Aging happens but fires don't have to...

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It's more likely that an electrical fire will occur in a place you can't easily see, although overloaded cords in contact w combustibles can also present a hazard in plain sight.

Waste heat generated by electrical current can cause wiring hidden within a home's walls to expand and contract, eventually loosening it. Once that wiring is loose, the electricity can arc, with a heat output reaching 1,500 to 1,800 degrees Fahrenheit.  

One benefit of Belleville spring washers includes compensating the effects of thermal cycling by maintaining sufficient bolt load; therefore, reducing hot spots. Heat is produced on electrical connections from the electrical resistance between the conductive material and the bolt. Hot spots occur with the increase of resistance due to the loosening of the joint. The result of a hot spot can be a catastrophic failure.

Another condition that Belleville's compensate for is creep. Properly used Belleville's maintain the desired load, despite any conductor creep and, again, reduce the opportunity for a failure.

Electrical connections may loosen because of embedment relaxation, which over time causes microscopic high points on both the threads and mating surfaces of the connection to relax. Belleville springs counteract the effects of embedment relaxation.

Vibration is another factor that can loosen bolted electrical connections that don’t include Belleville spring washers. The Belleville acts as a shock absorber by maintaining a constant sufficient load on the connection.

Thermal cycling, creep, and embedment relaxation are no match for Belleville springs. Quality Belleville springs will keep bolted connections tight!

The temperature of an electrical arc can be hotter than the surface of the sun.

That's more than enough to ignite wood or old insulation under normal circumstances, but in San Francisco,  Inside a house in dry months, the relative humidity within the walls can drop to that of the average desert, turning studs -- wooden wall supports -- into kindling, easily ignited by an arcing current.

Here we arrive at one of the problems with electrical fires: By the time you see smoke coming out of your outlet, a fire has most likely already begun and is spreading out of sight within your walls and up to your attic. It's easy for a homeowner who has turned off the power to a burning socket to think that they've taken care of the problem. But an unseen fire may already be building beyond the outlet.

Even worse, electrical fires can be particularly tricky to put out. Since they involve electricity, using water to put out the fire can cause electrocution. Chemical powders can cause the fire to smolder then reignite. 

TFCI thermal fault outlets protect "glowing connection".

Top Causes of Arc Faults

• Loose or improper connections, such as electrical wires to outlets or switches
• Frayed appliance or extension cords
• Pinched or pierced wire insulation, such as a wire inside a wall nipped by a nail or a chair leg sitting on an extension cord
• Cracked wire insulation stemming from age, heat, corrosion, or bending stress
• Overheated wires or cords
• Damaged electrical appliances
• Electrical wire insulation chewed by rodents

GFCI protects people from electric shock. AFCI protects against electrical fire. Both together provide very thorough  protection for the system. Adding TFCI (thermal fault as above) is the most complete protection available today.