With new technical equipment, a robust and stable electrical system is a must. Single-family and multifamily dwellings, commercial buildings and manufacturing facilities all use major and minor electronic equipment. Computers, appliances, dimmers, smoke alarms, fire alarms, luminaires with LEDs and other electrical equipment require overvoltage and undervoltage protection. This protection can ensure proper equipment operation and prevent major issues.

NEC guidance

The 2023 National Electrical Code provides guidance and installation procedures for correct protection of sensitive electronic equipment and helps ensure proper operation. Article 242 provides the general, installation and connection requirements for overvoltage protection and overvoltage protective devices, such as surge protective devices (SPDs). 

The proper application of Article 242 generally requires the installation of a system of overvoltage protective devices with progressively faster-acting devices installed from the electrical service to the electronic equipment requiring protection. 

In residential and small commercial buildings, the SPD is usually located at or close to the electrical service. In larger homes and bigger commercial and most industrial facilities, a Type 1 SPD is installed either before the electrical service main disconnecting means or immediately after. Subsequent levels of Type 1 or Type 2 SPDs are installed downstream at intermediate points within the distribution system. 

A good idea is to provide a Type 3 surge-protective receptacle or Type 3 relocatable power tap called a “point-of-use” device. This device is located at a point directly supplying the transient-­sensitive equipment. The function of this point-of-use SPD is to remove small transients that may pass through the Type 1 or Type 2 SPDs and be delivered to the electronic equipment. 

These point-of-use SPDs can also provide protection from surges generated in the building.

Suppression for safety

Surges in electrical equipment can be caused by voltage spikes and power surges from lightning strikes, power line issues, downed power lines from a storm or automobile accident, large motor startups and transient voltage line noise. An electrical surge, or power surge, is an intense, short-duration voltage increase that travels through the electrical wiring that transmits power or data. 

An increase in voltage lasting 3 nanoseconds (one-billionth of a second) or more is called a power surge or transient voltage. If the increase lasts less than 3 nanoseconds, it is commonly called a spike. Both spikes and power surge can damage electronic equipment by exceeding the circuit’s rated voltage and cause the diodes and transistors to exceed their rating. 

An SPD comes into play when the voltage rises above an accepted level. It suppresses the excess voltage by shunting it to the ground to prevent it from causing harm. Internal components called metal oxide varistors absorb excess voltage and divert it to the equipment grounding conductor, thus preventing it from reaching the connected equipment. 

To function effectively, an SPD must be connected to a properly installed branch circuit with an appropriately sized equipment grounding conductor. Some surge protectors have built-in LEDs that alert users of possible wiring supply problems and a green LED to indicate proper device operation. A device where the LED turns from green to red indicates the need to replace the device or at least check it for proper operation.

Grounding and bonding

NEC Article 250 covering grounding and bonding is also extremely important for electronic equipment protection. There are a number of specific sections in Article 250, such as 250.6, 250.94, 250.96(B) and 250.146(D), that address installations of electronic equipment. NEC 250.6 ensures objectionable current is prevented and thus is essential for the correct functioning of electronic devices. 

This section states the following: “The grounding and bonding of electrical systems, circuit conductors, surge arresters, surge-protective devices, and conductive normally non-current-carrying metal parts of equipment must be arranged and installed in a manner that will prevent objectionable current.” 

The other three sections [250.94, 250.96(B), and 250.146(D)] all deal with electronic equipment sensitive to stray currents and reflected high-frequency noise and signals. These circulating and stray currents can cause major problems with electronic equipment, so it’s necessary to isolate it from the effects of such stray circulating currents. 

Major problems with sensitive electronic equipment can be minimized by properly applying the NEC requirements. Ensuring a good, stabilized grounding system and SPDs can work wonders in protecting sensitive electronic equipment.

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