GFCI-breaker limitations
Ground Fault Circuit Interrupter (GFCI) devices are designed to protect people from electrical shock by interrupting the flow of electricity when the device detects a ground fault. The UL 943 standard sets the requirements for different classes of GFCI devices such as how often self-testing is required and define a “trip curve” that establishes a relationship between minimum time to interrupt. Ground fault protection can be achieved using multiple different types of devices, the most common of which are GFCI circuit breakers and GFCI receptacles. However, there are some limitations to using GFCI breakers that you should be aware of that can often lead towards using external GFCI devices, GFPE devices, or other residual current monitors.
Location (breaker panel vs. adjacent to device)
Sometimes breaker panels are not the ideal location for a GFCI or device, such as cases where alarm indicators and access to any test/reset functions are best to have mounted directly adjacent to the device or receptacle that is being protected. Breaker panels are often in service rooms or areas that have restricted access, whereas external GFCI devices can mounted anywhere between the breaker panel and the target device/receptacle.
Analysis/communication
Most GFCI breakers are simple devices and do not have any features to support advanced analysis. External GFCIs and Residual Current Monitors can be a better choice in some situations because they often include features to support deeper fault analysis or useful information for preventative maintenance. Examples include on-device displays like those available on the Bender RCM420 and RCMS490-D, locally stored fault or residual current history, or communication ports for passing status and history to controllers, computers, or SCADA systems. Many Bender residual current monitors can be used with advanced communication capability when paired with COMTRAXX devices like COM465IP.
Drawing 1: MarinaGuard diagram paired with multiple Bender devices
In the diagram above, we see an example of how multiple Bender devices such as RCMS490, RCM410R, RCM420, and MarinaGuard can communicate data. These devices can report out to a dedicated display like the CP9xx...i Series devices or utilize a COM465IP to connect to a wider network over ethernet.
3-phase power or high amperage loads
Some application where NEC requires GFCI protection such as commercial kitchens often require electrical equipment with higher amperage ratings or 208V 3-phase power. Unfortunately, GFCI breakers are usually only compatible with loads under 50 amps and single-phase voltage sources. In such cases, external GFCI devices with higher amperage ratings would be more appropriate.
Adjustability
Though GFCIs require strict compliance to a standardized trip curve, some applications (that are not required to use a GFCI by NEC) are better served by GFPE (Ground Fault Protection Equipment). GFPE devices devices such as the LINETRAXX RCM410R-2 conform to the UL1053 standard and are primarily for equipment protection over personnel protection. Because of this, there is more flexibility in the trip and/or alarm characteristics including the option to have adjustable trip levels and time delays. Adjustable residual current trip levels can allow fine-tuned protection to a particular application or the flexibility for one type of device to cover a broad range of systems. The ability to adjust time delays can also eliminate race-conditions when multiple ground fault monitoring devices are used in a single system. This scenario is a common in dock and marina applications and can be addressed using devices like the MarinaGuard.
Nuisance tripping
GFCI breakers can trip frequently due to various reasons such as too many appliances being protected by the GFCI or wire length being too long (creating high leakage capacitance) for the equipment being protected by the GFCI. Since GFCI breakers are compact and low cost, they often cannot have particularly advanced filtering capability compared to external GFCI devices, GFPE devices, or other residual current monitoring devices. It is important to minimize nuisance tripping not just to prevent unnecessary downtime, but for safety reasons as well – as frequent tripping may lead some to disable/remove the ground fault protection completely, which exposes personnel to danger and possibly violating National Electrical Code (NEC).
In conclusion, GFCI circuit breakers offer an inexpensive and simple way to add GFCI protection to a circuit or system, but they also have several limitations that often result in other solutions being superior.