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TM 10-4930-238-12&P
2-7. ASSEMBLY AND PREPARATION FOR USE - Continued.
c.
Grounding Procedures - Continued.
Table 2-1. Required depths for ground rods
Type of soil
Depth of ground rod
Coarse ground, cohesionless sands and gravels
6 feet
Inorganic clay, claying gravels, gravel-sand clay,
4 feet
claying sands, sandy clay, gravelly day, and silty
day
Silty gravel, gravel-sand-silt, silty sand, sand, silt,
3 feet
peat, muck, and swamp soil
(3) Methods of Grounding. There is no quick or easy way to test the adequacy of a ground. The
. .
testing procedures (See FM 10-68 Appendix E) are complex and the equipment is bulky and
expensive. For these reasons, several levels or methods of grounding and bonding are re-
quired to meet the various operational needs of the Army. The three methods/levels are listed
in order of preference.
(a)
(b)
Method 1: equipment is grounded to a rod or rods that have measured resistance to
ground equal to or less than 10,000 ohms. Ground the refueling system to this tested
ground rod. In addition, the nozzle is bonded to the vehicle/aircraft. (See paragraph
2.8(b) Bonding) Use of this method is required unless conditions, as described below,
prevent its use. Method I is the only standard of grounding acceptable, without authoriza-
tion, at any fixed airfield or refueling point. It is the safest method.
Method 2: In some instances, equipment is not available to test resistance to ground.
Method 2 uses an untested ground - a grounding system based on the knowledge that
damp earth will accept and drain off an electrical charge. Utilize method 2 when the loca-
tion, tactical situation, or type of operation makes it impossible to test ground rods.
Ground equipment to a rod or rods driven a specific depth into the ground depending on
the type of soil (see Table 2-1) at the site. The depth to which the rods must be driven
is determined by the normal depth of permanent ground moisture in the various types
of soils. The commander of the operating ‘[nit must authorize the use of method 2. This
method is less desirable. Employ method 2 when impossible to use method 1.
Death or serious injury may occur if proper bonding procedures are
not followed. (See paragraph 2.8(b) Bonding) While using method 3,
an object with a different electrical potential (any object that not part
of the bonded system) should not come into contact with the bonded
equipment when a flammable vapor-air mixture maybe present.
(c) Method 3: When the climate, terrain, or tactical condition makes it impossible to secure
a satisfactory ground rod, requirements to ground the fuel dispenser (system or refueler)
may be waived. However the requirement to bond the fueI dispenser to the aircraft/ve-
hicle may not be waived under any circumstances Method 3 relies on bonding alone.
(See paragraph 2-8(b) Bonding) Bonding is made between the aircraft/vehicle and the
refueling system or refueler along with the nozzle and the aircraft/vehicle. A contact be-
tween an unbended object and the system could produce a spark that could set off an
explosion or fire. Method 3 procedures are authorized by the commander of the unit one
organizational level above the operating unit. This is the least desirable method since
it involves bonding only!
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