Answer / n arunkumar

CT secondary is 5A in Low voltage systems because we need
more graduation in measurement of current.Moreover measuring
range is small in LT system. but in High voltage system, the
measuring range is more.we need more accuracy. so we prefer
1A secondary in HT system.

Answer / k.prakashchandra

Earlier they were using electromagnetic relays and
meters.Hence for accuracy and workability higher current
was required. Now a days CTs of 1 A secondaries are
used ,as electronic meters and relays have replaced them

Answer / nagarjuna

most of the relays work at lower rating generally 5 amps.we
get more accuracy with small rating.so that relays r
generally 5 amps

Answer / yo

my wish.

Answer / sobhuza, za

5A CTs are used beacuse they are cheaper than 1A Cts for
the same primary rating.I mean 600/1A CT is more expensive
than 600/5A CTs as more turns are in the former. 5A CTs
also imply that under full load conditions, 5A is flowing
between the CTs and the relays. Therefore there will be a
large volt-drop if the CTs are far away from the relays.
This is the reason why it 5A CTs are used for indoor
switchgear. Recall that the indoor switchgear houses the
relays as well so the CTs and the relays are closer to one
another. Therefore you will note that 5A CTs are not used
for outdoor CTs.

Answer / jaywant

Becoz it is a standard rating

Answer / sud

becoz all the relay are working in 5A range...

We have two Al.busbars each of size 125mm*10 mm connected in parallel.To increase the current rating ,can we connect third busbar of size 100mm*10mm in parallel to existing two busbars?In my opinion ,if we connect busbars of different sizes in parallel,then the busbar of lowest size will take much current.So this type of paralleling should be avoided .Am I correct?

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