Grounding vs Bonding issue.

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sparkey874

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Erie, PA in the Civilian work
Good evening. I am a Seabee in Iraq and I have an issue with bonding vs grounding. I have 2 150Kw gen set's in series puttinf out 3 phase 4 wire 390v with a seperate ground wire. They are feeding a MDP. This MDP feed's the motor pool shop and the CHU's <sort of like work site trailer's> as well as other various building on site. Our Task Force Safety did an electrical inspection of the system and said the ground/neutral bar needed to be bonded at the CHU's and the metal braid in the wire's <200mm> needed to be used as the ground from the genset to the MDP. Also the ground rod's <earth ground> at each CHU was ineffective and ground needed to go back to the MDP as well as the MDP neutral/ground bar be bonded also. Also back a few year's ago a 30 ft trench was dug and <3> 9 ft ground rod's were buired to make an effective earth ground. This is almost impossable to do out here in the desert! OK so far? Now, When I went to bond the ground and neutral bar at the CHU, the main in the Pwr Pnl tripped. If I removed the ground wire and touched the ground and neutral bar's with a jumper it DIDN'T trip. Aas I understand it there are a total of 3 seperate grounding systems, and the only real way to fix it is to rewire from the genset's with a single ground to the MDP and ground it and bond it at the same time. Then carry the bonding at the MDP to the various buildings. Does this make sense to you? The TFS gent is a very demanding man. I explained what I felt was the problem and why we needed to do a rewire, but he said I was wrong. Is there any NEC that will help me here? Thank you for your help in advance.
R/
CE2 <SCW> Kennedy
 
Does the main in the power panel have Ground Fault protection?
 
I think the bond SHOULD take place at the MDP. I don't think there should be no bond at the CHU's. You could be flowing neutral current on that braided wire,,,,but most likely it's just confusing the ground fault in your MDP.
 
The ground rods have no role in preventing electrical shocks.
What you need at the generator is a 'system bonding jumper (SBJ)' from the neutral to the case of the generator. This allows the fault current from some thing that is energized to get back to its source. The NEC states the SBJ is at the source or first disconnecting means.
And to really protect against electrical shock, use a GFCI.
PM me with your mailing address and I will mail you a copy of Mike Holts Grounding Vs Bonding text.
Thanks for your service,
Tom, USN 1970-1976, MM1
 
I was part of TF Safe at the start up, and I never saw a single ground wire ran with the feeders, though I am not doubting you. What was typically seen was the 3 phase conductors ran with a neutral to the MDP's, SDP's, and then a ground came out with the conductors to the CHU's. Since there was no ground wire, each panel needed to be bonded or else fault current could not get pack to the source.

For the panel tripping in the CHU double check that the RCD breaker is wired properly. If the RCD is wired properly, I would almost guarantee there is a ground and neutral wire ran to the CHU, and the reason the breaker trips is from the RCD sensing a imbalance due to the bond. I typically recall the CHU's having a ground wire ran to them, so they were not bonded.

The easy way to tell over there if you need to bond the ground and neutral is by the wires. If the supply is three phases and a neutral, you need to bond. If the supply is three phases, a bond, and a ground wire don't bond.
 
I forgot to say I assume the main breaker in the CHU is a RCD, and that would totally explain the problem.

As for the steel braid, it has been about a year since I was there, and I may be wrong, but I don't think the NEC allows the steel braid to be used as the grounding conductor (don't have my NEC handy); the steel braid is to protect the conductor. However the British Code allows the braid to be used as the grounding conductor if certain calculations are performed and documented. The NEC is the standard, but the contractors can file appeals to allow British standards to be accepted as well. With that being said, the steel braid was almost always cut down so it could fit into a way too small lug.

We had the contractors connect the steel braid to ground on one end only.

Can you take pics of the panels on the gens, MDP's, SDP's, and CHU panels. Unless you did the wiring, you have a rare base camp. I have been or know someone who has been to pretty much every camp in Iraq, and grounding conductors are few and far between from the gens to mdp's. Once again I am not doubting you, just basing it off of my experiences.

I will dig through my notes this weekend to and get the references I used for your type of situation. Feel free to PM me any questions about this or any other TF SAFE situations you need help on, and I will do my best to help you out.

SSG Gray
249 EN BN A CO.
 
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mxstar and all. Thank you for your help in this. I am trying to get a meeting with the TFS gent, but our scheduals are not helping. Beside's this issue I am leading a crew to wire up a PEB <Pre Enginnered Building> and a few other task's at hand. LOL, I guess I'll sleep on the way back to the states. Ok, to clarify, There is a ground wire run from the ground lug to the MDP. Each genset also has another ground run from the breaker frame to the aforementioned buried ground rods. At the MDP I have 2 ground wire's from the genset, all the ground's from the various breaker, at the ground lug it goes back to the buried ground rods. At the CHU's, each CHU has a ground carried from the MDP to the pannel and has 2 individual ground point's on the frame leading to another ground rod. These ARE NOT connected to the PP. Does this sound right to anyone? I also read that the at the MDP I need to make the Bond between ground and neutral. This will make it so I don't have to bond at the individual pannels? Thank you all for you help in this matter. I know this is a SUPER IMPORTANT issue and I want to get it right. Last year they had a fatality in one of the wet chu's and I don't want that to happen on my watch.

