50 51
Appendix: loop Resistance Analysis
Loop resistance includes ground resistance value of point A to the ground,
resistance of ground down lead metal conduct, resistance of metal over head
wires, connection resistance between the ground down lead and metal over head
wires (contact resistance), composite resistance value of point B to the ground,
namely the parallel value. The ground net A and B have not been connected
underground, requiring different ground net.
Equipment
Over head ground wire
Ground down lead
Ground surface
Ground net A
Ground net B
If there is no over head wires between the ground net A and B, namely no metal
connection on ground, the ground net A and B is single point ground and shall be
tested as the single point ground.
If the parallel value of ground A and B loop measured by 2-point method is 5.0 :
RA+RB+R over head wire +R ground down lead=5.0 as over head wires and
ground down lead are metal conduct with low resistance, which can be neglected,
the real ground resistance value of the ground net A, B in parallel to ground shall
definitely 2.5 then we can judge if the real ground resistance value of the
ground net A, B in parallel is qualified. If real ground resistance value of the
ground net A, B in serial is smaller than the required value of engineer standard,
the ground net A, B is all qualified.
The loop resistance test requires that the ground net A, B is different and
disconnected with each other underground. If the ground net A, B are connected
underground, the metal loop resistance value measured by the meter shall be
very small, about few hundredths , not the ground resistance. Thus, the meter
is easy to detect the metal loop connection resistance value and equal potential
resistance value and applicable to detect the connection and welding between
metal loops.
UT276A/278A OPERATING MANUALUT276A/278A OPERATING MANUAL
To Next Page
Loading...
