METREL A1472 Manual de usuario

Leakage current clamp

A 1472, A1579

User manual

Version 1.2, Code no. 20 752 271

Distributor:

Manufacturer:

METREL d.d.

Ljubljanska cesta 77

1354 Horjul

Slovenia

web site: http://www.metrel.si

e-mail: metrel@metrel.si

Version note

1.1: manual is valid also for A 1579

Mark on your equipment certifies that this equipment meets the

requirements of the EU (European Union) concerning safety and

electromagnetic compatibility regulations.

No part of this publication may be reproduced or utilized in any form or by

any means without permission in writing from METREL.

A 1472, A1579 Leakage current clamp

1Warnings...........................................................................................4

2Description of leakage current clamp .............................................5

2.1 Meaning of symbols....................................................................6

3Maintenance......................................................................................7

3.1 Inspection ...................................................................................7

3.2 Cleaning......................................................................................7

3.3 Service and calibration................................................................7

4Leakage current clamp operation....................................................8

4.1 Measuring of leakage currents....................................................8

4.1.1 Origins of leakage currents......................................................8

4.1.2 Leakage currents in normal operation.....................................9

4.1.3 Leakage currents in fault conditions......................................10

4.1.4 Problems caused by leakage currents...................................11

4.2 Measuring leakage currents with current clamps.......................13

4.2.1 Direct method........................................................................13

4.2.2 Differential method................................................................14

4.3 Testing procedures...................................................................15

4.3.1 Finding sources of excessive leakage current.......................15

4.3.2 Insulation resistance testing..................................................17

4.4 Influencing quantities ................................................................18

4.4.1 Influence of nearby external magnetic field ...........................18

4.4.2 Influence of load current in differential leakage current test...18

4.4.3 Influence of external electric field..........................................19

4.4.4 How to recognize accuracy problems ?.................................19

4.4.5 How to minimize the influencing quantities............................19

4.4.6 Consideration of influencing quantities..................................20

4.5 Other important current clamp parameters................................21

4.5.1 High measuring range...........................................................21

4.5.2 Clamp diameter.....................................................................21

4.5.3 Protection category...............................................................21

5Technical specifications ................................................................22

A 1472, A1579 Leakage current clamp

1 Warnings

To ensure a high level of operator's safety during using of the leakage

current clamp the following warnings have to be considered:

Do not use the current clamp if any damage is noticed!

Do not leave open signal output terminals of the current clamp

with current output (A 1472, A 1579) during measurement to avoid

damage and electric shock on secondary side. Never enclose

conductor in the jaw unless the clamp is connected to measuring

instrument!

Consider all generally known precautions in order to avoid risk of

electric shock while dealing with electric installations and

equipment!

Do not extend hands over protection barrier during measurement

to prevent of electric shock!



Symbol on the current clamp indicates possible hazardous live

conditions if the required safety measures are ignored.

Only a competent, authorized person is allowed to carry out

service intervention!

If the leakage current clamp is used in a manner not specified in

this User manual, the provided protection can be impaired!

The leakage current clamp may only be used within the operating

ranges as specified in this User manual.

A 1472, A1579 Leakage current clamp

2 Description of leakage current clamp

The A 1472 is a 1000/1 ratio leakage current clamp for measuring

alternating currents in the range from 0.5 mA to 10 A.

The A1472 current clamp is specially designed to be used in combination

with METREL DeltaPAT testers.

Refer to chapter 5. Technical specification for list of all measuring

instruments suitable to work with the A1472 current clamp.

Main clamp parts:

1. Current sensor

2. Protection barriers

3. Conductor opening

4. Signal output terminals

A 1472

2.1 Difference to A 1579

The leakage current clamps differs only in applied safety banana

colours (4), those are red and black for the A 1579 instead green and

brown for the A 1472.

A 1579

Warning:

Do not leave open signal output terminals of the current

clamp during measurement to avoid damage and electric

shock on secondary side, never enclose conductor in the

jaw unless the clamp is connected to measuring

instrument!

A 1472, A1579 Leakage current clamp

2.3 Meaning of symbols

Symbol on the current clamp indicates that it is

possible to use the current clamp on non-insulated

conductors.

Symbol on the current clamp indicates possible

hazardous live conditions if the required safety

measures are ignored.

Symbol indicates that the current clamp can be

applicable in presence of external magnetic fields of

up to 100 A/m.

> 100 A/m

A 1472, A1579 Leakage current clamp

3 Maintenance

3.1 Inspection

To maintain operator safety and ensure reliability of the current clamp it is

good practice to inspect it on a regular basis. Check that the enclosure and

connections are undamaged.

The jaw surface must be clean. Pollution on jaw surfaces reduces the

current clamp sensitivity.

3.2 Cleaning

Use a soft cloth moistened with soapy water or alcohol to clean non-

metallic surface of the current clamps and leave them to dry totally before

using it.

