Question 1

What is the Utilisation cat for NS MCCB and ICS and ICU percentage ?

Accepted Answer

IEC 60947 define ICS as the "rated service short-circuit breaking capacity" while ICU as the "rated ultimate short-circuit breaking capacity". The Ics is a percentage of Icu. For "Utilization Category B" breakers, Ics is always equal to Icu. An example for Utilization Category B breakers from our range is the Masterpact ACB series. The ACB range is the only range with Utilization Category B. MCCBs from our range (Compact NSX, Compact NS and Easypact MCCB series), however, are considered as "Utilization Category A" breakers and thus Ics is a percentage from Icu (not necessarily equal to Icu as in the case of Utilization Category B breakers). For MCBs, Ics is a percentage (usually 50~100%) of Icu as well. This is usually illustrated in the respective products' catalogues and datasheets.Some breakers are "Utilization Category A" yet still Ics is 100% of Icu and this is considered to be an advantage for the breaker. By all means, you have to refer to the respective product catalogue which will illustrate clearly the values of Icu and Ics.Please find attached an extract from the IEC illustrating the difference between "Utilization Category A" and "Utilization Category B" breakers as well as the standard percentages of Ics with respect to Icu. You can also find attached pages from some of our product catalogues (MCBs, MCCBs, ACBs) illustrating how Ics is expressed as percentages of Icu.

Question 2

Please advice if RCCB 30mA sensitivity is enough for human safety or not?

Accepted Answer

Regarding the residual current devices ,are used mainly for human protection against direct and indirect contact,and they are defined by their sensitivity and interference immunity (type AC,A,SI and B).Please refer to catalog pages attached for the selection of the suitable type and some characteristics of these devices.

Question 3

What is Meant by Rated Conventional thermal current  of a Contactor ?

Accepted Answer

The conventional free air thermal current is the maximum value of test current to be used for temperature-rise tests of unenclosed equipment in free air. The value of the conventional free air thermal current shall be at least equal to the maximum value of the rated operational current of the unenclosed equipment in eight-hour duty. Free air is understood to be air under normal indoor conditions reasonably free from draughts and external radiation.

Question 4

What are the definitions for "Residual Earth Fault protection" and "Source Ground Return" ?

Accepted Answer

please find below the definitions for "Residual Earth Fault protection" and "Source Ground Return"1- Residual Earth Fault protection: The function determines the zero-phase sequence current, i.e. the vector sum of the phase and neutral currents2-Source Ground Return :Using a special external sensor, this function directlymeasures the fault current returning to the transformer via theearth cable and It detects faults both upstream and downstream of the circuitbreaker.Please note that it is recommended for Source Ground Return to consider:1- The maximum distance between the sensor and the circuit breaker is ten meters2- Use a 4P circuit breaker in order to isolate the neutral when the breaker is open and in order also to avoid the effect of the third harmonic which is flowing mainly on the neutral bar, and which could provoke unexpected tripping.Kindly find attached guide for Ground fault protection, where you can find the following:- page 18: for installation precautions.- pages 34 to 36 :how to make choice concerning the GFP (Ground Fault protection) based on the installation conditions.- page 37 to 51 wiring and Schneider offer according to GFP.

Question 5

How to extract the MCL file and convert into CID/ICD file from Easergy Micom Px4x relays?

Accepted Answer

Description: Extract the MCL file and convert into CID/ICD file from Easergy Micom Px4x relays Product family: Easergy Micom Px4x relays Resolution Please find attached the procedure to extract MCL file & and convert into CID/IID file .

Question 6

We are getting “NIC not fitted” in the Micom P642 events What is the meaning of this alarm?

Accepted Answer

Issue/description: Meaning of getting “NIC not fitted” in the Easergy Micom P642 events Product family: Easergy Micom P642 Resolution: This alarm means that Network Interface Card not fitted/failed. Please check the Network Interface Card & contact our local customer care with the below details for further investigation: 1) Micom system file i.e. .studioarch file included .Set .PSL ,log files(events, Disturbance records & fault records) & Can you please arrange MCL file of unhealthy & healthy relay and complete network architecture directly extracted from the affected relays( (not in PDF format) Thanks to share the below details also:2) Hope your team checked the Ethernet board response through DOS command.NIC No response is major alarm and it means Ethernet card is not responding.Can you check and send some picture or video for both the port 1 & Port 2 during testing with rear ports.3) Can you explain the problem in details ie. when/what condition this issue has appeared 4) Could you provide some data during fault (which relays, relays events) and network traces for deep investigation . Above details are mandatory to investigate preliminary level further . Describe in detail:• Nature of the problem• Approximate date/time when issue appeared• Approximate date/time when troubleshooting and data collecting was done• Tests already executed with the results• Confirmation if captured frames are time synchronised with tested system• List of devices with their IP addresses involved in the troubleshooting• List of the files attached to help in the further investigation. • Any observations which can help Local customer care support's contact can find with the below SE link:https://www.se.com/eg/en/work/support/customer-care/contact-schneider-electric.jsp

Question 7

The Power/Heat Loss of iC60N MCBs & Vigi iC60 RCDs with catalogue pages.

Accepted Answer

Data required in the attached document .

