If the fault affects the entire house, where should you begin your isolation?

Beginning your isolation at the ground block is the most effective approach when the fault affects the entire house. The ground block serves as a central point where the incoming service from the outside world connects to the home’s internal wiring system. By starting your isolation process there, you can accurately determine whether the issue originates outside the home (such as a problem with the external service) or within the house's wiring.

Isolating at the ground block allows you to check for potential faults in the grounding or bonding connections, which could be the source of the issue affecting all circuits. This method also helps ensure that you are addressing the problem at a point that can affect the entire system, rather than narrowing down to segments of the wiring that may not be the root cause.

Attending to the main service panel would typically allow for checking the primary power supply, but if the issue spans the entire house, the ground block is often where potential grounding issues may originate. Checking at junction boxes or external taps might not provide a comprehensive view of the entire system and might lead to unnecessary troubleshooting steps that could be bypassed by starting at the ground block.