Article 242 — Overvoltage Protection (SPDs)

Article 242 was created by merging the old surge-arrester and surge-protective-device articles into one place. It defines the types of SPDs (Type 1 ahead of the service disconnect, Type 2 on the load side, and so on) and how they must be connected, rated, and coordinated with the system voltage.

The Code has begun requiring SPDs where the load matters — for example at dwelling services and in certain critical systems — recognizing that a surge event can wipe out everything from the HVAC board to the panel electronics in an instant. Article 242 is where those installation rules live.

When it applies

Article 242 pulled the old surge rules together into one place for overvoltage protection, mainly surge protective devices. It covers the SPD types, where they connect, and increasingly where they are required, such as at dwelling services. The job of an SPD is to clamp transient spikes, from switching or nearby lightning, before they reach sensitive electronics.

Common mistakes

• Installing a Type 1 or Type 2 SPD with long, looping leads, the extra inductance ruins its clamping response, keep the leads short and straight.
• Picking the wrong SPD type for the location relative to the service disconnect.
• Assuming a panel SPD protects everything, sensitive gear often still wants point-of-use protection downstream.

In the field

Every modern home is full of boards that hate transients, chargers, inverters, comms gear. I keep the SPD leads as short as physically possible, because a beautifully rated device on twelve inches of coiled wire barely does its job.