3 Phase Panelboards with Single phase loads?
3 Phase Panelboards with Single phase loads?
(OP)
Hi,
I have been giving the duty of designing the electrical system for our new company building and I have no experience with a commericial electrical so I was hoping someone out there could give me a hand.
I am trying to size breakers for panelboards in a new commercial building for our company. We have a 347/600V 800A main service coming into our buidling and then will have various transformer and panels in order to provide our desired voltages around the building and shop. We will be using all 3 phase panels and I am wondering how I go about making sure that the main breaker of each panel is sized appropriately.
For example one panelboard is 120/208V with about 45 circuits at 15A per circuit. Since this is a 3 phase panel can we assume that the main breaker for that panel would be 45*15/3 = 225A, therefore the breaker that is equal to or a bit greater the 225A?
As well as sizing the transformers I would just be:
S=root3(225A)(208V) correct?
Thanks in advance for your help and suggestions
I have been giving the duty of designing the electrical system for our new company building and I have no experience with a commericial electrical so I was hoping someone out there could give me a hand.
I am trying to size breakers for panelboards in a new commercial building for our company. We have a 347/600V 800A main service coming into our buidling and then will have various transformer and panels in order to provide our desired voltages around the building and shop. We will be using all 3 phase panels and I am wondering how I go about making sure that the main breaker of each panel is sized appropriately.
For example one panelboard is 120/208V with about 45 circuits at 15A per circuit. Since this is a 3 phase panel can we assume that the main breaker for that panel would be 45*15/3 = 225A, therefore the breaker that is equal to or a bit greater the 225A?
As well as sizing the transformers I would just be:
S=root3(225A)(208V) correct?
Thanks in advance for your help and suggestions






RE: 3 Phase Panelboards with Single phase loads?
There are code requirements regarding the minimum loading you must assume for general use receptacles. There is also a minimum loading you must assume for an entire facility based on the type of facility and the square footage. Keep in mind that you can only load a breaker to 80% of its rating if the load is considered continous (180A for a 225A breaker.) Be sure to allow some room for future loads.
Let us know what standards apply in your jurisdiction (NEC? CEC?) and you may get more specific answers. You should become very familiar with the codes that apply to your design.
RE: 3 Phase Panelboards with Single phase loads?
RE: 3 Phase Panelboards with Single phase loads?
Generally, one will attempt to balance the single phase loads on each panel and feeder for reasons other than breaker sizing. Occasionally, one phase ends up with a slightly higher connected load and that may push you to the next wire and/or breaker size.
RE: 3 Phase Panelboards with Single phase loads?
David Castor
www.cvoes.com
RE: 3 Phase Panelboards with Single phase loads?
8-104 - Maximum Circuit Loading (80%/125% loading rule is covered here)
8-106 - Use of demand factors
8-210 - Other types of occupancy (and Table 14) (minimum service size based on square footage)
For transformers, see 26-240. If it is an office space with a large number of PC's or other harmonic generating loads, you should consider using a K-rated transformer.
RE: 3 Phase Panelboards with Single phase loads?
This project is far too complex for you to attempt to design. you need someone who has more experience to assist you.
RE: 3 Phase Panelboards with Single phase loads?
Bill
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"Why not the best?"
Jimmy Carter
RE: 3 Phase Panelboards with Single phase loads?