1 joule per second equals 1 watt

The short circuit current curve look like a short parabola and that is defined as x2 so:  

E= ∫i2 dt - meaning it is the area below the curve.

According to the calculus rule it is calculated as I2t joules.  

or also:

Power = VI = I2R in watts

and so

Electrical energy= Power(watts) x time = (I2 x R) x time (seconds) in Joules.

but what if the R is so small compared to I one can ignore it, then Energy = I2t joules  

***Maybe the mathematicians out there will kill me for this but it is how I understand it.

SANS give pre-requisites for components first.

For a circuit breaker it must, at a specific voltage (considering the circuit power factor) and the fault current equalling its rated breaking capacity or lower be capable of breaking the circuit. gs

5.1.3 - EFP

UL 508, Industrial control equipment.

6.7.2.1 Overload protection:
The rated current of the overload protective device shall not
exceed the current-carrying capacity of the conductor it protects, except in the case of circuits in which the presence of overload protection could create a dangerous situation, such as in circuits for lifting magnets

BTW: No mention of the component current ratings?gs

4.4.4.1

Reference:- ABB Comparison of tripping characteristics for miniature circuit-breakers

For protection against overload, the protective device must be selected  based on the current carrying capacity

Ib ≤ In ≤  Iz (standard)

Idesign ≤ Icb ≤  Icable (gs)

and

I2 ≤ 1.45 x Iz (standard)

Ioperation ≤ 1.45 x Icable (mine)

Ib= Design current of a circuit

In= Rated current of the protective device

Iz= Current carrying capacity of the cable in accordance with IEC/HD 60364-5-52

I2 = Current ensuring effective operation in the conventional time of the protective device

Exception: Where the assembly including the overcurrent devices protecting the feeder(s) are
listed for operation at 100% of their rating, neither the ampere rating of the overcurrent device nor the ampacity of the feeder conductors shall be less than the sum of the continuous load plus the noncontinuous load.

Only breakers listed for 100% application,
and so labelled can be applied under the exception (for example loads Frame and R Frame 140G’s that are specifically marked and rated 100%).

Breakers without a 100% application listing and label are applied at 80% of rating
 

I could not find above in NEC 2011 - so I struck it through. 

II. Branch-Circuit Ratings 210.19 Conductors — Minimum Ampacity and Size.
(A) Branch Circuits Not More Than 600 Volts.
(1) General. Branch-circuit conductors shall have an ampacity not less than the maximum load to be served.

Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum branch-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.

Exception: If the assembly, including the overcurrent devices protecting the branch circuit(s), is listed for operation at 100 percent of its rating, the allowable ampacity of the branch circuit conductors shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.
 

Informational Note No. 1: See 310.15 for ampacity ratings of conductors.
Informational Note No. 2: See Part II of Article 430 for minimum rating of motor branch-circuit conductors.
Informational Note No. 3: See 310.15(A)(3) for temperature limitation of conductors.

Meaning:

For <=600V circuits

Icable>=Iload

For assembly NOT listed for 100% operation:

***Not considering adjustment factors.

Mixed loads(Non-Cont and Cont) Icable>Sum of Inoncont +125%Icont

For assembly listed for 100% operation:

Mixed loads(Non-Cont and Cont) Icable > Sum of Inoncont + Icont

=============

(B) Overcurrent Devices Rated 800 Amperes or Less.
The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met:
 

(1) The conductors being protected are not part of a branch circuit supplying more than one receptacle for cord
and-plug-connected portable loads.
 

(2) The ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit
breaker without overload trip adjustments above its rating (but that shall be permitted to have other trip or
rating adjustments).
 

(3) The next higher standard rating selected does not exceed 800 amperes.
(C) Overcurrent Devices Rated over 800 Amperes.

 Where the overcurrent device is rated over 800 amperes, the ampacity of the conductors it protects shall be equal to or greater than the rating of the overcurrent device defined in
240.6.

Meaning: Except if a small conductor (the lord alone knows what this is) If <800amp one an select a one size higher fuse - as long as such size is <800Amp.

For higher the 800Amp it must be same as cable or by some 240.6

4:7:3: Unless otherwise specified
– Non thermal overloads no change -5 “C to +40 ‘C;

-Thermal overloads - reference temperature of +30 “C +- 2 “C. Manufacturer shall provide variations data (see 7.2.1.2.4, item b)).

