Megger DET14C User manual

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M
DET14C and DET24C
Digital Earth Clamp-on Tester
USER GUIDE

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GSAFETY WARNINGS
These safety warnings are provided to ensure the safety of personnel and proper operation of the instrument.
■Safety warnings and precautions must be read and understood before the instrument is used. They must be observed during use.
■Do not leave the instrument connected to the system under test when not in use.
■Do not touch circuit connections and exposed metalwork of the installation or equipment under test.
■Do not use the instrument or connect it to any external system if it shows any visible signs of damage, malfunction or if it has been stored in unfavourable
conditions.
■Always keep body parts behind the tactile barrier on the handles of the instrument.
■Always inspect the instrument prior to use. Replace any defective parts immediately or return the instrument to an authorised service centre for repair.
■Do not use the instrument or connect it to any external system if the casing is open or any parts of the case are missing.
■Do not use rechargeable batteries in this instrument.
■Always use caution when clamping the instrument around energised electrical conductors.
■Always use extreme caution when clamping around bare conductors: under fault conditions, high voltages and currents may be present and may pose a shock
hazard.
■The instrument is not suitable for measuring AC currents in multi-core cables or DC currents.
■The instrument should not be used if any part of it is damaged.
■This instrument is not intrinsically safe and must not be used in hazardous atmospheres.
■If this equipment is used in a manner not specified by the manufacturer, the protection provided by the equipment may be impaired.
■Use extreme caution when using the instrument in proximity to bare conductors. Avoid contact between the metal in the jaws and bare conductors. A short
circuit would create an arc-flash explosion hazard
NOTE:
THE INSTRUMENT MUST ONLY BE USED BY SUITABLY TRAINED AND COMPETENT PERSONS.
Users of this equipment and/or their employers are reminded that National Health and Safety Legislation requires them to carry out valid risk assessments of all
electrical work so as to identify potential sources of electrical danger and risk of electrical injury such as inadvertent short circuits.
The safety warnings provided in this document are indicative of safe practice and shall not be considered exhaustive. Additionally, they are not intended to replace
local safety procedures where the instrument is being used.

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CONTENTS
GSAFETY WARNINGS..................................................................... 2
CONTENTS....................................................................................... 3
GENERAL DESCRIPTION ................................................................ 4
APPLICATION................................................................................... 6
MODES OF OPERATION................................................................. 8
GENERAL OPERATION.................................................................... 9
GENERAL SPECIFICATIONS ......................................................... 12
MEASUREMENT SPECIFICATIONS............................................... 14
ORDERING INFORMATION AND ACCESSORIES........................ 15
PREVENTATIVE INSTRUMENT MAINTENANCE.......................... 15
REPAIR AND WARRANTY .............................................................. 17
Symbols used on the instrument
GCaution: refer to accompanying notes.
tEquipment protected throughout by Double
Insulation.
cEquipment complies with current EU directives.
N13117
Equipment complies with current “C tick”
requirements.
Do not dispose of in the normal waste stream.
Equipment can be clamped around and removed
from hazardous live conductors [IEC 61010-2-032
Type A clamp].
Equipment not suitable for use where the
magnetic field exceeds this limit.
CAT IV 600 V
Overvoltage category IV (equipment installed at or
near the origin of the electrical supply to a
building.)
600 V refers to the rms phase-to-earth voltage that
this instrument can withstand to the overvoltage
category IV rating.

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GENERAL DESCRIPTION
The DET14C and DET24C represent a new generation of
earth/ground clamp-on resistance testers. These instruments
induce a test current into earth systems and measure ground
resistance in multi ground installations without needing to
disconnect the ground. They offer market leading access,
advanced features, simple operation and CAT IV 600 V safety
protection.
Designed with flat core ends, they prevent dirt build up,
ensuring measurement integrity and improved reliability over
products with interlocking teeth. Other enhancements over
current generation products include improved accuracy and up
to 300% increase in battery life. In electrically noisy
environments the built-in filter function offers increased noise
immunity.
DET14C and DET24C also offer a true RMS AC current
measurement facility up to 35 Amps. The instrument’s ability to
measure current flowing in an earth cable is a useful safety
feature, especially if the earth cable has to be disconnected. A
high current flow to earth could draw an arc on disconnection
with potentially severe consequences.
The elliptical shaped head design offers improved access to
cables and earth straps in constrained spaces (locations). The
clamp head accommodates up to 39 mm diameter cable and
50 mm earth tapes making them suitable for use in power
stations, sub-stations, towers and many more facilities. Operation
in dark and restricted areas is facilitated by a display with
backlight and an audible tone associated with the hold key. (The
special jaw opening mechanism ensures proper jaw closure yet
minimises the force required to open them).
The DET14C offers storage of results for later on-screen recall
and the DET24C supports a download of results via IrDA-to-USB
link into PowerDB and Power DB Lite, Megger’s Acceptance &
Maintenance Test Data Management software. Stored data is
indexed using a sequential serial number together with a time
and date stamp for each record.
FEATURES AND BENEFITS
■39 x 55 mm elliptical head
■Auto-current measurement safety feature
■Memory to record and view results
■Automatic self calibration
■Auto ranging
■High and low alarms
■Real time clock for date and time stamping of results
DET24C ADDITIONAL FEATURES
■IrDA USB interface to PC
■Advanced memory functionality with download
■Megger PowerDB/PowerDB LiteTM compatible

