Ground Fault Inspection Testing

Global Power Services is certified to conduct GFI inspections in Los Angeles and San Diego County and surrounding areas. Los Angeles and San Diego County requires testing companies or laboratories to be certified with their respective department of building and safety, to perform ground fault equipment testing and calibration.

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Los Angeles County
Department of Public Works Building and Safety Division
 900 S. Fremont Avenue
Alhambra, CA 91803

LAC Testing Company Cert. Doc.

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San Diego County
Department of Building and Safety
 5201 Ruffin Road
San Diego, California, 92123
858-565-5920

SDC Testing Company Cert. Doc.

NEC Testing Requirements

The National Electrical Code® (NEC® ) has specific ground fault equipment protection requirements in 215.10, 230.95, 240.13 and 517.17. Ground fault relays (or sensors) are used to sense low magnitude ground faults. When the ground fault current magnitude and time reach the G.F. relay pick up setting, the control scheme signals the circuit disconnect to open.

NEC 70, Article 230.95
Ground-Fault Protection of Equipment

Ground-fault protection of equipment shall be provided for solidly grounded wye electric services of more than 150 volts to ground but not exceeding 1000 volts phase-to-phase for each service disconnect rated 1000 amperes or more. The grounded conductor for the solidly grounded wye system shall be connected directly to ground through a grounding electrode system, as specified in 250.50, without inserting any resistor or impedance device.

The rating of the service disconnect shall be considered to be the rating of the largest fuse that can be installed or the highest continuous current trip setting for which the actual overcurrent device installed in a circuit breaker is rated or can be adjusted.

NEC 70, Article 517.17
Ground-Fault Protection

(C) Selectivity. Overcurrent Ground-fault protection for operation of the service and feeder disconnecting means sh all be fully selective such that the feeder device, but not the service device, shall open on ground faults on the load side of the feeder device. Separation of ground-fault protection time-current characteristics shall conform to manufacturer’s recommendations and shall consider all required tolerances and disconnect operating time to achieve 100 percent selectivity.

(D) Testing. Overcurrent When equipment ground-fault protection is first installed, each level shall be performance tested to ensure compliance with 517.17(C).

Ground Fault Protection (GFI)

Ground Fault Protection (GFP)

Description:
Ground Fault Protection (GFP), commonly known as GFI protection, is designed to detect and interrupt ground faults in an electrical system, minimizing the damage to electrical equipment when low-level phase current returns to the supply transformer through a ground-return path.A ground fault occurs when a current travels outside its intended path, such as when electricity flows directly to the earth or to a grounded part of the system. This can happen due to insulation failure, conductive dust, moisture, or damage to electrical components. Ground faults pose serious hazards, including fire risk, equipment damage, and electric shock.

How Does it Work:
Ground fault protection devices monitor the balance of current in a circuit. In a perfectly balanced circuit, the current flowing into the circuit should equal the current flowing out. Any imbalance suggests a leakage current, indicating a ground fault. Common ground fault protection devices include Ground Fault Circuit Interrupters (GFCI) and equipment with integral ground fault protection like certain types of circuit breakers.

GFCI:
Ground Fault Protection should not be confused with GFCI’s which are designed to prevent shock by tripping at the 5-mA level on single-phase systems. Ground fault protection does not protect people from electrical shock, it does not prevent ground faults from happening, and it does not protect a system against high-level faults. High-level faults must be cleared by fuses or by circuit breakers which limit the energy let through to the fault.

