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Total Building Load in KVA

Michael Brennan
Hi All,


I have been asked to provide the total electrical load of a building.  The max load per phase is 426.3A, on a 3-phase supply.  The majority of this is made up of 1-phase (230V) loads, with a few 3-phase loads mixed in there.  I have designed the electrical distribution such that the loads are split as equally as possible, but I have a question on how to calculate the total KVA value for this supply.  I'm getting a little confused with the information provided online and thought I would check this with a reliable source (you guys!).  Can someone confirm which of the following is the correct calculation, please?


1) I = 426.3A (per phase).  V = 400V (per phase).  Therefore: (426.3 * 400 * 1.732) / 1000 = (426.3 * 692.8) / 1000 = 295.34KVA


2) I = 426.3A (per phase).  V = 230V (per phase).  Therefore: (426.3 * 230 * 1.732) / 1000 = (426.3 * 398.36) / 1000 = 169.82KVA


Many thanks in advance,


MJB
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  • 0
    Okay thank you, that's a very fair point and makes sense.  I feel like the total load is larger than required by gut feeling but perhaps it is about right.


    I have 7 sub DB's feeding from one main DB.  I have taken diversity into account separately on each DB but not between the DB's.  I was not sure if I should take that into account additionally or not.  I have assumed the following rules for diversity:
    • Socket circuits: 100% largest circuit, 50% remaining circuits.

    • Lighting (LED): 90% of all lighting circuits.

    • Heating: 100% heating control panel circuit

    • Ventilation: 100% first circuit, 75% remaining circuits

    • Chillers: 100% first chiller, 75% second chiller

    • Cookers: 100% largest circuit, 80% second-largest circuit, 60% remaining circuits

    • Dishwasher: 75% circuit

    • Walk-in Refrigerators: 100% largest, 75% second largest


    I have assumed these rules for each individual DB.  Each DB serves different areas, so I'm not sure if I can apply diversity between the DB's additionally to the diversity already applied separately?

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  • 0
    Okay thank you, that's a very fair point and makes sense.  I feel like the total load is larger than required by gut feeling but perhaps it is about right.


    I have 7 sub DB's feeding from one main DB.  I have taken diversity into account separately on each DB but not between the DB's.  I was not sure if I should take that into account additionally or not.  I have assumed the following rules for diversity:
    • Socket circuits: 100% largest circuit, 50% remaining circuits.

    • Lighting (LED): 90% of all lighting circuits.

    • Heating: 100% heating control panel circuit

    • Ventilation: 100% first circuit, 75% remaining circuits

    • Chillers: 100% first chiller, 75% second chiller

    • Cookers: 100% largest circuit, 80% second-largest circuit, 60% remaining circuits

    • Dishwasher: 75% circuit

    • Walk-in Refrigerators: 100% largest, 75% second largest


    I have assumed these rules for each individual DB.  Each DB serves different areas, so I'm not sure if I can apply diversity between the DB's additionally to the diversity already applied separately?

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