Hello everyone, I came across conflicting answers to my question. In my panel there are three breakers 6A for the power supply(it is writing in manual) and 5A for drive1 and 5A for drive 2.(writing in manual) The panel must meet the requirements of UL508. I think the main breaker should be not less than 16A. or 16 A Exactly. The rating plate should also show 16A. Am I correct in my calculations? Thank you!
Main CB
- Thread starter Karlag12
- Start date
cardosocea
Member
I think you'd need to provide us with the loads connected to the different breakers to be able to assess that? 16A does seem a bit low for all of what you're planning to power it from.
What does “writing in manual” mean?
I_Automation
Lifetime Supporting Member
WAG- textbook specifics to answer the homework question
I wish it was a homework.
))jaden
Member
Is this an operating panel, or a new design?
I wish it was a homework.
Seriously, what does “written in manual mean”? My curiosity is killing me.
I_Automation
Lifetime Supporting Member
If it's not homework then the answer is no.
Drive 1 has a 5 amp breaker, which means it will probably be rated at 3 amps max.
Your calculation for the main breaker is to add up all the max amp draws, not the breaker sizes. Then calculate the needed main size.
Drive 1 has a 5 amp breaker, which means it will probably be rated at 3 amps max.
Your calculation for the main breaker is to add up all the max amp draws, not the breaker sizes. Then calculate the needed main size.
jraef
Member
I interpreted it to mean that is where he is getting the information from.
jraef
Member
Correct. Look at the actual LOADS that are connected to the devices, the motors and the power supply. Find the largest load Full Load Current rating, multiply it by 1.25, then add that to all of the other connected Full Load Current ratings, that is the minimum size of your breaker.
So for example if the motors connected to the drives are 3A each and the Power Supply takes 5.5A, then you would take (1.25 x 5.5) + 3 + 3 = 12.875A,so a 15A breaker would be fine (15A is the smallest circuit you can use as a feeder anyway).
We don't have 16A breakers here, so you will not find a UL listed 16A breaker.
I_Automation
Lifetime Supporting Member
Aye, big names have them as well SqD, Allen Bradley. Multi 9 / 1489-M series.
For full load amps to size a main breaker/fuse disconnect as others said you need to add up the loads. Highest motor load x1.25+other loads. IF you fall somewhere between a breaker/fuse size I do believe closest size up is acceptable.
jraef
Member
I don't consider MCBs to be suitable for use as Main breakers on industrial controls, they are only rated for 10kAIC, most industrial plants will have more than that as Available Fault Current. I only use MCCBs as Main breakers.
Good point, not sure UL508A does either. But still here is a valid AB MCCB rated @ 16A (140G-G6C3-C16)
Link below seemed like a decent white paper (from what I skimmed) for the OP, section 5.3 gets into Incoming supply circuit and disconnect PG:69
https://assets.new.siemens.com/siem...23763f167/controlpanelna-guideline-icp-us.pdf
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