If your home is older – built before 1990 – or has not had an electrical upgrade since then, you may have a split bus panel that is not safe. Federal Pacific split bus electrical panels lost their UL rating about 25 years ago, due to a high failure rate in the effectiveness of its panel breakers. If you own one, it needs to be replaced immediately.
Tips from Wilcox Electric
Electrical panel upgrades (2)
A Heavy Up involves increasing the amperage to your old home’s service panel so that your electrical system can handle a higher load than it was designed to. Typically, this involves increasing the amperage from 100 amps to 200 amps. The chances are that the more historic (that is, old) your home, the greater the need for a "heavy up" to increase the capacity of the electrical panel.