Answer / k.prakashchandra

In usual practice, the carrying capacity of copper is taken
as 2.5 A/sq mm and 1.5 for Al.If the load is steady and
continuous 60 % of these values are adopted.

Answer / jamil

According to NEC , i want to reduced grounding cable from
4mm2 to 2.5 mm2 ,can u give me technical sheet to depend it
from NEC

Answer / hari

Cable size should be 25 Sq.mm

For Ex: 1000A MCCB
For Al - We have to Consider 0.8/Sq.mm
For Cu - We have to Consider 1.6/Sq.mm

For 1000A = 1000*0.8
= 800A
We have to go for (100X10)mm Bus Bar

Answer / balraj.gabriel

There is no formula for calculating the cable size. Usually
the cables are sizing based on standards like NEC,BEC.,
etc. if you want to size the cable you first choose the
std, which is using in ur location.as per NEC std just
multiply the 100*1.25=125A, choose the cable ( table-
310.16) for that size. after you choose the cable you have
to derate the cable for your laying location & way of
laying.

Answer / shirish

Theory for Cable Sizing.
From Ohms law, the voltage drop in an electrical conductor is
V = I R
where
I = Current, amps
R = Resistance, Ohms

The electrical resistance can be derived from the properties of the conductor material.
R = ρ L / A
where
ρ = Resistivity, Ω mm2 /m
L = Length, m
A = Cross sectional area, mm2
Watch the units in the above equation.

The resistance can also be expressed in terms of the material conductivity (ψ) which is just the reciprocal of the resistivity.
R = L / (ψ A)

Table 1. Typical material electrical conductivity
Material Conductivity, ψ
Copper 58
Aluminium 36
Mild Steel 7.7

Combining Ohms law with the resistance expression, we get.
V = (I L) / (ψ A)

Now, we can define an acceptable voltage drop in a conductor. I have calculated the voltage drop that was used in several published tables and get around 5.5 Volts.
We could therefore re-arrange this equation to give the cable size. But cables come in standard sizes measured in mm2. In addition, you also need to consider the maximum current for each cable size.

Table 2. Conductor sizes and maximum currents
Cable Size, mm2 1.5 2.5 4 6 10 16 25 35 50 70 95 120 150 185 240 300
Maximum current, A 13 21 28 36 46 61 81 99 125 160 195 220 250 285 340 395
So, the theory is relatively simple, let us now see how to use the program.

Answer / amrish sharma

there is no funda or formula to get size of conductor wrt
to load. just calculate the ampere of the load, and then as
per ampere ,,, as per the cross sectional area of the
conducter like 1.5mmsq can bear the 4-6amp load,,,so on..

As we know that during saturation test of CT from secondary side, the current in secondary shoots up after core saturation. How core saturation effects the secondary current?

2 Answers  

Why the Motor takes High Current in Starting time?

5 Answers  

How could I get a certificate of competency as Electrical Supervisor? I have completed By BTech in Electrical this year(2012) for VJTI Mumbai Maharashtra. Is it compulsory to be produced while joining?

0 Answers   ONGC,

There are 2 motors without name plate and terminal but one is DC motor and another is induction motor.How one can identify which one is DC and which one is AC motor?

6 Answers  

How much pf maintan in dg set in 6o% load,when Dg runnig Neutaal Earthing removed what happen.

0 Answers  

What is Generator Protection & Transformer Protection?

3 Answers   Areva,

how can tell us the AC indoor or outdoor which Tr and formulls

0 Answers   Mukand,

how nautral is provided for return path is 3 phase induction motor

0 Answers   SNGPL,

Thumb rule of cable size(rm>30 rm)X multiplying factor=ampere

0 Answers   Kazi Farms, SKI Carbon Black,

What are the protections for safe running of electric generator?

0 Answers   Hetero,

Is there any Institution (Not AMIE)for giving B-Tech/M-tech in Electrical engineering for those who r in service? Give the details please.

2 Answers  

What is the Full form of Rccb,MCCB,

11 Answers   Marriott, Maruti Suzuki, MCB, PCC, RCCB, Torrent Pharma,