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| Products > Heavy Duty High Power > FAQ |
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FAQ |
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1. Some of TRC's HD-PRO units are called
GFCI's others are called ELCI's. Why the two definitions?
Q. Some of TRC's HD-PRO units are called
GFCI's others are called ELCI's.
A. GFCI's (Ground Fault Circuit Interrupters) are considered personnel protection devices, whereas ELCI's (Equipment Leakage Circuit Interrupters) are considered equipment protection devices.
A. Effectively they work the same way. They both sense unwanted current to ground and shut power off, however, a GFCI (by commonly accepted US standards) must shut power off when it senses current leakage of 6mA maximum, whereas an ELCI can be set to shut off power at almost any current leakage level.
Q. Why not have all devices set to sense 6mA?
A. The main reason is nuisance tripping. The higher the voltage (example: 480V vs. 120V) or the heavier the current (example: 80A vs.15A) the more likelihood of natural leakage. TRC has selected levels that are in line with heavy-duty machinery and applications.
Q. Does that mean that anything over 6mA will not offer human protection?
A. No, what it really means is that personnel protection standards for high current and voltage higher than 120V above ground, have not been established by UL. Consequently, until this issue is addressed, any trip level over 6mA can only be called an ELCI. If a person touches a 120V line (across the line and neutral conductors), approximately 100mA's will flow through their body. An ELCI with a 10 or 30mA trip level will shut off the power long before maximum current is reached.
Q. What trip levels does TRC use?
A. TRC manufactures HD-PRO™ units with trip settings that vary from 6mA minimum to 30mA maximum.
Q. Is tripping at 30mA dangerous to humans?
A. European countries use trip levels of 10mA and 30mA for their personnel protection standards. Both US and European safety experts consider 50 to 60mA's a dangerous current level for human body exposure. The most important question is "how fast will the power shut off once current leakage has started through the human body?". The US standard for allowable trip time is 25mS or less (Europe allows approximately 40mS). All of the TRC units meet the 25mS standard.
Q. Why do the Europeans have a different standard than the US?
A. It is difficult to set up tests that are consistent because of all the variables: The human body varies in size and conductivity, the area of contact and the location of contact with voltage and ground varies, the amount of water or moisture and the amount of minerals in water or moisture varies, and the conductivity of the ground varies. Add to that the varying sensitivity of each person's heart to defibrillate when subjected to 50 or 60Hz of alternating current. UL has taken an ultraconservative approach to personnel protection by setting standards that try to protect the entire population. The Europeans set standards premised on protecting the vast majority or approximately 95% of the population.
A. It would be highly unlikely to have a situation where you would receive exactly 6mA flowing through your body. Generally speaking, the adult body resistance allows approximately 100mA of current to flow when it comes in contact with the line voltage (120V) and a good ground. As the voltage increases (240V - 480V), the current increases proportionally (200mA - 400mA). Whether you detect 6mA or 30mA is not relevant in this situation. Again, what is important is how fast power is removed (less than 25mS or 40mS).
Q. How do you know that is really safe?
A. You don't, all you can do is review history and experience. There will always be degrees of electrical safety, never absolute safety.
Q. Why hasn't UL developed and the NEC adopted a standard for Heavy Duty GFCI's?
A. In July 1995, UL established a new category of electrical devices called Ground Fault Equipment Protection Circuit Interrupters (GFEPCI), subsequently changed to Equipment Ground Fault Protective Devices (EGFPD). For the first time, this category establishes a listing standard for devices that are intended to disconnect the electric circuit from the source of supply when the ground-fault current exceeds the ground-fault pick-up level marked on the device*. This new category allows ground-fault pick-up levels (trip levels) ranging from 6mA to 50mA. The NEC and any OSHA, NFPA regulations may be changed in subsequent years, once the availability of Equipment Ground Fault Protective Devices becomes common knowledge and specific application guidelines can be identified.
Q. Why is TRC putting a product on the market that is not mandated?
A. Although mandates do drive markets, more and more companies consider safety a top priority. No one wants to have an electrical accident that could have been avoided. While no electrical protection product is fail safe, the TRC portable HD-PRO™ series of GFCI/ELCI devices offer substantial personnel shock protection.
Q. You offer a feature called 6.10.30™, when would this feature be needed?
A. Depending on the type of equipment to be protected, the normal leakage to ground may vary. Many users will want to set the trip level high enough that normal leakage will not cause the unit to nuisance trip, but low enough to detect a ground fault that will provide both personnel and equipment protection. Adjustable settings allow the user to select and lock in the optimum trip level at 6mA, 10mA or 30mA.
*Excerpted from: Underwriters Laboratories Subjects 1053(943) letter "New Category for Ground-Fault Equipment Protection Circuit Interrupters (KCZI)" dated July 26, 1995. |
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