Manual Gossen Metrawatt PROFITEST MXTRA (page 19 of 96) (English)

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GMC-I Messtechnik GmbH 19

1) Measuring Contact Current Without Tripping the RCD

Measuring Method

The instrument uses a measuring current of only 1/3 nominal

residual current for the determination of contact voltage U

IN

which occurs at nominal residual current. This prevents tripping of

the RCCB.

This measuring method is especially advantageous, because

contact voltage can be measured quickly and easily at any electri-

cal outlet without tripping the RCCB.

The usual, complex measuring method involving testing for the

proper functioning of the RCD at a given point, and subsequent

substantiation that all other systems components requiring pro-

tection are reliably connected at low resistance values to the

selected measuring point via the PE conductor, is made unneces-

sary.

N-PE Reversal Test

Additional testing is conducted in order to

determine whether or not N and PE are

reversed. The pop-up window shown at

the right appears in the event of reversal.

Attention!

Execute a data backup before starting measurement and

switch off all consumers in order to prevent the loss of

data in data processing systems.

Start Measurement

Amongst other values, contact voltage U

IN

and calculated earth-

ing resistance R

appear at the display panel.

Note

The measured earthing resistance value R

is acquired

with very little current. More accurate results can be

obtained with the selector switch in the R

position.

The DC + function can be selected here for sys-

tems with RCCBs.

Unintentional Tripping of the RCD due to Bias Current within the System

If bias currents should occur, they can be measured with the help

of a current clamp transformer as described in section 13.1 on

page 50. The RCCB may be tripped during the contact voltage

test if extremely large bias currents are present within the system,

or if a test current was selected which is too great for the RCCB.

After contact voltage has been measured, testing can be per-

formed to determine whether or not the RCCB is tripped within

the selected time limits at nominal residual current.

Unintentional Tripping of the RCD due to Leakage Current in the Measur-

ing Circuit

Measurement of contact voltage with 30% nominal residual cur-

rent does not normally trip an RCCB. However, the trip limit may

be exceeded as a result of leakage current in the measuring cir-

cuit, e.g. due to interconnected power consumers with EMC cir-

cuit, e.g. frequency converters and PCs.

2) Tripping Test after the Measurement of Contact Voltage

➭ Press the



key.

The tripping test need

only be performed at

one measuring point for

each RCCB.

If the RCCB is tripped at nominal residual current,

the MAINS/NETZ LED blinks red (line voltage disconnected) and

time to trip t

and earthing resistance R

appear at the display

panel.

If the RCCB is not tripped at nominal residual current,

the RCD/FI LED lights up red.

Contact Voltage Too High

If contact voltage U

IN

, which has been measured with 1/3 nomi-

nal residual current I

N

and extrapolated to I

N

, is > 50 V (> 25 V),

the U

LED lights up red.

If contact voltage U

IN

exceeds 50 V (25 V) during the measuring

sequence, safety shut-down occurs.

Note

Safety Shut-down: At up to 70 V, a safety shut-down is

tripped within 3 seconds in accordance with IEC 61010.

Contact voltages of up to 70 V are displayed. If contact voltage is

greater than 70 V, U

IN

> 70 V is displayed.

Limit Values for Allowable, Continuous Contact Voltage

The limit for allowable, continuous contact voltage is U

=50V for

alternating voltages (international agreement). Lower values have

been established for special applications (e.g. medical applica-

tions: U

=25V).

Attention!

If contact voltage is too high, or if the RCCB is not

tripped, the system must be repaired (e.g. earthing resis-

tance is too high, defective RCCB etc.)!

3-Phase Connections

For proper RCD testing at three-phase connections, the tripping

test must be conducted for one of the three phase conductors

(L1, L2 and L3).

Inductive Power Consumers

Voltage peaks may occur within the measuring circuit if inductive

consumers are shut down during an RCCB trip test. If this is the

case, the test instrument may display the following message: No

measured value (– – – ). If this message appears, switch all power

consumers off before performing the trip test. In extreme cases,

one of the fuses in the test instrument may blow, and/or the test

instrument may be damaged.

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