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									Earth Leakage Circuit Breakers
Application guide

I ELCB should always be included               earth leakage. The more complicated            I Breaking capacity and short
  in the following types of electrical         the electrical wiring system the greater       circuit protection
  installations                                the accumulated effect of leakage              G Earth fault current breaking
1. Where there is danger of people             current. Consequently, if a too sensitive      capacity
   coming in contact with live                 ELCB is selected there is the possibility      ELCB detects earth fault current and
   conductors.                                 of mistripping because of this effect.         breaks the circuit. Select an ELCB
2. Where line voltage to ground                Generally, taking the case of a 30mA           which has an adequate breaking
   exceeds 150V AC.                            ELCB, constantly leaking current, in some      capacity as well as the appropriate
3. Inside buildings in which are stored        cases, would trip the breaker in the circuit   earth fault current expected to occur
   inflammable or explosive materials.         of motor load over 50A or in the circuit of    in the circuit. The earth fault current
4. Where heating elements are                  lamp load over 100A. However the 30mA          values are determined according to the
   embedded in concrete.                       ELCB will normally be suitable for home        circuit voltage (Voltage to ground) and
5. Where heating panels or pipes, or           or small shop use.                             resistance. In some cases a massive
   portable heaters are installed.                                                            earth fault current, which could have a
6. Where heating elements are                  (b) In this system an ELCB is provided         value as much as the short circuit
   installed in the ground or in water or      to each branch feeder. This system will        current, could flow.
   mud.                                        cost more because of the greater
7. In underwater lighting system for           number of ELCB's but since only the            G Short-circuit breaking capacity
   swimming pool use.                          circuit where the earth fault occurs           Besides earth fault current and
8. Where portable electrical equipment         trips the other feeders will not be            overcurrent the short-circuit current
   and tools are used.                         affected by the outage. This system is         flows into the ELCB. Thus it is
9. Where electrical equipment is used in       to be preferred where there is danger          necessary to consider its magnitude.
   dangerous locations, such as in water,      to life from electric shock using high         Generally the breaking capacity of
   wet place, on metal platforms, etc.         sensitivity current type ELCB.                 an ELCB tends to be less than a
10.Where emergency or temporary                                                               corresponding MCCB. In case the
   wiring is installed, such as flood-                                                        short-circuit current is too big for the
   lighting, temporary traffic signals or                                                     ELCB to handle it is necessary to
   signs, etc.                                                                                install back-up protection using MCCB,
                                                                                              fuse or similar devices.
I Check points for selecting ELCB                                                             To determine short-circuit currents
1. Sensitivity current                                                                        please refer to FUJI with details
2. Earth fault current breaking                                                               of your application.
   capacity                                    (a)
3. Short-circuit breaking capacity                                                            G SG and EG series
4. Operating time                                                                             This series provides protection in three
5. Selective protective coordination                                                          ways, against earth fault current,
6. Rated voltage and frequency                                                                overcurrent and short-circuit current.
7. Rated current
8. Detecting device
I  Selection of sensitivity current
• Appropriate sensitivity current
should be selected after considering              Load
the application purpose.
 Select ELCB with a sensitivity of less than
30mA where risk of human life is
 present and between 200mA and
500mA for protection against fire
due to electrical leakage.
• Protection system
ELCB are generally arranged in one of
the following ways.                                                                  ELCB
(a) In this case a wide range of protection
can be achieved economically using a
single ELCB unit. However, if an earth
fault occurs in only one branch of the
circuit the main ELCB will trip and all
feeders will stop. It will take time to          Load
isolate and repair the trouble.
Also, in any circuit there will be a minute

                                                                           Fuji Electric FA Components & Systems Co., Ltd./D & C Catalog
07/120                                                                                         Information subject to change without notice
                                                                                           Earth Leakage Circuit Breakers
                                                                                                      Application guide

I  ELCB operating time                            Example (A).....                            Instantaneous type
                                                                              ELCB            operating characteristic
The safe limit of current time that a
human being can withstand is 30mA                                                                     15mA             100mA 250mA
                                                                      500mA                           30mA             200mA 500mA
sec. Thus an ELCB for shock protection
must satisfy operating time less than

                                                                                                                         Main circuit
30mA sec/total current through body

(mA). So, assuming that the resistance

of a human body is 500 and the
voltage to ground 200V the body
current will be 200V =400mA
Hence the ELCB must operate within
  400mA =0.075 s.
FUJI ELCB's meet this requirement
and so ensure complete and certain                                                                                               Current
safety in operation.
                                                   Example (B).....                           Time delay type
I   Selective earth-fault current                                                             operating characteristic
    breaking coordination                                                                             15mA             100mA 250mA
                                                                                                      30mA             200mA 500mA
Where several ELCB's are provided
between the power source and branch

load, consideration must be given to

                                                                                                                         Main circuit
the appropriate selection of operating

time and sensitivity current. In case                         30mA
the sensitivity current of the branch circuit
ELCB is higher than that of the main
circuit ELCB, mistripping may occur             100mA
because selective protective coordination
is lost as is seen in example (B).
Therefore the arrangement given in                                                                                               Current
example (A) could be employed. That
is, the less sensitive ELCB should be
positioned nearest to the power source.         However, using this method perfect            I  Rated voltage
                                                earth fault protection cannot be              When selecting solid-state amplifier                           07
                                                expected. This is because even if the         type ELCB's make sure that a correct
                                                ELCB's are installed according to their       rated voltage is chosen. This is not
                                                sensitivities, i.e., 500mA, 200mA,            necessary in the case of the permanent
                                                30mA, the operating times are the             magnet ELCB, since in this case no
                                                same. Consequently, if the earth fault        outside control source is required.
                                                should occur in branch load the main
                                                circuit ELCB might trip. Thus the nearer      I  Rated current
                                                an ELCB is positioned to the                  FUJI ELCB's are calibrated for ambient
                                                power source the slower its operating         temperature of 40°C. Overheating may
                                                time should be.                               be expected if ELCB's are used at
                                                In order to meet this requirement FUJI        their maximum rated current at
                                                can supply earth leakage protective           ambient temperatures exceeding 40°C.
                                                relays provided with a time delay             Select a rated current with a suitable
                                                function. Since its operating time is         allowance. The load should be around
                                                adjustable between 0.2 and 2 seconds          80% of the rated current.
                                                it facilitates the selection protective
                                                coordination of systems of all kinds.
                                                These protective relays are generally
                                                installed in main circuits in
                                                combination with MCCB.

Fuji Electric FA Components & Systems Co., Ltd./D & C Catalog
Information subject to change without notice                                                                                                        07/121

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