Megger BT51 Operating Manual

Digital Milliohmmeter
BT51

USER GUIDE

GUIDE DE L’UTILISATEUR

GEBRAUCHSANLEITUNG

GUÍA DEL USUARIO

M

2

Safety Warnings

■ Safety Warnings and Testing Precautions must be read and understood before the instrument is used.

They must be observed during use.

■ Circuit under test must be switched off, de-energised and isolated before any test connections are made.

■ Test leads and handspikes must be in good order, clean and with no broken or cracked insulation.

■ Circuit connections must not be touched during a test.

■ The instrument must be earthed (grounded) when connected to a mains power source (for battery charging).

■ Replacement fuses must be of the correct type and rating.

■ The instrument should not be used if any part of it is damaged.

■ Refer to pages 7 and 8 for further explanations and precautions.

■ No user serviceable parts inside the instrument. Do not operate this equipment if damaged or faulty.

Return to authorised Megger Service centre for repairs

■ Disconnect the mains lead before changing the mains inlet fuse. Always replace the fuse with one of the correct rating

to ensure protection from fire: 100mA(T)HBC 250V 20mm.

■ Warning! This instrument is measurement category O which means it is not rated for mains connection.
The measurement circuit will detect hazardous voltages up to 240V, but is not rated for higher voltage transients that occur on mains circuits.
Do NOT use where accidental connection to live mains circuits may occur.

NOTE - THE INSTRUMENTS MUST ONLY BE USED BY SUITABLY TRAINED AND COMPETENT PERSONS.

CAT II - Measurement category II:

Equipment connected between the electrical
outlets and the user’s equipment.

CAT III - Measurement category III:

Equipment connected between the
distribution panel and the electrical outlets.

CAT IV - Measurement category IV:

Equipment connected between the origin
of the low-voltage mains supply and the
distribution panel.

3

Features - Caractéristiques - Merkmale - Características

Hinged lid

Couvercle amovible
Abdeckung mit scharnieren
Tapa con bisagras

Terminals

Bornes
Anschlüsse
Terminales

Dangerous voltage warning light

Tension dangereuse voyant d’avertissement
Gefährliche spannung Warnanzeige
Tensión peligrosa
Luz de advertencia

Indicating light for “test current flowing’
Voyant d’« écoulement du courant de test »
Anzeige für ‚prüfstrom fließt’
Luz indicadora de ‘circulación de corriente de

prueba’

Digital display
Afficheur numérique
Digitales display
Pantalla digital

Battery charging neon light

Voyant néon de charge

de la batterie

Neonanzeige für die akkuladung

Luz de neón de carga de la batería

Mains supply fuse

Fusible de l’alimentation secteur

Netzversorgungssicherung

Fusible de alimentación de red

Battery charger socket cover

Couvercle de la prise du

chargeur de batterie

Abdeckung der akku-ladesteckdose

Tapa de toma para cargador

de batería

Detachable hinges

Charnières amovibles
Abtrennbare scharniere
Bisagras desmontables

Range selector switch

Commutateur de sélection
de gamme

Bereichswahlschalter
Conmutador de escalas

Low battery voltage warning light

Voyant d’alerte de batterie faible
Warnanzeige für niedrige Akkuspannung
Luz de advertencia de tensión de

batería baja

4

Contents Guide de l’utilisateur p13 Gebrauchsanleitung p23 Guía del usuario p37

Safety Warnings 2

General Description 6

Applications 7

Specification 8

Operation 9

Warning 11

The detachable lid 11

Performing a test 11

Using alternative leads 10

Charging the battery 10

Outline Diagram 4

Repair and Warranty 12

End of life disposal 12

5

General description

The BT51 uses the four terminal measurement principle. Current generated
within the instrument, passes between the current terminals C1 and C2 via
the test sample. The voltage across the test sample is measured across the
potential terminals P1 and P2.

The test current, of nominally 2A, is measured by monitoring the voltage
drop across an internal series resistor. The instrument compares this
voltage with the voltage across the P1 and P2 terminals and a ratiometric
measurement is performed. On the lower range a voltage amplifier is used.
Because the measurement is ratiometric the reading is unaffected by minor
variations of test current.

There are two measuring range, 2000 mW and 20 mW, selected by the
rotary switch that is also used to turn the instrument off. The readings are
indicated on a 31⁄2 digit light emitting diode display which is easily seen in
poor lighting conditions.

