Rish Insu 5Dx
7
4.4
DESCRIPTION OF MEASURING LEADS
CAPTION:
1.
Hand protection
2.
Safety areas
Fig. 2: Measuring leads
4.5
GUARD LEAD
In some cases, measurements could be affected by surface currents. By applying voltage to an
insulation to be measured, there may be two distinct currents: one flowing in the test piece, the
other flowing on its surface. In case you want to measure only the resistance due to current Im
flowing in the test piece Rx (which is the significant one), it is necessary to absorb the surface
current If using another lead.
Fig. 3: Currents flowing in the test piece
4.6
NOTES ON THE INSULATION MEASUREMENTS
Measuring a high resistance such as the insulation resistance is very difficult as the value of the
currents considered may be very low. When measuring, to prevent making mistakes, it is therefore
necessary to take the following precautions:
CAUTION
Keep the measuring leads suspended above the path or, anyway, make sure the
leads do not make contact in more of one point
While measuring high resistances, the area around the measuring instrument and
the appliance being tested must be free. It is recommended to use the timer
function so that the operator may keep at due distance from the leads and from
the resistance to be tested
It is recommended to use the GUARD lead to measure resistances of some tens of
G
or higher
While use the instrument with main supply, it's important to check that the
earthed resistance pole to measure is connected to the instrument Rx+
Terminal
