Strube, Dann. Understanding Grounding As a Firesafety Necessity. Fire
Journal. January/February 1989. p. 62+
Abstract: This article explains the importance of grounding systems
and how their malfunction can result in fire. Many insulation failures are
mistakenly identified as short circuits, when they are really ground faults.
A ground fault is a failure between a conductor and a grounded surface.
A short circuit is a failure between two circuit conductors.
When a short circuit occurs, the over-current protection device will
promptly open the circuit, which results in very little damage. A ground
fault can cause much more damage, especially if the equipment is installed
properly. A malfunctioning return path can cause an arcing ground fault
that could continue for a long period of time, eventually igniting combustibles.
This heating can cause insulation of other conductors to fail, causing a
short circuit. Investigators are quick to blame the short circuit for the
fire. However, if the short circuit had occurred earlier, the over-current
device would have opened the circuit, preventing the fire. The real blame
is the ground fault.
The article explains other situations when ground faults result in fires.
In order to prevent this, section 250-251 of the National Electric Code
provides safety requirements for grounding electrical equipment. The ground
path must be permanent and continuous. It must have the capacity to safely
conduct the fault current that will be imposed on it. It must also have
low impedance to limit the voltage and allow the protective devices to operate.
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