Is this Grounding Diagram correct?

[roger]

When is the dielectric fitting absent? And where is it present?

Not that it makes any difference to the NEC but you will probably find your answer between NFPA 54 through 58 .

Roger

 

[mbrooke]

I won't say that I might have been wrong, but I may have finished a bit short on being right. :angel: I see it that way as well (notwithstanding any previous comments). The diagram mentions a detail for bonding metal pipes elsewhere on the same sheet, but it is not in our field of view. So it wasn't clear whether the pipes shown on the right side were all internal to the building, as opposed to extending into the dirt outside the building.

That brings me back to the original question. Yes, a #6 is likely too small. We don't know what the minimum size needs to be, because the OP does not tell us the size of the service conductors. We can infer, however, that a 3/0 is an acceptable bonding conductor size. That is because all the GECs - except those serving the water pipe and the CEE, which have smaller allowances - are 3/0. But I suspect that is overkill. You don't need a 3/0 GEC for services smaller than 1100 MCM, and that would be good for a 600 amp service. The OP mentions something about 200 amp breakers, but it is not clear whether the main board shown on the diagram is rated for 200 amps or for something higher.

I uploaded the main switchboard (3,000 amp main) in my first post - click on the small image to the bottom left. This is why I make 1 image per post threads, but then it looks to spam-y.

Anyway:

The service conductors are 24 # 600 kcmil phase and 6 # 4/0 neutral.

 

[mbrooke]

Not that it makes any difference to the NEC but you will probably find your answer between NFPA 54 through 58 .

Roger

Not to the NEC- but in my world should conditions arise where the water main can carry hundreds of amps of current so can a gas main. Which is why I'm guessing the fitting is required and the NEC assumes its in place.

 

[charlie b]

The service conductors are 24 # 600 kcmil phase and 6 # 4/0 neutral.

In that case, the drawing you posted has an error. 250.104(A) does not say the bonding jumper to the water pipe is sized per Table 250.66, but rather per Table 240.102(C)(1). The two tables are identical until you get beyond 1100 KCMIL. 250.66 stops the GEC sizes at 3/0, regardless of how much beyond 1100 KCMIL the service conductors might be. 250.102(C)(1) does not stop there. It tells us to size the bonding jumper at 12.5% of the service conductor size. In your case, 8 sets of 600 KCMIL times 12.5% gives you a bonding jumper size of 600 KCMIL.

Separate from that, the other metal pipes get bonding jumpers sized on the basis of the Equipment Grounding Conductor associated with the circuit most likely to be the one that energizes the pipe. For example, if the nearest branch circuit or feeder to a gas pipe is rated at 200 amps, the EGC would be #6. So perhaps the drawing is correct, for the pipes other than the water pipes. At least the note on the right side, describing the basis for the jumper size for the non-water pipes, is correct.

 

[charlie b]

. . . but in my world should conditions arise where the water main can carry hundreds of amps of current so can a gas main. Which is why I'm guessing the fitting is required and the NEC assumes its in place.

The fitting is not relevant to this discussion. If a circuit causes the gas pipe to become energized, current will flow along the pipe to the location of the bonding jumper, and from there back to the main panel. That will cause a trip of the breaker for the circuit that energized the pipe. Your "hundreds of amps" of current will not flow into the dirt, whether or not a fitting is installed that would prevent the gas pipe from serving as a grounding electrode.

Forgive me if I belabor something you already know. But current never seeks a path that will take it into planet Earth. Rather, it seeks a path back to its own source. Current can flow through planet Earth. But unless it is driven by a medium voltage or high voltage source (i.e., higher than 4000 volts), the current will never be high enough to trip the source breaker.

 

[mbrooke]

In that case, the drawing you posted has an error. 250.104(A) does not say the bonding jumper to the water pipe is sized per Table 250.66, but rather per Table 240.102(C)(1). The two tables are identical until you get beyond 1100 KCMIL. 250.66 stops the GEC sizes at 3/0, regardless of how much beyond 1100 KCMIL the service conductors might be. 250.102(C)(1) does not stop there. It tells us to size the bonding jumper at 12.5% of the service conductor size. In your case, 8 sets of 600 KCMIL times 12.5% gives you a bonding jumper size of 600 KCMIL.

Separate from that, the other metal pipes get bonding jumpers sized on the basis of the Equipment Grounding Conductor associated with the circuit most likely to be the one that energizes the pipe. For example, if the nearest branch circuit or feeder to a gas pipe is rated at 200 amps, the EGC would be #6. So perhaps the drawing is correct, for the pipes other than the water pipes. At least the note on the right side, describing the basis for the jumper size for the non-water pipes, is correct.

Big Help, thank you!


Question- structural steal is always a grounding electrode regardless of how the foundation is set- correct?

 

[mbrooke]

The fitting is not relevant to this discussion. If a circuit causes the gas pipe to become energized, current will flow along the pipe to the location of the bonding jumper, and from there back to the main panel. That will cause a trip of the breaker for the circuit that energized the pipe. Your "hundreds of amps" of current will not flow into the dirt, whether or not a fitting is installed that would prevent the gas pipe from serving as a grounding electrode.

Forgive me if I belabor something you already know. But current never seeks a path that will take it into planet Earth. Rather, it seeks a path back to its own source. Current can flow through planet Earth. But unless it is driven by a medium voltage or high voltage source (i.e., higher than 4000 volts), the current will never be high enough to trip the source breaker.

But those hundreds of amps (from say an open service or utility neutral) will flow through the city gas piping system just as with a water main.

A ground rod is limited to #6 because dirt just can't carry much current, however a city water supply can carry hundreds of amps during an open neutral or similar event.

However, if the gas pipe has #10 running to it because a 30amp circuit is likely to energize it, that #10 can melt and start a fire during an open neutral event.

Otherwise #6 would be sufficient for a metal water pipe GE.

 

[oldsparky52]

....

2) A 600amp circuit could energize the fire sprinkler pipping as much as a 200amp circuit.

If that is your determination, then #6 is indeed too small.

It reads to me that this is all up to what size circuit is "likely" to energize the piping system. That is sure subjective.

 

[mbrooke]

If that is your determination, then #6 is indeed too small.

It reads to me that this is all up to what size circuit is "likely" to energize the piping system. That is sure subjective.

Yup, and subjectivity opens up a lot of debate.