R-56 Communication Site Grounding guidelines question

I suspect this refers to the "main bonding jumper".

Grounding and bonding is the I believe the largest and hardest section to understand in the NEC. The neutral bonding jumper is only done at the service. This is the only place the neutrals and grounds are common. With out the bond the neutral is not a grounded conductor. Try Soars Book on Grounding explanations that are not out in space.

On Sun, 2 May 2004 09:34:53 -0400 nospam wrote: | Not sure if anyone here is familiar with the term | "R-56 Standards & Guidelines". It's a collection of | codes (NEC, etc), that Motorola compiled - along | with a set of best practices - that are recommended | when installing new communications equipment sites. | | Having said that, one of the items mentioned is to | have the "neutral bonding conductor" connected to the | grounding strip in the service panel. | | Which should in turn be presumably connected to | earth ground.

It should be connected to at least TWO earth grounds.

| Now, if you connect neutral to ground, and you have | a "short" condition - aren't you in effect providing | a circuit path to still operate the equipment ? (in | other words, mis wire something to work off hot and | ground, it'll still run - since ground and neutral are | already jumpered together!).

Yes, if something is miswired by being attached to the grounding conductor instead of the neutral conductor, it could function correctly.

| What safety does this provide ?

Separate neutral and grounding conductors are intended for cases where the wiring is correct, and a fault occurs. Fault current on the neutral has to go all the way back to the point where neutral and ground are bonded before it can come back along the grounding wire to any grounded chassis. That forces a single reference to ground and zero current in the grounding wire, and thus zero potential between a grounded chassis and actual earth ground (like a water pipe or wet concrete floor).

The bonding is not intended to provide safety for cases where the circuit is miswired using the grounding wire instead of the neutral wire. Historically, since the days of Thomas Edison, the neutral wire was considered to be the ground safety wire. In cases of imbalance (of which a line-to-ground fault is a serious case), voltage can be present on the neutral-pretending-to-be-ground wire. This is due to the voltage drop along the conductor back to where it is grounded to earth. Humans touching a chassis connected to neutral, and also to some true ground source, get that voltage drop applied to them (they become a new neutral path). In the case of a fault, the current, and thus the voltage drop, can be substantial. In the case of a neutral circuit failure, equipment may still operate, but the hazard is also now worse.

The whole purpose of a separate grounding (not neutral) wire is to provide a means to reference ground on equipment chassis in a way where circuit imbalances (which should not cause power interruption) do not introduce voltages to humans coming into contact with equipment.

Of course, in fault conditions, the fault could very well be from line to ground instead of neutral. There is no perfect safety anywhere. It's just better WITH a ground wire than without.

One way to enhance safety is to use radial ground wiring. Instead of having a ground wire jump from one outlet to another, the ground wire for each goes all the way back to a panel. You probably should also have each outlet on a separate circuit breaker. While a home might have many outlets wired in sequence for unanticipated usage, in an industrial setting, most outlets are there for a definite purpose. Those should be individually protected, which gets you that radial ground wiring.

| Or am I missing something ?

Perhaps you are missing a thorough safety inspection that would detect a miswired circuit.

You could also install ground current sensing equipment attached to either an alarm or a shunt trip. One sensor would concurrently measure all current carrying conductors, including neutral, in a single CT window. As long as all current returns by no other path than these conductors, then you do not have a ground fault. You could further put a sensor on the actual grounding conductor as a means to detect after-the-fact wiring errors if you are paranoid. But the extra sensor would be redundant since such an error would be detected by a current imbalance in the current carrying conductors. Such sensors would be located between the neutral-to-ground bonding point and the loads.

If you have a mission critical data center or communications center, these sensors would trigger alarms. Otherwise a "minor" wiring accident in one part of the data center could trip everything on the same system. Wiring each individual circuit through its own GFI breaker can help isolate areas and prevent a massive outage. A GFI breaker has a miniature current imbalance sensing system. These are not generally used in a data or communications center.

Safety training for all staff that could be doing any work on equipment (not just those authorized to work on power circuits) should be part of the program.

If earthing for 60 hertz power, then length of wire is mostly irrelevant. But earthing for transient protection means every foot, every sharp, bend, every splice is a problem. NEC requirements are only for human safety. For transistor safety, even those NEC requirements are exceeded.

To better understand the c> Not sure if anyone here is familiar with the term

Hi, thank you for the information.

The explanation of what a neutral/ground bond is not designed to do (provide protection against miswired equipment) was helpful.

Here's another "ground" question. If one is installing an AC power panel, does the neutral/ground bond on that panel connected to ground - can that same ground be connected to the transformer ground feeding that power panel ? (a 480 step down transformer) ?

What's confusing is the "separately derived electrical system" concept vs. the idea of potential ground loops (which presumably would not occur if it's the same earth ground ?). - AND "new service" (ie. a new panel), requires a "new" separate ground (or at least that's what I was told).

