User manual

GMC-I Messtechnik GmbH 15

Maximum Allowable Protective Conductor Resistance Values Depending upon Cable Length

Under no circumstances may a value of 1 Ω be exceeded. The table is also valid for cable

reels and extension cables.

Attention!

The alligator clip (3) must make good contact with the housing of the device under

test!

The connector cable must be moved during measurement, section by section over

its entire length – for permanently installed devices only in so far as the cable is ac-

cessible during repair, modification or testing. If the resistance value fluctuates during

this manual test which is essential for continuity testing, it must be assumed that the

protective conductor is damaged, or that one of its connection points is defective.

Defects of this type must be corrected before any further tests are performed.

5.3.1 Special case: permanently connected instruments

A resistance value of up to 1 Ω measured between a suitable earthing contact and all

exposed conductive parts which might become charged with voltage in the event of an error

is allowable for permanently installed devices.

In the case of data processing systems or combinations of permanently installed individual

devices, the network should be decoupled and individual measurements should be per-

formed. If decoupling is not feasible, individual measurements may be performed at

interconnected devices.

Length to [m] 5 12. 5 20 27.5 35 42.5 50

more than 50

Max. resistance

[Ω]

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

To housing for measurement of protective conductor resistance

KS17-4