Electrical Thumb Rules
This technical article deals with the electrical thumb rules related to cable capacity, current capacity of equipment, earthing resistance, minimum bending radius of a cable, insulation resistance, transformer and lightning arrestor parameters, diesel generator, and current transformer (CT).
Electrical Thumb Rules For:
- Cable Capacity
- Current Capacity of Equipment
- Earthing Resistance
- Minimum Bending Radius of a Cable
- Insulation Resistance
- Lightning Arrestor
- Transformer
- Diesel Generator
- Current Transformer
- Quick Electrical Calculation
Cable Capacity
The component that ultimately affects a cable’s current carrying capability is the maximum operational temperature that the cable can withstand throughout its lifespan without incurring damage or degeneration. The heat produced in the cable arises from (a) ohmic losses in the conductor, (b) dielectric losses in the insulating medium, and (c) sheath and intersheath losses.
The created heat is emitted to the environment. The current capacity is dependent upon the conductivity of the surrounding medium, resulting in varying ratings for the same cable based on whether it is buried or exposed.
1. For Cu Wire Current Capacity (Up to 30 Sq.mm) = 6× Size of Wire in mm2
Example:
- For 2.5mm2 = 6 × 2.5 = 15 Amp,
- For 1mm2 = 6 × 1 = 6 Amp,
- For 1.5mm2 = 6 × 1.5 = 9 Amp
2. For Cable Current Capacity = 4× Size of Cable in mm2
Example: For 2.5mm2 = 4 × 2.5 = 9 Amp.
3. Nomenclature for cable Rating = Uo / U
where:
- Uo = Phase-Ground Voltage,
- U = Phase-Phase Voltage,
- Um = Highest Permissible Voltage
Current Capacity of Electric Motor
The torque required by the motor is the criterion for determining the appropriate drive size. Horsepower ratings (HP), although provided by drive manufacturers as a reference for the maximum motor size in most applications, lack precision.
For applications requiring continuous torque, the suitable drive may be considered “oversized” in relation to the motor. Typically, general-purpose constant torque drives have an overload current capacity of around 150% for one minute, relative to nominal output.
Should an application surpass these limitations, a bigger drive must be specified.
- 1-Phase Motor draws Current = 7 Amp per HP.
- 3-Phase Motor draws Current = 1.25 Amp per HP.
- Full Load Current of 3 Phase Motor = HP × 1.5
- Full Load Current of 1 Phase Motor = HP × 6
- No Load Current of 3 Phase Motor = 30% of FLC
- KW Rating of Motor = HP × 0.75
- Full Load Current of equipment = 1.39 × KVA (for 3-Phase 415 Volt)
- Full Load Current of equipment = 1.74 × kW (for 3-Phase 415 Volt)
Earthing Resistance
Historically, an earthing system characterized by low overall earth resistance was thought to be safe. Nonetheless, a direct correlation between the resistance of the earthing system (such as 1Ω or 10Ω) and the likelihood of a fatality occurring in any specific scenario does not exist.
A comprehensive study that considers every relevant factor and provides a realistic evaluation of the risks is thus essential.
- 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)
The basic understanding of an earthing protection system (diagram and definitions)
Minimum Bending Radius for Cables
Training refers to the installment of cable when it is not subjected to tension. Bending refers to the installment of cable when subjected to tension. The objective of cable installation is to minimize mechanical stresses to preserve the cable’s physical and electrical properties during its predicted service life.
Bends in conductors, multi-conductor cables, or conductor assemblies must be handled in such way that the cable will not be damaged.
The issue is made worse by the presence of jackets that obscure the damage on most tapes. The extruded polymers used for insulating shields initially provide adequate conductivity and coverage to meet acceptance tests, but then fail prematurely due to corona at the shield/insulation interface.
- Minimum Bending Radius for LT Power Cable = 12 × Dia of Cable.
- Minimum Bending Radius for HT Power Cable = 20 × Dia of Cable.
- Minimum Bending Radius for Control Cable = 10 × Dia of Cable.
Insulation Resistance
When any electrical equipment is new, the electrical insulation should be in the best possible state. Moreover, manufacturers of cables, wires, electric motors, transformers, and similar equipment have consistently improved their insulation for industrial applications. Nonetheless, even today, insulation is susceptible to numerous factors that might lead to its failure, including mechanical damage, vibration, extreme temperatures, pollutants such as dirt and grease, corrosive vapors, process-related moisture, or simply humidity on a humid day.
