Selection of 3P-TPN-4P MCB & Distribution Board

Type of breakers based on number of pole:

• Based on the number of poles, the breakers are classified as

1. SP – Single Pole
2. SPN – Single Pole and Neutral
3. DP – Double pole
4. TP – Triple Pole
5. TPN – Triple Pole and Neutral
6. 4P – Four Pole

1.     SP ( Single Pole ) MCB:

• In Single Pole MCCB, switching & protection is affected in only one phase.
• Application: Single Phase Supply to break the Phase only.

2.     DP ( Double Pole ) MCB:

• In Two Pole MCCB, switching & protection is affected in phases and the neutral.
• Application: Single Phase Supply to break the Phase and Neutral.

3.     TP ( Triple Pole) MCB:

• In Three Pole MCB, switching & protection is affected in only three phases and the neutral is not part of the MCB.
• 3pole MCCB signifies for the connection of three wires for three phase system (R-Y-B Phase).
• Application: Three Phase Supply only (Without Neutral).

4.     TPN (3P+N) MCB:

• In TPN MCB, Neutral is part of the MCB as a separate pole but without any protective given in the neutral pole (i.e.) neutral is only switched but has no protective element incorporated.
• TPN for Y (or star) the connection between ground and neutral is in many countries not allowed. Therefore the N is also switches.
• Application: Three Phase Supply with Neutral

5.     4 Pole MCB:

• 4pole MCCB for 4 wires connections, the one additional 4^th pole for neutral wire connection so that between neutral and any of the other three will supply.
• In 4-Pole MCCBs the neutral pole is also having protective release as in the phase poles.
• Application: Three Phase Supply with Neutral

Difference between TPN and 4P (or SPN and DP):

• TPN means a 4 Pole device with 4th Pole as Neutral. In TPN opening & closing will open & close the Neutral.
• For TPN, protection applies to the current flows through only 3 poles (Three Phase) only; there is no protection for the current flow through the neutral pole. Neutral is just an isolating pole.
• TP MCB is used in 3phase 4wire system. It is denoted as TP+N which will mean a three pole device with external neutral link which can be isolated if required. 
• For the 4 pole breakers, protection applies to current flow through all poles. However when breaker trips or manually opened, all poles are disconnected.
• Same type of difference also applies for SPN and DP.

Where to Use TP, TPN and 4P in Distribution panel:

• For any Distribution board, the protection system (MCB) must be used in the incomer. For a three phase distribution panel either TP or TPN or 4P can be used as the incoming protection.
• TP MCB: It is most commonly used type in all ordinary three phase supply.
• TPN MCB: It is generally used where there are dual sources of incomer to the panel (utility source and emergency generator source).
• 4P MCB: It is used where is the possibility of high neutral current (due to unbalance loads and /or 3^rd and multiple of 3^rd harmonics current etc) and Neutral / Earth Protection is provided on Neutral.

Where to use 4 Pole or TPN MCB instead of 3 Pole (TP) MCB.

• Multiple Incoming Power System:
• When we have a transformer or a stand-by generator feeding to a bus, it is mandatory that at least either of the Incomers or the bus coupler must be TPN or 4-Pole Breaker please refers IS 3043.
• In multi incomer power feeding systems, we cannot mix up the neutrals of incoming powers to other Power Source so we can use TPN or 4P breakers or MCB instead of TP MCB to isolate the Neutral of other power sources from the Neutral of incomer power in use.
• We can use 4 Pole ACB instead of TP for safety reasons .If there is power failure and DG sets are in running condition to feed the loads, if there is some unbalance in loads(which is practically unavoidable in L.V. distribution system ), depending of quantum of unbalance, there will be flow of current through Neutral. During this time, if Power Supply Utility Technicians are working, and if they touch the neutral conductors(which is earthed at their point ) they will likely to get electric shock depending on the potential rise in common neutral due flow of current through Neutral conductor as stated above. Even fatal accident may occur due the above reason. As such, it is a mandatory practice to isolate the two Neutrals.
• We can use 4-pole breakers or TPN Breakers when the system has two alternative sources and, in the event of power failure from the mains, change-over to the standby generator is done. In such a case, it is a good practice to isolate the neutral also.
• 4 pole circuit breakers have advantages in the case when one of the poles of the device will get damage, and it also provides isolation from neutral voltage.
• Normally, Neutral is not allowed to break in any conditions, (except special applications) for human & equipment safety. So for single incomer power fed systems, 3P breaker is used, where only phases are isolated during breaking operations.
• Where We have dual Power like in DG & other electricity supply sources ,it is required to isolate neutral, where neutral needs to be isolated  in internal network TPN MCB or 4P MCB can be used.

Where to use 4 Pole MCB instead of TPN MCB

• Any Protection Relay used on Neutral (Ground Fault Protection of Double ended System):
• The use of four poles or three poles CB will depend on system protection and system configuration.
• Normally in 3phase with neutral we just use 3pole CB and Neutral is connected on common Neutral Link but if application of 3pole will affect the operation of protective relay then we must use 4pole CB.
• System evaluation has to be required to decide whether three-pole circuit breakers plus neutral link can be used or four-pole breakers are required.
• If unrestricted ground fault protection is fitted to the transformer neutral, then the bus section circuit breaker should have 4-poles and preferably incomer circuit breakers should also have 4-poles because un cleared ground fault located at the load side of a feeder have two return paths. As shown in fig a ground fault on a feeder at the bus section “A” will have a current return path in both the incomers, thus tripping both Bus. The sensitivity of the unrestricted ground fault relay is reduced due to the split current paths.