A green L.E.D. indicator light glows when the test current is passing
between the C1 and C2 terminals as a test is made. A red neon light
adjacent to the terminal, illuminates as a warning of the presence of a
dangerous voltage, should the test lead probes be accidentally placed
across a “live”circuit. The instrument incorporates a relay protection
circuit (effective up to 240 V a. c. ) should such a connection occur. This
protection becomes operative at low voltages and the neon warning light
shows when a dangerous voltage is present. Both the neon warning light
and the protective relay are effective irrespective of whether or not the
instrument has been turned on prior to the probes being placed across the
voltage source.

Power for the instrument and the test circuit is obtained from internal
rechargeable NiCd cells. When the battery needs recharging a red L.E.D.
“low battery voltage” warning light illuminates next to the display. An
integral charger unit is fitted accompanied by a warning neon light to show
when the battery is under charge, and a fuse for protection.

Note :- It is advisable to ensure that the battery cells are fully
charged before embarking upon any tests.

The instrument is contained in a robust plastic case with a hinged
detachable lid that will automatically become unclipped if it is accidentally
thrown or dropped open, thus preventing damage to the hinges.

A variety of test lead set, some with duplex handspikes are available as
optional extras.

6

Applications

The BT51 is designed to measure the resistance of the bonding of
metalwork on large frames and structure, earth bond, able bond, lightning
conductors etc. and to check bus bar continuity. It is also able to measure
the resistance of the bonding of metalwork on aircraft. It has a resolution
of, 0,01 mW, and is able to check the resistance between metal points on
the aircraft structure

Symbols used on the Instrument

 Caution, refer to accompanying documents

Equipment complies with current EU Directives

This equipment should be recycled as electronic waste

Power cord: If the power cord plug is not suitable for your

type of socket outlets (receptacles) do not
use an adaptor

You should use a suitable alternative power
cord, or if necessary change the plug by
cutting the cord and fitting a suitable plug

The colour code of the cord is

Earth (Ground) Yellow/Green
Neutral Blue
Phase (line) Brown

If using a fused plug, a 3 Amp fuse to BS 1362 should be fitted

Note: A plug severed from the power cord should be
destroyed, as a plug with bare conductors is hazardous in
a live socket outlet

7

Specifications

Ranges 2000 mΩ resolution 1 mΩ

20.00 mΩ resolution 0.01 mΩ

Test current 2 A to 2.5 A at any reading

Accuracy (0˚C to 50 ˚C) ± 1% ± 2 digits

Display 3 ½ digit L. E. D.

Temperature Range Operating 0 ˚C to +50 ˚C

Storage –20 ˚C to +50 ˚C

Protection Relay protection for up to 240 V a.c. power source applied
240 V model 100 mA (T) fuse 20 mm x 5 mm ceramic (For charging circuit)

115 V model 250 mA (T) fuse 20 mm x 5 mm ceramic (For charging circuit)

Power Supply Internal 4 Ah NiCd rechargeable cells and charging unit.
Normal charging time at 240 V is 10 hours

Safety The instruments meet the requirements for double insulation to IEC 61010-1.

E. M. C. In accordance with IEC 61326-1

Dimensions 344 mm (131⁄2 ins) x 245 mm (9 5⁄8 ins) x 158 mm (61⁄4 ins)

Weight 4.5 kg (10 lb)

Cleaning Wipe disconnected instrument with a clean cloth dampened with soapy water or Isopropyl Alcohol (IPA).

Operational uncertainties Refer to www.megger.com

See Earth Leakage tolerance for 60Hz operation.

8

Operation

WARNING

Ensure that the equipment or conductor to be tested is de-energised before
connecting the instrument.

THE DETACHABLE LID

The lid hinges are fitted with spring loaded clips and are designed in this
way for two reasons. Firstly, if the lid is accidentally thrown open to its full
extent the hinges will not be strained or broken but the lid will be safely
unclipped. Secondly, the lid can purposely be removed if required when
the instrument is in use by simply opening it up to its full extent and gently
pressing down on the opening edge while holding the tester body firm.
The hinges will then unclip. To replace the lid, hold it vertically and push the
hinges back into their clips again while restraining the instrument. Then fold
the lid shut.

PERFORMING A TEST
(assuming duplex handspikes are used)

1. Connect the test leads to the instrument terminals
current leads to C1 and C2, potential leads to P1 and
P2. Note:- Duplex handspikes provided by Megger
Limited are identified as follows: The current lead is
black and the spade connector is stamped with a ‘C’,
the potential lead is red and the spade connector
is stamped with a ‘P’. On the handspikes themselves, the
potential spike is marked with a ‘P’.

