Hello “dereckbc”:
You are confusing the “common mode” term with the “normal mode” one. “Normal mode” suppression is “somehow” present in the “common mode”, can you see why? Draw the diagram. But I’m sure for most commercial TVSSs, this “somehow” I’ve mentioned set us outside the IEEE 587 guidelines.
Second, the only point in which NG protection is irrelevant is very close to the N-G bonding point, but only as long as that bonding remains intact. Depending on the needs it could be necessary to have NG protection even for Class C TVSSs (most integrated units I have seen include it).
United Power has a simple yet interesting article about this topic:
http://www.unitedpowercorp.com/technical/ModularSurge.htm. I’m wondering myself if being so “definitive” as you were could drive someone for the wrong way. Maybe we should be more careful with our comments. It could be better to point the direction instead of dictating the solution.
Regards,
Joe.-