• For System Stability :
• In an unbalanced 3phase system or a system with non-linear loads, the neutral gives the safety to the unbalanced loads in the system and therefore It must not be neglected. In perfectly balanced conditions the neutral functions as a safety conductor in the unforeseen short-circuit and fault conditions. Therefore by using 4-pole MCB will enhance the system stability.
• 4 Poles will be decided after knowing the Earthing Systems (TT, TN-S, TN-C, IT).

(1) IT (with distributed neutral) System:

• The Neutral should be switched on & off with phases.
• Required MCB: TPN or 4P MCB.

(2) IT (without distributed neutral) System:

• There is no neutral.
• Required MCB: TP MCB.

(3) TN-S System:

• Required MCB: TP MCB because even when neutral is cut off system remains connected with Ground.

(4) TN-C System:

• Required MCB: TPN or 4P only, because we cannot afford to cut neutral doing so will result in system loosing contact with Ground.

(5) TN-C-S System:

• Neutral and Ground cable are separate
• Required MCB:  TP MCB Because Neutral and Ground cable are separate.

(6) TT System: 

• Ground is provided locally
• Required MCB:  TP MCB because ground is provided locally.
• Conclusion: Its compulsory to use TPN in TN-C system rest everywhere you can use MCB.

Nomenclature of Distribution Board:

• Distribution Box can be decided by “way” means how many how many single phase (single pole) distribution. Circuit and Neutral are used.

1)     SPN Distribution Board (Incoming+ Outgoing)

• 4way (Row) SPN = 4 X 1SP= 4Nos (Module) of single pole MCB as outgoing feeders.
• 6way (Row) SPN = 6 X 1SP= 6Nos (Module) of single pole MCB as outgoing feeders.
• 8way (Row) SPN = 8 X 1SP= 8Nos (Module) of single pole MCB as outgoing feeders.
• 10way (Row) SPN = 10 X 1SP= 10Nos (Module) of single pole MCB as outgoing feeders.
• 12way (Row) SPN = 12 X 1SP= 12Nos (Module) of single pole MCB as outgoing feeders.
• Normally single phase distribution is mainly used for small single phase loads at house wiring or industrial lighting wiring.

2)     TPN Distribution Board (Incoming, Outgoing)

• 4way (Row) TPN = 4 X TP= 4nos of 3pole MCB as outgoing feeders =12 No of single pole MCB.
• 6way (Row) TPN = 6 X TP= 6nos of 3pole MCB as outgoing feeders =18 No of single pole MCB.
• 8way (Row) TPN = 8 X TP= 8nos of 3pole MCB as outgoing feeders =24 No of single pole MCB.
• 10way (Row) TPN = 10 X TP= 10nos of 3pole MCB as outgoing feeders =30 No of single pole MCB.
• 12way (Row) TPN =12 X TP= 12nos of 3pole MCB as outgoing feeders =36 No of single pole MCB

How to save Electrical energy at Home

How to save  Electrical energy at Home

In our home we use lot of electrical equipment like Tv, Freeze, Washing machine,Mp3 player. music system, computer laptop. But we have not adequate knowledge for how to use this electrical equipment in proper way Due to this ignorance we are paying more electricity Bill which we are not actually use.
Do you know in actual we are consuming more electricity or paying more amounts what we actually not use it?
According to the energy auditors we can easily save between 5 and 10% of their energy consumption (and costs) by changing our behavior such as switching electrical equipment off at the mains rather than leaving it on standby, turning off lights when they’re not being used
By saving Electrical energy will directly reflected to saving money so it is very necessary to under stood ghost unit or amount which we are paying without using the appliances.
The major appliances in your home — refrigerators, clothes washers, dishwashers — account for a big chunk of your monthly utility bill. And if your refrigerator or washing machine is more than a decade old, you’re spending a lot more on energy than you need to.
Today’s major appliances don’t hog energy the way older models do because they must meet minimum federal energy efficiency standards. These standards have been tightened over the years, so any new appliance you buy today has to use less energy than the model you’re replacing. For instance, if you buy one of today’s most energy-efficient refrigerators, it will use less than half the energy of a model that’s 12 years old or older.

Lighting

• Get into the habit of turning lights off when you leave a room. —-Saving Energy 0.5 %
• Use task lighting (table and desktop lamps) instead of room lighting.
• Take advantage of daylight
• De-dust lighting fixtures to maintain illumination—–Saving Energy 1 %
• Compact fluorescent bulbs (CFL):

1. CFL use 75% less energy than Normal bulbs.
2. CFL are four times more energy efficient than Normal bulbs.
3. CFL can last up to ten times longer than a normal bulb.

• Use electronic chokes. in place of conventional copper chokes.—-Saving Energy 2 %
• Get into the habit of turning lights off when you leave a room.
• Use only one bulb for light fittings with more than one light bulb, or replace additional bulbs with a lower wattage version.
• Use energy-saving light bulbs that can last up to ten times longer than a normal bulb and use significantly less energy. A single 20- to 25-watt energy-saving bulb provides as much light as a 100-watt ordinary bulb.
• Use tungsten halogen bulbs for spotlights—they last longer and are up to 100% more efficient.
• Fit external lights with a motion sensor.
• Use high frequency fittings for fluorescent tubes because they cut flicker and are even more efficient than energy-saving light bulbs. They are suitable for kitchens, halls, workshops and garages.

Save on Your Fridge & Freezer:

• Defrost your fridge regularly.
• Check that the door seals are strong and intact.
• Don’t stand Freezer’s Back Side too near the Wall.
• Avoid putting warm or hot food in the fridge or freezer—it   requires more energy to cool it down.
• Clean condenser coils twice a year.
• Get rid of old refrigerators!  They use twice the energy as new Energy Star® models.
• Keep refrigerators full but not overcrowded.
• Defrost your fridge regularly. When ice builds up, your freezer uses more electricity. If it frosts up again quickly, check that the door seals are strong and intact.
• Do not stand the fridge next to the oven or other hot appliances if you can help it. Also ensure there is plenty of ventilation space behind and above it.
• Keep the fridge at 40°F and the freezer at 0°F. Empty and then turn your fridge off if you go on a long vacation (but make sure you leave the door open).
• Aim to keep your fridge at least three-quarters full to maintain maximum efficiency. A full fridge is a healthy fridge.
• Avoid putting warm or hot food in the fridge or freezer—it requires more energy to cool it down.

