Separate buildings from a single 1200 Amp service?

[moose351]

Im an Air Force electrician in Iraq, and Im trying to figure out if what is installed is safe and correct. We have 6 facilties in a row that are fed by the same Main Distribution Panel. The MDP is fed by a 1200A Double throw switch, which is in turn fed by 2 800kw Generators that only run one at a time. From 1200 amp MDP, it then supplies each building a 250 Amp service. No grounds were pulled from the MDP to each building. They drove ground rods and bonded the EGC to the neutral bus in the panel inside each building. Is this correct? Also, the generators and double throw were bonded to a single ground rod, and the MDP has its own ground rod. These two ground rods are also bonded together, and they are about 10 ft apart. They also have the neutral and ground bonded at the transfer switch, and then again at the MDP....Is any of this right? Any help would be appriciated!....SSgt Kincaid

 

[iwire]

From 1200 amp MDP, it then supplies each building a 250 Amp service. No grounds were pulled from the MDP to each building. They drove ground rods and bonded the EGC to the neutral bus in the panel inside each building. Is this correct?

Yes, it is one of the correct methods that can be used.

I don't know if the NEC applies to this installation but it complies with NEC 250.32(B)(2).

Also, the generators and double throw were bonded to a single ground rod, and the MDP has its own ground rod. These two ground rods are also bonded together, and they are about 10 ft apart. They also have the neutral and ground bonded at the transfer switch, and then again at the MDP....

This has put all the electrode bonding jumpers in parallel with the neutral.

If I understand the installation correctly I would bond at the generator and not at the DT switch or the MDP.

 

[tryinghard]

...From 1200 amp MDP, it then supplies each building a 250 Amp service. No grounds were pulled from the MDP to each building. They drove ground rods and bonded the EGC to the neutral bus in the panel inside each building. Is this correct?

This is correct if: the feeders are installed in PVC (not conductive material), and there is no ground fault protection at the service disconnect.

This method goes against everything data-communications hate because this system uses the neutral (return conductor) as its equipment ground (bond), so current will exist on the ground (bond) conductor. Data-communication technician?s work very hard to keep their grounding clear of any current, (i.e. isolated grounding, separation for voltage?); this system puts the current there on purpose! But if installed as noted above it will be safe.

 

[iwire]

This method goes against everything data-communications hate because this system uses the neutral (return conductor) as its equipment ground (bond), so current will exist on the ground (bond) conductor. .

If the electrical system is installed correctly it will not make a difference to data communications system.

Electrically it is no different then a standard utility service.

 

[Dennis Alwon]

This is correct if: the feeders are installed in PVC (not conductive material), and there is no ground fault protection at the service disconnect.

There is more to it than what is stated above. If there is any metallic pathway between the building then a EGC must be use. Thus if there is a copper water pipe, telephone wire, metal conduits, etc then you do need the EGC

 

[iwire]

There is more to it than what is stated above. If there is any metallic pathway between the building then a EGC must be use. Thus if there is a copper water pipe, telephone wire, metal conduits, etc then you do need the EGC

True, but there is more to it then that.

Any of those metallic paths that would also have to be bonded to the grounding systems in both buildings before the requirement for an EGC would kick in.

 

[tryinghard]

If the electrical system is installed correctly it will not make a difference to data communications system.

Electrically it is no different then a standard utility service.

I do agree and I also believe this is true in systems including an EGC, so much so that isolated grounding is not needed for data-communication reasons.

 

[tryinghard]

There is more to it than what is stated above. If there is any metallic pathway between the building then a EGC must be use. Thus if there is a copper water pipe, telephone wire, metal conduits, etc then you do need the EGC

True, but there is more to it then that.

Any of those metallic paths that would also have to be bonded to the grounding systems in both buildings before the requirement for an EGC would kick in.

Well maybe its best practice to install the EGC either way? This does line up better with 250-24(A)(5) & 250-32(B)(1)

 

[tryinghard]

Looks like 2008 clarifies this 250-32(B) issue to be an exception to the rule. In other words the grounded conductor can common with equipment grounding and electrodes if it is an existing system and the three listed criterions are met.

I understand this to mean the rule is to install and EGC, do you see it the same?