Ungrounded systems that are not entirely or very substantially in metal enclosed wiring or a metal frame building have far more than their fare share of lightning damage. The primary culprit is static electricity buildup from Saint Elmo's Fire, which is a form of low energy lightning and a single episode can last for an hour or 2. This was what Benjamin Franklin picked up with his kite experiment - if he had picked up anything stronger he would have been toasted. Essentially, in addition to strikes that you can see and hear there is a more or less steady trickle of static electricity on the order of microamperes per square foot and anything that acts as an antenna gets charged up. Also, someone else posted something to the effect that lightning strikes that you can see and hear can produce a 1 inch spark across a gap 10 top 15 miles away if the gap is connected to a long wire antenna.

I have worked with a number of 277Y480 volt solidly grounded systems and 480 ungrounded. The 277Y480 solidly grounded systems that I have encountered have ZERO lightning damage in spite of no surge arrestors. I have experience with ungrounded 480 volts 3 places in Cleveland, Ohio:

1. International Exposition Center has essentially no lightning damage because most of the system is in EMT. Those portions that are in cords for trade shows are lying on the floor and are shielded by building steel from static charge and electromagnetic pulse. The parts that supply rooftop air conditioners and exhaust fans are in conduit. The original exhaust fans lived for about 60 years.

2. Precision Metalsmiths also have an ungrounded system for motors with only about 5 feet of open wiring where it connects to First Energy's transformer. They have another system with a longer drop and it is for process heating only. The first system has very little in the way of motor damage in part because the ground detector uses 200 watt light bulbs and also acts as a static electricity drain.

3. Aluminum Waste Technology has 1 solidly grounded 277Y480 volt system and a number of 480 ungrounded systems. Every other time it rains they lose 1 or 2 pieces of expensive equipment. All of these systems have extensive amounts of PVC conduit an 2 of them have overhead wiring. The 277Y480 solidly grounded system has ZERO lightning damage under the same conditions.

Oh yeah, some people over at www.eng-tips.com who are with the oil industry say that PVC coated steel conduit is useless under corrosive condtions.

Mike Cole, mc5w at earthlink dot net