AIR CONDITION UNIT

• For Home Purpose use Window unit Instead Of Split Unit.
• For Office and Commercial Purpose Use Split AC instead of Window unit.
• Consider installing a programmable t. Just set the times and temperatures to match your schedule and you will save money and be comfortably cool when you return home.
• Get air conditioner maintenance each year.
• Checks the condenser coils, the evaporator coils, the blower wheel, the filter, the lubrication and the electrical   contacts.
• Replace worn and dirty equipment for maximum efficiency.
• Replace air conditioner filters every month.
• Turn off central air conditioning 30 minutes before leaving your home.
• Consider using ceiling or portable fans to circulate and cool the air.
• Try increasing your air conditioner temperature. Even 1 degree higher could mean significant savings, and you will probably not notice the difference.
• Keep central air conditioner usage to a minimum—or even turn the unit off—if you plan to go away.
• Consider installing a programmable thermostat. Just set the times and temperatures to match your schedule, and you will save money and be comfortably cool when you return home.
• Get air conditioner maintenance each year—ensure your service person checks the condenser coils, the evaporator coils, the blower wheel, the filter, the lubrication and the electrical contacts. Replace worn and dirty equipment for maximum efficiency.
• Replace air conditioner filters every month.
• Buy the proper size equipment to meet your family’s needs—an oversized air conditioner unit will waste energy.
• If you have a furnace, replace it at the same time as your air conditioner system. Why? Because it is your furnace fan that blows cool air around your home, and a newer furnace fan provides improved air circulation all year round, plus saves energy costs.

Water Heater:

• Check your hot water temperature. It does not need to be any higher than 140°F for washing purposes.
• Plug the basin or bath when you run any hot water.
• Use a timer to make sure the heating and hot water are only on when needed.
• Insulate your hot water pipes to prevent heat loss, and your water will stay hotter for longer. Plus, you will also use less energy to heat it. And simply fitting a jacket onto your hot water tank can cut waste by up to three quarters.
• Take showers—a bath consumes 5 times more hot water. Buy a low-flow showerhead for more efficiency and it will pay for itself in no time.
• Avoid washing dishes under hot running water, and do not pre-rinse before using the dishwasher.
• Repair dripping hot water taps immediately
• Make sure hot water taps are always turned off properly.

Washing Machine:

• Wash full loads of Washing Machine—you will use your machine less often, saving time, and it is more energy-efficient.
• Wash at a lower temperature or the economy setting to save even more.
• Use the spin cycle, and then hang washing out rather than tumble drying—your clothes and linens will smell fresher!
• If you need to tumble dry, try a lower temperature setting.
• Use your dryer for consecutive loads, because the built-up heat between loads will use less energy.

Oven/Electrical Cooker:

• Make sure your oven door closes tightly.
• Use a microwave rather than conventional oven, when possible.
• Keep the center of the pan over the element, and keep the lid on when cooking on the stovetop.
• Only boil the amount of water that you need—just ensure there is enough water to cover the heating element. Turn the element or electric kettle down as soon as it reaches the boiling point.

COMPUTER / LAPTOP

• Buy a laptop instead of a desktop, if practical. —-Saving Energy 5 %.
• If you buy a desktop, get an LCD screen instead of an outdated CRT.
• Use sleep-mode when not in use helps cut  energy costs by approx  40%.
• Turn off the monitor; this device alone uses more than half  the system’s  energy.
• Screen savers save computer screens, not energy.
• Use separate  On/Off switch Socket Instead of One.
• Laser printers use more electricity than inkjet printers.

FAN:

• A ceiling fan in operation through out night will gobble up 22 units in a month.
• There is a wrong notion that fan at more speed would consume more current.
• Fan running at slow speed would waste energy as heat in the regulator.
• The ordinary regulator would take 20 watts extra at low speed.
• The energy loss can be compensated by using  electronic   regulator

Buy efficient electric appliances:

• They use two to 10 times less electricity for the same functionality, and are mostly higher quality products that last longer than the less efficient ones. In short, efficient appliances save you lots of energy and money.
• In many countries, efficiency rating labels are mandatory on most appliances. Look Energy Star label is used.
• The label gives you information on the annual electricity consumption. In the paragraphs below, we provide some indication of the consumption of the most efficient appliances to use as a rough guide when shopping. Lists of brands and models and where to find them are country-specific and so cannot be listed here, but check the links on this page for more detailed information.
• Average consumption of electric appliances in different regions in the world, compared with the high efficient models on the market

Ghost consumers:

• Identify the “ghost consumers” which consume power – not because they are in use, but because they are   plugged in and are in stand-by mode.
• The TV consumes 10 watt power When It’s is in Stand by Mode.

Ex.  TV is in stand-by-mode  for 10 hours a Day.
Energy Consumption  /  Day= 10 X 10 = 100 Watts. = 0.1 KWH.
Energy consumption /  Month= 1X100X30=3000 Watts=3KWH ( Unit) .
Energy Consumption in Rupees. = 3 X 4 = 12 Rs/Month.

• The TV consumes 5 watt power when we  don’t  plug out from switch Board.

Ex.  TV is in un Plug Mode for 10 hours a Day.
Energy Consumption  /  Day= 5 X 10 = 50 Watts. = 0.05 KWH.
Energy consumption /  Month= 1X50X30= 1500 Watts=1.5 KWH ( Unit) .
Energy Consumption in Rupees. = 1.5 X 4 = 6 Rs/Month.