2:4:37: - and 2:5:30 could not find references

DEFINING THE TRIPPING CURVE

4.7.4 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.
 

NOTE It is recommended that the current be plotted as abscissa and the time as ordinate, using logarithmic scales.

Furthermore, in order to facilitate the study of co-ordination of different types of over-current protection,

Meaning:

4:7:3: Unless otherwise specified
– Non thermal overloads no change -5 “C to +40 ‘C;

-Thermal overloads - reference temperature of +30 “C +- 2 “C. Manufacturer shall provide variations data (see 7.2.1.2.4, item b)).

Uo is the nominal voltage to earth.
Ia is the current required to achieve the disconnection time as given in the Regulations.
 

Cmin is the minimum voltage factor to take account of voltage variations depending on time and place, changing of transformer taps and other considerations.
 

NOTE: For a low voltage supply given in accordance with the Electricity Safety, Quality and Continuity. Regulations 2002 as amended, Cmin is given the value 0.95.

6.6.1.16 Where the prospective fault level of the supply cannot be determined, a fault current meter may be used (see 8.5.2).
 

6.6.1.17 All disconnecting devices in a distribution board
a) shall be protected by a fully rated short-circuit protective device, and
b) when used in combination with a short-circuit protective device (see 6.7.4), shall have a conditional short-circuit current rating (see 3.22.1) appropriate to its condition of installation, but of not less than 2,5 kA

Rated short-time withstand current (Icw)

The rated short-time withstand current of a circuit-breaker is the value of short-time withstand current assigned to that circuit-breaker by the manufacturer under the test conditions specified In 8.3.6.2.

 For a.c., the value of this current is the r.m.s value of the a,c. component of the prospective short-circuit current, assumed constant during the short-time delay.

The short-time delay associated with the rated short-time withstand current shall be at least 0,05 s,

Preferred values being as follows:

0,05 –0,1 –0,25–0,5–1 S

The rated short-time withstand current shall be not less than the appropriate values shown in table 3

Table 3- Minimum values of rated short-time withstand current

In = CB rated current

In <2500 ->12xIn or 5 kA, whichever is the greater

In >2500 ->30 kA

 -------------============--------

110.9 Interrupting Rating.Equipment intended to interrupt current at fault levels shall have an interrupting ratin
not less than the nominal circuit voltage and the current thais available at the line terminals of the equipment.
Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage not less than the current that must be interrupted.
 

110.10 Circuit Impedance, Short-Circuit Current Ratings, and Other Characteristics.

The overcurrent protective devices, the total impedance, the equipment shortcircuit current ratings, and other characteristics of thecircuit to be protected shall be selected and coordinated to permit the circuit protective devices used to clear a fault to do so without extensive damage to the electrical equipment
of the circuit.

This fault shall be assumed to be either between two or more of the circuit conductors or between an
circuit conductor and the equipment grounding conductor(s) permitted in 250.118.

Listed equipment applied in
accordance with their listing shall be considered to meet the requirements of this section.

======

230.208 Protection Requirements. A short-circuit protective device shall be provided on the load side of, or as an integral part of, the service disconnect, and shall protect all
ungrounded conductors that it supplies.

The protective device shall be capable of detecting and interrupting all values of current, in excess of its trip setting or melting point, that can
occur at its location.

A fuse rated in continuous amperes not to exceed three times the ampacity of the conductor,

*I dont have 60 898

IEC classifies MCBs into three category depending upon their “Quality of current
limiting” & let through energy of a circuit breaker on short circuits. Permissible let to energy values for circuit breakers with rated current up to and including 16A as per

EN60898 are:
Class 1 No limitation
Class 2 290 kA²S
Class 3 84 kA²S -

*All Hager mcb are class 3

IEC 60364

UL489

UL1077

CSA c22.2 No 5.02CSA c22.2 No 235-04

UNLESS

The over current device can sit anywhere in the cable as long as no connections to/from it

AND

entire length protected against shorts circuit OR

cable shorter then 5mtrs

not near flammable materials

not likely to cause humans harm

I spent a lot of time trying to get to grips with this - I get this feeling this commission could not get consensus the matter of "anywhere in the cable"...thus the strange additions. Flammable and human safety? Really?

Now the challenge: Overload unit can be anywhere in the cable but the whole cable must be short circuit protected?

Mechanical protection or another electrical component?

