GFCI Receptacles and GFCI Circuit Breakers - Nuisance Tripping Concerns
GFCI Receptacles and GFCI Circuit Breakers - Nuisance Tripping Concerns
(OP)
Another engineer just performed a punch list inspection with the electrical contractor for a project that we recently completed. The contractor informed him that the GFCI receptacles serving the electric water coolers, which are required to be GFCI-protected as of the 2008 NEC, were frequently tripping. The issue was allegedly resolved by installing standard receptacles in conjunction with GFCI circuit breakers. There are several things that I don't understand.
1. How common is GFCI nuisance-tripping on small refrigeration equipment and other fractional horsepower motor loads? In addition to electric water coolers, the NEC now requires GFCI protection for vending machines and many other appliances. Furthermore, all 120-volt receptacles in commercial kitchen facilities, which often contain refrigerators, ice makers, etc. - require GFCI protection. It was my understanding that older GFCI and AFCI devices were subject to nuisance tripping on these types of loads, but I thought these issues were resolved by manufacturers long ago.
2. Why would a GFCI breaker necessarily be less prone to nuisance tripping? When considering leakage current via shunt capacitance, one would think that the reverse is true. I believe SquareD recommends a maximum one-way circuit length of 200 feet for their GFCI breakers. In a scenario in which I had an electric water cooler or similar appliance located more than 200 feet from its source panelboard, what would be the best strategy to provide reliable GFCI protection?
3. Are some GFCI receptacles less prone to nuisance-tripping than others? Are there certain manufacturers that anyone can recommend (or not recommend)?
4. How likely is it that the electric water coolers are simply defective? I believe they're all brand new, in excellent condition, and installed properly.
Thanks in advance for any input provided!
1. How common is GFCI nuisance-tripping on small refrigeration equipment and other fractional horsepower motor loads? In addition to electric water coolers, the NEC now requires GFCI protection for vending machines and many other appliances. Furthermore, all 120-volt receptacles in commercial kitchen facilities, which often contain refrigerators, ice makers, etc. - require GFCI protection. It was my understanding that older GFCI and AFCI devices were subject to nuisance tripping on these types of loads, but I thought these issues were resolved by manufacturers long ago.
2. Why would a GFCI breaker necessarily be less prone to nuisance tripping? When considering leakage current via shunt capacitance, one would think that the reverse is true. I believe SquareD recommends a maximum one-way circuit length of 200 feet for their GFCI breakers. In a scenario in which I had an electric water cooler or similar appliance located more than 200 feet from its source panelboard, what would be the best strategy to provide reliable GFCI protection?
3. Are some GFCI receptacles less prone to nuisance-tripping than others? Are there certain manufacturers that anyone can recommend (or not recommend)?
4. How likely is it that the electric water coolers are simply defective? I believe they're all brand new, in excellent condition, and installed properly.
Thanks in advance for any input provided!






RE: GFCI Receptacles and GFCI Circuit Breakers - Nuisance Tripping Concerns
Mike Halloran
Pembroke Pines, FL, USA
RE: GFCI Receptacles and GFCI Circuit Breakers - Nuisance Tripping Concerns
Bill
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"Why not the best?"
Jimmy Carter
RE: GFCI Receptacles and GFCI Circuit Breakers - Nuisance Tripping Concerns
A couple of theories: GFCI current sensors in receptacles, being smaller than breakers, may have magnetics that saturate more easily from motor start currents. Or, motor start capacitors may have some capacitance to ground that causes trips. Although this case would seem to cause nuisance trips for either receptacles or breakers equally.
RE: GFCI Receptacles and GFCI Circuit Breakers - Nuisance Tripping Concerns
The problem is not leakage or water in the devices. It is about increased capacitive currents due to high-frequency contents in the motor voltage. That current comes eventually from the grid (rectified in the inverter's grid rectifier) and therefore cannot be distinguished from "true" ground faults.
The same thing happens on a smaller scale if there are frequency inverters connected to the PCC. HF pollution is spread from the PCC to all outlets and there, HF currents are flowing through cable and motor capacitances to ground. This indirect "ground current" is orders of magnitudes lesser than the current measured on inverter supply lines. But still problematic enough to cause nuisance tripping.
Improved filters between inverters and grid often helps. Sine-wave inverters always helps.
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: GFCI Receptacles and GFCI Circuit Breakers - Nuisance Tripping Concerns
Other than that, I suspect Gunnar is correct (as usual) in his assessment.
RE: GFCI Receptacles and GFCI Circuit Breakers - Nuisance Tripping Concerns
It's pretty rare that we design a 120-volt receptacle circuit with a one-way length exceeding 200 feet, but it does happen on occasion when we are faced with unusually stringent requirements (from an architect, interior designer, or some other building design professional) regarding where we place subpanels.
RE: GFCI Receptacles and GFCI Circuit Breakers - Nuisance Tripping Concerns
I'm glad you mentioned "specification grade" receptacles, because I've been wondering about that for quite some time! What does it mean, exactly? I do know what hospital grade receptacles are, but, in terms of build quality and features, I'm not sure about specification grade.
RE: GFCI Receptacles and GFCI Circuit Breakers - Nuisance Tripping Concerns
For receptacles, Hubbell has been the accepted quality standard that everyone else tries to compete against, even going so far as to copy the Hubbell model numbers.
Hospital grade is different. These have specific requirements for insertion and removal force. I would never specify these except in patient care areas. People hate them.