- and line-
voltage wiring unless thermostat cable insulation is supposed to be rated
for line voltage. The thermostat cable I've seen is CL2 with a 105C
temperature rating but says nothing special about voltage. Is it 300V
or 600V rated?
Manufactures get to do what ever they want when the designs are submitted to
the testing agencies like UL and CSA. I worked for an electrical
manufacture that ran line and low voltage in the same bundle ty-wrapped
together. As long as you see the acceptance sticker on it chalk it up to
the way of the world.
Check out a electric waterheater. Fed with a minimum of #10 and inside the
manufactures use #12.
Air conditioner condensers are the same situation
I agree; appliance manufacturers get a lot of leeway from UL.
Practices which wouldn't be permitted by NEC are routinely
OK'd *inside* the appliance where UL feels the mfr has
sufficient control to satisfy some minimal level of safety.
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