Calculation of cable size

Hello,

Considering total connected load sometimes would be misleading. for example some process lines which consist large AC motors but effective load on the input transformer is negligible as most part of the energy need is taken care by the regenerative function. Hence while selecting the cables and transformer it would be prudent to consider the operating loads at peak performance.

Sitaram
 
> How to calculate cable size, switchgears and fuses for feeders and
> equipment?

A very rough and ready way to calculate cable size is to count the number of cores, divide by the average diameter of cores then multiply the result by 3.14 (Pi)
 
<pre>>R 161A
>S 145A
>T 117A
>Power(KW) ?
>Phase to phase voltage =380v
>Cosine of phi =0.8</pre>
first of all the load is not balanced. it is not a sign of healthy system.<pre>
still we r consider the highest amps i.e. 161
KW=1.732*V*I*Cos phi/1000
=1.732*380*161*.8/1000
=84.7</pre>
 
ssatta (Prince)... the current values clearly indicate an ampere unbalance. In fact the Ampere Unbalance Factor (AUF) per NEMA is 36%. Per IEC it is 44%!

Your power calculation, however, is suspect. Using the maximum line-current and a guess-timate that PF is equal to 0.8, is incorrect.

The Unbalance Factor is is quite clear. Secondly, if the phase to phase values were measured at the motor terminals, and they were all 380V, then the motor is faulted!

What are you trying to determine? Can you provide additional detail. How about its nameplate data, to start?

Regards, Phil Corso
 
>> cable size [in mm2] = 18*meters*amp)/v*1000

> What does 18 stand for?

18 stands for voltage drop (mv/Am)
 
Ssatta (Prince)... further to my 14-Dec-11 post:

1) Using V, A, and PF parameters presented, total power drawn from supply is 43kW.

2) Ignoring PF presented, then total power drawn from supply is 61kW.

Regards, Phil Corso (cepsicon[at]AOL[dot]com)
 
B
DEAR

YOU MUST CHOSE THE HIGHEST CURRENT VALUE TO CALCULATE THE MAX POWER (KW) AND CHOSE THE LOWEST VALUE OF CURRENT FOR MIN POWER (KW).
 
even my opinion was too late. i would like to share to all guys on this forum on how to size the transformer, busbar, breakers (ACB or MCCB).

In he first place, Engineer can decide whatever he want and believe that the calculation his done is correct. IEC is not telling how much the sfe factor to consider during sizing therefore is up to engineers on how to be safe in sizing with respect to the connecte load.
The most important things to calculate the above items is to know the ELECTRICAL LOAD ANALYSIS(ELA).

Electrical engineer should consider all the possibility in sizing the equipment (diversity factors, Load Factors , KW, Eff, PF, KVA rating)
In designing the system and decided the size of the transformer bus and breaker.the ELA is the key on deciding the proper rating of equipment... Take note and put in mind that the motors will not operate beyond the rated current or equal in rated value (nameplate)! the total connected load will be decided by ELA and sizing the busbar as well the transformer and ACB as well. The short circuit value during fault is based also in larger connected load value and multiplying by 10 (assuming) for easily identify the Ka rating... somehow ETAP software is the best of the best for calculation the Short circuit value and load flow analysis in identifying if the transformer is overload or under load ... friendly user software thumbs up!!
 
T
> Calculation Example
> 1. Say Total Connected load in KW=1100
> 2. Therefore Total I/P in kw = 1100/0.86 = 1279
> 3. Total I/P in KVA = 1390
> 4. Total KVA required = 1390*1.2=1668

> Therefore by considering the future connection you can select 2000 KVA transformer for the above said example.

greetings,

i would like to ask about that factor [1.2] entered in that last equation. what's that factor called and what is it about?
 
S

Sanjay Shirsat

How this figure 1390 comes (Total I/P in KVA = 1390)? please clarify.

> For you clarification of Transfomer Sizing calculation could be followed as

> 1. Calculate Total Connected Load (KW)
> 2. Calc the Total I/P in KW (Considering 85% efficiency)
> 3. Calc Total I/P in KVA (Considering 0.92 Power Factor)
> 4. Required KVA by multiplying the Total I/P in KVA by 1.2 times.
>
> Calculation Example
> 1. Say Total Connected load in KW = 1100
> 2. Therefore Total I/P in kw = 1100/0.86 = 1279
> 3. Total I/P in KVA = 1390
> 4. Total KVA required = 1390*1.2=1668
>
> Therefore by considering the future connection you can select 2000 KVA transformer for the above said example.
 
B
There are generally well accepted codes, standards, and practices that cover this in depth. Which one(s) would apply to your particular situation depends on many factors including (but not necessarily limited to) geographic location, voltage, and end user preferences.

In general, it is about Ohm's law and how high of a temperature the wire insulation can take before it is degraded.
 
>> cable size[in mm2] = (18*meters*amp)/v*1000

> What does 18 stand for?

please clarify ASAP.
if i have this type of specification (below mention), then which size of cable i can use for this DB? (i can use 4c, 70mm2) but i am worry about how can i calculate for gating correct size. please share any formula for calculation.

3Ph.4w, 60hz, 220v, 160 total connected load 58kw.

thanks in advance
 
H
How to calculate cc of the cable calculation steps

I know that CC is for fuse factor but i have cables on a tray with a tray underneve the tray so I have to use a factor does this mean i Use the factor as part as the grouping factor because I know that

THE INSTALLATION METHOD AND FUSE FACTOR = CC

iN THE BOOK IT SAYS BURIED DIRECT IN GROUND 0.9 ONE CABLE WITH A BS3036 FUSE 0.725= CC

SO

DOES TRAPEZE BRACKET 2 TRAYS GO PART OF THE GROUPING FACTOR Cg OR PART OF THE CC FACTOR FOR CABLE EQATIONS TO FIND OU RATING OF CABLE It OR Iz
 
Top