Test Procedure
Visual and Mechanical Inspection:
  1. Compare equipment nameplate data with drawings and specifications.
  2. Inspect physical and mechanical condition.
  3. Inspect anchorage and alignment.
  4. Verify the unit is clean.
  5. Operate the circuit breaker to insure smooth operation.
  6. Inspect operating mechanism, contacts, and arc chutes in unsealed units.
  7. Perform adjustments for final protective device settings in accordance with the coordination study.
Insulation Test:
  1. Perform insulation-resistance tests on each pole, phase-to-phase and phase-to-ground with the circuit breaker closed, and across each open pole.
    1. Phase conductor to adjacent Phase conductor
      (A-ph & B-ph, B-ph & C-ph, C-ph & A-ph)
    2. Phase to Ground Bus
      (A-ph & ground, B-ph & ground, C-ph & ground)
    3. Line-side Phase to Load-side Phase
      (A-ph & neutral, B-ph & neutral, C-ph & neutral)
  2. Test voltage shall be applied to each conductor for one minute.
    3. Neta Table 100.1
    NETA Table 100.1 shows recommended minimum test result values
  3. *Perform insulation-resistance tests on all control wiring with respect to ground. Applied potential shall be 500 volts dc for 300-volt rated cable and 1000 volts dc for 600-volt rated cable. Test duration shall be one minute. For units with solid-state components, follow manufacturer’s recommendation.
Contact Resistance Test:
  1. Perform a contact/pole-resistance test.
  2. Compare bolted connection resistance values to values of similar connections. Investigate values which deviate from those of similar bolted connections by more than 50 percent of the lowest value.
  3. Micro-ohm or dc milli-volt drop values shall not exceed the high levels of the normal range as indicated in the manufacturer’s published data. If manufacturer’s published data is not available, investigate values that deviate from adjacent poles or similar breakers by more than 50 percent of the lowest value.
Electrical Test Procedure
  1. Determine ground-fault pickup and time delay by primary current injection.
    Ground fault pickup values shall be as specified, and the trip characteristic shall not exceed manufacturer’s published time-current tolerance band.
  2. Verify neutral CT (current transformer) polarity

Low Voltage Circuit Breaker Ground Fault Sensing

Current Transformers (CTs):
Ground fault sensing in low voltage circuit breakers typically involves three or four current transformers (CTs) that monitor the current flowing through the circuit's phase conductors and the neutral wire. The CTs measure the current in each phase conductor and potentially the neutral conductor. In an ideal scenario with no ground faults, the sum of the currents in a three-phase system should equal zero — what comes in must go out. This is based on Kirchhoff's Current Law.

Electronic Trip Unit:
This is the brain of the circuit breaker, which receives inputs from the CTs. It continuously monitors the currents and uses programmed algorithm to decide when to trip the breaker based on the sensed current conditions.

The electronic trip unit uses the residual method, calculating the vector sum of the currents measured by the CTs. In a balanced, no-fault condition, this sum should be zero.

\( \Large I_{a}+I_{b}+I_{c} = I_{n} \)

\( \Large I_{a}+I_{b}+I_{c}- I_{n} = 0\)

trip units allow for adjustment of the ground fault detection settings, including the trip threshold and delay. These settings can be finely tuned to balance between sensitivity (to quickly detect and respond to real faults) and selectivity (to avoid nuisance tripping from transient imbalances or non-hazardous events).

The ground fault pickup settings are usually a multiple of the current sensor rating (CT or ln), in steps of 0.1 xCT.

The maximum GF pickup value is limited to 1200 A per UL standard.

Trip Mechanism Activation:
Once an imbalance is detected and if this imbalance exceeds a pre-set threshold (indicative of a ground fault), the electronic trip unit triggers the tripping mechanism. This mechanism physically opens the breaker contacts, interrupting the circuit and isolating the affected portion to prevent damage and ensure safety.

Common Breaker GFI Failures

Reverse Polarity (Residual System)

Reverse polarity in current transformers (CTs) can indeed arise from two main scenarios: A physically flipped CT or the reversed secondary wiring connections . Both scenarios disrupt the accurate sensing and measuring of currents, which are critical for protection devices like circuit breakers to function correctly. Here’s a breakdown of how each can cause reverse polarity:

Direction of Current
When installing current transformers, it's crucial to adhere to the directional markings on the CT casing. These markings typically include a solid dot or specific terminal labels such as P1 and P2.

The P1 terminal should face towards the incoming power source, which means that current enters the CT from this side. The P2 terminal should face towards the load, indicating the direction in which the current exits the CT.

In a properly installed ground fault system, both phase current and neutral return current vectors summing up to equal zero

\( \Large I_{a}+I_{b}+I_{c}= I_{n} \)

\( \Large I_{a}+I_{b}+I_{c}- I_{n} = 0 \)

In a system with a flipped CT or reversed neutral CT polarity, both phase current and neutral return current vectors will sum up to a non-zero sum value even in a fault-free conditions or cause a zero-sum when a fault exists

\( \Large I_{a}+I_{b}+I_{c}+ I_{n} \ne 0 \)

Bonding Jumper

Purpose
The switchboard bonding jumper connects the metal frames and enclosures of switchboards and other electrical equipment to the system ground. This ensures electrical continuity, which is essential for t he safe operation of the electrical system.

