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Date: Fri, 10 Nov 2000 03:38:00 -0800 (PST)
From: mnewsletter@mtlnh.com
To: dfossum@enron.com
Subject: Surge Protection and Grounding
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If you have missed any of the Newsletters on IS Barriers in Div 2, Zener
Barriers, Ground Monitoring Systems, Surge Protection, Process I/O,
Rotational Speed Application, or Intrinsically Safe Pneumatic Valves, please
click your reply button and note same.

Is Grounding a Substitute for Surge Suppression Protection?

One of the most common questions regarding Surge Suppression is whether it
is necessary when a grounding system exists. Proper grounding is necessary
for the Instrumentation and Automation systems in use today, but is no
substitute for Surge Suppression equipment in preventing electrical system
damage. Grounding should only be part of the strategy in preventing
equipment damage from electrical surges.

An electrical surge is a burst of voltage that lasts only a matter of
microseconds but which generates very large amounts of current, and this
current must be diverted away from the electrical equipment to be protected.
Some people hold the opinion that if a grounding system is installed, the
electrical system voltage will rise together and lower together and that no
damage to the equipment will occur. While this could be true in theory, the
reality is that very few installations are isolated from other voltages. For
example, the addition of computers with modems or network cards introduces
another ground into the system.

If the two buildings are separated electrically, then the possibility of
damage is minimized, but it is more likely that modems or data lines
interconnect the buildings. A typical scenario might be:

 A lightning strike in the vicinity of one building increases the
 ground potential to 200KV.

 The resistance of the ground decreases this voltage to 15KV
 by the time it gets to the ground circuit of that building.

 As the voltage decreases over the distance to the adjacent
 building, it has lowered to 3KV, with a resulting difference
 of 12KV.

In such a case, the voltage difference between the two buildings generates a
surge current large enough to destroy the communication lines between the
two buildings, and no grounding system can prevent the damage to the
communication ports of the computers. Similarly, any instruments mounted
outdoors can have the same type of voltage difference from the control panel
to which they are connected.

Therefore, while good grounding is essential, it will not neutralize the
potential damage to equipment and processes caused by a surge event.

To discover how you can benefit from an MTL solution in a variety of
applications, visit us at www.mtlnh.com, www.mtl-inst.com, and/or
www.telematic.com. You may call MTL at (800) 835-7075 for the location of
the MTL Representative nearest to you.

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