With reference to 4.4.5.2.1and Fig. G.1, short-circuit protective device P 2may be moved up to 3 m from the origin (O) of the branch circuit (S2) provided that there is no other connection or socket-outlet on this length of the branch circuit, and in the case of 4.4.5.2.1
the risk of short-circuit, fire and danger to persons is reduced to a minimum for this length.

but:

4.4.4.2 Position of devices for overload protection
4.4.4.2.1 A device ensuring protection against overload shall be placed at the point where a change, such as a change in cross-sectional area, nature, method of installation or in constitution,
causes a reduction in the value of current-carrying capacity of the conductors, except where
4.4.3.2.2and 4.4.3.3 apply.

4.4.4.2.2 The device protecting the conductor against overload may be placed along the run of that conductor if the part of the run between the point where a change occurs (in cross-sectional area, nature, method of installation or constitution) and the position of the protective device has neither branch circuits nor socket-outlet circuits and fulfils at least one of the following two conditions:
a) it is protected against short-circuit current in accordance with the requirements stated in 4.4.5;
b) its length does not exceed 3 m, it is carried out in such a manner as to reduce the risk of shortcircuit to a minimum, and it is installed in such a manner as to reduce to a minimum the risk of
fire or danger to persons (see also 4.4.5.2.1).
NOTE: For installation according to a) see Figure F.1.
For installation according to b) see Figure F.2

_a) there is no branch circuit or socket-outlet between the point where there is a reduction in the conductor's current-carrying capacity and the point where the device is installed, and

b) the entire length of the conductor is protected against short-circuit, or
 

6.7.3.2

4.4.5.2 Position of devices for short-circuit protection A device ensuring protection against short-circuit shall be placed at the point where a reduction in the cross-sectional area of the conductors or another change causes a change to the current-carrying capacity of the conductors, except where 4.4.5.2.1, 4.4.5.2.2or 4.4.5.3 applies.
4.4.5.2.1 The various cases stated in the following sub clause shall not be applied to installations situated in locations presenting a fire risk or risk of explosion and where special rules for certain
locations specify different conditions. The device for protection against short-circuit may be placed other than as specified in 4.4.4.2, under the following conditions.

In the part of the conductor between the point of reduction of cross-sectional area or other change and the position of the protective device there shall be no branch circuits nor socket-outlet circuits
and that part of the conductor shall:
a) not exceed 3 m in length, and
b) be installed in such a manner as to reduce the risk of a short-circuit to a minimum,

and so forth and so forth...

4.4.4.3.1 General Devices for protection against overload need not be provided:
a) for a conductor situated on the load side of a change in cross-sectional area, nature, method of installation or in constitution, that is effectively protected against overload by a protective device placed on the supply side;

b) for a conductor that is not likely to carry overload current, provided that this conductor is  protected against short-circuit in accordance with the requirements of 4.4.4 and that it has neither branch circuits nor socket-outlets;

c) at the origin of an installation where the distributor provides an overload device and agrees that it affords protection to the part of the installation between the origin an d the main distribution point of the installation where further overload protection is provided.

Alsocheck: The requirements for overcurrent protection devices are for use in industrial cabinets
(Industrial Control Panels) anchored in the UL 508A

210 - Branch circuits

215 - Feeders

240 - Overcurrent Protection

VC8035 -

VC8036 -

IEC 60947-2 (circuit breaker design and manufacturing)

IEC 60364, § 434.5.1 (electrical distribution network).

UL1066 - LV AC and DC CB in Enclosures

UL 489: Molded-Case Circuit Breakers, Molded-Case Switches and Circuit Breaker Enclosures

UL 489 MCCB: MCS(Molded Case Switches) & Circuit Breaker Enclosures.

IEC 60947-2.2003

This gives procedure for the testing not method to confirm. Maybe this is outdated.

A lower rated breaking capacity is permitted if another protective device having the necessary breaking capacity is installed on the supply side.

In that case,

 the characteristics of the devices shall be coordinated so that the energy let through by these two devices does not exceed that which can be withstood without damage by the device on the load side and the conductors protected by these devices.

THIS IS ALL TO DO: Check that the source I2t energy is below a certain value for bottom component.

Not just for cascading but for anything below a circuit breaker...like a contactor or switch.

Knowing the let through energy of a supply SCPD one just has to ensure the load side component kA (over time) is higher than this. Its like choosing a fuse. 

Actually cascading table per supplier is redundant!