These adversaries of insulation operate at varying extents over time, compounded by existing electrical strains. As pinholes or cracks form, moisture and contaminants infiltrate the insulation surfaces, creating a low-resistance pathway for leakage current.
In the absence of inspections, a motor with weak insulation may provide a risk of electric shock when energized and is also susceptible to burnout. What was once effective insulation has transformed into a partial conductor.
- Insulation Resistance Value for Rotating Machine = (kV+1) MΩ.
- Insulation Resistance Value for Motor (IS 732) = ((20 × Voltage (L-L)) / (1000 + (2 × kW)).
- Insulation Resistance Value for Equipment (<1KV) = Minimum 1 MΩ.
- Insulation Resistance Value for Equipment (>1KV) = kV 1 MΩ per 1kV.
- Insulation Resistance Value for Panel = 2 × 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 = (2 × Name Plate Voltage) +1000
- Test Voltage (D.C) for Meggering = (2 × Name Plate Voltage).
- Submersible Pump Take 0.4 KWH of extra Energy at 1 meter drop of Water.
Further Study – Measurement of insulation resistance (IR)
Lightning Arrestor
Lightning arresters are engineered to restrict line-to-ground voltage during lightning strikes or other extreme transient voltage situations. Certain earlier gap-type lightning arresters unintentionally short-circuited the line or equipment, resulting in the circuit breaker tripping. The breaker would thereafter reclose once the transient overvoltage condition had gone. The lightning arrester protects nearby equipment against high-voltage transient events.
For instance, consider an 11 kV lightning arrester installed on a 7.2 kV line to neutral system. The lightning arrester will operate if the line-to-neutral voltage above roughly 11 kV. Electrical equipment connected to this distribution system might have a flashover rating of 90 kV.
Consequently, the arrester limited the high-voltage transient, so preventing flashover or insulation breakdown in the electrical equipment.
Arrestor have two ratings:
- MCOV = Max. Continuous Line to Ground Operating Voltage
- Duty Cycle Voltage (Duty Cycle Voltage > MCOV).
Design study for 33/11 kV substation, distribution and protection in the city of Kenya
Transformer
Transformers operate through the integration of two physical laws. Physical law #1 asserts that a voltage is generated in any conductor subjected to a varying magnetic field. Physical law #2 asserts that an electric current passing a conductor generates a magnetic field. Transformers integrate these concepts by employing two wire coils and changing voltage source. The current in one coil of the transformer induces a voltage in the coil on the opposite side.
The two coils are interconnected through the magnetic field.
This notion is crucial as the entire electric power system relies on these interactions. Upon close examination, the voltage on one side of a transformer is directly proportional to the turns ratio, whereas the current on the opposite side is inversely proportional to the turns ratio.
Figure 1 – Transformer windings
The transformer seen in Figure 1 has a turns ratio of 2:1. A transformer with a 2:1 turns ratio, as depicted in Figure 4-4, will produce 120 Vac at 2 amps on its secondary winding (right side) when 240 Vac at 1 amp is connected to its primary winding (left side), as illustrated in Figure 2.
Figure 2 – Transformer turn ratio
Note: Power is 240 watts on both sides (i.e., voltage multiplied by current). As previously mentioned, increasing the voltage, such as in transmission lines, reduces the current and hence diminishes system losses dramatically.
- Current Rating of Transformer = kVA × 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 / 1.732 × Volt (Phase-Phase)
- Typically the local utility provides transformers rated up to 500 kVA For maximum connected load of 99 kW,
- Typically the local utility provides transformers rated up to 1250 kVA For maximum connected load of 150 kW.
- The diversity they would apply to apartments is around 60%
- Maximum HT (11kV) connected load will be around 4.5 MVA per circuit.
- 4 No. earth pits per transformer (2 No. for body and 2 No. for neutral earthing),
- Clearances, approx.1000 mm around TC allow for transformer movement for replacement.
Contract drawings for a power transformer – The checklist you should always follow
Diesel Generator
Generators may be classified as synchronous or asynchronous. Asynchronous generators are sometimes known as induction generators. The construction is fundamentally identical to that of an induction motor. It features a squirrel-cage rotor and a wrapped stator. An induction generator is a motor operated over its specified synchronous speed, hence producing electricity. It will function as a motor while operating below synchronous speed.