Question 8

Can we install Earth Fault protection for a Three pole ACB with micrologic 6 or 7 trip unit without external Neutral CT?

Accepted Answer

There are two types of ground-fault protection: 1- Residual: The function determines the zero-phase sequence current, i.e. the vector sum of the phase and neutral currents 2- Source Ground Return: Using a special external sensor, this function directly measures the fault current returning to the transformer via the earth cable. In case of 3 pole breaker (4-wire system), for ground-fault protection, it is mandatory to install an external CT for calculating the current to ground, thanks to a vectorial sum of phases and neutral currents. While for the 4 pole CB, it is not mandatory to install an external CT.

Question 9

What is meant by Symmetrical and Asymmetrical breaking currents?

Accepted Answer

issue:Customer wants to know the value of the symmetrical and asymmetrical breaking current of the circuit breaker and what do they mean.Environment:Circuit Breaker Resolution:- Symmetrical breaking current is the RMS value of AC component of short circuit current at the instant of separation of the contacts. It does not take into account the DC offset.- Asymmetrical breaking current is is the RMS value of the combined sum of the DC and AC components of the short circuit current at the instant of separation of the breaker contacts. This DC offset is of decaying nature which is dictated by the time constant of the system. As shown in the above picture the DC offset decays in a few cycles and is left only with the symmetrical component. Hence if a breaker has to close before the DC component decays, then the breaker’s breaking capacity is to be calculated for the asymmetrical current at the time of breaking.

Question 10

What is the selection criterion of Circuit Breakers for the Capacitor bank application.

Accepted Answer

The selection should be done after derating the Circuit Breaker taking into consideration voltage variation and capacitors tolerances that could increase nominal current up to 1.5In. The Derating factor of 1.5In Where In = Q/ ( Square root of 3 ) Un Q = Capacitor Power Un = Nominal Voltage Choose the Micrologic with delay time selection, so that the Circuit Breaker does not trip due to initial high inrush current. Also to be taken into account are the parameters like supply frequency, operating voltage & harmonics level of the power system for such application. Refer the attached sheet for further details for selection of Circuit Breaker for Capacitor duty application. Note: Use the phase barrier between the phases in Circuit Breaker to prevent flashover due to heavy inrush current.

Question 11

In a 3 phase system, why does the meter still show voltage reading on one of the phases even after breaking the phase circuit?

Accepted Answer

Issue:Testing phase loss on a meter doesn't result in a null voltage reading.Environmnet:EasyLogic Series Power MetersPowerLogic Series Power MetersResolution:The voltage seen is what we call "phantom voltage", its a known phenomenon with all high impedance power meters. These phantom voltages are normal artifacts of the design and should not pose any safety concerns to the end user.In some cases it'll probably disappear by power cycling the meter. Most power meters are not designed to monitor phase loss, as it'll always assume the presence of the 3 phases and the neutral, depending on your parameters setup. External devices are used to detect such occurrences, like phase control relays.

Question 12

what are the benefits of short circuit current limiting?

Accepted Answer

Benefits of limiting:Long installation service lifeThermal effectsLower temperature rise at the conductor level, hence increased service life for cables and all components that are not self-protected (e.g. switches, contactors, etc.)Mechanical effectsLower electrodynamic repulsion forces, hence less risk of deformation or breakage of electrical contacts and busbars.Electromagneticeffects Less interference on sensitive equipment located in the vicinity of an electric circuit.Savings through cascading Cascading is a technique derived directly from current limiting: downstream of a current-limiting circuit breaker it is possible to use circuit breakers of breaking capacity lower than the prospective short-circuit current (in line with the cascading tables). The breaking capacity is heightened thanks to current limiting by the upstream device. Substantial savings can be achieved in this way on switchgear and enclosures.Discrimination of protection devices The circuit breakers' current limiting capacity improves discrimination with the protection devices located upstream: this is because the required energy passing through the upstream protection device is greatly reduced and can be not enough to cause it to trip. Discrimination can thus be natural without having to install a time-delayed protection device upstream.

Question 13

Why is Neutral and Earth (Ground) Connection forbidden Downstream from Main Panel?

Accepted Answer

The question is often asked what is the maximum voltage permitted between the Neutral and Earth (Ground) conductor and if the Neutral and Earth can be bridged to achieve a zero value.This can be a difficult topic, in fact in many cases it can be dangerous. As you will see from the attached document, there are many reasons why it is not allowed.

Question 14

Which RL(lead resistance from CT to relay) is to be used in Knee Voltage calculation if Current Transformers (CTs) used in High Impedance Restricted Earth Fault are at different distances from relay?

Accepted Answer

Issue:Having two different values for RL ( Lead resistance from the CT to the relay); RL from the phase CT to the relay and RL from the neutral point CT to the relayEnvironment:Protection Function ANSI 64refHigh impedance differentialSepam 80 Current Transformer requirementResolution:In any application where the high impedance differential is used, all the CTs must have the following:- the same ratio,- the same magnetizing curve (same minimum Vk),- the same maximum Rct (current Transformer secondary winding resistance),- if the relevant CTs are not at the same distance from the relay, take the maximum RL.Attached Cahier Technique no.194 for more information about high impedance calculation

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