| Here are my thoughts: | | Theoretically, one could argue that an individual grounding conductor from | each device back to the main bonding point would be the most reliable, since | nothing that happens anywhere else could adversely affect any other device's | ground integrity. Obviously, this is impractical in terms of the number of | grounding conductors. You grouped things as appliances, raceways, etc, which | is a compromise, and I am not sure it accomplishes anything. It reduces the | number of conductors, but is still probably impractical. I am of course not | addressing systems such as hospital patient care with isolated grounds, etc.
The hospital case varies substantially, not only based on constant human contact to equipment, but also issues like perceived liability, as well as operational interference to very sensitive and life critical devices.
| Current industry design practice in the US is to properly bond every exposed | surface to a common egc system. Certain requirements, such as using pigtails | at receptacles and switches, prevent the most common possible interruptions | of that grounding system, but do not eliminate every possibility. Using | green wires instead of relying on conduit connections alone is a big | reliability improvement. I have not seen any studies or statistics proving | that our current industry practice is inadequate based on the number of | electric shocks/electrocutions on properly grounded systems. These accidents | more often appear to be the result of improper grounding.
I've been looking for an AC/MC cable that includes a conductor in continuous contact with the inside of the outer metallic armor, while also having a green insulated inner conductor. It seems all the cables with the contact conductor expect it to also be used as the grounding conductor. It seems all the cables with a green insulated conductor don't have an armor contact conductor. The reason I want both is to not depend on the armor as the grounding, but to have it well grounded anyway. This is for RF purposes so that the cables exhibit a consistent behaviour in radio fields.
| The "double framed" appliance concept is an interesting one, but certainly | not one that can be universally implemented. I am not sure it is necessary | if you prevent exposure to the live conductor to begin with. Remember that | typically a fault occurs within the appliance. We already have double | insulated appliances which accomplish the same thing except when they get | wet! In that case, the "double framed" would offer an advantage of a | grounded barrier to prevent a conductive water film on the outside.
I really don't see that many double frame or double insulated appliances. That is, unless they count paint as insulation, in which case there are a few more.
| Given a choice of using solid copper wire or a GFCI to protect a receptacle | or appliance, the solid copper is preferred over an electronic circuit. The | GFCI is acceptable practice where there is no copper ground (ie. older | two-wire systems), as it is better than no protection at all.
Agreed. But I'd still prefer separate conductors, one for the ground pins of the outlet strips (fed through the UPS if there is one in the cabinet), and one separate one for the rack cabinet frame itself. But having only one in common is better than none. And having two with both meeting at a subpanel in the computer room is better than having only one alone (IMHO).
| The bottom line is that I believe the current grounding practices are | adequate, when PROPERLY executed. I have seen older systems that were well | grounded because someone took the care to do it right. The biggest issue I | see is when poor workmanship or improper installation compromises the | grounding system. Even in industrial environments there are | "do-it-yourselfers" who don't have a clue. You won't eliminate this type of | problem by designing a "better" more expensive and complex system that won't | get done right anyhow.
One problem I have seen in more than a couple computer room installations that were grounded is that the rack ground wires were run separate from the power conductors. In some cases I found that instead of grounding them at the electrical panel (which was present) they were grounded by other means. In one case, grounded to a building beam by means of paint scraped off and using a clamp. In another, grounded to a water pipe (it was copper where atatched, but I could not verify if it was copper all the way, or commonly bonded with the electrical system very well). And in yet another, grounded to the A/C freon line. Luckily, I've not yet seen a case of grounding to a natural gas line. All these cases would definitely fail to come close to "adequate, when PROPERLY executed". Sadly, people thought they had grounded things, as they are often told to do that, but not how. And they wonder why they are getting such high error rates on ethernets, etc.