Installing Circuit Breakers and Current Transformers

"Keep to the code." Johnny Depp

My friend i would support Jonny Depps advice to Keep to the code.and do your home work

crm

The Q is not clear. Be specific.

The Incoming circuit breaker the current rating should be equal to or less than the transformer current rating. The feeder circuit breakers should be 50 % more than the feeder load & should be to the nearest higher size.

Current transformers to be 50 % more than the current rating of the circuit load to have better accuracy.

Mr Sri... Can you write the basis of your reply with supporting documents/ standards etc?

Mr B.........

The incomer ACB rating has to be equal to or less than the transformer secondary side current rating as we cant draw more than this current from the transformer.

As regards the CT for a particular circuit the CT primary current has to be 50% more than the rated primary current. For example a circuit carrying 100 amps we select a CT of rating 150/5 & not 100/5 since it reaches the point of saturation. Similarly we cant put a 200/5 CT because of less accuracy at the minimum load. Therefore with our experince we decide like this.

This is all with our experince & we need not open a Standard for this. We can check a standard where we require certain vital aspects like CLEARANCES, MEASUREMENT PROCEDURES,SAFETY ASPECTS etc.

Finally who the hell are you to ask for supporting ducuments? Are you the Governor general? Mind it, You are also a normal person like me in this forum to share ideas & not act like an advocate.

Wear a black coat , stand under a banion tree & eat peanuts at leisure.

A minimum decorum is expected in this forum from all of us and it is not a place for a not a slanging match.

As far as Mr Das has referred- it may pl be understood that the requirements - are for HT and LT Lines. And working on HT lines are playing with personnel safety. I don't think that any country will allow things with experience to over-rule the necessary electricity codes.

SABNAVEES

Sorry to point this out, I don't want you to feel like we are all jumping up on you, we are really only concerned that the questioner receive quality information from this process.

In a good discussion, many ideas being offered and weighed can lead to greater understanding, even sharpening the wisest among us. The guru was not born a guru, it was a process of mistakes and experience that produced the guru.

Now I must share with you that a CT already has the factors you are wanting to add, built into the CT.

Please look at the label on a CT and you will see a detail like "rating Factor 2.0" for example. This means that the CT will not saturate until at least 200% loaded. I regularly see CT rating factors up to 4.0 (400% of nameplate amps).

Also, circuit protection is more complex than a 'rule of thumb' answer can provide. If you will notice, a code book is not very thin, and the tables are many and detailed. Each table has specific terms of usage in the header, and several footnotes below. This should give you an idea why you received so much feedback to a simple answer stated with such authority.

Your experience can be a valuable thing, and thank you for the willingness to share, but please allow us be kind and to suggest that you begin with "in my opinion," or "As I have experienced" or "in my understanding", and always be prepared at any age or any level to add to your own experience.

My dear friends,

I am very sorry & regret for the aggressive attitude I showed. It has called for a long discussion & drifted from the main topic of technical discussions. I assure I will not repeat this as it affects the decorum. Mr Das I apologise.

Mr Sab...

Have you considered ACB derating? Transformer secondary current at the lowest tap?

150% CT margin is much higher, it's ok with 125%. CT should get saturated beyond its rated primary current to protect it.

I requested to know if there is any guideline, or standard to enrich my knowledge. There is no question to be a governor etc. CR4 is a forum for sharing knowledge.

Thanks for your communication.

Johnny is the one to listen to here....Stick to the code!

Always keep in mind that the Codes are based on the minimium safety standards. Anything less than that is ridiculous anything more is just smart.

Do not guess and respect the power!