• The cell phone charger uses 3 watt per hour when plugged.
• Mosquito mats consume 5 watts per hour.
• If you use an electric geyser, do not leave it in thermostat mode, for it causes standing losses of 1-1.5 units

Calculate Size of Contactor, Fuse, C.B, O/L  of DOL Starter

• Calculate Size of each Part of DOL starter for The System Voltage 415V ,5HP Three Phase House hold Application Induction Motor ,Code A, Motor efficiency 80%,Motor RPM 750 ,Power Factor 0.8 , Overload Relay of Starter is Put before Motor.

Basic Calculation of Motor Torque & Current:

• Motor Rated Torque (Full Load Torque) =5252xHPxRPM
• Motor Rated Torque (Full Load Torque) =5252x5x750=35 lb-ft.
• Motor Rated Torque (Full Load Torque) =9500xKWxRPM
• Motor Rated Torque (Full Load Torque) =9500x(5×0.746)x750 =47 Nm
• If Motor Capacity is less than 30 KW than Motor Starting Torque is 3xMotor Full Load Current or 2X Motor Full Load Current.
• Motor Starting Torque=3xMotor Full Load Current.
• Motor Starting Torque==3×47=142Nm.
• Motor Lock Rotor Current =1000xHPx figure from below Chart/1.732×415

Locked Rotor Current
Code	Min	Max
A	1	3.14
B	3.15	3.54
C	3.55	3.99
D	4	4.49
E	4.5	4.99
F	5	2.59
G	2.6	6.29
H	6.3	7.09
I	7.1	7.99
K	8	8.99
L	9	9.99
M	10	11.19
N	11.2	12.49
P	12.5	13.99
R	14	15.99
S	16	17.99
T	18	19.99
U	20	22.39
V	22.4

• As per above chart Minimum Locked Rotor Current  =1000x5x1/1.732×415=7 Amp
• Maximum Locked Rotor Current =1000x5x3.14/1.732×415=22 Amp.
• Motor Full Load Current (Line) =KWx1000/1.732×415
• Motor Full Load Current (Line) = (5×0.746)x1000/1.732×415=6 Amp.
• Motor Full Load Current (Phase)=Motor Full Load Current (Line)/1.732
• Motor Full Load Current (Phase)==6/1.732=4Amp
• Motor Starting Current =6 to 7xFull Load Current.
• Motor Starting Current (Line)=7×6=45 Amp

(1) Size of Fuse:

Fuse  as per NEC 430-52
Type of Motor	Time Delay Fuse	Non-Time Delay Fuse
Single Phase	300%	175%
3 Phase	300%	175%
Synchronous	300%	175%
Wound Rotor	150%	150%
Direct Current	150%	150%

• Maximum Size of Time Delay Fuse =300% x Full Load Line Current.
• Maximum Size of Time Delay Fuse =300%x6= 19 Amp.
• Maximum Size of Non Time Delay Fuse =1.75% x Full Load Line Current.
• Maximum Size of Non Time Delay Fuse=1.75%6=11 Amp.

(2) Size of Circuit Breaker:

Circuit Breaker as per NEC 430-52
Type of Motor	Instantaneous Trip	Inverse Time
Single Phase	800%	250%
3 Phase	800%	250%
Synchronous	800%	250%
Wound Rotor	800%	150%
Direct Current	200%	150%

• Maximum Size of Instantaneous Trip Circuit Breaker =800% x Full Load Line Current.
• Maximum Size of Instantaneous Trip Circuit Breaker =800%x6= 52 Amp.
• Maximum Size of Inverse Trip Circuit Breaker =250% x Full Load Line Current.
• Maximum Size of Inverse Trip Circuit Breaker =250%x6= 16 Amp.

(3) Thermal over Load Relay:

• Thermal over Load Relay (Phase):
• Min Thermal Over Load Relay setting =70%xFull Load Current(Phase)
• Min Thermal Over Load Relay setting =70%x4= 3 Amp
• Max Thermal Over Load Relay setting =120%xFull Load Current(Phase)
• Max Thermal Over Load Relay setting =120%x4= 4 Amp
• Thermal over Load Relay (Phase):
• Thermal over Load Relay setting =100%xFull Load Current (Line).
• Thermal over Load Relay setting =100%x6= 6 Amp

(4) Size and Type of Contactor:

Application	Contactor	Making Cap
Non-Inductive or Slightly Inductive ,Resistive Load	AC1	1.5
Slip Ring Motor	AC2	4
Squirrel Cage Motor	AC3	10
Rapid Start / Stop	AC4	12
Switching of Electrical Discharge Lamp	AC5a	3
Switching of Electrical Incandescent Lamp	AC5b	1.5
Switching of Transformer	AC6a	12
Switching of Capacitor Bank	AC6b	12
Slightly Inductive Load in Household or same type load	AC7a	1.5
Motor Load in Household Application	AC7b	8
Hermetic refrigerant Compressor Motor with Manual O/L Reset	AC8a	6
Hermetic refrigerant Compressor Motor with Auto O/L Reset	AC8b	6
Control of Restive & Solid State Load with opto coupler Isolation	AC12	6
Control of Restive Load and Solid State with T/C Isolation	AC13	10
Control of Small Electro Magnetic Load ( <72va span="">	AC14	6
Control of Small Electro Magnetic Load ( >72VA)	AC15	10

• As per above Chart
• Type of Contactor= AC7b
• Size of Main Contactor = 100%X Full Load Current (Line).
• Size of Main Contactor =100%x6 = 6 Amp.
• Making/Breaking Capacity of Contactor= Value above Chart x Full Load Current (Line).
• Making/Breaking Capacity of Contactor=8×6= 52 Amp.