The induction generator lacks an exciter and must function in conjunction with the utility or an alternative source. The induction generator requires VARs from an external source to produce power. The induction generator functions at a slip frequency, thereby synchronizing its output frequency with that of the utility.
The generator’s construction ensures excellent reliability and minimal maintenance. A minimum of protective relays and controls is mandated. The primary drawbacks are its requirement for VARs from the system and its inability to function as a standby or emergency generator.
Nonetheless, synchronous generators are the most used. Their production is dictated by their field and governor controls. Changing the current in the DC field windings regulates the voltage output. The frequency is regulated by the rotational speed. The torque produced on the generator shaft by the driving engine regulates the power output.
The synchronous generator provides accurate regulation of the electricity it can produce. In cogeneration applications, it can enhance the system’s power factor.
- Diesel Generator Set Produces = 3.87 Units (kWh) in 1 Litter of Diesel.
- Requirement Area of Diesel Generator = for 25 kW to 48 kW = 56 m2, 100KW = 65 m2.
- DG less than or equal to 1000 kVA must be in a canopy.
- DG greater 1000 kVA can either be in a canopy or skid mounted in an acoustically treated room
- DG noise levels to be less than 75 dBA 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.
Spreadsheet to Calculate Short Circuit Capacity of Diesel Generator Synchronizing Panel
Current Transformer
The primary issue is that the CT core be appropriately dimensioned to fulfill the burden requirements. The burden covers both the associated metering burden and the lead burden. The metering class current transformer is designated with an accuracy rating corresponding to each standard burden for which it is were eligible. An illustration presented in IEEE C57.13 is 0.3 B-0.1 and B-0.2, 0.6 B-0.5.
The numeral following the letter B denotes the standard impedance in Ohms with a power factor of 0.9. The values 0.3 and 0.6 denote the accuracy class.
The auxiliary transformer is designed to saturate at currents exceeding several tens of amperes. When selecting metering or auxiliary current transformers, the design burden must be accurately aligned with the actual connected burden.
Utilizing a connection with a lower burden than the design burden of the current transformer will let greater currents to pass through the metering apparatus before saturation occurs.
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, 15 VA 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).
IEC and NEMA/IEEE ratings of current transformers (CTs) in medium voltage applications
Quick Electrical Calculation
| 1 HP = 0.746 kW | Star Connection |
| 1 kW = 1.36 HP | Line Voltage = √3 Phase Voltage |
| 1 Watt = 0.846 Kla/Hr | Line Current = Phase Current |
| 1Watt = 3.41 BTU/Hr | Delta Connection |
| 1 kWh = 3.6 MJ | Line Voltage = Phase Voltage |
| 1 Cal = 4.186 J | Line Current = √3 Phase Current |
| 1 Tone = 3530 BTU | |
| 85 Sq.ft Floor Area = 1200 BTU | |
| 1 Kcal = 4186 Joule | |
| 1 kWh = 860 Kcal | |
| 1 Cal = 4.183 Joule |
Related electrical guides & articles
Jignesh Parmar
Electrical Middle management professional having more than 22 years rich and dynamic experience in Project Execution / Project Management / Designing / Maintenance diversifies from Electrical Power Transmission (400KV/220KV/66KV)- Distribution(11KV/220V) to Lifts-HVAC-Ventilation-Fire Fighting-Fire Alarm-Lifts-CCTV-Stack Parking Works (High Rise Buildings, Townships, Shopping Complex, Commercial Complex, School, Temple).Profile: Jignesh Parmar
THANKS FOR SHARING THE THUMB RULES
Dear parmar ji,
You are a great person, of Modi vision, make in India, you are making our indian technicals lerning strong.
Thanks for best effort.
useful for engineers those who works in projects
Perfect
NICE AND PRACTICALLY APPLICABLE METHODS INVOLVED ….THANKS
i learned many things by your post. thank you .
Dear sir,
how to make calculate , cable size 3cx70 sqmm copper pvc insulated double gi strip armoured,
pl clear this point the conductivity of armour shall not less then 75% of the conductivity of larg core
how many copper strip use for the conductivity maintain.
What would be current carring capacity of cable in 3phase system?