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Figure 1: DET14C / DET24C Instrument Front View
Figure 2: DET14C / DET24C Instrument Rear View
1. Clamp jaws
2. Tactile barrier
3. Rotary switch
4. HOLD button
5. LCD display
6. Keypad
7. Tactile barrier
8. Lever
9. Battery cover/label

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Figure 3: DET14C / DET24C Instrument Bottom
View
1. Wrist strap loop
2. IrDA window
Figure 4: DET14C / DET24C Instrument Display
View
Save Tick = set
Open Cross = not set
Delete Warning refer to user guide
IrDA download Signal noise detected
Alarm Less than
Filter More than
Battery
Hold
Date formats
Hours, minutes, seconds
Clamp open
1
2

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APPLICATION
The DET14C / DET24C digital earth clamp meters are particularly
suitable for measuring earth resistance in various installations
such as buildings, pylons and RF transmitter sites without system
disconnection. In addition, they can be used for the inspection
and verification of lightning protection systems and virtually any
installation where a current loop can be generated.
Principle of Operation
A defined test voltage is injected into the system under test using
a voltage transducer coil to induce a current, I, to flow which can
be measured by the current sensing coil. The resistance follows
from Ohm’s law, R = V/I.
The system shown in Figure 5 can be simplified to the resistance
of the electrode under test, Rg and the resistance of the other
electrodes in parallel, i.e. R1 || R2 || R3… || Rn. Therefore, the
current induced by the test voltage is I=V/[Rg+(R1 || R2 ||
R3… || Rn)]. It follows that as the resistance of the other
electrodes in parallel approaches zero, then the resistance
measured, approaches the value of the electrode under test.
Figure 5: Example earthing system suitable for
clamp meter

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MODES OF OPERATION
The DET14C / DET24C can operate in one of three main modes,
selected using the rotary switch:
OFF – Turn instrument off
Ω- Resistance measurement
A - Current measurement
Fn - Setup and configuration
When in a measurement mode, there are other functions which
are selected using the buttons:
HOLD – Hold the displayed measurement value.
– Enable / disable display backlight.
- Enable / disable buzzer function.
- Save displayed result to memory.
When in the setup and configuration mode (Fn), some buttons
have different functions:
- Increment value.
- Decrement value.
- Advance to next field.
OK – Accept value.
Figure 6: Main mode selection using the rotary
switch
Figure 7: Other functions using buttons

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GENERAL OPERATION
Powering on the Instrument
The instrument is switched on by turning the rotary switch to
one of the three mode positions, i.e. Ω, A or Fn. The Ω
(resistance) and A (AC current) measurements are both auto-
ranging.
Fig 8. Resistance measurement mode
Measuring Resistance Mode
With the resistance (Ω)mode selected simply open the clamp
and clamp around a ground conductor to be measured. The
instrument automatically senses the jaw opening and activates
the open jaw icon ( ) on the display. As soon as the jaw is
closed the open icon is removed and a resistance measurement
is initiated. A reading is taken periodically and the display
updated until the user presses the HOLD key to freeze the
reading or turns off the instrument.
Resistance measurements in high noise environments can be
problematic resulting in no reading. The DET14C / 24C
instruments incorporate a noise symbol ( ) to indicate
presence of noise during a measurement. A filter function
indicated by the filter icon ( ), is activated automatically in the
presence of noise. The filter results in a slightly longer
measurement period but offers improved noise immunity.
Measuring Current Mode
To measure true RMS AC current simply set the rotary switch to
the current mode (A) and clamp around the cable or tape to be
measured. RMS current is displayed on the screen in either A or
mA.

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HOLD
The HOLD key can be used to freeze a result in either resistance
or current mode. Once held, the result can be saved to memory
using the save () button.
HOLD has two modes depending on when it is activated:
If a measurement is in progress and HOLD is pressed it
will freeze the result even if the clamp is opened and
removed from the unit under test.
The user may also use the HOLD function with the clamp
closed before a measurement is taken. This mode assists
users to take readings in difficult to reach areas where the
instrument display may not be visible during the
measurement. Depressing the HOLD button for two
seconds with the clamp closed and no conductor present
will activate an automatic hold of the next result. HOLD
will flash on screen until the measurement is taken or it
times out. The instrument will sense open jaws, closed
jaws and take a reading, then freeze the reading on
screen and beep to indicate that the measurement is
complete.
Backlight
A low intensity backlight is provided on the instrument display to
facilitate measurements in dark conditions. The backlight button
( ) toggles the backlight on and off. An auto off timer will
switch the backlight off after 20 seconds to conserve power.
Saving Data
Data is saved in either resistance mode (Ω) or current mode (A).
Pressing the save key () will record a result with a time and
date stamp. It is important to regularly ensure that the time and
date settings are correct. Time and date are set from the
Function mode (Fn).
Function Mode
The Function mode (Fn) contains five minor functions on the
instrument:
Recall records ( )
Delete records ( )
Download via IrDA-to-USB ( )
Alarm setting ( )
Set Time/Date (H:M:S/D:M:Y M:D:Y Y:M:D )
In Function mode (Fn) the buttons shown in Figure 7 operate as
arrow buttons and are depicted in green matching the green
(Fn) icon on the rotary switch. The right arrow button is used to
scroll through minor functions in the order listed.