Electrical Thumb Rules (Part 1)

Electrical Thumb Rules For:

• Cable Capacity
• Current Capacity of Equipment
• Earthing Resistance
• Minimum Bending Radius
• Insulation Resistance
• Lighting Arrestor
• Transformer
• Diesel Generator
• Current Transformer
• Quick Electrical Calculation
Cable Capacity

• For Cu Wire Current Capacity (Up to 30 Sq.mm) = 6X Size of Wire in Sq.mm
  Ex. For 2.5 Sq.mm = 6×2.5 = 15 Amp, For 1 Sq.mm = 6×1 = 6 Amp, For 1.5 Sq.mm = 6×1.5 = 9 Amp
• For Cable Current Capacity = 4X Size of Cable in Sq.mm, Ex. For 2.5 Sq.mm = 4×2.5 = 9 Amp.
• Nomenclature for cable Rating = Uo/U
• where Uo = Phase-Ground Voltage, U = Phase-Phase Voltage, Um = Highest Permissible Voltage

Current Capacity of Equipment

• 1 Phase Motor draws Current = 7Amp per HP.
• 3 Phase Motor draws Current = 1.25Amp per HP.
• Full Load Current of 3 Phase Motor = HPx1.5
• Full Load Current of 1 Phase Motor = HPx6
• No Load Current of 3 Phase Motor = 30% of FLC
• KW Rating of Motor = HPx0.75
• Full Load Current of equipment = 1.39xKVA (for 3 Phase 415Volt)
• Full Load Current of equipment = 1.74xKw (for 3 Phase 415Volt)

Earthing Resistance

• Earthing Resistance for Single Pit = 5Ω, Earthing Grid = 0.5Ω
• As per NEC 1985 Earthing Resistance should be < 5Ω.
• Voltage between Neutral and Earth <= 2 Volt
• Resistance between Neutral and Earth <= 1Ω
• Creepage Distance = 18 to 22mm/KV (Moderate Polluted Air) or
• Creepage Distance = 25 to 33mm/KV (Highly Polluted Air)

Minimum Bending Radius

• Minimum Bending Radius for LT Power Cable = 12 x Dia of Cable.
• Minimum Bending Radius for HT Power Cable = 20 x Dia of Cable.
• Minimum Bending Radius for Control Cable = 10 x Dia of Cable.

Insulation Resistance

• Insulation Resistance Value for Rotating Machine = (KV+1) MΩ.
• Insulation Resistance Value for Motor (IS 732) = ((20xVoltage (L-L)) / (1000+ (2xKW)).
• Insulation Resistance Value for Equipment (<1kv strong=""> Minimum 1 MΩ.
• Insulation Resistance Value for Equipment (>1KV) = KV 1 MΩ per 1KV.
• Insulation Resistance Value for Panel = 2 x KV rating of the panel.
• Min Insulation Resistance Value (Domestic) = 50 MΩ / No of Points. (All Electrical Points with Electrical fitting & Plugs). Should be less than 0.5 MΩ
• Min Insulation Resistance Value (Commercial) = 100 MΩ / No of Points. (All Electrical Points without fitting & Plugs).Should be less than 0.5 MΩ.
• Test Voltage (A.C) for Meggering = (2X Name Plate Voltage) +1000
• Test Voltage (D.C) for Meggering = (2X Name Plate Voltage).
• Submersible Pump Take 0.4 KWH of extra Energy at 1 meter drop of Water.

Lighting Arrestor

Arrestor have Two Rating:

1. MCOV=Max. Continuous Line to Ground Operating Voltage.
2. Duty Cycle Voltage. (Duty Cycle Voltage > MCOV).

Transformer

• Current Rating of Transformer = KVA x 1.4
• Short Circuit Current of T.C /Generator = Current Rating / % Impedance
• No Load Current of Transformer =< 2% of Transformer Rated current
• Capacitor Current (Ic) = KVAR / 1.732xVolt (Phase-Phase)
• Typically the local utility provides transformers rated up to 500kVA For maximum connected load of 99kW,
• Typically the local utility provides transformers rated up to 1250kVA For maximum connected load of 150kW.
• The diversity they would apply to apartments is around 60%
• Maximum HT (11kV) connected load will be around 4.5MVA per circuit.
• 4No. earth pits per transformer (2No. for body and 2No. for neutral earthing),
• Clearances, approx.1000mm around TC allow for transformer movement for replacement.

Diesel Generator

• Diesel Generator Set Produces = 3.87 Units (KWH) in 1 Litter of Diesel.
• Requirement Area of Diesel Generator = for 25KW to 48KW = 56 Sq.meter, 100KW = 65 Sq.meter.
• DG less than or equal to 1000kVA must be in a canopy.
• DG greater 1000kVA can either be in a canopy or skid mounted in an acoustically treated room
• DG noise levels to be less than 75dBA at 1 meter.
• DG fuel storage tanks should be a maximum of 990 Litter per unit. Storage tanks above this level will trigger more stringent explosion protection provision.

Current Transformer

Nomenclature of CT:

• Ratio: input / output current ratio
• Burden (VA): total burden including pilot wires. (2.5, 5, 10, 15 and 30VA.)
• Class: Accuracy required for operation (Metering: 0.2, 0.5, 1 or 3, Protection: 5, 10, 15, 20, 30).
• Accuracy Limit Factor:
• Nomenclature of CT: Ratio, VA Burden, Accuracy Class, Accuracy Limit Factor.Example: 1600/5, 15VA 5P10  (Ratio: 1600/5, Burden: 15VA, Accuracy Class: 5P, ALF: 10)
• As per IEEE Metering CT: 0.3B0.1 rated Metering CT is accu­rate to 0.3 percent if the connected secondary burden if imped­ance does not exceed 0.1 ohms.
• As per IEEE Relaying (Protection) CT: 2.5C100 Relaying CT is accurate within 2.5 percent if the secondary burden is less than 1.0 ohm (100 volts/100A).

