How a BusBar Should be Rated

October, 16 2014

Until now, there was no consistent method of rating busbars which made it difficult to determine the appropriate busbar for the application. The American Boating and Yacht Council (ABYC) is considering adding busbar ratings to the Electrical Section E11. Other organizations, including the Institute of Electrical and Electronics Engineers (IEEE), currently offer guidance.

The IEEE states a busbar should be rated at the highest amperage passing through any section of the busbar, with a maximum of a 50° C rise in temperature from an ambient temperature of 50° C.

Blue Sea Systems uses a more conservative threshold of a 40° C rise in temperature since busbars are often located in hot engine rooms. This rating method avoids excess terminal temperature at the wire termination.

Factors Influencing BusBar Ampacity Ratings:

  1. Material: The rating of any busbar is based on both the cross section of the bus and the material used. Blue Sea Systems uses Tin-Plated Copper C11000 which has more than 3.5 times the electrical conductivity as brass, used by some manufacturers.
  2. Cross Section: A thicker cross section provides more material for electron flow and a larger surface area for efficient cooling.

Carefully compare cross sections of a bus and do not rely solely on published ratings.

Blue Sea Systems
BusBar Cross Section and Ampacity Rating
19mm x 25.5mm = 484mm
Rating: 600A
BusBar Cross Section and Ampacity Rating
7.5mm x 25.5mm = 191mm
Published Rating: 650A

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