On Monday, October 19, 2015 at 10:31:49 PM UTC-4, Uncle Monster wrote:
I should have written that the surge arrester was sacrificed to protect the equipment since the cell towers received a lot of lightning strikes and transients on the power lines. A lighting strike can blow primary surge arresters right off the wall. The secondary arresters can also burn out at the same time but the equipment will remain undamaged.


Many manufacturer stopped putting MOVs inside electronics where effective protection cannot exist. For example, Apple stopped doing it after the Apple II. Superior protection is routinely inside all electronics - often using techniques not using protectors. For example, a computer's PSU will convert a surge into clean, stable, low voltage DC to power its semiconductors. Other techniques include filters and galvanic isolation.

Surges that can overwhelm this protection must be connected low impedance to earth - either via a hardwire or via a properly sized protector - that must not fail.

MOVs, not connected low impedance to earth, must 'magically' absorb surge energy. Numbers. How many joules do MOVs absorb? Hundreds? Destructive surges are hundreds of thousands of joules. What will that MOV do? Catastrophically fail in a manner that its manufacturer says must never happen. Catastrophically fail in a manner that causes fires. That damage is completely, absolutely, and unconditionally unacceptable. No way to say this any stronger. No protector must be catastrophically damaged by a surge.

BTW, telco protectors intentionally fail shorted. Not fail catastrophically. Remain shorted so as to continue acting as a surge protector while notifying humans of its acceptable failure.

Direct lightning strikes without damage - even to protectors - is routine. Why would anyone deny what even manufacturer spec numbers state? Lightning typically is 20,000 amps. So a 'whole house' protector is 50,000 amps. Because protection means even the protector remains undamaged. Because protectors that fail catastrophically (sacrificial) create fires. Those catastrophic failures are why UL 1449 was created - because plug-in protectors create fires.

A major difference exists between degradation (normal failure mode) and sacrificial (catastrophic) failure. Sacrificial protectors are not providing effective protection - for the same reason fuses and circuit breakers do not provide protection.

One can install protectors to let a customer suffer damage. A protector does not do protection. Its earth ground does protection. Simply remove (or forget to install) that low impedance (ie less than 10 foot) ground wire. Most (even a technician here) would not know to look for that missing protection. Most assume a protector (not its earth ground) does protection. Missing earth ground means protection does not exist. Then a surge will hunt for earth ground destructively via interior phone systems.

If a protector is not properly earthed (ie using receptacle safety ground), then it cannot do effective protection. A protector is only as effective as its earth ground. Protectors must be properly sized and earthed so as to remain functional after each surge. So that robust protection already inside all equipment is not overwhelmed/