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Fire hazard in your home

 

Burned house exterior

KDE Electric is highly experienced with burned-out residences due to fires, for in the last twelve months we rewired six houses that were completely burned because of electrical failures. Most of our experience comes from dealing with service panels that lose the grounding system during time, due to rusting (oxidation) and house vibrations. The old panel (especially the round fuses type Edison, see bellow picture) is a potential fire hazard.

If a panel looses its ground, the neutral circuit will stay at a higher voltage other than zero. The neutral point from the panel will then be at higher voltage than the neutral point from the utility transformer due to the impedance of this circuit.

We soon found that the neutral point in the house panel could be up to 40 Volts when measured beside a good ground. It becomes a shock hazard and a fire hazard because the circuit breaker will now stay loaded at a different voltage, (40V smaller in our example) than the nominal (120V or 240V).

Burned house interiorIn case of overload or short circuit, it will not trip or will trip later and not in the nominal time range. In this case, the circuit is overloaded, heating all the elements from it, and finally, when the insulation between wires is destroyed, the fire occurs.

Burned house floor

Another potential fire hazard is the old metal clad cables that don’t have the ground wire incorporated in them. This type of cables exist most often in old houses built before 1950. They are a potential fire hazard due to the fact that the metallic spiral becomes so rusted through the years,that the metallic shield does not consist of a shield like a pipe anymore.

Instead, it is like a continuous spiral inducing a lot of inductance in the grounding circuit in case of a short circuit. This shield inductance is an electric barrier when it comes to tripping the breaker.

The breaker will not have enough current to be tripped, and if this spiral cable touches another spiral cable or a metal pipe, then the difference in voltage between such a bad cable and a good metal cable will end up acting like a resistor heating up the point of contact until everything will burn out.

To us, these metallic spiral cables that are not longer the metal-clad (MC) type are the cause of all fires. In the picture at right we had such a fire. Here we see the starting point of the fire in the house. When two of this tree cable touched the fire was evident. The problem with this type of cables in homes is that they are very difficult to be removed.

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