A ballast for a gas discharge lamp comprising a first circuit portion for providing power to a lighting load and a second circuit portion for processing data exchanged with a communication link, the first circuit portion receiving power from an AC main supply for conversion to a form suitable to supply power to the lamp, and the second circuit portion having a power supply supplied from the AC main supply, the power supply being coupled at the input of the AC main supply to the first circuit portion, further comprising a first protection circuit coupled in series with the AC main supply for protecting the first and second circuit portions in the event of an electrical circuit failure leading to an overcurrent condition, the power supply for the second circuit portion being coupled such that it is protected by the first protection circuit; further comprising a second protection circuit disposed in series with the first circuit portion and providing protection only in the event of electrical failure leading to an overcurrent condition in the first circuit portion; the second protection circuit adapted so that in the event of electrical failure in the first circuit portion, the second protection circuit will discontinue the supply of current to the first circuit portion, thereby preventing an overcurrent in the first protection circuit that would cause the first protection to interrupt current, and thereby allowing the first protection circuit to continue to supply electrical current to the second circuit portion.