2. Turn the range selector switch to the appropriate
position.

3. If it is desired check that the instrument is
functioning correctly by touching the two handspikes
onto a known low resistance piece of metal with the
potential spikes as close as possible to each other.

A zero reading should be obtained on the digital L.E.D. display.

Note:- Current will only pass when the circuit is completed between the
C1 and C2 spikes. The green L.E.D. light will illuminate to indicate when
this occurs. Make sure also that the low battery warning light does not
illuminate.

4. Press the handspike sets down on to the equipment
or conductor to be tested. (The handspikes may be as
far apart as the lead length will allow).

5. Read the resistance measured from the digital display

6. If the over-range symbol appears on the display when
the 20 mW range is in use i.e. a ‘I’ as the left
hand digit with the remaining L. E. D’s blank, turn the
selector switch to the 2000 mW range and repeat the
test. If the over-range symbol (i.e a ‘I’ as the left hand
digit) appears again the resistance being measured is
outside the range of the instrument.

9

Operation

7. After testing remove the handspike, turn the
selector switch to ‘Off’ and disconnect the test leads.

Caution:~ When the instrument is used for measuring an
inductive load, a voltage spike will appear across
the terminals. This occurs when the instrument is
switched between ranges or the test leads are
connected or disconnected. The instrument will
withstand voltage spikes caused when measuring
inductive loads (which include the test leads) of up to
250 mH.

USING ALTERNATIVE LEADS

For any of the C1, C2, P1 and P2 connection, test leads terminated with
bulldog clips or clamp connectors may be used. Single handspikes are
also suitable. Alternative test leads are available from Megger Limited (see
Accessories, page 11).

The testing procedure as given above should be followed. However, it must
be remembered when using fixed current connection, that as soon as the
connections are made and the circuit completed, the test current will flow
unless the selector switch is in the ‘Off’ position. Therefore, in order to
conserve battery power, it is advisable, whatever type of connections are
used to keep the time for the test as short as possible

With the fixed type of current connection, keep the selector switch in the
‘Off’ position while the connections are made and until the test is ready to
be performed

CHARGING THE BATTERY

If while performing a test the “low battery voltage” warning light
illuminates the batteries must be recharged.

1. Lift the battery charger socket cover to expose
the charger socket.

2. Connect a suitable three-pin plug to the battery
charger mains supply lead. Ensure that the earth wire
in the supply lead is connected so that the instrument
is earthed when charging the battery

3. Plug the lead into the instrument and then into
a convenient mains supply socket and switch on.

4. Allow the battery to charge for 10 hours.

Note ~ The instrument may be used to perform tests during charging,
providing the battery is not completely exhausted and has been allowed
a little time to recover its voltage. The mains supply cannot fulfill the test
current requirements ·without the aid of the battery. In these circumstances
problems in measurement may arise due to mains interference. A longer
charging time must be allowed if battery charging and testing are carried
out simultaneously. The battery will not be damaged by a longer charging
period.

5. After charging, switch off the mains power supply,
remove the charging lead and replace the battery
charger socket cover.

10

ACCESSORIES - Supplied with the instrument

Supply lead for battery charging
Part No. 25424-860
Duplex handspikes with 2.5m (8 ft) test leads
Part No. 6111-022
User Guide
Part No. 6170-921

ACCESSORIES - Supplied at extra cost

Duplex handspikes with 6.1m (20 ft) test leads
Part No. 6111 -023
Duplex handspikes with 9.1m (30 ft) test leads
Part No. 6111 -024
Accessory pouch, nylon
Part No. 6420-096
Single handspike (1) for potential measurement. 2m/7ft
Part No. 242021-7

Accessories

11

Repair and Warranty

The instrument circuit contains static sensitive devices, and care must
be taken in handling the printed circuit board. If the protection of an
instrument has been impaired it should not be used, and be sent for repair
by suitably trained and qualified personnel. The protection is likely to be
impaired if, for example, the instrument shows visible damage, fails to
perform the intended measurement, has been subjected to prolonged
storage under unfavourable condition, or has been exposed to severe
transport stresses.

New Instruments are Guaranteed for 1 Year from the Date of Purchase by
the User.

Note: Any unauthorized prior repair or adjustment will
automatically invalidate the Warranty.

