Testing and Inspection of Bonding/Grounding
systems
The proper installation of bonding and grounding devices is
important in the protection of personnel and equipment. At the time of
installation a resistance test is needed to confirm electrical continuity
to ground. In addition, an effective inspection and maintenance program is
needed to ensure continuity adequacy of the
system.
In evaluating maintenance requirements,
the bonding and grounding system can be divided into three
categories:
- The point-type clamps equipped with
flexible leads used for temporary bonding of portable containers to the
building grounding system.
- The fixed grounding cables and bus
bars used to connect the flexible leads and fixed equipment to
ground.
- The earthing electrode
itself
The flexible leads are subject to mechanical damage and wear, as well as
corrosion and general deterioration. For this reason they should be
inspected frequently. This inspection should evaluate cleanliness and
sharpness of the clamp points, stiffness of the clamp springs, evidence of
broken strands in the cables, and solidity of cable attachments. A more
thorough inspection should be made regularly, using an intrinsically-safe
ohmmeter to test ohmic resistance and
continuity.
One lead of the ohmmeter is connected to
a clean spot on the container, the other lead is connected to the paint
grounding bus, metallic piping, or other fixed equipment. The measured
resistance should be less than 25 ohms, and will usually be about one
ohm.
The fixed leads and the bus bars are not usually as subject to injury or
wear as the temporary connectors. These should be checked with an ohmmeter
on an annual basis. One lead of the ohmmeter should be connected to the
fixed lead or bus bar, the other lead should be connected to the plant
earthing electrode or to the structural steel of the building. The
measured resistance should be less than one
ohm.
Conductive hoses should be checked
regularly, and after repair or replacement, for electrical continuity and
resistance. The conductive segments may break and may not be repaired
properly, thus rendering the hoses nonconductive or with an abnormally
high resistance. Nonconductive hoses having an internal spiral conductor
should be installed so that the spiral conductor makes contact with
adjacent metallic fittings.
Earthing Electrodes
The final component of the bonding/grounding system is the
“earthing electrode” which passes static charges into the soil. This may
be a device installed solely for grounding purposes, such as a driven rod
(copper clad) or buried plate, or it may be an underground metal water
pipe. If the building has a steel structure frame that is grounded for
lighting protection or is otherwise effectively grounded, this grounding
is adequate for static grounding; no separate static earthing electrode is
needed.
Underground piping equipped with cathodic
protection is not a suitable ground. Underground piping made of
cement-asbestos or plastic would not be satisfactory as a ground. It is
also possible for metal piping to have sections of plastic or
cement-asbestos which would make it unsatisfactory. Water meters should
have jumper cables permanently installed around them to provide a
continuous electrical path. When underground piping is utilized as a
ground, any disconnections for alterations or repair may make the
grounding system
ineffective.
Sprinkler piping and electrical conduit
should be avoided because of the increased resistance to ground caused by
joints and connectors. A break in continuity can also result when piping
and conduit are removed for repair or alterations. |
Grounding Verification Control
System
Properly labeled “The Invisible Enemy”, static electricity cannot
be seen but poses extreme risks if not properly attended to. Yet we rely
on a visual means to confirm that a ground clamp and lead are in place for
proper grounding or bonding, with periodic confirmation via resistance
meters. Newer “electronic verification systems” now take the guesswork out
of proper grounding techniques. These verification systems offer a
continuous means of visual/electronic confirmation of ground to a
high-integrity ground point (ground bus). Through “interlock” functions
they can control pumps, valves, motors, etc. or interface with a PLC or
DCS control system to ensure that nothing happens until a good ground is
achieved. They may also initiate sound alarms if required. Further
information on the various systems can be found in this
booklet.
Drawings of Typical Arrangements for
Grounding
| Drawing
|
Item
|
| TA-1
|
Ground Connection of
building Ground Bus |
| TA-2
|
Permanent-Fixed,
Equipment Ground Extension to Building Ground “bus”
|
| TA-3
|
Small Ground
Clamp |
| TA-4
|
Large Ground
Clamp |
| TA-5
|
Building Ground “Bus”
Extension to Portable Solvent Containers |
| TA-6
|
Grounding “Tap”
Connection to Building Ground “Bus” |
| TA-7
|
Typical Arrangement -
Grounding of Portable “Material Transfer Chute” |
| TA-8
|
Pipe Grounding
Jumper |
| TA-9
|
Pipe Grounding
Clamp |
| TA-10
|
Typical Grounding
Arrangement at “Drop Valve” of Thinning or Mixing
Tank |
| TA-11 |
Typical Grounding
Arrangement of Laboratory Mixing Unit |
| TA-12 |
Typical Grounding
System Standard Arrangement at Thinning or Mixing Equipment
|
| TA-13 |
Typical Grounding
System for Small Volume Solvent Handling |
| TA-14 |
Typical Grounding
System for Small Volume Solvent Handling
|
| TA-15 |
Typical Small Change
Can Grounding Arrangement for Solvent Handling
|
| TA-16 |
Typical Portable Tank
and Drum Transfer Area Static Grounding Arrangement |
| TA-17 |
Typical Grounding
System for Small Volume Solvent Handling |
| TA-18 |
Typical Arrangement
for Static Grounding of 55 Gallon Drums in Storage Rack
|
| TA-19 |
Ground Verification,
Drums and Totes |
| TA-20 |
Ground
Verification, Railcar and Tanker Trucks
|
| TA-21 |
Ground Verification,
Fiber Bags |
| TA-22 |
Ground Verification,
Plant Process |
| TA-23 |
Typical Tank Car or
Truck loading/Unloading Grounding Arrangement
|
The drawings
shown in this book are approved concepts. If there is any question
regarding local fire codes, check with your Fire Marshall.
|