Very good info. for all engineers
Dear sir , need overload current carrying capacity for MV cable with trefoil and flat touching condition with different hours.
Generally 1 /2/3/4/6/8/10/12/24 hour run with 60% / 75%/90% & 30% overload condition with respectively above mentioned time durations so please how can calculate in easy format.
Need Cable current carrying capacity for 3 Phase Cable
can we use 2 x 16sq.mm x 4core and 1 x 10sq.mm x 4core power cable instead of 1 x 35sq.mm x 4core cable for the connectivity of Diesel Genset (60 KVA) to ATS panel 20 feet apart.
Please advice…
2x16mm2 4-core cable which is 2 run of 16mm2 4-core cable is more than enough to connect 60kVA generator to ATS panel
giving that the generator current = 86.6A
We Have a powerloom factory…with each one has 330 watts 3 phase induction motor voltage -220 freq-50hz
we have used 4 sq mm for mainline and 2.5sqmm for each motor for 12 motors.
Can We Connect that same 4 sq.mm for another 12 motors or we have to add 4 sq mm wire…Help me with your knowledge
YES.
We bundled conductors instead of single conductors for ac transmission to reduce skin effect.
If you provide two cables 4Cx35 Sq mm for one cable 4Cx35 Sq. mm then the system is sufficient and addition of 4Cx10 Sq mm will make it extra strong.
Yes you can
Hi Sir,
In a substation we use different connectors, like, bus support, couplers, body & cap connector etc, I would like to know what each component is rated for with respect to ampacity. How can we calculate that, is there a way to do that.
Excellent and neat write up, keep the great work !!
3phase 40A energy meter 17Nos in one apparetment.
How much amps switch rating and transformer is required?
Typically the local utility provides transformers rated up to 1250kVA For maximum connected load of 150kW.
Power factor*KVA=KW
0.8*1250=1000KW
But here answer is 150KW
How it will calculate?
Sir, one of my client wants to take connection having his required load 70 KW. In fact I have maximum feeder capacity in the existing panel 100 AMP TPN,MCCB-16 KA. Please suggest me the Feeder specification, so that I can install it in my panel in the spare box. also please eleborate the formula to select.
Thank you sir. This is very needful to us.
Sir,
I need to know the load calculations of
2core 1sqmm al ar cable = Amps
1sqmm cu cable = Amps
Tor electrical calculation should we take 1HP= 735.5W or 746W
1HP=746W
Dear sir
Twin core flat aluminium pvc insulated cable when we are supply current one core than earthing second core why ?
Dear sir
I need your expertise ON TRIPOING OF 220KV EHV transmission line, during lightening.
Need your help. Can I have your contact number please.
Very very nice ..very very useful informations &Calculations..thank u very much
For 4Cx 6sqmm cu at cable, you can go with 4Cx 25 sqmm Al AR XLPE cable. And for 3Cx4sqmm you go with 16sqmm if the length is less than 80 to 100mts.
load calculation of3.5*300 sq mm al. cable
For single core house wiring to 1.5 sq. Mm. How much current take ?
2800KW, 12Amps 1 phase AC load and distance between incoming supply source to load point is 1500mtr. Cable laid in under ground and HDPE pipe. now can you please suggest cable size and voltage drop calculation
How to select ct burden when current 1000A and voltage 433 v for metering and capacitor panel realy operating purpose.
Regards
Avinash Lahane
M-9225305991
i want to replace 4c*6sqmm copper armed cable with aluminium armed cable can u suggest the thickness of aluminium cable .and also i want to replace 3c*4sq mm copper with aluminium can u please suggest the thicknesses of aluminium cable
How to calculate the full load current of a 3 phase submersible,440V?
Sir
What are the details of motor installed in washing machine to be found out to select strength of wire ie. 2.5 s.qm or 4.5 sq.m or 1.5 sq.m wire to give power supply?
whether 15 amp.plug and socket can be powered with 1.5 sq.m flexible wire already given for 5 amp socket in the boar or more than 1.5 sq. metre strength wire to be used?
your kind reply will be useful for me.
Somasundaram N
Dear Sir
Can We use 4mmx4core copper armoured cable for 10HP motor coupled with 60LPM hyraulic pump. Application is for chopping/cutting of scrap sheet after blanking
pls see size of cable. i think it should be higher. you can follow chart for “current vs size of cable”. also different chart for Cu and Al is there
Can I use 25x2x0.75sqmm twisted,shielded cable instead of 50×0.75sqmm shielded cable?