60 947-2: ANNEX A

The term “coordination” includes consideration of discrimination (see 2,5.23 of Part 1 and
also 2,17,2 and 2.17.3) as well as consideration of back-up protection (see 2.5.24 of Part 1).
Consideration of discrimination can in general be carried out by desk study (see clause A.5),
whereas the verification of back-up protection (Cascading gs) normally requires the use of tests (see clause A,6).

Found no ref to 2.5.23

2.17.2:

Total discrimination (total selectivity) over-current discrimination where, in the presence of two over-current protective devices in series, the protective device on the load side effects the protection without causing the other protective device to operate

2.17.3
partial discrimination (partial selectivity)
over-current discrimination where, in the presence of two over-current protective devices in series, the protective device on the load side effects the protection up toa given level of over current, without causing the other protective device to operate

---------===========-------

The obvious is that the information all provided by manufacturer and the components comply to relevant standards.

Ultimately: The maximum conditional short-circuit current (see 2.5.29 of Part 1) shall not exceed the rated ultimate short-circuit breaking capacity of the SC PD.

C1=source cb

C2=load cb

IEC 60947.2.2003

A.5 Verification of discrimination
Discrimination can normally be considered by desk study alone, i.e. by a comparison of the
operating characteristics of C1 and the associated SCPD, for example, when the associated
SCPD is a circuit-breaker (C2) provided with an intentional time-delay,

The manufacturers of both the C1 and the SCPD shall provide adequate data concerning the relevant operating characteristics so as to permit Is to be determined for each individual association.

In certain cases, tests at Is are necessary on the association, for example
— when C1 is of the current-limiting type and C2 is not provided with an intentional time-delay;
— when the opening time of the SCPD is less than that corresponding to one half-cycle,
To obtain the desired discrimination when the associated SCPD is a circuit-breaker, an
intentional short-time delay may be necessary for C2.

Discrimination may be partial (see figure A.4) or total up to the rated short-circuit breaking
capacity Icu (or Ics) of C1. For total discrimination, the non-tripping characteristic of C2 or the pre-arcing characteristic of the fuse shall lie above the tripping (break-time) characteristic
of C1.
Two illustrations of total discrimination are given in figures A.2 and A.3.

Meaning: All they say is that the two cb curves must be adjacent in all respects at all times...other wise its only partially protected.

I.O.W C2 must be more sensitive / closer to the tripping points

A.6 Verification of back-up protection

A.6.1 Determination of the take-over current: -Compliance with the requirements of A.3,2 can be checked by comparing the operating characteristics of Cl and the associated SCPD for all settings of Cl and, if applicable, for all
settings of C2.

A.6.2 Verification of back-up protection
a) Verification by tests.
Compliance with the requirements of A.3.3 is normally verified by tests in accordance with A.6.3. In this case, all the conditions for the tests shall be as specified in 8.3.2.6 with the
adjustable resistors and inductors for the short-circuit tests on the supply side of the
association.

---------

A.3.3 Behaviour of Cl in association with another SCPD
For all values of over-current up to and including the short-circuit breaking capacity of the
association, Cl shall comply with the requirements of 7,2.5 of Part 1, and the association shall comply with the requirements of 7.2.1,2.4, item a).

7.2.5 Ability to make and break under short-circuit conditions

7.2.1 Operating conditions

Meaning: C1 must just be capable of switching SCC

---------
b) Verification by comparison of characteristics
In some practical cases and where the SCPD is a circuit-breaker (see figures A,4 and A.5),
it may be possible to compare the operating characteristics of Cl and of the associated
SCPD, special attention being paid to the following:
– the Joule integral value of C1 at its Icu and that of the SCPD at the prospective current of association;
– the effects on C1 (e.g. by arc energy, by maximum peak current, cut-off current) at the peak operating current of the SCPD.

Meaning: we need to know the I2t energy as % of RSCC

In some practical cases and where the SCPD is a circuit-breaker (see figures A,4 and A.5),
it may be possible to compare the operating characteristics of Cl and of the associated
SCPD, special attention being paid to the following:
– the Joule integral value of Cl at its /CU and that of the SCPD at the prospective current of association;
– the effects on Cl (e.g. by arc energy, by maximum peak current, cut-off current) at the peak operating current of the SCPD.

