No, a standard GFCI receptacle or circuit breaker will not function properly with a 440/120V, 3PH, 3W ungrounded system using two 60V conductors to create 120V. Here's why: GFCI Operation

GFCIs work by detecting an imbalance between the current flowing through the hot conductor(s) and the neutral conductor. If there's a difference, it indicates current is leaking to ground, and the GFCI trips.

Ungrounded Systems

Your system is ungrounded. This means there is no intentional connection to earth. For a GFCI to detect a ground fault, there must be a path for current to flow back through the GFCI sensor. In an ungrounded system, there's typically no such path until a second fault occurs on a different phase.

Two 60V Conductors

Using two 60V conductors to create 120V for the GFCI load further complicates the situation. There is no neutral (grounded conductor) in this configuration. The GFCI requires the presence of a grounded neutral conductor within its internal sensing circuit. Without it, it cannot monitor the differential current flow necessary to detect a ground fault.

Specialized Monitoring

To monitor for ground faults in ungrounded systems, you need specialized ground fault detection or monitoring systems (GFM). These systems typically involve:

Ground Detectors

These devices continuously monitor the insulation resistance to ground. When the resistance drops below a pre-set level, indicating a ground fault, an alarm is triggered. They do not trip a circuit breaker, but alert personnel to investigate and correct the fault.

Ground Fault Relaying

More sophisticated systems use current transformers to monitor for leakage current to ground. These systems can trip a circuit breaker, but they are designed specifically for ungrounded systems and require careful coordination.

Implications



Standard GFCIs won't work

Installing standard GFCIs on your current system will either: not work at all (not trip under fault conditions), nuisance trip (trip randomly), or damage the GFCI device.*

False Sense of Security

Using a GFCI that is not designed to work with your power system will give a false sense of security and will not protect personnel.

Recommendations


Do not install standard GFCIs

They are not designed for your type of ungrounded power system.2.

Consult with Electrical Engineering and Safety Experts

Get advice from qualified electrical engineers or safety consultants experienced in marine electrical systems and, specifically, ungrounded power systems.3.

Install Ground Fault Monitoring (GFM) Systems

Consider installing a proper ground fault detection or monitoring system appropriate for ungrounded systems. The best system will depend on the size of your electrical system, the criticality of the loads, and your overall safety requirements.4.

Regular Insulation Testing

Implement a program of regular insulation resistance testing on your electrical system. This is a crucial preventative maintenance measure for ungrounded systems.5.

Bonding

Ensure proper bonding of all metallic enclosures and equipment to a common ground point to minimize voltage differences in the event of a fault.6.

Training

Make sure your crew is trained on the proper operation and maintenance of ungrounded systems and ground fault monitoring equipment.

In summary, GFCIs are not compatible with your ungrounded 440/120V system. You need to use specifically designed ground fault detection systems and implement a comprehensive electrical safety program. Flag for review