R/
CE2
 
Hopefully I understand correctly, and if so, yes, you need a bond between your equipment grounds and neutral at MDP. This provides the ground path for current to flow back to the generator in the event of a fault. (The earth will not carry enough current to trip the OCP)
If you have a separate grounding conductor run to your sub-panel, there is no bond between neutral-equipment ground at those panels.
 
Is the 600 A breaker the one that trips when you install the ground/neutral bond? If it is I must not be thinking of the same kind of CHU. To me a CHU is a Containerized Housing Unit. They typically had a 60 A RCD breaker in them. The MDP would have a 600 A main that would feed multiple SDP's which would then feed all the CHU's.

The problem you are experiencing with the breaker tripping when installing the ground/neutral bond was what we did to test the functionality of the RCD breakers.
 
Augi47.
Yes, I need to connect a bond at the MDP. The TFS gent said all PP's nned to be bonded.. I explined the we bond only at MDP, it carries through to the rest of the distrabution circuit. There is a seperate ground ran at the CHU's to a grounding rod. This ground's the shel of the CHU in case of lightning or dead short to the frame in the CHU. <being they are all metal construction>.
 
and your separate ground to the CHU's should be bonded to the disconnect means and to the grounding electrode. The CHU should have a grounding electrode system also (all covered in 250.32)

and most importantly, as Tom says, Thank You for your service to our Country!
 
MXstar;
It is the 60A breaker at the CHU that is tripping. I went back and looked again and relized why we were tripping the breaker when we tried to bonded it as it is. We were creating a dead short from the neutral bar to the frame of the CHU's, NOT back to the MDP. The ground rod's only protect from lightning strikes and dead short's in the CHU wires. I must say, the first time I looked a the PP at the CHU I almost lost it. They are using a 3 phase 4 wire breaker with only 4 wires. They used the "ground" <yellow with green strip> wire as a hot and it was NOT reidentified at the PP or the MDP. Who ever wired this up has NO IDEA how dangerous they made it. I'm surprised TFS didn't pitch a fit! The whole electrical distrabution system over here on all of our bases is in terrable shape. Between our under qualified electrical personnel, both military and civilian, the lask of supplies and budget, and please don't even get me started, and the effort's of the Iraqi electrican's it is a wonder that more folks haven't been killed! I know TFS has a rough job and I appriciate what they do to for us, but TFS, KBR , or who ever is taking over for them, and the military need to sit down and come up with a standard for electrical work here and HOLD ALL PERSONNEL ACCOUNTABLE for their actions! Is there a way to fix this problem in your opinion. Ok, gotta get back to work. Updating plan's for work tomorrow. Does it ever end?? LOL, Nope

R/
CE2 Kennedy
 
augie47 said:
and your separate ground to the CHU's should be bonded to the disconnect means and to the grounding electrode. The CHU should have a grounding electrode system also (all covered in 250.32)

and most importantly, as Tom says, Thank You for your service to our Country!
Click to expand...

so the CHU should have it own ground rod and should be connected to the ground bar to be a part of the total grouning system? Is this correct? I don't have my code book handy right now so I'm nor sure what's covered in 250.32. Thanks.
PS: Pround to serve my country and greatful to all who support us no matter what the current "feeling's" are on the war.

R/
Matthew Kennedy
 
see if this helps:
250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s).
(A) Grounding Electrode. Building(s) or structure(s) supplied by feeder(s) or branch circuit(s) shall have a grounding electrode or grounding electrode system installed in accordance with Part III of Article 250. The grounding electrode conductor(s) shall be connected in accordance with 250.32(B) or (C). Where there is no existing grounding electrode, the grounding electrode(s) required in 250.50 shall be installed.
Exception: A grounding electrode shall not be required where only a single branch circuit, including a multiwire branch circuit, supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the normally non?current-carrying metal parts of equipment.
(B) Grounded Systems. For a grounded system at the separate building or structure, an equipment grounding conductor as described in 250.118 shall be run with the supply conductors and be connected to the building or structure disconnecting means and to the grounding electrode(s). The equipment grounding conductor shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The equipment grounding conductor shall be sized in accordance with 250.122. Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s).
 
TFS, KBR , or who ever is taking over for them, and the military need to sit down and come up with a standard for electrical work here and HOLD ALL PERSONNEL ACCOUNTABLE for their actions!

They did, and came up with 2005 NEC. The problem is money. TF SAFE is only doing inspections, not working on stuff. When I did it, my hands were tied because due to contracts we were not allowed to do any work, and I saw some really shady stuff.
 
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