The suitability of the association may be evaluated by considering the maximum total
operating I2t characteristic of the SCPD, over the range from the rated short-circuit breaking
capacity Icu(or Ics) of C1 up to the prospective short-circuit current of the application, but not
exceeding the maximum let-through I2t of C1 at its rated short-circuit breaking capacity or
other lower limiting value stated by the manufacturer.
NOTE Where the associated SCPD is a fuse, the validity of the desk study is limited up to Icu of

Confirm I2t of the cb mechanism of its capability to pass the I2t energy (Icu cb = Icu of SCPD but almost always they are the same so device...so?

A.6.3 Tests for verification of back-up protection
If C1 is fitted with adjustable over-current opening releases, the operating characteristics shall
be those corresponding to the minimum time and current settings,
If C1 can be fitted with instantaneous over-current opening releases, the operating
characteristics to be used shall be those corresponding to Cl fitted with such releases,
If the associated SCPD is a circuit-breaker (C2) fitted with adjustable over-current opening
releases, the operating characteristics to be used shall be those corresponding to the
maximum time and current settings.
If the associated SCPD consists of a set of fuses, each test shall be made using a new set of
fuses, even if some of the fuses used during a previous test have not blown

Where applicable, the connecting cables shall be included as specified in 8.3.2.6.4 except that,
if the associated SCPD is a circuit-breaker (C2), the full length of cable (75 cm) associated with
this circuit-breaker may be on the supply side (see figure A.6).
Each test shall consist of a O–t–CO sequence of operations made in accordance with 8.3.5 of
this standard, ‘whether at /Cu or /C~, the CO operation being made on Cl.
 

A test is made with the maximum prospective current for the proposed application, This shall
not exceed the rated conditional short-circuit (see 4.3.6.4 of Part 1),
 

A further test shall be made at a value of prospective current equal to the rated short-circuit
breaking capacity /Cu (or /CS) of Cl, for which test a new sample Cl may be used, and also, if
the associated SCPD is a circuit-breaker, a new sample C2.

a) if the associated SCPD is a circuit-breaker (C2):
– either both Cl and C2 shall trip at both test currents, no further tests then being
required.
 

This is the general case and provides back-up protection only.
– or C1 shall trip and C2 shall be in the closed position at the end of each operation, at
both test currents, no further tests then being required,
This requires that the contacts of C2 separate momentarily during each operation. In this
case restoration of the supply is provided, in addition to back-up protection (see note 1 to
figure A.4), The duration of interruption of supply, if any, shall be recorded during these
tests.
– or C1 shall trip at the lower test current, and both C1 and C2 shall trip at the higher test
current.
This requires that the contacts of C2 separate momentarily at the lower test current.
Additional tests shall be made at intermediate currents to determine the lowest current at
which both C1 and C2 trip, up to which current restoration of supply is provided. The
duration of interruption of supply, if any, shall be recorded during these tests.

– or C1 shall trip at the lower test current, and both C1 and C2 shall trip at the higher test
current.
This requires that the contacts of C2 separate momentarily at the lower test current.
Additional tests shall be made at intermediate currents to determine the lowest current at
which both C1 and C2 trip, up to which current restoration of supply is provided. The
duration of interruption of supply, if any, shall be recorded during these tests.
b) if the associated SCPD is a fuse (or a set of fuses):
—
In the case of a single-phase circuit at least one fuse shall blow;
— in the case of a multi-phase circuit either two or more fuses shall blow, or one fuse shall
blow and C1 shall trip.

A.6.4 Results to be obtained
Subclause 8.3.4.1.7 of Part 1 applies.
Following the tests, C1 shall comply with 8.3,5.3 and 8.3.5.4
In addition, if the associated SPCD is a circuit-breaker (C2), it shall be verified, by manual
operation or other appropriate means, that the contacts of C2 have not welded.

Above is the real tests conditions  to confirm cascading

Emax: 400 to 5000A

but I saw the SACE can go to 6300A

Models:

MF Fixed magnetic
MA Adj. magnetic

Use of Equipment (b) Electric power and lighting circuits.

(2) Reclosing circuits after protective device operation. After a circuit is de-energized by a circuit protective device, the circuit protective device, the circuit may not be manually

reenergized until it has been determined that the equipment and circuit can be safely energized. The

repetitive manual reclosing of circuit breakers or  reenergizing circuits through replaced fuses is prohibited.

Note: When it can be determined from the design of the circuit and the overcurrent devices involved that the automatic operation of a device was caused by an overload rather than a fault condition, no examination of the circuit or connected equipment is needed before the circuit is reenergized.

64