Bus Bar Rating

Busbar design is, like cable sizing, one of CR4's most popular topics. Enter the appropriate words into the Search This Forum box on the right, and all sorts of previously-enjoyed information will be revealed. Far better, one hopes, than this thread becoming labelled a duplicate and closed?

Thanks PWSlack.

However the replies are contradicting. Some may agree that the circuit breaker and bus bar ratings are the same; while others state that the rating of the bus bar should be greater than the circuit breaker one. What would you say??

The circuit breaker has to protect the cabling and busbars downstream. Otherwise there is no point in having it.

British Standard 7671 says this, rather than any individual. These things are not, after all, matters of opinion!

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Thanks. In this case it should be 200Amps.

The choice is up to you. Are you ever going to need extra power distrubuted?? You can oversize the buss now while you are doing the installation in that case. My opinion would be to oversize to what you feel your future load may be. A lot of the cost will be in the installation and upsizing by 40 amps(or more) on the buss should be relatively inexpensive at the start as you are basically looking at conductor size only. Then if you need more power to the buss, changing out the main(and possibly feed lines to the buss if you don't do it start with) will be all you have to do.

Always try to look into the future to see what is going to be required for power and distribution of same. A few extra $ up front now can save a lot of $$$$ down the road.

My impression is you try to guess the possible bus bar rated current according to the existing circuit breaker.

"To guess" it is not a technical way to appreciate this.

You have to calculate the bus bar steady state maximum permissible current according to losses and cooling process and to check the dynamic stability to short-circuit. You may state at first the maximum available current -in both cases-and to follow a suitable calculation mode-IEC 60909 , IEC 60865, IEC 60694 and so on.

The circuit breaker will protect the entire installation-cables mainly.

Most panels are marked what the maximum panel rating is.

The bus bar feeding the 160 amp MCB should be rated for a minimum of 160 amp.

It is not acceptable nor is it safe to assume the next higher rating of any MCB.

The MDB is designed for a maximum rated amperage and voltage value that cannot be exceeded.

There should be an OEM tag located somewhere on the board/panel that gives the voltage rating, the maximum bus current rating, and the maximum allowable current rating of the Main Circuit Breaker permitted to be installed.

If this information is not available on/in the MDB or is not ledgible, contact the manufacturer for clarification before proceeding.

Having a breaker with a 160A rating indicates that you are not in North America, so I can't address rules applicable to your location, but in general, I have seen they tend to be the same or similar.

Here, a basic standard circuit breaker is often referred to as being "80% rated", meaning it can only be loaded to 80% of it's value continuously (defined as 3 hours or more). The main reason for this is because our rules on sizing conductors call for the conductor to be sized for 125% of the continuous load, and 80% is the inverse expression of 125%. So in theory if you used CONDUCTORS rated for 160A, you could not use a 200A circuit breaker because even though that is can be loaded to 160A, your CONDUCTORS cannot be loaded to more than 128A.

But bus bar is sized and rated for 100% of the continuous load so you COULD feed bus bar sized for a 160A load with a 160A breaker. But because the breaker mfrs know that most breakers are only going to be able to be loaded to 80%, they now design them that way. So if you WANT to get 160A continuous current through it, you would buy a 200A standard breaker (200A x 80% = 160A), or a 160A breaker that carries a "100% rated" listing.

Who is installing this electrical equipment?

1. You are posting anonymously!
2. You do not seem capable of installing this equipment!
3. Hire a competent licensed electrician!

You are endangering yourself and any other person that would be in that structure!

If you install it and there is a fire or electrical shock and someone dies, you will be held criminally liable and the insurer will most likely deny any damage claim!

That means they will sue you if you're not in prison or they may sue your estate which means your family will bear the burden of your inexperience!

• Hire a competent licensed electrician!
• Hire a competent licensed electrician!
• Hire a competent licensed electrician!
  

Calculate the SC level at the incoming CB. Busbar should withstand,without melting, any value current for which CB provide protection.

Which electrical code are you working with, Mildred?