Heavy Up is one of those peculiar, specialized terms in the world of home renovation and electrical systems. Essentially, it means to increase the amperage coming into your house, so that your electrical system can handle today's appliances, lights, computers, TV's, etc. A typical heavy-up is one in which an older house needs to be upgraded to a panel of more amps. In older homes there are the fused type panels that have about 4 to 6 circuits for the entire house. A heavy up or panel up-grade is needed to increase the number or circuits thus prevent over loads. A heavy up do not prevents over loads.You  have to run independent circuitry for new loads.