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LET US BRING YOUR

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21st

CENTURY

MSHA

Spring Thaw

Title 30 CFR

Part 57

12028

30 CFR § 57.12028

Testing grounding systems.

Continuity and resistance of grounding systems shall be

tested immediately after installation, repair, and

modification; and annually thereafter.

A record of the resistance measured during the most

recent test shall be made available on a request by the

Secretary or his duly authorized representative.

Mine Safety and Health Administration Program Policy

Manual

56/57.12028 Testing Grounding Systems

This intent of this standard is to ensure that continuity and resistance

tests of grounding systems are conducted on a specific schedule.

These tests will alert the mine operator if a problem exists in the

grounding system which may not allow the circuit protective devices

to quickly operate when faults occur.

With the exception of fixed installations, numerous fatalities and injuries have occurred due to high resistance or lack of continuity in equipment ground systems.

These accident could have been prevented by proper testing and maintenance of grounding systems.

Grounding systems typically include the following:

Equipment grounding conductors - the conductors used to connect the metal frames or enclosures of electrical equipment to the grounding electrode conductor.

Grounding electrode conductor - the conductors connecting the grounding electrode to the equipment grounding conductor.

Grounding electrodes - usually driven rods connected to each other by suitable means, buried metal, or other effective methods located at the source, to provide a low resistance earth connection.

Operators shall conduct the following tests:

Equipment grounding conductors - continuity and resistance must be tested immediately after installation, repair, or modification, and annually if conductors are subjected to vibration, flexing or corrosive environments.

Grounding electrode conductor - continuity and resistance must be tested immediately after installation, repair, or modification, and annually if conductors are subjected to vibration, flexing or corrosive environments.

This is my personal experience discovered during a motor frame ground resistance test.

It has became my experience that using a digital multimeter such as a

Fluke, is not the best device to test frame grounding. The digital multimeter has

been designed not to load electronic equipment, and equally does not load our

ground systems enough either. Due to long wire length (capacitance) and earth

voltage the multimeter will give erroneous readings. This type of meter only

loads the circuit with low voltages (<1 volt) and very low currents (<6 ma). The

meter type that has given me the best results is a continuity meter. A continuity

meter will put out higher voltages (>3.5 volts) and currents (>200 ma). This will

load the circuit enough to produce a good reading. Although one other meter is

very good and preferred to do this test, but the cost is high and few companies

or contractors have one. This meter would be a micro-ohm meter. It will load

the test circuit to 10 amps.

During this test due to the fact that meter leads are only 3 to 6 feet

long, it will become necessary to string a piece of test wire through the

plant. This wire will be connected from the motor conduit entry box to

the source of power. Thus operations will need to be stopped.

Each motor in the plant must be checked. While the electrician has the

cover off the motor a visual check should be preformed. This visual

check is to confirm that the ground wire is sufficient size and a positive

connection is still made. Please don’t forget that you must lock-out and

tag-out the electrical source, also use all PPE!

Sample Frame Ground Test Report

Grounding electrode test varies from motor frame resistance test.

In order to do a test on the grounding electrodes, you will need

a meter called a earth ground resistance meter. This type of meter

is used with three leads, one is connected to the ground

electrode, the second connected to a point 100 feet out, and

the third moved in 10 foot interval's between the other two. The

readings should be plotted and should reflect a leveling off in the

area around 60 feet, with a value of <25 ohms (in the mining

industry we prefer lower). During this test it is very important to

have the POWER OFF AND USE THE CORRECT PPE! The

ground wire should be disconnected from the rest of the plant.

During this disconnection potentially DANGEROUS VOLTAGES

can result.

Sample Earth Ground Report

Please don’t forget many of the fatalities in the past have

been from Inadequate ground systems!

A good ground system is Important for the protection of

personnel!

Since a good ground is not needed for equipment to operate

we sometimes forget about it.

This is the reason for our annual test!

The following slides display some of the different meters.

Please feel free to ask any questions during this time,

And I would like to

Thank you very much for your time.