You're looking for a ground fault detection system for a single-phase, ungrounded (often called "floating") power system, similar in concept to those used on three-phase ungrounded systems, but designed for two lines. These are less common than the three-phase versions, but they do exist.Here's a breakdown of how they work and where to find them

How it Works (Concept):

The principle is the same as with three-phase ungrounded systems:1. Artificial Neutral (or Neutral Point)

Since an ungrounded system doesn't have a neutral, a ground fault detection system needs to create a reference point to measure voltage against. This is usually done with resistors.2.

Resistor-Based Voltage Division

Two identical resistors are connected in series between L1 and L2. The midpoint of these resistors creates a pseudo-neutral, which is then connected to ground through a monitoring device (usually a sensitive relay or a high impedance voltmeter).
3.

Ground Fault Detection



Normal Operation

In a healthy system, the voltage between this pseudo-neutral and ground is close to zero. Both L1 and L2 are "floating" at some voltage relative to ground, but the resistors create a balance.

Ground Fault

If a fault occurs from L1 or L2 to ground, the voltage between the pseudo-neutral and ground will increase. The magnitude of the increase depends on the fault resistance and the value of the resistors used to create the pseudo-neutral.4.

Alarm/Indication

The monitoring device (relay or voltmeter) is set to trigger an alarm (light, buzzer, relay contact closure, etc.) when the voltage between the pseudo-neutral and ground exceeds a certain threshold. The threshold is set to be sensitive enough to detect a ground fault but not so sensitive that it triggers false alarms due to normal system capacitance or leakage.

Why Use High Impedance?

The resistors used in this type of system are typically high-impedance. This is for several reasons: Limiting Fault Current

The high impedance limits the fault current that flows if a ground fault occurs. This is desirable in ungrounded systems because it allows the system to continue operating, even with a ground fault present (although you must find and fix the fault promptly). The fault current is low enough to avoid damage.

Preventing Arc Flash

By limiting the fault current, the risk of arc flash is reduced.

Measuring Actual Voltage

A high impedance, high sensitivity voltmeter is required to detect a ground fault without shorting the circuit, which would cause an arc flash.

Why is it Different than a GFCI? GFCI

GFCIs measure the difference in current between the line and neutral conductors. If the current isn't balanced (i.e., some current is leaking to ground), it trips. GFCIs are designed to protect people from shock.

Ungrounded Ground Fault Detection (as you're asking about)

This is designed to detect the presence of a ground fault without interrupting power. It's intended to protect equipment and to allow the system to keep running (at least temporarily) while the fault is located and repaired. It's a warning system, not an immediate trip system.

Where to Find Them (Manufacturers/Suppliers)

Finding pre-packaged, off-the-shelf units for single-phase ungrounded systems can be tricky. Here are some options, ranging from the most likely to the least:1.

Custom Panel Builders/Electrical Engineering Firms

This is often the best route. Look for companies specializing in custom control panels or electrical systems for industrial applications, especially those with experience in ungrounded systems. They can design and build a system tailored to your specific voltage, current, and sensitivity requirements. Explain that you need a ground fault detection system for a 1-phase, 2-wire ungrounded power system. They will assemble the resistors, relay, and indicator lights into an enclosure.2.

Look for High-Resistance Grounding (HRG) Systems

While typically used on three-phase systems, you can often adapt the principles and components of an HRG system for a single-phase application. You would essentially be using only one phase of the HRG system. Companies that make HRG systems often offer customization options. Search for terms like: "High Resistance Grounding Systems" "Ungrounded Ground Fault Detection" "Neutral Grounding Resistor (NGR) Systems" (although, again, you'd be adapting the components). Be prepared to explain that you need it for a single-phase, two-wire ungrounded system.3.

Companies to Contact

(Based on their general offerings; you'll need to confirm suitability for single-phase ungrounded):

Littelfuse

They have ground fault relays and protection devices. Check their catalog and talk to a sales engineer.

Eaton

They offer ground fault protection relays. Again, check their specs carefully and confirm suitability.

Schneider Electric

Similar to Eaton and Littelfuse; check their catalog.

Post Glover Resistors

They manufacture high resistance grounding resistors, which is a key component. You'd need to integrate it with a relay and indicator.

Mersen (Ferraz Shawmut)

They offer ground fault protection devices.

Bender

Bender specializes in ground fault monitoring, but their products may be more geared towards isolated power systems in hospitals. Still worth checking.4.

DIY (If You Have Expertise)

If you have a strong electrical engineering background, you could design and build the system yourself, sourcing the resistors, relay, and indicator lights separately. This is not recommended unless you are highly qualified. It involves working with potentially dangerous voltages and currents.

Important Considerations When Specifying/Designing



System Voltage

The L1-L2 voltage of your system is critical for selecting the correct resistors and relays.

Fault Current Limit

Determine the maximum fault current you want to allow to flow in the event of a ground fault. This will influence the resistor value. A common value is 5mA.

Sensitivity

How sensitive do you need the detection to be? Lower resistance values will allow you to detect smaller ground faults, but they will also allow higher fault currents.

Relay/Monitoring Device

Choose a relay or voltmeter with an appropriate input voltage range and sensitivity. Look for devices with adjustable trip points.

Indicator Lights/Alarm

Select appropriate indicator lights or an audible alarm to alert personnel to the ground fault.

Enclosure

Enclose the components in a suitable enclosure (NEMA rated if necessary).

Safety

Proper grounding and wiring practices are essential for safety. Always* disconnect power before working on electrical equipment. Consult with a qualified electrician.

In summary, finding a ready-made, off-the-shelf ground fault detection system for a single-phase, ungrounded power system is not as straightforward as for a three-phase system. Your best bet is to work with a custom panel builder or an electrical engineering firm experienced in ungrounded systems. Be prepared to provide them with detailed information about your system's voltage and current requirements. Flag for review