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GFK-0825F B-1
Installing Additional Suppression
This appendix describes some precautions that can be taken in an installation to help assure proper
operation.
It is possible some installations might exceed the surge immunity capabilities specified in chapter
1. This is most likely in outdoor installations or where the power source is from another building or
ground system. It is prudent to provide local transient protection.
Note
MOVs do a good job of absorbing transients on communications, control, and
power lines, provided the total energy of those transients does not exceed the
rating of the device.
However, if the energy of the transient exceeds the rating of the device, the MOV
may be either damaged or destroyed.
This failure may not be visibly or
electrically evident.
MOVs should be regularly inspected for signs of damage to
assure continued protection against transients. For some applications, periodic
replacement of critical MOVs is recommended, even if they do not show signs of
damage.
Suppression at the Power Lines
Protection can be provided by connecting higher-energy MOVs across the power lines (for
instance, between Hot and Neutral) and from line to frame ground (safety ground). This triangular
configuration requires three MOVs for each long power feed. If the total power feed length is about
100 feet or less, one set of MOVs should be enough for any number of devices. The axial-leaded
LA series of MOVs from Harris is often used. The 14mm size, model V130LA10 rated at 38
joules is usually sufficient. The MOVs used should be able to handle most line transients.
Measurement of actual transients may be required in extreme cases to decide what MOVs to use.
B
Appendix