NEC 70E-2024, 250.30(A)(1)(b)
NEC requires the system bonding jumper–when installed at the first disconnecting means–to connect the grounded conductor to the:

  • Supply-side bonding jumper
  • Metal enclosure of the disconnecting means
  • Equipment grounding conductor(s)

Purpose
Misplacement or incorrect installation of a bonding jumper can significantly compromise ground fault protection in an electrical system. If the bonding jumper is misplaced, several key issues can arise, impacting safety and system reliability. Here’s how ground protection can be affected:

Ineffective Neutral Current Path
If the bonding jumper is placed on the load side of the neutral CT, this could result in currents flowing through unintended paths, such as the structural steel of a building or piping systems. The Breaker will sense a smaller magnitude of return current, resulting in slower operation or failure of protection devices to trip in case of a fault.

NETA Test Procedure
Ground-Fault Protection Systems, Low-Voltage
Acceptance Testing
A. Visual and Mechanical Inspection
  1. Compare equipment nameplate data with drawings and specifications.
  2. Inspect the components for damage and errors in polarity or conductor routing.
    1. Verify that ground connection is made on the source side of the neutral disconnect link and on the source side of any ground fault sensor.
    2. Verify that the neutral sensors are connected with correct polarity on both primary and secondary.
    3. Verify that all phase conductors and the neutral pass through the sensor in the same direction for zero sequence systems.
    4. Verify that grounding conductors do not pass through the zero sequence sensors.
    5. Verify that the grounded conductor is solidly grounded.
  3. Verify the unit is clean.
  4. Inspect bolted electrical connections for high resistance using one or more of the following methods:
    1. Use of low-resistance ohmmeter in accordance with Section 7.14.B.1.
    2. Verify tightness of accessible bolted electrical connections by calibrated torquewrench method in accordance with manufacturer’s published data or Table 100.12.
  5. Verify correct operation of all functions of the self-test panel, if applicable.
  6. Verify that the control power transformer has adequate capacity for the system.
  7. Set pickup and time-delay settings in accordance with the settings provided in the owner’s specifications. Record appropriate operation and test sequences as required by NFPA 70, National Electrical Code, Article 230.95.
B. Electrical Tests
  1. Perform resistance measurements through bolted connections with a low-resistance ohmmeter, if applicable, in accordance with Section 7.14.A.4.1.
  2. Measure the system neutral-to-ground insulation resistance with the neutral disconnect link temporarily removed. Replace the neutral disconnect link after testing.
  3. * Perform insulation resistance test on all control wiring with respect to ground. Applied potential shall be 500 volts dc for 300-volt rated cable and 1000 volts dc for 600-volt rated cable. Test duration shall be one minute. For units with solid-state components or control devices that cannot tolerate the applied voltage, follow manufacturer’s recommendation.
  4. Perform ground fault protective device pickup tests using primary injection.
  5. For summation type systems utilizing phase and neutral current transformers, verify correct polarities by applying current to each phase-neutral current transformer pair. This test also applies to molded-case breakers utilizing an external neutral current transformer.
  6. Measure time delay of the ground fault protective device at a value equal to or greater than 150 percent of the pickup value.
  7. Verify reduced control voltage tripping capability is 55 percent for ac systems and 80 percent for dc systems.
  8. Verify blocking capability of zone interlock systems.
C. Test Values – Visual and Mechanical
  1. Compare bolted connection resistance values to values of similar connections. Investigate values which deviate from those of similar bolted connections by more than 50 percent of the lowest value. (7.14.A.4.1)
  2. Bolt-torque levels shall be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.12. (7.14.A.4.2)
D. Test Values – Electrical
  1. Compare bolted connection resistance values to values of similar connections. Investigate values which deviate from those of similar bolted connections by more than 50 percent of the lowest value.
  2. System neutral-to-ground insulation resistance shall be a minimum of one megohm.
  3. Insulation-resistance values of control wiring shall not be less than two megohms.
  4. Results of pickup test shall be greater than 90 percent of the ground fault protection device pickup setting and less than 1200 amperes or 125 percent of the pickup setting, whichever is smaller.