Application :- I need to transmit 230VAC power from stepper drives to motor.
SIR,
FOR 100 KW SOLAR PLANT CAN I USE 4C*70 SQ.MM(COPPER) TELL ME ITS ENOUGH.FROM ACDB TO EXISTING PANEL
Hi fella,
I came across this website and got lost in wire Vs cable hurricane :) Later in comments I’ve seen cables AKA “bunch of wires” explanation. Where I got stuck is, according to your statement
“Cable Current Capacity = 4X Size of Cable in Sq.mm, Ex. For 6 Sq.mm = 4×6= 24 Amp.”
Yet in the mean time, I’ve witnessed mine sq.mm wire stood against the current capacity of around 28A for nearly 30minutes!!! Its details are Unsheated,Copper made,No. of wires/Wire dia metre=85/.30. So I’m expecting 6xSize in sq.mm instead of 4XSize in sq.mm. So I want you to clearly tell me what does wire Vs cable means?
its really helpful i am very thank full to you for your this kind of act.
hi
finaly i found nice web site to improve my knowledge. i have to know if i communicates RS485 data with 1.5sq mm 2 core twisted wire without sheld and run the wire 60 mtrs what will happen.
pls advice
Here we using the load 3.6Amps and the same we are using the wire 2.5Sq.mm.If it is ok or we need to change.
Hi,
We have the Main Panel MCCB of 400A 4P and the load is 120kVA. The client has provided raw power using 4 core 95Sqmm Aluminum Armoured cable. Please let me know whether the raw power cable is fine for our load?
Also what is the load 95sqmm can take?
Hi,
According to load the cable size is good enough, and the cable can carry up to 220A current which means 120Kw or 140KVA
Thanks. Very effective information.
Please give me a clear idea how can I find the contactor rating & over load relay rating for Star-delta Starter. Give me this example for 30kW motor.
Very useful make PDF and publish for download
Please correct 2.5×4 = 9Amps to = 10Amps.
in cable current capacity thumb rule.
Intresting and educative forum for power engineers
This forum is indeed amazing quite educative.
Keep up the good work.
Thank you.
Sir, How do the GEB pole lines are identified for phase , neutral and earthing. Reason for my asking is all the lines ( Either 3 or 5 for single and 3 phase ) are same and there is no distinction. Recently in our street light pole tuble light connection, an electricians has given some wrong connection by joining 2 wires either in phase or in neutral. Because of this many of our street people have lost TV, Fridge, AC, Digital wall clock etc. The GEB officials said that Munipal contractor has done the mistake while rectifying the defect in the pole street light. This is the reason why want to know for easy identification of these Phase, Neutral and Earthing wires of GEB Pole. pls. explain with sketch or drawing for easy understanding.
Dear Sir,
Would you please advise how can I connect 2 numbers of single phase 3000VA 230V 50 HZ UPS
in Parallel for redundancy… Appreciate your early response
Thanks and regards
Joseph Puduvala
Hi,
These single phase ups can be connect in parallel only when there Output voltage and frequency are same. so please communicate with service provider to set voltage and frequency of both ups on same value and then your can synchronize the ups.
Regards
Vinay kumar
It’s awesome page..I love to visit the page but there are no answers posted for all the questions asked by the Engineers..And I would love to join this group on LinkedIn or FB to gain some knowledge about the EEE.Thank you so much guys for your time and patience.
Anyone please suggest me a book or a site to learn from basics to the core subject of Electrical Engineering including the calculations.
.You guys TC!!
Current capacity of aluminium cable
Hi i have a question
we require 100KVA DG as part of the factory setup can anyone explain how much capacity of transformer will be needed, is there a possibility to determine the transformer capacity based on the DG or let me know if you need the machinery list thanks in advance
Hi,
To calculate capacity of Transformer,you have to calculate the load of plant and also consider extension of load in future. then maximum load should be less than 80% of transformer capacity.It does not depend on your D.G availability.
Thanks
Vinay
In a 3 phase motor we use 10 mm cable one phase taking 40 amp for example how much total current of this motor
Can you give motors equations for Induction motors, DC Motors ect.
