Electrical Fires

We all know that in order to make a call on a fire we need to identify a heat source , a fuel source and an event or person that brought the two together. Often in the absence of other causes many company officers and investigators want to lean toward either electrical or careless smoking as causes. To better understand what CAN cause an electrical fire here is some basic electric theory. First definitions:
Voltage is electrical pressure that moves the electron through the conductor. Think of it as PSI.
AMPS is the rate at which they flow (current) or GPM.
OHMS is the opposition to current flow or Resistance.
Watts is the quantitative measure of how much work was done or power used.

Next we need to look at how to apply this knowledge to determine if an overloaded circuit or resistive heating situation could exist. Ohms law and Joules law can be used to figure out if we are in excess of what the system can hold.

Ohms law: E (volts)= R (resistance) X I (Current)
Joules law: W (Watts) = I (Current) X E (volts)

A simple calculation may work like this: You find that a space heater was plugged into one of the cheap brown extension cords at the point of origin. By obtaining an exemplar you know it is rated for 13 amps. The heater was a 1500 Watt heater and we know that household current is 110 volts. (AC current is just that alternating it averages out to be 110V but can be 100-120Volts) Using Joules law we can determine if too much current was flowing through the extension cord. 1500 Watts / 120 Volts = AMPS

12.5 AMPs through a 13 amp cord. This would not be a competent heating source. Now add the lamp and TV into the same cord you can see how you can begin to prove your theory using the laws of electricity. Remember that resistive heating occurs over time.
Always check electrical systems with your own meter NEVER trust that it's been shut off.

Stay safe...
dave