  5. The ground fault protective device shall operate when current direction is the same relative to polarity marks in the two current transformers. The ground fault protective device shall not operate when current direction is opposite relative to polarity marks in the two current transformers.
  6. Relay timing shall be in accordance with manufacturer’s published data but must be no longer than one second at 3000 amperes in accordance with ANSI/NFPA 70, National Electrical Code, Article 230.95.
  7. The circuit interrupting device shall operate when control voltage is 55 percent of nominal voltage for ac circuits and 80 percent of nominal voltage for dc circuits.
  8. Results of zone-blocking tests shall be in accordance with manufacturer’s published data and design specifications.
Ground-Fault Protection Systems, Low-Voltage
Maintenance Testing
A. Visual and Mechanical Inspection
  1. Inspect the components for damage and errors in polarity or conductor routing.
    1. Verify that the ground connection is made on the source side of the neutral disconnect link and also on the source side of any ground fault sensor.
    2. Verify that the neutral sensors are connected with correct polarity on both primary and secondary.
    3. Verify that all phase conductors and the neutral pass through the sensor in the same direction for zero sequence systems.
    4. Verify that grounding conductors do not pass through zero sequence sensors.
    5. Verify that the grounded conductor is solidly grounded.
  2. Prior to cleaning the unit, perform as-found tests.
  3. Clean the unit.
  4. Inspect bolted electrical connections for high resistance using one or more of the following methods:
    1. Use of a low-resistance ohmmeter in accordance with Section 7.14.B.1.
    2. Verify tightness of accessible bolted electrical connections by calibrated torquewrench method in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.12.
  5. Verify correct operation of all functions of the self-test panel.
  6. Verify pickup and time-delay settings in accordance with the settings provided in the owner’s specifications. Record appropriate operation and test sequences as required by NFPA 70 National Electrical Code, Article 230.95.
  7. Perform as-left tests.
B. Electrical Tests
  1. Perform resistance measurements through bolted connections with a low-resistance ohmmeter in accordance with Section 7.14.A.4.1.
  2. Measure the system neutral-to-ground insulation resistance with the neutral disconnect link temporarily removed. Replace neutral disconnect link after testing.
  3. * Perform insulation-resistance tests on all control wiring with respect to ground. The applied potential shall be 500 volts dc for 300-volt rated cable and 1000 volts dc for 600-volt rated cable. Test duration shall be one minute. For units with solid-state components or control devices that cannot tolerate the applied voltage, follow manufacturer’s recommendation.
  4. Perform ground fault protective device pickup tests using primary current injection.
  5. For summation type systems utilizing phase and neutral current transformers, verify correct polarities by applying current to each phase-neutral current transformer pair. This test also applies to molded-case breakers utilizing an external neutral current transformer.
  6. Measure time delay of the ground fault protective device at a value equal to or greater than 150 percent of the pickup value.
  7. Verify that reduced control voltage tripping capability is 55 percent for ac systems and 80 percent for dc systems.
  8. Verify blocking capability of zone interlock systems.
C. Test Values – Visual and Mechanical
  1. Compare bolted connection resistance values to values of similar connections. Investigate values which deviate from those of similar bolted connections by more than 50 percent of the lowest value. (7.14.A.4.1)
  2. Bolt-torque levels should be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.12. (7.14.A.4.2)
D. Test Values – Electrical
  1. Compare bolted connection resistance values to values of similar connections. Investigate values which deviate from those of similar bolted connections by more than 50 percent of the lowest value.
  2. System neutral-to-ground insulation resistance should be a minimum of one megohm.
  3. Insulation-resistance values of control wiring should be comparable to previously obtained results but not less than two megohms.
  4. Results of pickup test should be greater than 90 percent of the ground fault protection device pickup setting and less than 1200 amperes or 125 percent of the pickup setting, whichever is smaller.
NETA ATS / MTS
TABLE 100.12
Neta Table 100.12
Neta Table 100.12