Cable Sizing

This could easily be one of those questions of the "If you have to ask, you aren't qualified for the job that you are trying to do" type.

Which of those two figures do you think represents the current above which the MCCB will trip?

yes, iam just a begineer and iam not exactly from core electrical. so i have make sure before i do some thing wrong.

Don't they have the answer in the back of the book?

This is not a task for someone who is "just a beginner and iam not exactly from core electrical". You need to hire a qualified electrician to do this for you.

If you decide to proceed without qualified help, you will most likely cause some serious and expensive damage as a minimum and perhaps cause death(s) including your own if you really mess things up.

Also see previous threads on CR4 for this commonly-asked question.

What are "AF" and "AT"?

Is this a motor load, a heater load, a combination load, or what?

Local code(s) will govern, and nonlocal advice may not match.

Why are they using 160 A MCCB with trip setting of 60 A? If it is a FDB, 63 A MCB should rather be used...

It could be because the PSSC is too high for an MCB.

It could also be because the designer specified that an MCCB must be used.

In some countries, and in many industrial applications, MCBs are not all that highly regarded as branch circuit protectors.

I agree, of course, with all other "experienced" engineers-"experienced" means sometime "old guy".However all of us were once upon a time "inexperienced" engineer-and a tiny advise was important. If meaning of AF-is "ampere frame" and "AT "is "ampere rated" then you'll see the AT defines the physical dimensions only, but AT it is the rated. So your cable has to be rated according to AT.

See also:

http://cr4.globalspec.com/thread/36609

it's okay if you don't know about something, it is more important that you want to know something. Also in my opinion, equation never being stupid but ans could be.

Now answering to your question, with exact load, you need to calculate length from source to load for voltage drop. Cable size can be decided based on load rating and allowable voltage drop.

Provide exact load type, length so i can suggest cable length

DHARAMRAJSINH-

Yes, it is okay if you don't know about something. It is more important to "know which things you don't know about" than it is to want to know something. This aids an engineer to know what he can solve and what he is not capable of solving.

In my opinion, some equations can be real stupid and their answers even more stupid and ridiculous. This is very prevalent in engineers with big egos, even bigger mouths and tiny brains. This condition is often described as "diarrhea of the mouth and constipation of the brain".

Good Luck, Old Salt

Old Salt,

this forum is for technical discussion, some one has asked the question for solving there doubts.

Instead of giving lecture on use less things in technical forum, it is batter to talk only technical tings.

Good luck,

Dharamrajsinh

DHARAMRAJSINH-

Out of respect to the other 66,215 members of CR4, this will be my only reply to your posting concerning the purpose of this forum. Many of the members of this forum are very enlightening contributors, they deserve better than what you have attempted to say. May I state that at 5 days with the forum you may want to observe more about its function and participant's practices. Many others have started out that way and are welcome and respected members. Most other members want them here as contributors.

Lyn- Thank You!

Good Luck, Old Salt

The method of installation and its length are also factors. British Standard 7671 gives full protocols for this task. If in doubt, consult a qualified Electrician.

The number of threads about cable sizing has grown over the years to the point of its becoming tiresome. Entering the words 'Cable Sizing' into the Search this Forum box to the right will bring sufficient bedtime reading to provide a cure for insomnia.

The key to the design of a circuit such as this (I'm assuming a simple circuit) is the incoming fault level. Find out what that is and proceed from there. The downstream breaker will do nothing for you if the cable has become a fuse!!! It sounds as if you have this circuit breaker which you are going to use regardless......beware. You need the following information: incoming fault level, cable length, supply protection rating and timing and breaker rupturing capacity; then you can get someone to design it for you.

PeterT in 12 is a good answer..... but as others have said, allow for volts drop as well, if the cables are long.

This kind of calculator is really good.