Electrical Field Test Procedures as per International Codes & Standards

Electrical field test procedures are essential for verifying the safety, performance, and reliability of electrical equipment and systems in real-world conditions. These procedures encompass a range of tests designed to assess various aspects of electrical installations, components, and devices. Depending on the specific standards and requirements of organizations like IEEE, ANSI, NEMA, UL, and IEC, the nature of these tests can vary widely. However, there are some common types of field tests that are frequently conducted across many sectors of the electrical industry.

The following Electrical Field Test Procedures are based on industry standards (IEEE, ANSI, NEMA, UL, and IEC) as well as the basic requirements of several major equipment manufacturers. The Electrical Field Test Procedures describe the minimum requirements to ensure that the electrical equipment addressed will perform reliably and in accordance with industry standards.

1. Insulation Resistance Test – IR Test.

Measure the insulation resistance of electrical equipment phase to phase and phase to ground for one (1) minute. Test voltage and minimum acceptable values.

Equipment Voltage Rating	Recommended Test Voltage
100 – 250	500
251 – 600	1000
601 – 5000	2500
Over 5000	5000

Values of insulation resistance less than manufacturer’s minimum or rated voltage + 1kV in megohms should be investigated. Over potential or high potential tests should not proceed unless insulation resistance levels are equal to or above the listed minimum values.

2. High potential Test – HIPOT Test.

Direct Current.

A DC high potential test (controlled over voltage test) is one in which the increase of applied direct voltage is controlled.  The measured current is continuously observed for abnormalities with the intention of stopping the test before breakdown occurs.

•      A polarization index test should be performed on large rotating equipment by applying an initial voltage step of about one-third of the recommended maximum voltage from the above table and maintain the voltage at a constant level for 10 minutes. The polarization index is calculated by dividing the one-minute resistance value by the ten-minute resistance value. The index value should be 2 or greater values less than this should be investigated. After the initial ten-minute test, the D. C. test voltage should be increased in 10 uniform steps, each step being one-minute in duration, up to the maximum recommended D. C. value.
• In high potential testing of cable, the D. C. test voltage is applied in a minimum of four steps (each step approximately equal to the rated rms voltage of the cable) of one (1) minute duration each, except for the final test voltage which shall be maintained for fifteen (15) minutes.

Alternating Current.

Perform AC high potential test phase to ground and phase to phase.  Potential application shall be for one (1) minute. Test voltage shall be in accordance with the manufacturer’s recommendations.  When the manufacturer’s recommended values are not available the values in the values listed in the following table can be used but should be considered the maximum voltage to be applied.  Increase the voltage at the rate of 1 kV per second until the maximum recommended test voltage is reached.

Maximum high potential test voltages.

Equipment Rated KV	Test Voltage KV
	A.C.	D. C.
2.5	6.0	10.0
5.0	14.0	24.0
15	27.0	46.0
35	60.0	102.0

Recommended maximum values of field test voltages are determined by the following:

A. C. test volts = 0.75 X (2 X equipment maximum voltage + 1kV).

The D. C. test voltage is 1.4 X [0.75 X (2 X equipment maximum voltage + 1kV)].

The AC high potential test results are evaluated on a go, no-go basis by slowly raising the test voltage to the required value of final test voltage and maintaining for one (1) minute.

3. Low Voltage Cables.

Perform DC High Potential Testing on critical cables after installation.  Test each cable with respect to ground and adjacent cables.  Test value shall be reviewed with the proponent.  The DC test voltage shall not exceed 1.4 X (2 X rated voltage + 1000).

4. Switchgear and Metal Enclosed Bus.

Perform AC high potential tests on each bus section, phase to phase and phase to ground for one (1) minute.  Maximum test voltage shall be as listed above.

5. Contact Resistance.

Measure and record the contact resistance of each phase line to load, of bus, breakers and contactors.  For equipment 600 amps and higher, values of resistance in excess of 200 micro-ohms and deviations of more than +/- 20% must be investigated. The contact resistance is measured with the circuit breaker/contactor in the closed position. The contactor must be closed and latched not held closed by hand pressure.

Thermo-vision Inspection.

Electrical equipment safely accessible and visible such as outdoor bus connections, isolation switches, terminations on circuit breakers and transformers should be checked with Thermo-vision for temperature abnormalities.

6. New Insulating Oil Test Requirements.

The following table lists the Dielectric Fluid Specifications for new insulating Oil as Received from the supplier. Note that the values listed are described as minimum or maximum recommended values.

The oil must be tested before oil filling of the equipment begins and, depending on the results of the test and the operating voltage of the equipment, may require processing before it is put into the equipment.  See P-051 for additional information.

Dielectric Fluid Specification (New Insulating Oil as Received Before Transformer Filling)

TEST	LIMIT VALUE	TEST RESULTS
Dielectric strength D-877, kV, minimum	30
Power Factor, D924, 25 deg., % maximum. 100 deg., % maximum	0.050.30
Interfacial Tension D 971, mN/M minimum	40
Color, D-1500 ASTM Units maximum	0.5
Visual Examination D1524	Bright and Clear
Acid Number D974, mg KOH/g, maximum	0.03
Water Content, D 1533, ppm, maximum	35

7. Torque Test Values for Electrical Connections.

The following torque table is for general reference.  The manufacturers recommended torque values should be used.  In the absence of manufacturer’s recommendations, the following values are the recommended maximum torque values that should be applied.  Note that grade 5 hardware should be used in switch gear as a minimum.

U.S. STANDARD BOLT TORQUE FOR BUS CONNECTIONS HEAT TREATED STEEL (MAXIMUM).

GRADE	SAE NO. 1&2	SAE NO. 5	SAE NO. 6	SAE NO. 8
MINIMUMTENSILE (PSI)	64K	105K	133K	150K
BOLT DIAMETER		TORQUE (FT-LBS)
1/4	5	7	10	10.5
5/16	9	14	19	22
3/8	15	25	34	37
7/16	24	40	55	60
1/2	37	60	85	92
9/16	53	88	120	132
5/8	74	120	167	180
3/4	120	200	280	296
7/8	190	302	440	473

Reduce the maximum torque values listed by 10% to 20% for plated or lubricated bolts.

Silicon Bronze.

Bolt Diameter and Thread	1/4 – 20	5/16 – 18	3/8 – 16	7/16 – 14	1/2 – 13	9/16 – 12	5/8 – 11
Torque in Ft-lb	6	10	18	29	40	53	86

Insulation resistance test, ac high potential test, dc high potential test, contact resistance test, insulating oil test are test to be discussed in this article. Electrical Field Test Procedures as per Standard.