Quick Electrical Calculation

1HP = 0.746KW	Star Connection
1KW = 1.36HP	Line Voltage = √3 Phase Voltage
1Watt = 0.846 Kla/Hr	Line Current = Phase Current
1Watt = 3.41 BTU/Hr	Delta Connection
1KWH = 3.6 MJ	Line Voltage = Phase Voltage
1Cal = 4.186 J	Line Current = √3 Phase Current
1Tone = 3530 BTU
85 Sq.ft Floor Area = 1200 BTU
1Kcal = 4186 Joule
1KWH = 860 Kcal
1Cal = 4.183 Joule

Electrical Thumb Rules (Part 2)

Electrical Thumb Rules

Useful Electrical Equations

• For Sinusoidal Current: Form Factor = RMS Value/Average Value =1.11
• For Sinusoidal Current: Peak Factor = Max Value/RMS Value = 1.414
• Average Value of Sinusoidal Current (I_av) = 0.637 x Im (Im = Max.Value)
• RMS Value of Sinusoidal Current (I_rms) = 0.707 x Im (Im = Max.Value)
• A.C Current = D.C Current/0.636.
• Phase Difference between Phase = 360/ No of Phase (1 Phase=230/1=360°, 2 Phase=360/2=180°)
• Short Circuit Level of Cable in KA (I_sc) =
  (0.094 x Cable Dia in Sq.mm) /√ Short Circuit Time (Sec)
• Max.Cross Section Area of Earthing Strip (mm2) = √(Fault Current x Fault Current x Operating Time of Disconnected Device ) / K
  K = Material Factor, K for Cu = 159, K for Al = 105, K for steel = 58 , K for GI = 80
• Most Economical Voltage at given Distance = 5.5x√((km/1.6)+(kw/100))
• Cable Voltage Drop (%) =
  (1.732 x current x (RcosǾ+jsinǾ) x 1.732 x Length (km) x 100) / (Volt(L-L) x Cable Run.
• Spacing of Conductor in Transmission Line (mm) = 500 + 18 x (P – P Volt) + (2 x (Span in Length)/50).
• Protection radius of Lighnting Arrestor = √h x (2D-h) + (2D+L).
  Where h= height of L.A, D-distance of equipment (20, 40, 60 Meter), L=V x t (V=1m/ms, t=Discharge Time).
• Size of Lightning Arrestor = 1.5x Phase to Earth Voltage or 1.5 x (System Voltage/1.732).
• Maximum Voltage of the System = 1.1xRated Voltage (Ex. 66KV = 1.1 × 66 = 72.6KV)
• Load Factor = Average Power/Peak Power
• If Load Factor is 1 or 100% = This is best situation for System and Consumer both.
• If Load Factor is Low (0 or 25%) = you are paying maximum amount of KWH consumption. Load Factor may be increased by switching or use of your Electrical Application.
• Demand Factor = Maximum Demand / Total Connected Load (Demand Factor <1 li="">
• Demand factor should be applied for Group Load
• Diversity Factor =
  Sum of Maximum Power Demand / Maximum Demand (Demand Factor >1)
  Diversity factor should be consider for individual Load
• Plant Factor (Plant Capacity) = Average Load / Capacity of Plant
• Fusing Factor = Minimum Fusing Current / Current Rating (Fusing Factor>1).
• Voltage Variation (1 to 1.5%) = ((Average Voltage – Min Voltage) x 100)/Average Voltage
  Ex: 462V, 463V, 455V, Voltage Variation= ((460 – 455)  x 100)/455 = 1.1%.
• Current Variation (10%) = ((Average Current – Min Current) x 100)/Average Current
  Ex: 30A,35A,30A, Current Variation = ((35-31.7) x 100)/31.7 = 10.4%
• Fault Level at TC Secondary
  = TC (VA) x 100 / Transformer Secondary (V) x Impedance (%)
• Motor Full Load Current = Kw /1.732 x KV x P.F x Efficiency

Electrical Thumb Rules (Part 3)

Electrical Thumb Rules

Size of Capacitor for Power Factor Correction

For Motor
Size of Capacitor = 1/3 Hp of Motor ( 0.12x KW of Motor)
For Transformer
< 315 KVA	5% of KVA Rating
315 KVA to 1000 KVA	6% of KVA Rating
>1000 KVA	8% of KVA Rating

Earthing Resistance value

Earthing Resistance Value
Power Station	0.5 Ω
Sub Station Major	1.0 Ω
Sub Station Minor	2.0 Ω
Distribution Transformer	5.0 Ω
Transmission Line	10 Ω
Single Isolate Earth Pit	5.0 Ω
Earthing Grid	0.5 Ω
As per NEC Earthing Resistance should be <5 .0="" strong="">

Voltage Limit (As per CPWD & KEB)

Voltage Limit (As Per CPWD)
240V	< 5 KW
415V	<100 kva="" td="">
11KV	<3 nbsp="" td="">
22KV	<6 mva="" td="">
33KV	<12 mva="" td="">
66KV	<20 mva="" td="">
110KV	<40 mva="" td="">
220KV	>40 MVA

Voltage Variation

> 33 KV	(-) 12.5% to (+) 10%
< 33 KV	(-) 9% to (+) 6%
Low Voltage	(-) 6% to (+) 6%

Insulation Class

Insulation	Temperature
Class A	105°C
Class E	120°C
Class B	130°C
Class F	155°C
Class H	180°C
Class N	200°C

