This is typically the first step when specifying your switchboard, which dictates the incoming breaker rating and therefore the maximum current rating of your switchgear main busbars.

 

This requirement is commonly governed by your buildings required current rating (Amps), wattage (W) output, commonly know as your buildings load, which dictates your transformer input supply, transforming your M.V (Medium Voltage) supply to 400-433V output which feeds and powers your building's infrastructure.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Detailed below are typical commonly used transformer sizes, expressed in both KVA and MVA with the converted current ratings and main incomer breaker sizes for typically 11KV to 0.400KV applications:

 

Transformer 500KVA (0.5MVA) = 722A, typically 800A Main Incomer Device & 800A Main Busbar Rating

Transformer 630KVA (0.63MVA) = 909A, typically 1000A Main Incomer Device & 1000A Main Busbar Rating

Transformer 800KVA (0.8MVA) = 1155A, typically 1250A Main Incomer Device & 1250A Main Busbar Rating

Transformer 1000KVA (1MVA) =1444A, typically 1600A Main Incomer Device & 1600A Main Busbar Rating

Transformer 1250KVA (1.25MVA) = 1804A, typically 2000A Main Incomer Device & 2000A Main Busbar Rating

Transformer 1500KVA (1.5MVA) = 2165A, typically 2500A Main Incomer Device & 2500A Main Busbar Rating

Transformer 1600KVA (1.6MVA) = 2309A, typically 2500A Main Incomer Device & 2500A Main Busbar Rating

Transformer 2000KVA (2MVA) = 2887A, typically 3200A Main Incomer Device & 3200A Main Busbar Rating

Transformer 2500KVA (2.5MVA) = 3608A, typically 4000A Main Incomer Device & 3600/4000A Main Busbar Rating

Transformer 3150KVA (3.15MVA) = 4546A, typically 5000A Main Incomer Device & 5000A Main Busbar Rating

Transformer 4000KVA (4MVA) =5773A, typically 6300A Main Incomer Device & 6300A Main Busbar Rating

 

Please note the above is based upon a 3 phase 400V application, due to this being the worst case requirement, due to this providing the greatest max curent over greater voltage applications that typically ranging from 400-433V.