Electric furnace wire heating up

You need to use rated breaker and did you find a fault for why the breaker shorted?

the 3 amp fuse protects low voltage side of transformer. if it's blowing on a call for cooling wire pair going to outside unit bad or contactor in outside unit.

1) You got a FIRE truck coming.

2) Wire is too small.
Problem is NOT circuit breaker.

3) Both 240Volt appliances on same breaker is a hazard, especially if space available in 200 amp service panel for more breakers.

4) Usually each 240V appliance has separate breaker.

5) Circuit breaker trips because of High heat on the wire.
If wire gets hot, it will start a fire inside the wall.

Electric code requires wire-size match breaker-size.

6) If you put larger amp breaker on same wire that is getting hot, then wire will get hotter.
Result: FIRE truck middle of night with folks jumping out window in glass-cut bare run across yard.

7) Each appliance has volts and watt rating on label.
EVERY appliance has label.

8) For example stove might be rated 8000 watts and 240Volt.
8000 watts divided by 240 volts = 33.3 amps
Stove would require 40 amp breaker and 8 gauge wire.

9) How to figure it out:
http://waterheatertimer.org/Color-codewire.html
http://waterheatertimer.org/How-to-install-a-subpanel.html

10) Do same calculation for new furnace.
12000 watt furnace divided by 240 volts = 50 amps.
Use 60 amp breaker and 6 gauge wire.

11) Summary: fixya wants you to be safe, and buy stuff showing in the ads.
Use a bigger breaker ONLY when bigger wire is also installed.
Call furnace installer, the installer should know to check safe wiring before installing.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Breakers trip because of heat.
When heat from wire exceeds breaker rating, it trips.
Something is causing heat on the wire, wire is too small for the amp draw, there is short circuit, or breaker is bad.
Replace breaker and/or test wire.

Put amp-meter on wire and read amp draw through wire.
Amps cause heat. That's why high voltage lines from power station are high-volt-low-amp so there is no heat loss with long distance transmission, until transformer at home converts electricity to lower volts and high working amps with enough power to run electrical devices.
Same is true for AC and DC circuits.
If amp reading on wire exceeds rating on breaker for length of time, then breaker will trip.
The fact that the breaker lets current (amps) to flow for a period of time before tripping is because the breaker is probably rated for slow-acting, or it takes a while for amp draw to heat the wire.

Following image shows amp-meter that clips over wire to get amp reading.
http://waterheatertimer.org/pdf/Which-is-best-gas-water-heater.pdf

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Disconnect the black power wire where it is connected to the furnace with breaker off. Put a wire nut on it and then turn the breaker on. If it continues to trip, the problem is not the furnace and you will have to trace the power wire back to the breaker box to find problem. Next, disconnect the black wire from the breaker (with breaker off) and then snap breaker on. If it trips, bad breaker. If the furnace was disconnected and breaker did not trip, you have a short either on the P C Board or the transformer.

you said it yourself. when an electrical device is running it produces amps, with every amp is a unit of heat. breakers are heat sensitive as well. so you might want to consider a new breaker. newer breakers are made out of better materials that are able to displace heat more efficiently. or check to make sure the screws on the terminals where the wires go in are tight. if there is a loose connection that will increase the units of heat traveling through the termination. or, worse case scenario, like when all hope is lost. splice in some more wire, correctly, emphasis on correctly, and relocate the breaker. perhaps use insulation around the breaker, non flammable of course.

Most likely not.Heating equipment circuit breakers have to be calculated at 100% of the load continuous. That would mean the circuit breaker would have to be rated at 45amps continuous. Most breakers are not. Most breakers are rated at 80% of their rating for continuous loads. So if you installed a 60 amp circuit, 80% of 60 = 48 amps. This would fit your requirement. That would be a 60amp breaker, with #6 cu conductors.

First HACR is heating, air conditioning,refrigeration. So in other words you could use it on an electric furnace or air conditioning.
IS this the main breaker for the panel? or for and electric furnace. I'm assuming its for the furnace, perhaps back up heat for heat pump. See if there is another disconenct on the furnace, turn it off and see if the breaker resets. IF so you have a short or overload in the furnace.
If' it IS the main for the panel, turn off all the other breakers in the panel, and try to reset the breaker. If that works, turn the other breakers back on one at a time. IF it "POPS" then it is tripping. Don't keep resetting, find the problem.

It sounds like this circuit breaker is worn out and needs to be replaced. good luck

This is a dangerous situation! There is a short in the furnace. It is NOT a breaker problem! You need to check the current draw in the furnace circuit, This requires an Amprobe meter. If you don't have one, contact a technician at once! You have a fire hazard!

Ray