Well, yes and no. If the power cord from the AC supply goes directly into the KSU AND the grounding conductor is extended within the KSU to a metal KSU ground plane, then the system is "effectually" grounded via the electrical cord.
There are plenty of KSUs that have the power cord enter the KSU cabinet and then go to a transformer and the grounding conductor is connected to a piece of copper or aluminum "foil" square gluded to the KSU plastic housing. There is no way this is an effective ground.
Then there are the system with external power supplies that require a ground be externally connected.
Here where it really comes down to a point. The CO telephone cable head ground and the KSU ground should be exactly the same, provided the building ground at the main service panel and the telco cable head ground are less than .1 volt difference.
IT people are much too cavalier when it comes to grounds. They think a cabinet ground is sufficient if the cabinet is grounded to the "floating" rack. This is ridiculous.
When I was at Bell, it was manditory that the ground for the cable head, PBX and all ancillary equipment be identical. When the 1978 NEC came out, we were required to make sure the building ground and our ground were identical and it has been that way ever since.
But, of course, the Bell system never actually adopted the NEC as a standard. The IEEE National Electrical Safety Code was the actual "Standard" that the Bell System adopted as the official code. This may be recognized by all the OSP people as the "Code Bible." Within that code, it is manditory that all sheath, ground lugs and grounding "devices" be bonded together and extended to all equipment served by such devices. Here is where it gets a little complicated. In large buildings where the primary electrical supply may be 480VAC or higher and individual floors are supplied through transformers, bonding becomes a nightmare, both for the electrician and the telephone company. Here's where impedance mismatches can cause more harm than not having a ground at all. That is why one may see a 1/0 ground cable running to all floors from the teleco cable head in the large buildings to maintain a good cable ground.
Rcaman
Last edited by Rcaman; 03/17/14 10:43 AM.