Notes!

Do not use liquids based on petrol or hydrocarbons!

Do not spill cleaning liquid over the current clamps!

To clean jaw cut surfaces use slightly oiled soft cloth.

3.3 Service and calibration

It is essential that your clamp is regularly calibrated in order to guarantee

the technical specification listed in this User manual. We recommend 2-

year calibration interval. Metrel encloses an original calibration certificate

with every new instrument and current clamp.

For recalibration and repairs under or out of warranty time please contact

your distributor for further information.

A 1472, A1579 Leakage current clamp

4 Leakage current clamp operation

4.1 Measuring of leakage currents

4.1.1 Origins of leakage currents

Leakage currents are currents driven by active conductors of a distribution

system or electrical equipment to earth and/or protective conductors.

Leakage currents flow wherever a conductive path (resistance and/or

capacitance) is applied between active and earthed conductors/protected

parts. Fig.1 shows leakage currents that usually flow in electrical

installations in normal operation.

Fig. 1 Leakage currents in electrical installations in normal operation

The relation between leakage current and (insulation) resistance between

line and earth is defined by the Ohm’s law.

 

)(/

_ kRUmAIinsnomresleak

Eq. 1

Ileak_res.................resistive leakage current in mA

Unom...................nominal line voltage, e.g. 230 V

Rins....................resistance in kΩ

The relation between leakage current and capacitance between line and

earth is shown in Equation 2.

   

nFCfUmAInomcapleak  6

_1028.6

Eq. 2

Ileak_cap.................capacitive leakage current in mA

Unom...................nominal line voltage, e.g. 230 V

f.........................mains frequency

C(nF).................capacitance in nF

Capacitive and resistive leakage currents are forming the overall (total)

leakage current. For continuous leakage currents of main frequency,

Equation 3 can be used.

 

2_capleakresleakleakage IImAI

Eq. 3

Ileakage.................overall leakage current

Shapes of leakage currents are usually much more complicated. That will

be described later in this article.

A 1472, A1579 Leakage current clamp

4.1.2 Leakage currents in normal operation

Typical leakage currents in normal operation are:

Leakage currents caused by input filters in electrical equipment

connected between live and earth (filters, monitors). The capacitors

in input filters have a capacitance of ca. 10 nF to 100 nF (see Fig.1).

Leakage currents caused by conductors’ insulation resistance and

their capacitances to earth. Long power cables have a lower

insulation resistance and higher capacitances. The capacitance

between a cable and earth is typically about 150 pF/m (sse Fig. 1).

Leakage currents produced by frequency converters, switch mode

power supplies, different rectifiers and similar equipment. The

shape and frequency of this leakage currents can vary from pure

d.c, pulsed d.c. components up to very high frequency.

In general, leakage currents in normal operation increase with the size of

the electrical installation and the number of connected loads.

Table 1 shows the values of leakage currents for some typical

capacitances and resistances.

Capacitance

Capacitive leakage current

@ 230V/ 50Hz

Note

1 nF

0.072 mA

Typical values of

capacitors in input

cables

10nF

0.72 mA

100nF

7.2 mA

1uF

72 mA

Capacitance of long

power cables

Resistance

Resistive leakage current

@ 230V/ 50Hz

10 kΩ

23 mA

500 kΩ

0.46 mA

1.00 MΩ

0.23 mA

Typical limits for

insulation resistance

2.00 MΩ

0.115 mA

Table 1: Leakage current / capacitance relations

In Table 2 typical values of leakage currents for different types of electrical

equipment are shown.

Equipment

Leakage current

Stationary PC system

1 to 3

Photocopy machine

0.5 to 1.5

Floor heating

1mA / kW

Input EMC filter

1 mA

Printer/ fax

up to 1 mA

Photocopy machine

up tp 1.5 mA

Laundry machine, drying machine

up to 2 mA

Cookers, heaters

1mA / kW

Installed power cable 100 m

1 mA

A 1472, A1579 Leakage current clamp

4.1.3 Leakage currents in fault conditions

Faults in electrical installations and equipment can cause additional

continuous or

short-lasting leakage currents. Typical faults that can cause increased

leakage currents are:

Deterioration of insulation (because of pollution, moisture,

corrosion). This is causing a gradual increase of the resistive

leakage current,

Faults in electronic equipment.

If the neutral and PE wiring are connected together anywhere in the

installation this can result in an improper current distribution

through the neutral and PE conductors.

Typical faults that usually results in a high fault current that will immediately

trip the protective devices are:

Misswiring like changing the N and PE conductors.

Breakdown of insulation between active parts and earth anywhere

in installation or equipment

Short-lasting leakage currents are often a result of:

A sudden change in the voltage or current between active parts

and PE. This can result in a short leakage currents from several us

up to 100ms . Lightning and switching on/ off large loads can cause

such changes.

Fig.2: Fault leakage currents in electrical installations

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