Instrument Repair and Spare Parts

For service requirements for Megger Instruments contact:
Megger Limited or Megger
Archcliffe Road Valley Forge Corporate Center
Dover 2621 Van Buren Avenue
Kent, CT17 9EN. Norristown, PA 19403
England. U. S. A.
Tel: [phone] Tel: [phone]
Fax: [phone] Fax: [phone]
or an approved repair company.

Approved Repair Companies

A number of independent instrument repair companies have been approved
for repair work on most Megger instrument, using genuine Megger spare
parts. Consult the Appointed Distributor / Agent regarding spare parts,
repair facilities and advice on the best course of action to take.

Returning an Instrument for Repair

If returning an instrument to the manufacturer for repair, it should be sent
freight pre-paid to the appropriate address. A copy of the Invoice and of the
packing note should be sent simultaneously by airmail to expedite clearance
through Customs. A repair estimate showing freight return and other
charges will be submitted to the sender, if required, before work on the
instrument commences.

WEEE

The crossed out wheeled bin placed on the Megger products is a reminder
not to dispose of the product at the end of it’s product life with general
waste.

Megger is registered in the UK as a Producer of Electrical and Electronic
Equipment.

The Registration Number is WEE/HE0146QT

Batteries

The crossed out wheeled bin placed on the batteries is a reminder not to
dispose of them with general waste at the end of their life.

This product contains a NiCad battery pack 7.2V 4Ah (6VR4)
Battery replacement should only be performed by a Megger authorised

repair agent, who will correctly dispose of the spent battery.
For the purpose of end of life disposal only, the battery can be accessed by

removing the four recessed screws on rear of instrument and lifting off front
panel.

Spent NiCad batteries from the BT51 are classified as Industrial

12

Milli-ohmmètre numérique
BT51

GUIDE DE L’UTILISATEUR

GEBRAUCHSANLEITUNG

GUÍA DEL USUARIO

M

Précautions de sécurité

■ Lisez attentivement et comprenez les consignes de sécurité et les précautions à prendre pour les
tests avant d’utiliser l’appareil.

■ Elles devront être respectées lors de l’utilisation de l’appareil.

■ Le circuit à tester doit être éteint, hors tension et isolé avant d’effectuer les connexions pour les tests.

■ Les cordons et les pointes de touche doivent être propres et en bon état, leur isolant ne doit être ni brisé, ni fissuré.

■ Les connexions des circuits ne doivent pas être touchées lors d’un test.

■ L’appareil doit être relié à la terre lorsqu’il est branché sur le secteur pour recharger la batterie.

■ Les fusibles de rechange doivent être de type et de calibre appropriés.

■ L’appareil ne doit pas être utilisé si l’un de ses composants est endommagé.

■ Reportez-vous aux pages 16 et 17 pour de plus amples explications et précautions.

■ Aucune pièce réparable par l’utilisateur à l’intérieur de l’appareil. N’utilisez pas cet appareil s’il est endommagé ou défectueux.
Envoyez-le à centre de service Megger agréé pour le faire réparer.

■ Avertissement: débranchez le cordon d’alimentation avant de changer le fusible d’entrée secteur. Remplacez toujours le fusible
par un fusible de calibre correcte afin d’assurer la protection contre les incendies: 100 mA(T) HBC 250 V 20 mm.

■ Avertissement ! Cet appareil est classé en catégorie de mesure O, ce qui signifie qu’il n’est pas classé pour être connecté au secteur.
Le circuit de mesure permet de détecter des tensions dangereuses jusqu’à 240 V, mais n’est pas classé pour les tensions passagères plus élevée qui
se produisent sur les circuits du secteur. N’utilisez PAS l’appareil aux endroits où des connexions avec des circuits secteur sous tension pourraient
se produire.

REMARQUE: CET APPAREIL NE DOIT ÊTRE UTILISÉ QUE PAR DU PERSONNEL FORMÉ ET QUALIFIE.

CAT II - Mesure catégorie II : équipement

connecté entre les prises de courant et
l’équipement de l’utilisateur.

14

CAT III - Mesure catégorie III : équipement
connecté entre le tableau électrique et les prises
de courant.

CAT IV - Mesure catégorie IV : équipement
connecté entre la source d’alimentation électrique
à basse tension et le tableau électrique.

Précautions de sécurité 14

Description générale 16

Applications 17

Caractéristiques 18

Utilisation 19

Avertissement 19

Le couvercle amovible 19

Exécution d’un test 19

Utilisation d’autres cordons de test 20

Recharge de la batterie 20

Schéma de principe 4

Réparation et garantie 22

Élimination en fin de vie 22

Table des matières

15