tractor fires and block heaters ?

my thoughts are (and with experience) are that the fires actually start at the connection between the extension cord and the heater cord. When the connection starts getting a little corroded or worn, or maybe a little tarnish on the spades so the current doesn't travel through quite so good, heat is created, then that heat makes the connection even worse, thus more heat, until eventually sparks or melting and fire. In my case, the cord connection was right above the batteries, near a little engine grime, and up above the fuel tank, all good contributors to fire. I would guess that the higher the wattage, the more prone to starting a fire the heater would be. I think that the reason a tank heater starts less fires, is simply because tank heaters usually have a longer cord on them, and it is routed to where the end is in a not such a fire vulnerable spot. Therefore if the cord end gets hot and burns off in an area where there is nothing to burn, it simply burns off and probably falls clear, or blows a breaker. Just my 2 cents worth, Darrel

The heaters themselves don't usually catch fire unless all the coolant is gone; still will go to ground and pop a circuit before a fire.  As Darrel points out the connections get corroded or weakend and then heat develops, on the gas tractors it is worse as fuel fumes are ignited fairly easily.

I think one of the trouble spots is where the cord connects to the heating element. The insulation there gets hard with age because of the proximity to heat. And probably wasn't rated for being in an environment that hot whether from heater or from normal engine heat. That enviroment runs near 90 degrees C and much common wire is only rated for 60 degree C max and most of the time is expected to warm up close to that rating simply from current in a people comfortable environment. Wire can be had with silicone insulated rated at 200 C and would be better for that application. And then with more difficulty the conductor should be on the large side. For a 1 kW heater, 12 isn't too large with the high temperature 10 would be better. 10 probably can't be connected directly to the heating element, the makers didn't plan that far.

Oh yah, that old hardened insulation then falls off and lets there be shorts or the wire to flex more and break off strands to cause a local hot spot. I've see that happen to an old electric clock with a rubber insulated cord. The fire was starting when my mom noticed it just as we were about to go out the door. That electric clock was probably only 3 watts but always on and the rubber was old and hard. The much higher operating temperature of the block heater speeds up this process with old insulation.

One of my consulting cases involved the death of the user of an electric blanket where the blanket got folded and the low temperature rated cord from the controller got in the fold. The insulatiion softened and the wires touched and the arcs ignited the blanket while he was sleeping.

When a plug or a receptacle warms up more than the wire, its time to unplug it, and cut the offending end(s) off and turn them to scrap. Much stuff made these days is made of inferior materials cut much thinner than what passed UL tests and the result is heat that takes the temper off the spring brass, if there ever was any. The modern makers also know how to save materials cost by using fatter insulation on thin almost copper conductors. And the only way we can be sure of getting the copper we paid for is to cut the cord apart or run it to rated current and check how it warms up.

Gerald J.