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Steve G., Electrical Engineer
Category: Electrical
Satisfied Customers: 17729
Experience:  Spent 20 years as an Electrical Engineer, designing electrical plans and specifications.
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# My customer has a 1200 amp 480 volt 3 phase service. I want

### Customer Question

My customer has a 1200 amp 480 volt 3 phase service. I want to add a 200 amp breaker. This would bring the calculated load from 900 amps to 1100 amps. Will this pass code?
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: 1 week.
JA: Do you plan on doing the work yourself?
Customer: My electrical crew will do the work
JA: How old is the system in question? And have you consulted an electrician yet?
Customer: We are trying to decide if the main service can be loaded more than 80%
Customer: Question re-phrased: I have a 1200 amp service. The calculated load is 900 amps. Can I add another 150 amps to the panel?
Submitted: 8 days ago.
Category: Electrical
Expert:  Steve G. replied 8 days ago.

Hello there and welcome to Just Answer. My name is ***** ***** I will be assisting you today. I am an engineer with over 30 years of electrical and electronic training, repair and installation experience. I will try and answer your question accurately and precisely so that we can get you on your way.

I need to gather some more information from you in order to help.

Where did the figure of 900A come from? Did you add up the existing breakers, measure the existing current with an amprobe or find the engineering design documents?

Let me know.

Steve

Customer: replied 8 days ago.
The figures that i gave you are ficticious. The bot***** *****ne is this. Can my connected load exceed 80% of the panel's rating?
Expert:  Steve G. replied 8 days ago.

Right but how is that number derived?

The short answer is that the max design load on a 1200A breaker is 80% or 960A but how you come up with that 960A can vary based on the type of loads you have i.e. motors, branch circuits etc.

Steve