Urgent Help - Circuit breaker sizing

[Beta101]

Hi,
I am new to circuit breakers sizing and selection; I have been looking at an existing PLC panel schematic and trying to make sense of the design. I attached a snapshot sample schematic.

1) I am interested to find out from anyone as to how the design engineer has arrived to the nominated circuit breakers value and type.

2) Additionally, I would like to know what function would each CB play in the schematic. The CBs are tagged as CB10, CB12, CB24, CB28, CB24, CB58.

I would really appreciate if anyone could provide some help on this matter. Many thanks

 

[rbulsara]

Besides being in a wrong forum, just beware that this is a site for "professionals". There are schools and books for learning. Better yet learn from your seniors.

Rafiq Bulsara

http://www.srengineersct.com

 

[jraef]

Aside from Rafiq's sage advice, these are simply control circuit breakers. The sizing is typically based on a known load and the protection required by that load. So for example the 24VDC power supply he is using may say it needs a 6A circuit protector ahead of it. On the load side, the switching devices may only be rated to carry 2A so you must protect the contacts from excess current. Those could be a fuses or breakers, breakers allows for resetting.

He also seems to be using them as isolation switches, but to be honest, it looks a little "breaker happy" to me. He shows the 110VAC as L1 and L2, but 110VAC is almost always North America, in which case one side (L2 most likely) would be a grounded Neutral. I would not switch a grounded Neutral and in fact depending on where the installation is, that may not be permitted. But maybe it's not in North America or this is some sort of specialized equipment that requires it...

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[dpc]

And how is this urgent?

David Castor

http://www.cvoes.com

 

[wcarter]

Beta101,

Jraef is correct in the consideration in upon known loading. Also, you have to factor in available breaker sizes and rating. IE if you sized it for 9A and one is not made in that size, you would need a 10A. Also, breakers of this size are normally thermal or thermal-mag having a rating of only 80% meaning a 10A breaker is only rated for 8A.

We are pleased to help, since that is what this site is for.