Essentially, a new AC panel feeding a UPS, feeding a new room is going in, and we're attempting to get educated enough to be able to discuss the grounding concepts with the licensed electricians to convey what we need.

Any info/comments appreciated, thanks!

Google fails to produce results for the string, "R-56 Standards & Guidelines". Could you supply a URL where the text could be found?

Thank you.

Louis--

********************************************* Remove the two fish in address to respond

There is no grounding wire common to both transformer and building (unless transformer is part of the building). Utility transformer has its earth ground. The building must have its own single point earth ground. Wire does connect that transformer earth ground to building earth ground - the neutral wire. But wire is an electrical component. Those grounds - transformer and building - are electrically different even though they share opposite ends of the same neutral wire. This electrical difference is why something called ground loops exist and why each earth ground is a single point ground.

Implied by what was posted - the UPS is a building wide system. Therefore the UPS must have its own dedicated connection to building's single point earth ground. No earth ground means effective surge protection provided by a building wide UPS systems would not be effective. That UPS earth ground can be wired per NEC to breaker box. But that would compromise the UPS protection which requires a typically 'less than 10 foot' connection, short, direct, and independent to earth ground. Requirements that exceed what NEC demands. NEC requirements are only for human safety. Transistor safety requires additional considerations beyond what NEC requires; especially the concept of single point earthing.

Breaker box ground is where utility neutral, household circuit neutrals (white wires), safety grounds (green or bare wires), and earth ground wires all typically join. However that does not mean receptacle safety grounds (connected to that breaker box) are earth grounded. UPS connected to breaker box for power might also require a dedicated connection from UPS direct to earth ground. Distance from UPS via breaker box to earth ground would typically be too far. Distance from UPS to earth ground and how that wire is routed has special requirements beyond what NEC requires.

Notice the difference. Receptacles have a safety ground. But incoming telephone and CATV must connect to earth ground - not to safety ground. Even though breaker box does connect to earth ground, the telephone and CATV must connect to the earth ground side of that wire; not to breaker box. Yes, receptacle safety ground, building earth ground, breaker box ground, transformer earth ground, computer chassis ground, and computer motherboard ground are interconnected. But each ground is electrically unique. In this interconnected circuit, a new ground connection is defined by the purpose of that ground.

From a building wide perspective, this is what the earth ground system should look like:

or page 14 of or entitled "Measuring Ground Resistance at Cellular Sites,Microwave and Radio Towers"]

Another example demonstrating single point earth ground verse multiple wires entering (and earthed) at different locations:

That is the earth ground system. How the AC electric safety ground connects to the earth ground system is demonstrated in pictures at:

Notice that the PC in Figure 1 suffers surge damage if the phone line on right is far from AC electric on left. Figure 2 also demonstrates how earth ground from all three utilities - AC electric, CATV, and phone - are best installed to be less than 10 foot and connected to a single point earth ground. IOW AC electric safety ground and AC electric neutral wires connect from breaker box to earth ground via the one earthing wire that exceeds what NEC requires. Examples: less than 10 feet, no splices, no sharp bends, not inside metallic conduit, and routed separate from non-earthing wires.

Again, the idea is to earth for both human safety (NEC requirements) AND for transistor safety. The concepts were discussed in those above two discussion in misc.rural .

nospam wrote:

The R-56 concept is about transistor and human safety grounding. As noted previously, earth ground system connects to the safety ground system by interconnecting to central points - breaker box and earth ground rod. The single interconnection also avoids ground loops. Having every incoming utility ground separately until each ground wire meets at the single point ground also helps eliminate ground loops. Additional posts about these concepts mostly by ham radio operators:

Well I assert, from personal and broadcast experience spanning

The basic scenario is to install a Single Point Ground System

In a professional installation, there would be a ground ring

At least one poster correctly noted the wisdom of tying ground

nospam wrote:

|> Having said that, one of the items mentioned is to |> have the "neutral bonding conductor" connected to the |> grounding strip in the service panel. |>

|> Which should in turn be presumably connected to |> earth ground. |>

|> Now, if you connect neutral to ground, and you have |> a "short" condition - aren't you in effect providing |> a circuit path to still operate the equipment ? (in |> other words, mis wire something to work off hot and |> ground, it'll still run - since ground and neutral are |> already jumpered together!). |>

|> What safety does this provide ? |>

|> Or am I missing something ? |>

|>

| | Google fails to produce results for the string, "R-56 Standards & | Guidelines". Could you supply a URL where the text could be found?

Like many other standards (such as NEC), you have to pay for a copy of the standard. So in effect, you can only be safe if you have money, or are willing to risk going to jail for trafficking in illegal pirated copies of safety standards documents.