On Tuesday, October 20, 2015 at 4:55:00 PM UTC-4, trader_4 wrote:
Really? There is an earth ground on the line cards? In days gone by
you denied there was any protection on the line cards period.

I did not say that. You are again inventing fiction to only be nasty. Trader_4 has never worked in any facility that cannot have damage. He had absolutely no reason to believe a line card has an earth ground. I never said that. He is here only to be nasty and demaning. As he usually is.

Facilities that cannot have damage always implement the 'whole house' solution. As in always. Even 'point of connection' protectors (ie in HVAC equipment) need that protection. IEEE defines how effective a properly earthed 'whole house' solution is with numbers, "99.5% to 99.9% protection".

Once a major and destructive surge is earthed, then that adjacent (point of connection) protector might pick up some residuals. It might add another 0.2% protection. But if a 'whole house' protector is not properly earthed, then Dr Martzloff defines the problem in a conclusion of his 1994 IEEE paper:
Conclusion:
1) Quantitative measurements in the Upside-Down house clearly
show objectionable difference in reference voltages. These occur
even when or perhaps because, surge protective devices are
present at the point of connection of appliances.

Protector adjacent to equipment, in some cases, can compromise internal protection and make equipment damage easier. We demonstrated what Dr Martzloff defined. A power strip protector earthed a surge destructively through a network of powered off computers. We traced that surge current by identifying each damaged semiconductor on each printed circuit board. Few (the naysayer) here have that knowledge and experience. Or read IEEE papers on this subject.

Protection of equipment on earth is always about how a surge connects to earth. Either inside and destructively via (ie HVAC) equipment. Or harmlessly and outside on a lower impedance connection to earth.

BTW a grounded airplanes must be earthed to avert damaged. Every airplane is electrically connected to an earthing network inside the tarmac. Airplanes in the air are not damaged. Lightning is not hunting for earth destructively inside a plane that is not on earth. Trader_4 was told that repeatedly. He is simply reposting his lie hoping you are dumb enough to believe him. He is not here to be helpful or informative. So he again posts his airplane myth to keep you confused and ignorant.

Protection of HVAC equipment is about dissipating a potentially destructive surge harmlessly in earth - as was understood over 100 years ago.