242 – Overvoltage Protection

Change at a Glance:

New article added to provide the general, installation, and connection requirements for overvoltage protection and overvoltage protective devices. Relocates Articles 280 and 285 into a new Article 242.

Article 242 Overvoltage Protection

Part I. General
242.1 Scope. This article provides the general requirements, installation requirements, and connection requirements for overvoltage protection and overvoltage protective devices. Part II covers surge-protective devices (SPDs) permanently installed on premises wiring systems of not more than 1000 volts, nominal, while Part III covers surge arresters permanently installed on premises wiring systems over 1000 volts, nominal.
Informational Note: Article 242 combines and replaces Articles 280 and 285 in NFPA 70-2017.
242.3 Other Articles.
Table 242.3 Other Articles

Part II. Surge-Protective Devices (SPDs), 1000 Volts or Less
242.6 Uses Not Permitted.
242.8 Listing.
242.10 Short-Circuit Current Rating.
242.12 Type 1 SPDs.

(A) Installation.

(B) At the Service.
242.14 Type 2 SPDs.

(A) Service-Supplied Building or Structure.

(B) Feeder-Supplied Building or Structure.

(C) Separately Derived System.

242.16 Type 3 SPDs.
242.18 Type 4 and Other Component Type SPDs.
242.20 Number Required.
242.22 Location.
242.24 Routing of Connections.
242.26 Connection.
242.28 Conductor Size.
242.30 Connection Between Conductors.
242.32 Grounding Electrode Conductor Connections and Enclosures.

Part III. Surge Arresters, Over 1000 Volts
242.40 Uses Not Permitted.
242.42 Surge Arrester Selection.

(A) Rating.
(1) Solidly Grounded Systems.
(2) Impedance or Ungrounded System.

(B) Silicon Carbide Types.
242.44 Number Required.
242.46 Location.
242.48 Routing of Surge Arrester Equipment Grounding Conductors.
242.50 Connection.
242.52 Surge-Arrester Conductors.
242.54 Interconnections.

(A) Metal Interconnections.
(1) Additional Grounding Connection.
(2) Multigrounded Neutral System Connection.

(B) Through Spark Gap or Device.
(1) Ungrounded or Unigrounded Primary System.
(2) Multigrounded Neutral Primary System.

(C) By Special Permission.
242.56 Grounding Electrode Conductor Connections and Enclosures.

(See NEC for complete text)