What is equivalent size of cable will be used for earthing of DG sets and Transformer instead of cu /GI strip
Is considered the same cross sectional area or how to calculate
Esteemed sir
I want to know how to calculate current carrying capacity per square mm Arial bunched cable.
Sir, please give details about how to bend an earth cable to be connected to diesel generator of 25 KVA. Give me an idea how to bend it.
Dear Sir,
I want to know what is required AC cable size (in sqmm) for solar on grid 3phase 12.5kW inverter for inverter to ACDB?
4cx16 sqmm Cu.
We have infrared lamp resin curing plant & paper dryers. Total load is 330 KW. Connected with neutral and 3 phases i.e.each phase will have a load of 110 kw. Current 500 amp. What should the cable size and 3.5 core or 4 core. We will prefer copper.
how can we have check the copper nd aluminium cable size according to load via formula or trick ?
this is very urgent for me, pls help me sir ASAP.
Dear Sir,
your above mentioned information is very useful.But please mention the load capacity of aluminium cables also..for 30sqmm copper cable we can put a load of 120A??
Gd evening sir
Pls told me sir
How will be calculate cable size in mm^2
Pls told me a short trik
For example which size of cable should be use for 2500amp rating braker
Pls sir as soon as possible rply me
Thanks a lot sir
this helping me more……..
i just want solution for this. if i want to pass current of 1600 Ampere so what size of cable should i select?? cable size should in MM^2
It should be 400 Sq mm
Sir, can you say that how a dc current of 2.5 amps will flow through a wire of resistance 60 ohms? input is 36 volts 11 ah battery
Sir please tell me why 1hp single phase motor is 7ampere in single phase motor chart in ampere. But if we use the formula in ohms law to get ampere in single phase I = hp / VxExPF we only get only 4.23 ampere when voltage is 230v power factor is 0.9 and i used 0.85 efficiency.. Please teached me how to prove the electrical thumb rules.
what is the difference between “Cu Wire Current Capacity” and Cable “Cable Current 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.
Plz tell me how to calculate size of generator set for a specific submersible pump set i.i for specific hp motor? Thanks alot
pls tell me sir what cable needed for 32amp industrial socket and how we can determine if we need aluminium cable or cu cable or need 3 phase or single phase in general?
Super sir
7/16 cable size meanes what is the sqmm cable size in 3 phase supply 30kva load
wonderful informative portal….!!!
A perfect compilation. Thanks Jignesh. (Author)
how i find cable for a suitable load like a if load is 23 which cable is-perfect for this load and how i find by formula ?
Plz tell me how to tabulate the armoured cable size for a particular load.
i am living in FLAT WITH 3 BED ROOMS ONE DRAWING ROOM AND HAVE 5 ACs 2 TR AND WASHING MACHINE INDUCTION COOKER AND MICROWAVE WITH GEYSERS 25 LITERS IN BED ROOMS AND KITCHEN AND THE LOAD GRANTED IS 8KW.
THE EARTHING WIRE FROM MCB BOARD ON FIRST FLOOR TO METER ON GF IS OF 1 MM SQUARE .
IS THIS ENOUGH OR SHOULD I REPLACE WITH HIGHER CAPACITY
No Its not enough
If you are having a single phase meter use 1 no of 4 sq mm Cu wire
and if you are having a 3 phase meter use 2 nos of 4 sq mm wires
Tell me the short cut for calculating load for a flat
Please tell me how to find current rating of the conductor
Can we use 2 run of 25 mm sq instead of 50 mm sq cable of Cu. If yes then tell me full details and If not then tell me also full details.
How many distance between transformer and diesel genrator as per ie rules
I have a current transformer with 1 main meter outside the building and a control panel having 5 CT meters with black round coils inside the building. I want to know, A) when current pass through the Transformers, will the current be reduced or be the same and after that B) when current pass through the CT meters with black round coils, will the current be reduced or be the same. C) in the above process will the reading of the main meter be same or different, from the total reading of all the 5 CT meters.
What is the simple formula for electrical, current , voltage
Thanks sir u help for electrical problem .
we known low pf increase line current so does it increase kwh reading in metering…but pf varation is related also actually totally in reactive part…so what is the impact of pf in metering.