Standard Voltage Limit

Voltage	IEC (60038)	IEC (6100:3.6)	Indian Elect. Rule
ELV	< 50 V
LV	50 V to 1 KV	<=1 KV	< 250 V
MV		<= 35 KV	250 V to 650 V
HV	> 1KV	<= 230 KV	650 V to 33 KV
EHV		> 230 KV	> 33 KV

Standard Electrical Connection (As per GERC)

As per Type of Connection
Connection	Voltage
LT Connection	<=440V
HT connection	440V to 66KV
EHT connection	>= 66KV
As per Electrical Load Demand
Up 6W Load demand	1 Phase 230V Supply
6W to 100KVA(100KW)	3 Phase 440V Supply
100KVA to 2500KVA	11KV,22KV,33KV
Above 2500KVA	66KV
HT Connection Earthing
H.T Connection’s Earthing Strip	20mmX4mm Cu. Strip
CT & PT bodies	2Nos
PT Secondary	1Nos
CT Secondary	1Nos
I/C and O/G Cable+ Cubicle Body	2Nos

Standard Meter Room Size (As per GERC)

Meter Box Height	Upper level does not beyond 1.7 meter and Lower level should not below 1.2 meter from ground.
Facing of Meter Box	Meter Box should be at front area of Building at Ground Floor.
Meter Room / Closed Shade	4 meter square Size

Electrical Load as per Sq.ft Area (As per DHBVN)

Sq.ft Area	Required Load (Connected)
< 900 Sq.ft	8 KW
901 Sq.ft to 1600 Sq.ft	16 KW
1601 Sq.ft to 2500 Sq.ft	20 KW
> 2500 Sq.ft	24 KW
For Flats :100 Sq.ft / 1 KW
For Flats USS /TC: 100 Sq.ft / 23 KVA

Contracted Load in case of High-rise Building

For Domestic Load	500 watt per 100 Sq. foot of the constructed area.
For Commercial	1500 watt per 100 Sq. foot of the constructed area
Other Common Load	For lift, water lifting pump, streetlight if any, corridor/campus lighting and other common facilities, actual load shall be calculated
Staircase Light	11KW/Flat Ex: 200Flat=200×11=2.2KW
Sanctioned Load for Building
Up to 50 kW	The L.T. existing mains shall be strengthened.
50 kW to 450 kW (500 kVA)	11 kV existing feeders shall be extended if spare capacity is available otherwise, new 11 kV feeders shall be constructed.
450 kW to 2550 kW (3000 kVA)	11 kV feeder shall be constructed from the nearest 33 kV or 110 kV substation
2550 kW to 8500 kW (10,000 kVA)	33kV feeder from 33 kV or 110 kV sub station
8500 kW (10,000 kVA)	110 kV feeder from nearest 110 kV or 220 kV sub-station

Electrical Thumb Rule (Part 4)

Electrical Thumb Rules (Part 4)

1. Substation Capacity and Short Circuit Current Capacity

As per GERC
Voltage	Sub Station Capacity	Short Circuit Current
400 KV	Up to 1000 MVA	40 KA  (1 to 3 Sec)
220 KV	Up to 320 MVA	40 KA  (1 to 3 Sec)
132 KV	Up to 150 MVA	32 KA  (1 to 3 Sec)
66 KV	Up to 80 MVA	25 KA  (1 to 3 Sec)
33 KV	1.5 MVA to 5 MVA	35 KA (Urban) (1 to 3 Sec)
11 KV	150 KVA to 1.5 MVA	25 KA (Rural) (1 to 3 Sec)
415 V	6  KVA to 150 KVA	10 KA  (1 to 3 Sec)
220 V	Up to 6 KVA	6 KA  (1 to 3 Sec)

2. Substation Capacity and Short Circuit Current Capacity

As per Central Electricity Authority
Voltage	Sub Station Capacity	Short Circuit Current
765 KV	4500 MVA	31.5 KA for 1 Sec
400 KV	1500 MVA	31.5 KA for 1 Sec
220 KV	500 MVA	40 KA for 1 Sec
110/132 KV	150 MVA	40 KA or 50 KA for 1 Sec
66 KV	75 MVA	40 KA or 50 KA for 1 Sec

3. Minimum Ground Clearance and Fault Clearing Time

Voltage	Min. Ground Clearance	Fault Clear Time
400 KV	8.8 Meter	100 mille second
220 KV	8.0 Meter	120 mille second
132 KV	6.1 Meter	160 mille second
66 KV	5.1 Meter	300 mille second
33 KV	3.7 Meter	-
11 KV	2.7 Meter	-

4. Busbar Ampere Rating

For Phase Busbar	Aluminium 130 Amp / Sq.cm or 800Amp / Sq.inch.
For Phase Busbar	Copper 160 Amp / Sq.cm or 1000Amp / Sq.inch
For Neutral Busbar	Same as Phase Busbar up to 200 Amp than Size of Neutral Busbar is at least half of Phase Busbar.

5. Busbar Spacing

Between Phase and Earth	26mm (Min)
Between Phase and Phase	32mm (Min)
Busbar Support between Two Insulator	250mm.

