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Electrical Troubleshooting Quiz

Sep 2, 2010 3:47 PM

The office workstations have surge strips. Users plug their computers and monitors into these, and occasionally use the extra receptacles for various other small loads. Around the first of the year, there was a rash of computer failures. The vendor that does your computer support took a random sampling of these surge strips and found the metal oxide varistors (MOVs) were all blown. The strips were still supplying power, but they weren't providing any surge suppression. Further investigation revealed nearly every surge strip had this same kind of damage, and they were all replaced.

Recently, computer failures began happening again. This vendor did another sampling of the surge strips and found the blown MOV problem had returned. How do you solve this problem and prevent another recurrence?

Point-of-use surge protection cannot be the sole means of surge protection due to the energy levels involved. Take apart one of those surge strips, and look at the MOVs. Notice the distance between the terminals. Voltages that may occur at the service entrance can leap across this distance. Now, notice the size of the MOV. How much energy do you think it can safely dissipate?

A surge protection plan doesn't start at the point of use. It starts at the service, with surge arresters. These reduce the voltage and energy to levels the next stage of surge protection can handle, typically with surge protective devices (SPDs). Walk down this system, and see if it's properly coordinated.

Another issue is proper bonding. Where ground rods are used in place of bonding, voltage potentials can be large. Flashover then destroys connected equipment.

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