Answer / sam

current rating and insulation property are the main
constrain between ac & dc

Answer / avd

It does not matter much for AC or DC. The rms value of AC
is equal to DC. However if AC voltage rating is high then
you should cosider additional heating of cable due to AC
loses.

Answer / shyam

for selecting a cable for ac,its rms rating is to be
considered while for selecting cable for dc,its average or
dc value is to be considered.

Answer / rms

In selecting a cable it is based on the rms (root mean
square) value of the current. The fact is that rms value
produces the same amount or almost equal of energy like that
dc.

20A of dc= 20A of AC rms...

Answer / hdk

For DC, current distribution is uniform in all over cross section of cable so electrical cross-section = physical cross-section.

For AC, current distribution is non uniform due to the time varying nature of magnetic flux produces. So that Electrical Cross-section < physical cross-section. So Rdc<Rac.

So for AC to to transmit same current as of DC we need too select a cable which has more cross-section area than DC.
Rac=K×Rdc, where K=nearly 1.2

Answer / kanand078

its very simple
Ac power=VIcos@ w ,,
DC power=VI w

Answer / debadata

Selecting a cable is based upon the need of consumer.DC
cable is preffered for transmitting power at high voltages
because at increase of voltage level the size of conducter
increases in case of AC but the crossection area of
conductor can be decreased if it is transmitted in DC.IR
losses are low in case of transmission through DC.

Answer / koti

1. for both Rated current is RMS only.
2. fault current capacity of AC is higher than DC
3. Voltage drop is more in AC than DC due to Skin effect and
Impedance

Answer / awaken

it is always the current rating that is taken care of while
selecting cable since heat produced will have to be
withstand by the cable and stress factor ie the depth below
which the cable has to be layed or the dieelectric strength
between the conductor in case of ac. while in case of dc jus
current and stress factor. ie why conductors are preffered
using same current rating for overhead distr/trans.

Answer / rama

The average curent of DC is higher than AC .Same thumb rule
is used for selecting cable either DC or AC but insulation
depends on voltage level.
The loss in DC transmision is less than in AC transmission.

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