QUOTE(Mea Culpa @ Mar 4 2014, 03:07 AM)
... One of the common problems of HDTV is dead HDMI ports. Where do you think these overcurrent coming from?
Plenty of good questions.
Earth ground exists according to code for human safety. Codes really do not care about transistor safety. But use that same earth ground to also protect transistors. This earth electrode is completely diferent from one that might connect a lightning rod to earth. That is typically a comopletely different earth ground for a current path that never enters a building.
Now, if the AC electric earth ground did not exist, then a voltage difference could exist between the neutral or safety ground wire and the floor. That is a threat to human life if voltage is high enough. And an example of what is called a floating ground.
So that significant voltage differences do not exist between neutral, safety ground, and the floor, an earth ground connects to other grounds at a single point. Often the main power panel. In some older venues, the only earth ground is back at the transformer. That means less human safety and must be modified also for transistor safety.
For surge protection, this earth ground connection must be even shorter, have no sharp bends, and other electrical characteristics that exceed safety code requirements. Only then can every incoming wire be surge protected. If connected short to earth directly (ie cable TV) or via a 'whole house' protector (ie telephone, AC electtric).
High fise apartements might use a steel I-beam as an excellent earth ground. So some construction earths a main power panel to the attached or adjacent I-bean. As noted earlier, what is earth ground is unique to codes and how it was done in that building.
HDMI failure is a perfect example of a surge current that is both incoming and outgoing via the appliance. A common incoming path is AC mains. Since TV cable is often properly earthed, then a best outgoing path is via that HDMI port and somehow to cable. First a surge current is everywhere in a path from the cloud, through a TV, and out via cable to distant charges. Later a weakest point in that path fails. A most common 'weakest point' is the outgoing path - HDMI ports.
Protection means that current must not even enter a building. Then that current does not hunt for weak links including HDMI ports, USB ports, RS-232 connections, and RF amplifiers on satellite receievers. Usually (but not always), these damaged ports are the outgoing path. Not the incoming path as so many only speculate into a conclusion.
Damage from leakage is, well, galvanic isolation required in all electronics designs means the appliance will often withstand upwards of 1000 volt transients without leaking excessive current. And will leak only microamps in normal operation. Otherwise an RCD would intermittently nuisance trip.
All appliarnces have robust protection. That is why 'dirty' pouwer often from a UPS in battery backup mode causes no damage. Your concern is not 'near zero' surges so often hyped to promote magic plog-in protectors. Your concern is a rare surge, maybe once every seven years, that can overwhelm protection inside appliances. Surge protection is always about the big and destructive transient. Constant (and trivial) overvoltages cause no damage. Surge protector (not to be confused with the other word protect
ion) must be sized so as to not fail on destructive surges. Then a consumers does not know a surge even existed.
Many advocate fiber opitcs, et al to cure the problem. Why? For over 100 years - long beore fiber existed - these surges existed without damage. I recently defined major damage to one venue that was using fiber. Again, a surge entered on AC mains. It found earth ground destrutively via a multi-function printer on a fax connection. If replaces its surge protector to restore that printer. That phone line entered on fiber (for TV, internet, and phone). But again, the outgoing path to earth was that telephone line to a fiber optic interface box - that was properly earthed.
Again, protection is always about earthing every single incoming wire. If any wire enters without that low impedance connection to earth, then protection is compromised. Once that surge current is inside, it will go hunting destructively for earth via appliances of its choice. Protectiono is always about no surge current inside.
Do not put a protector on the HDMI port. Suggesting that says one does not get itt. What is a path from the cloud to distant earthborne charges? If that path has any reason to be inside a building, then protection is ineffective. Protection is always about connecting a current to earth as far as possible away from appliances. Protection increases with separation between appliances and a protector. Protection increases with every foot shorter from protector to earth. Obviously an HDMI protector has no place and does nothing useful in the well proven concepts of surge protection.