6. Sound Level of Diesel Generator (ANSI 89.2 and NEMA 51.20)

KVA	Max. Sound Level
<9 kva="" td="">	40 DB
10 KVA to 50 KVA	45 DB
51 KVA to 150 KVA	50 DB
151 KVA to 300 KVA	55 DB
301 KVA to 500 KVA	60 DB

7. IR Value of Transformer

IR Value of Transformer
Voltage	30°C	40°C	50°C
>66KV	600MΩ	300MΩ	150MΩ
22KV to 33KV	500MΩ	250MΩ	125MΩ
6.6KV to 11KV	400MΩ	200MΩ	100MΩ
<6 .6kv="" strong="">	200MΩ	100MΩ	50MΩ
415V	100MΩ	50MΩ	20MΩ

8. Standard Size of MCB, MCCB, ELCB, RCCB, SFU and Fuse

MCB, MCCB, ELCB, RCCB, SFU, Fuse – Standard Ratings
MCB	Up to 63 Amp (80Amp and 100 Amp a    per Request)
MCCB	Up to 1600 Amp (2000 Amp as per Request)
ACB	Above 1000 Amp
MCB Rating	6A,10A,16A,20A,32A,40A,50A,63A
MCCB Rating	0.5A,1A,2A,4A,6A,10A,16A,20A,32A,40A,50A,63A,80A,100A (Domestic Max 6A)
RCCB/ELCB	6A,10A,16A,20A,32A,40A,50A,63A,80A,100A
Sen. of ELCB	30ma (Domestic),100ma (Industrial),300ma
DPIC (Double Pole Iron Clad) main switch	5A,15A,30 A for 250V
TPIC (Triple Pole Iron Clad) main switch	30A, 60A, 100A, 200 A For 500 V
DPMCB	5A, 10A, 16A, 32A and 63 A for 250V
TPMCCB	100A,200A, 300Aand 500 A For 660 V
TPN main switch	30A, 60A, 100A, 200A, 300 A For 500 V
TPNMCB	16A, 32A,63A For 500 V, beyond this TPNMCCB: 100A, 200A, 300A, 500 A For 660 V
TPN Fuse Unit (Rewirable)	16A,32A,63A,100A,200A
Change over switch (Off Load)	32A,63A,100A,200A,300A,400A,630A,800A
SFU (Switch Fuse Unit)	32A,63A,100A,125A,160A,200A,250A,315A,400A,630A
HRC Fuse TPN (Bakelite)	125A,160A,200A,250A,400A.630A
HRC Fuse DPN (Bakelite)	16A,32A,63A
MCB/MCCB/ELCB Termination Wire / Cable
Up to 20A MCB	Max. 25 Sq.mm
20A to 63A MCB	Max. 35 Sq.mm
MCCB	Max. 25 Sq.mm
6A to 45A ELCB	16 Sq.mm
24A to 63A ELCB	35 Sq.mm
80A to 100A ELCB	50 Sq.mm

Electrical Thumb Rule (Part 5)

Electrical Thumb Rules  (Part 5)

1. Standard Size of Transformer (IEEE/ANSI 57.120)

Single Phase Transformer	Three Phase Transformer
5KVA, 10KVA, 15KVA, 25KVA, 37.5KVA, 50KVA, 75KVA, 100KVA, 167KVA, 250KVA, 333KVA, 500KVA, 833KVA, 1.25KVA, 1.66KVA, 2.5KVA, 3.33KVA, 5.0KVA, 6.6KVA, 8.3KVA, 10.0KVA, 12.5KVA, 16.6KVA, 20.8KVA, 25.0KVA, 33.33KVA	3KVA, 5KVA, 9KVA, 15KVA, 30KVA, 45KVA, 75KVA, 112.5KVA, 150KVA, 225KVA, 300KVA, 500KVA, 750KVA, 1MVA, 1.5MVA, 2MVA, 2.5MVA, 3.7MVA, 5MVA, 7.5MVA, 10MVA, 12MVA, 15MVA, 20MVA, 25MVA, 30MVA, 37.5MVA, 50MVA, 60MVA, 75MVA, 100MVA

2. Standard Size of Motor (HP)

Electrical Motor (HP)

1, 1.5, 2, 3, 5, 7.5, 10, 15, 20, 30, 40, 50, 60, 75, 100, 125, 150, 200, 250, 300, 400, 450, 500, 600, 700, 800, 900, 1000, 1250, 1250, 1500, 1750, 2000, 2250, 3000, 3500 and 4000

3. Approximate RPM of Motor

HP	RPM
< 10 HP	750 RPM
10 HP to 30 HP	>600 RPM
30 HP to 125 HP	500 RPM
125 HP to 300 HP	375 RPM

4. Motor Line Voltage

Motor (KW)	Line Voltage
< 250 KW	>440 V (LV)
150 KW to 3000KW	2.5 KV to 4.1 KV (HV)
200 KW to 3000KW	3.3 KV to 7.2 KV (HV)
1000 KW to 1500KW	6.6 KV to 13.8 KV (HV)

5. Motor Starting Current

Supply	Size of Motor	Max. Starting Current
1 Phase	< 1 HP	6 X Motor Full Load Current
1 Phase	1 HP to 10 HP	3 X Motor Full Load Current
3 Phase	10 HP	2 X Motor Full Load Current
3 Phase	10 HP to 15 HP	2 X Motor Full Load Current
3 Phase	> 15 HP	1.5 X Motor Full Load Current

6. Motor Starter

Starter	HP or KW	Starting Current	Torque
DOL	<13 hp="" td="">	7 X Full Load Current	Good
Star-Delta	13 HP to 48 HP	3 X Full Load Current	Poor
Auto TC	> 48 HP (37 KW)	4 X Full Load Current	Good/ Average
VSD		0.5 to 1.5 X Full Load Current	Excellent
Motor > 2.2KW Should not connect direct to supply voltage if it is in Delta winding

7. Impedance of Transformer (As per IS 2026)

>MVA	% Impedance
< 1 MVA	5%
1 MVA to 2.5 MVA	6%
2.5 MVA to 5 MVA	7%
5 MVA to 7 MVA	8%
7 MVA to 12 MVA	9%
12 MVA to 30 MVA	10%
> 30 MVA	12.5%

8. Standard Size of Transformer

Standard Size of Transformer	KVA
Power Transformer (Urban)	3, 6, 8, 10, 16
Power Transformer (Rural)	1, 1.6, 3.15, 5
Distribution Transformer	25, 50, 63, 100, 250, 315, 400, 500, 630