Surge/Lightning Protection

[X49]

I work with a lot of smaller facilities with low voltage electrical services(200-1000A) and I sometimes see a Secondary Surge Arrestor (MOV type) or lightning arrestor (spark gap type) on the line side of the main breaker.

This is usually in addition to a TVSS (Transient Voltage Surge Suppressor, MOV type) on the load side of the main breaker.

Now, I'd like to know whether or not it is worth installing a secondary surge arrestor since the TVSS units have higher surge ratings and lower clamping voltages. I guess the surge arrestor on the line side will protect the cables even if the breaker trips, and redundancy doesn't hurt.

Any thoughts?

Thanks

 

[7anoter4]

See "Selecting Transient Voltage Surge Suppressors"

http://www.wisconsinpublicservice.com/business/surge.aspx

and also:
"Fundamentals of Lightning Protection"

http://www.lightningsafety.com/nlsi_lhm/lpts.html#bonding