Utilization categories and Releases in circuit breakers

Circuit Breakers Utilization Categories:-

The utilization category of a circuit-breaker shall be stated with reference to whether or not it is specifically intended for selectivity by means of an intentional time delay with respect to other circuit-breakers in series on the load side, under short-circuit conditions ,

Attention is drawn to the differences of the tests applying to the two utilization categories

There are following types of utilization categories in Circuit breakers:-

(i)            Category A

These types of Circuit-breakers not specifically intended for selectivity under short- circuit conditions with respect to other short-circuit protective devices in series on the load side, i.e. without an intentional short-time delay provided for selectivity under short-circuit conditions, and therefore without a short-time withstand current rating.

(ii)          Category B

Circuit-breakers specifically intended for selectivity under short-circuit conditions with respect to other short-circuit protective devices in series on the load side, i.e. with an intentional short-time delay (which may be B adjustable), provided for selectivity under short-circuit conditions. Such circuit-breakers have a short-time withstand current rating as defined by manufacturer.

Releases in Circuit breakers

Releases referred to type of tripping applications requirement in circuit breakers, there are following types of releases available in circuit breakers.

(i)            Shunt release

(ii)           Over current release

There are following types of over current releases

(a)  Instantaneous

(b)  Definite time delay

(c)  Inverse time delay – This are two types of inverse time delay

    àIndependent of previous load

   à Dependent on previous load

(iii)          Under voltage releases

(iv)         Other releases

There is terms used more often that are Overload release and Short circuit releases.

Overload release- This term referred to for protection against overloads and

Short circuit release- This term is used to identify over-current releases intended for protection against Short circuits.

 There are following Characteristics associated with Different types of releases:-

(i)            Shut Release and Under-voltage release have similar types of characteristics that are:-

(a)  Rated control circuit voltage

(b)  Type of current

(c)  Frequency rating in case of alternating current

(ii)          Over current release have following characteristics:-

(a)  Rated current settings

(b)  Type of current

(c)  Frequency rating in case of alternating current

(d)  Current settings on front of MCCB or Circuit breaker

(e)  Time settings on front of MCCB or circuit breaker

Shunt release or under-voltage releases are used in Circuit breakers for breaking or opening the breaker in case of no supply or voltage below a certain level.

Rated current of Circuit breaker:- 

Rated current of a circuit breaker and its release is the RMS value of current corresponding to the maximum current setting which it shall be capable of carrying under the test conditions, without the temperature-rise exceeding the values specified in table below:-

Current setting of over-current releases

(i)            With Adjustable release:-

For circuit-breakers fitted with adjustable releases the current setting range shall be marked on the release or on its scale, the marking may be either directly in amperes, or as a multiple of the current value marked on the release.

(ii)          Without Adjustable release:-

In these breakers the marking may be done on the circuit-breaker. If the operating characteristics of the overload release comply with the requirements as per table below-,

It will be sufficient to mark the circuit-breaker with its rated current. In the case of indirect releases operated by current transformers, the marking may refer either to the primary current of the current transformer through which they are supplied, or to the current setting of the overload release. In either case, the ratio of the current transformer shall be stated. Unless otherwise specified

à The operating value of overload releases other than those of the thermal type is independent of the ambient air temperature within the limits of -5 “C to +40 ‘C;

à For releases of the thermal type, the values stated are for a reference temperature of +30 “C +- 2 “C. The manufacturer shall be prepared to state the influence of variations in the ambient air temperature.

Tripping time setting of over-current releases

1) Definite time-delay over-current releases

The time-delay of such releases is independent of the over-current. The tripping time setting shall be stated as the duration in seconds of the opening time of the circuit-breaker, if the time-delay is not adjustable, or the extreme values of the opening time~ if the time-delay is adjustable.

2) Inverse time-delay over-current releases

The time-delay of such releases is dependent on the over-current.

The time/current characteristics shall be given in the form of curves supplied by the manufacturer. These shall indicate how the opening time, starting from the cold state, varies with current within the range of operation of the release. The manufacturer shall indicate, by suitable means, the tolerances applicable to these curves.

These curves shall be given for each extreme value of the current setting and, if the time setting for a given current setting is adjustable, it is recommended that they be given in addition for each extreme value of the time setting.

Marking On Circuit Breakers

Each circuit-breaker shall be marked in a durable manner.

a)  The following data shall be marked on the circuit-breaker itself or on a nameplate or nameplates attached to the circuit-breaker, and located in a place such that they are visible and legible when the circuit-breaker is installed;

           (i)  Rated current (In);

     (ii) Suitability for isolation, if applicable, with the symbol

(iii) Indication of the open and closed positions, with O and I respectively, if symbols are used.

b) The following data shall also be marked externally on the circuit-breaker, except that they need not be visible when the circuit-breaker is installed;

      (i)       Manufacturer’s name or trade mark;

      (ii)      Type designation or serial number;

(iii)          IEC 60947-2 if the manufacturer claims compliance with this standard;

(iv)         Utilization category;

(v)          Rated operational voltage

(vi)         Rated impulse withstand voltage;

(vii)        Value (or range) of the rated frequency

(viii)       Rated service short-circuit breaking capacity at the corresponding rated voltage;

(ix)         Rated ultimate short-circuit breaking capacity at the corresponding rated voltage

(x)          Rated short-time withstand current, and associated short-time delay, for utilization category B;

(xi)         Line and load terminals, unless their connection is immaterial;

(xii)        Neutral pole terminals, if applicable, by the letter N;

(xiii)       Protective earth terminal, where applicable, by the symbol

(xiv)       Reference temperature for non-compensated thermal release, if different from 30 ‘C.

c) The following data shall either be marked on the circuit-breaker as specified in item b), or shall be made available in the manufacturer’s published information:

(i)       Rated short-circuit making capacity,

      (ii)       Rated insulation voltage, if higher than the maximum rated operational voltage,

(iii)          Pollution degree if other than 3;

(iv)         Conventional enclosed thermal current if different from the rated current,

(v)          IP Code, where applicable

(vi)         Minimum enclosure size and ventilation data (if any) to which marked ratings apply;

(vii)        Details of minimum distance between circuit-breaker and earthed metal parts for circuit-breakers intended for use without enclosures;

(viii)       Suitability for environment A or environment B, as applicable,

(ix)         R.M.S. sensing, if applicable

d) The following data concerning the opening and closing devices of the circuit-breaker shall be placed either on their own nameplates or on the nameplate of the circuit-breaker; alternatively, if space available is insufficient, they shall be made available in the manufacturer’s published information:

 (i)     Rated control circuit voltage of the closing device and rated frequency for alternating current

(ii)       Rated control circuit voltage of the shunt release and/or of the under-voltage release, and rated frequency for Alternating current;

(iii)         Rated current of indirect over-current releases;

(iv)         Number and type of auxiliary contacts and kind of current, rated frequency and rated voltages of the auxiliary switches, if different from those of the main circuit.

(v)          Terminal marking