A parallel fault is one in which there is a conduction path created between the phase and neutral conductors, between the phase conductor and ground (ground fault), or both.  Parallel faults are generally considered to be the most common type of fault.

There are three stages in the evolution of a parallel fault:
1. Leakage – Leakage currents will occur normally and safely in any cord set, related to the capacitance of the cable and the resistance of the insulation.  As long as the insulation is in good condition, small leakage currents are considered harmless and safe.
2. Tracking – As insulation degrades or becomes damaged over time, a conductive path may develop over the insulating surface.  This condition, known as tracking, may actually exacerbate insulation degradation.
3. Arcing – Arcing is the final stage in this process, where ionization of the air across the insulation gap occurs, providing a conduction path between live parts.  This arc generates intense amounts of heat leading to combustion.

Degradation can also occur internally to the insulation medium due to excessive heat.  Fire may start from either combustion of surrounding materials or the insulation itself, even in the absence of arcing.

A Ground Fault Circuit Interrupter is a LCPD specifically intended for the protection of people from shock hazard.  A GFCI is a device that will immediately stop the flow of electricity if it senses any voltage loss, whether the loss is through the ground wire or to your body.  It is a very superior device when compared to ground wires alone for protecting people against electric shock.  It works like this: Current normally flows from the black wire through the smaller of the two flat prongs on the plug.  Then it returns through the white or “neutral” wire flowing through the larger of the two flat prongs.  The GFCI measures the voltage flow at the incoming hot and at the outgoing neutral.  If there is any imbalance in these two measures, the circuit will be immediately tripped.  A difference as small as four or five milliamps is all that is required to stop the current flow.  The current is tripped in a fraction of a second, varying from one twentieth to one fortieth of a second’s time.

Based upon medical research, UL has specified the amperage trip levels for GFCI’s to be in the range of 4-6mA.  The lower bound exists to limit nuisance tripping since there is a level of leakage that would be considered both normal and acceptable. See our Shock Shield® product line.

A temporary receptacle is one that you might find at the end of an extension cord.  That receptacle is not part of the permanent wiring of the building and the cord would then need a GFCI.

There are a few key alternatives to consider in specifying the right GFCI for your application.  The primary areas are performance, configuration, load type(s), and environment.

When it comes to performance, all GFCI’s are not alike.  The first issue is the response to power interruption.  For applications where power tools are involved (such as temporary wiring), a manually resetable design is preferable.  One can easily see the risk associated with the unexpected restoration of power when a worker is handling a drill, saw, or other power tool.   See our Shock Shield® product line.   The only applications where an automatic restart upon return of power is preferred are unattended operation where damage to the load will occur if power is not restored.  This includes spas and freezers.  This automatic restart feature helps keep the spa hot and avoids spoilage of food in the freezer application.  See our Shock Shield® Auto Reset product line.   All units require a manual reset after a ground fault trip has occurred.

The trip setting of a GFCI is a nominal 4-6mA.  They are also available as equipment protection with higher trip settings, which may be desirable for applications with a high inherent leakage current such as heat tape and high current loads.  These devices are known as equipment leakage circuit interrupters, or ELCI’s.  See our Shock Shield® User Attachables, ELCI Panel Mount, and HD-PRO products.

Portable GFCI’s are available as a plug adapter or as a user-attachable product for 15 and 20 Amp cords.  They can be either part of the plug or attached in line with the standard cord sets.  It is critical that the GFCI be located near the plug so the entire cord is protected, not just the outlet(s).

They are also available as complete cord sets in lengths up to 100 feet for ratings as high as 40A/240V on single-phase applications.  The optional output connectors include a molded plug, a three outlet power block (commonly called a tri-cord), a quad box, or a mechanical connector. GFCI’s are now available in panel mount configuration to allow for bulkhead mounting.  The high current devices are typically supplied with two feet of cable on the input and output to allow for easy installation in a control panel.

The typical load or loads is critical.  This not only dictates the restarting design after a power outage, but also the output connector configuration.

The final item is the environment.  GFCI’s are normally used outdoors in direct light, heat, and cold.  Protection of the electronics and the connections is critical.  Use of silicon sealant has outperformed other means of weatherproofing such as grommets, which are prone to degradation in time in these harsh environments.