Please .I have a 500KVA what % of load should I load it considering the fact that max load is about 700Amp
Is your generator sets for emergency supply or prime supply? For Prime you can load up to 100% and 70% for emergency generator sets.
I want to take part in to the technical debates and weekly technical discussion.
How diesel engine frame should be grounded (I think shall be two earthing diagonal points ) according to NFPA 70 (NEC), could you please provide the supporting standard cod of this
Every Genset has predefined points to ground engine frame. Don’t forget to ground gas reservoir if it exist.
How to calculate Cable sizes for the Below in thumb rule,
01.Single core cable above 30Sqmm
02.Three phase cable size.
Pls send it with a clear Example
what is maximum distance between VCB panel and transformer at 11 kv voltage supply using HT cable of size 3cX95sqmm. Is it ok that transformer is installed at 150 meter away from VCB panel.
minimum 6 mtrs
SIR I JUST WANT TO KNOW THAT IN 3PHASE 4 WIRE ELECTRICAL DISTRIBUTION SYSTEM WHY THE RADIUS OF NEUTRAL WIRE IS LESS THAN OTHER WIRE?
Because in 3 phase 4 wire system only unbalance current pass from the nutural so current is never higher then half of the phase current,so purpose of aluminium saving its samller size then phase in power cable of higher size
Dear sir,
Please send me your mobile number because I talk personally with you so I request you please give me your mobile number
Thanks&Regards
Vagh Balu R
7698260140
Dear Jebalu, are ju crazy. There is inernet, no personalities!
what is the meaning of 2×6+4 for wire sizing?
What do you reckon on SWA 3 phase and Neutral Cable size?
Circuit 1
primary fuses, 16A and 20A = 36A
However, connected load is 9kVA and 3kVA = 17.3A and average consumption is 3kVA and 2kVA respectively, giving ~ 8A
Circuit 2
Primary fuses, 40A, 16A, 16A and 16A = 88A
However, nominal current is 33A, 6A, 8A and 11A, giving ~ 58A
Circuit 2
11kw fan with a 32amp supply
on Cable run of 150m
If the load requirement is 1200 kva , what kind of independent feeder should be considered , 11th or 33 kv
Hi need clarification to choose between 3 core, 3.5 core and 4 core for cable selection application. I know we choose 3.5 core and above in case of unbalanced loads any advice on making selection more clear is greatly appreciated
1 Phase Motor draws Current = 7Amp per HP.
Full Load Current of 1 Phase Motor = HPx6
I think full load current of 1 phase is too high, for examples, in catalog of manufacture, current of 1 phase motor 4HP only about 12A. Moreover, please clarify why percent of draw current and full load current is small (7/6), as i know that factor is 3/1.( In my country, there used 220V for line voltage and 380V for phase voltage). The same question for 3 phase motor.
What is the difference between line and phase?
line to line voltage means voltage between 2 line
and Phase voltage means voltage between 1 line and neutral
thanks 4 d info it was really
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Thanks
Thanks Dear sharing Such valuable data
sirs, for aluminium cables and wires current carrying was not indicated in the thumb rules.
Thank You For This and for those u cant understand this is only a thumb rule just to understand and remember
On the section current capacity of Equipments, it is written
# 1 Phase Motor draws Current = 7Amp per HP.
# 3 Phase Motor draws Current = 1.25Amp per HP.
I am not quite clear on these points. Please clarify. Does it mean if we have 3HP single phase motor then it will draw 21Amp current throughout its operation or during its starting?
These rules could be a little bit tricky unless you don’t know further connections …
Not all of them are aplicable in a different distribution systems worldwide, especially constants like •Current Rating of Transformer = KVA x 1.4, etc.
I suggest author should notice the conditions and input values in which are these rules aplicable and users should modify them according to a specific distribution system.
well said mate.!
pls tell me the difference between wire and cable.You mentioned different capacity for cu wire and a cable. You mean cable with aluminium conductor or something else..?Pls tell me..
cable is bunch of wires :-)
Please give me the solution for below mentioned problem..
Actually in our plant we having two 500 kva DG set and One dg is new one and other one is old …efficiency is different, so when switch on both and synchronizing.. some problem is occurring and i am not able to synchronizing. .. please give any solution for this problem
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Dear friend, just find the settings configuration in PCC2100 relay for parameter settings:)
kindly inform frm where did u get this useful information?