Question 1

What are the G1, G2, G3 and Gx classifications for the ANSI Standard, ANSI/ISA S71.04-1985, “Environmental Conditions for Process Measurement and Control Systems: Airborne Contaminants,”?

Accepted Answer

The G3 specification references the ANSI Standard, ANSI/ISA S71.04-1985, “Environmental Conditions for Process Measurement and Control Systems: Airborne Contaminants,” .The G reference refers to the severity and classification of the test and it can be G1 (Mild, Moderate, Harsh and Severe (G1, G2, G3 and Gx, respectively). The classification directly correlates with the level of corrosive effects in that environment and the standards define or characterise environments in terms of their overall corrosion potential.G1 Mild <300ÅAn environment sufficiently well-controlled such that corrosion is not a factor in determining equipment reliability.G2 Moderate <1000 ÅAn environment in which the effects of corrosion are measurable and corrosion may be a factor in determining equipment reliability.G3 Harsh <2000 ÅAn environment is which there is a high probability that corrosive attack will occur. These harsh levels should prompt further evaluation resulting in environmental controls or specially design and packaged equipment.GX Severe >2000 ÅAn environment in which only specially designed and packaged equipment would be expected to survive. Specifications for equipment in this class are a matter of negotiation between user and supplier.

Question 2

Do we have interlock option in RM6 to prevent closing of earthing switch onto a live (energized) cable?

Accepted Answer

RM6 does not offer this interlock feature; as an alternative solution, the use of manual mechanical based key interlocks (catalog page attached) according to the type of cubicle need to be considered.

Question 3

What is the function of BUCHHOLZ relay in oil-filled transformers?

Accepted Answer

Buchholz protection is normally provided on all transformers fitted with a conservator. The Buchholz relay is contained in a cast housing which is connected in the pipe to the conservator, as in figure shown. A typical Buchholz relay will have two sets of contacts. One is arranged to operate for slow accumulations of gas, the other for bulk displacement of oil in the event of a heavy internal fault. An alarm is generated for the former, but the latter is usually direct-wired to the circuit breaker trip relay. The device will therefore give an alarm for the following fault conditions, all of which are of a low order of urgency: a. hot spots on the core due to short circuit of lamination insulation b. core bolt insulation failure c. faulty joints d. interturn faults or other winding faults involving only lower power infeeds e. loss of oil due to leakage When a major winding fault occurs, this causes a surge of oil, which displaces the lower float and thus causes isolation of the transformer. This action will take place for: i. all severe winding faults, either to earth or interphase ii. loss of oil if allowed to continue to a dangerous degree

Question 4

What is the Reason of Earth leakage devices tripping without fault occurrence ?

Accepted Answer

Some types of electrical and electromagnetic interference caused by the network or its environment may affect the operation of earth leakage protection devices and causes their tripping without existence of fault ,which is known by Nuisance tripping (tripping in a non-dangerous situation).This type of tripping is caused by :1-A transient or continuous high-frequency voltage that is superimposed on the normal network voltage (50 Hz).2-High-frequency harmonics3-Low-frequency continuous leakage currents4-Switching capacitive or inductive components5-Common mode voltage surgesType SI RCDs have been designed to avoid nuisance tripping or non-tripping in case of polluted network, lightning effect, high frequency currents, RF waves, etc.

Question 5

What is the Acceptable value of contact resistance for 400V LV Switchboard busbar?

Accepted Answer

Contact resistance can be measured by millivolt drop test and it has to be found by real test. But, it is not a right method to validate any busbar joints. As per IEC 61439 - 1 & 2, temperature rise of a switchboard is important and it is already validated by type test. If the temperature rise is within control, it is really not required to worry about the contact resistance of busbar joints, voltage drops etc. To control the temperature rise, right busbar architecture and device has to be chosen from the derating table provided in the Catalogue / Technical Guide and right torque has to be applied on the connection bolts. If these parameters are ensured as per Okken / Blokset design instruction, the design will be safe.

Question 6

what is the Installation guide for RCCB for 3P without neutral ?

Accepted Answer

Please refer the attached document connection in 3P RCCB.You can follow the same document for connection in three-Phase without neutral.>> If you are using Acti9 range RCCB, You don't need to add the resistor with iID Acti9 RCCB. You can directly connect the 3 phase on 3 poles of RCCB (without neutral).>> If you are using the Multi9 ID range RCCB, we need to add a resistance with specific resistance values to be compliant with 380-415V. Please refer the attached sheet for connection & resistance values to e used with multi9 range of RCCB.The devices have a toroid which gets energized on out of balance currents and trips .The toroid does not care if there is 2 or 3 or 4 lines connected to it as far as out of balance current is concerned.If there is 3 phases + N then all the phases and N conductors will vector sum to zero - unless there is out of balance current = trip if exceeding the threshold..If there is 3 phases and No N conductor - then exactly the same applies = sum of the 3 currents = zero or you have a trip condition if the out of balance current is greater than the threshold.We can get by without having a N conductor connected to the RCCB as below - because the test button creates a resistive load outside the toroid at rated voltage to test trip the device.

Question 7

What does 1 way, 2 way and intermediate light switching mean?

Accepted Answer

There are 3 basic types of switches that are used for domestic purposes: 1 Way Switches: If a light switch is ‘1 way’ this means it is just an on/off switch. This is the simplest type of switch that you can get. The single switch controls a single light (or lighting circuit).2 Way Switches: A ‘2 way’ switch means there is another switch controlling the same light. These are often used on a stair case, large room with switches by each door.Intermediate Switches: If you need to control the lights from three places, say you have 3 entrances to a large room and need a light switch next to each one, you will need an intermediate switch. The light(s) can be switched on and off from anyone of 3 places. On the whole 2 or 3 gang switches will always be 2 way switches. If you are buying switches and don’t know exactly what you need, then it is often a good idea to get a 2 way switch anyway. This is because if you only need a 1 way switch, you can still use it by only connecting one of the terminals (L1 or L2) and common terminal. (If the switch doesn’t work the way you want it to, you can either turn the switch around or swap the L1 and L2 terminal).

Question 8

PowerLogic PM5000 Series (PM51xx, PM53xx, PM55xx, PM56xx) Modbus Register List

Accepted Answer

IssueRegister list for Modbus communication Product LinePM5110, PM5330, PM5340, PM5560, PM5563, PM56xx, PM57xx EnvironmentPower Meter Communications Modbus Register List CausePM5000 series register list is needed for Modbus communication ResolutionSee the attached documents for Register List. There are 2 files. One for the PM5100 and PM5300 series and the other file is for the PM5500, PM5600, and the PM5700 series.

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

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 12

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 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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