Main breaker rating and cable size calculation

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Old 03-30-10, 12:07 PM
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Arrow Main breaker rating and cable size calculation

I have a subpanel with 30 single branch breakers each of 30A and 3 double branch breakers each of 30A. The main supply is 110V. What will be the size of main breaker. Please tell me with details how it comes. And also the size of main cable to the main breaker.
Thanks in advance.
 
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Old 03-30-10, 12:28 PM
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Based on the info you provided no real accurate info can be given. Breaker rating do not equate to the actual load of the panel. Is this single phase or three phase? What is the voltage?

The cable would need to be sized for whatever size breaker is installed upstream of this panel.

What is this panel supplying? Thirty amp circuits are unusual, especially single pole.

Could you please add your location to your profile?
 
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Old 03-30-10, 12:46 PM
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I have added my location in profile (Riyadh, KSA).

Main breaker is three phase with 4 wire 3 phase supply.
This panel is supplying to lighting and power sockets of 110V and 220V (the double breakers are for 220V), rest of single breakers are for lighting fixtures and 110V.

Main voltage is 220V.

Thanks for reply in advance again.
 
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Old 03-30-10, 06:51 PM
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I am assuming this is a Saudi project, what code is the accepted one to follow in that contry? I doubt I could speak intelligently on their codes, but I do know the loads are necessary to calculate main breaker size in any country.
 
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Old 03-31-10, 02:26 AM
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Yes this is a school project in Riyadh Saudi Arabia. Here we use Saudi Building Codes alongwith the IEC codes.
 
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Old 03-31-10, 08:20 AM
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Ok, just to be clear you posted that your main is 110 volts. But in your 2nd post you said your main is 220 volts. You also said it is 3 phase, four wire correct?
 
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Old 04-03-10, 10:17 PM
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I think before the pros can give you a good solution, we need your load calculation. I would assume that the 3phase-4 wire you mention is 220v + neutral. I have worked before with projects using IEC or IEE (british standards) and I would suppose that the 30 nos. of 30A single pole will be 110V and the 3-nos of double pole 30A will be 220v. If I were to distribute your load, I will use 10 each 30A on each phase for the single pole and 3 each of 30A double pole (L1-L2) ,(L1-L3) (L2-L3). In this case it looks like you have a balanced load on all phases assuming your load are equal. Based on this scheme, you can now determine your load(in watts or Volt-Amperes)on each phase both for the 110v and 220v loads. Adding them will be your total connected load and whatever diversity factor applies will be your basis in determining your Main breaker or panel size and main cable size. Hope will be of help.
 
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Old 04-04-10, 01:46 AM
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Originally Posted by aqeelpk View Post
I have added my location in profile (Riyadh, KSA).

Main breaker is three phase with 4 wire 3 phase supply.
This panel is supplying to lighting and power sockets of 110V and 220V (the double breakers are for 220V), rest of single breakers are for lighting fixtures and 110V.

Main voltage is 220V.

Thanks for reply in advance again.
If my memory serve me right you are on 60 HZ system and you are useing 220Y127 volt system in wye format as far for the electrical reguations you are simauir to the UK system.

If that correct let me know maybe there is a answer or two I can able provide.

Merci,Marc
 
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