Two generators set up and hooked to a transfer switch. A fuel tank common for both sits between them. Distance from generator to fuel tank is 15 feet. Two ground rods are driven. Each generator is utilizing the two ground rods to meet the NEC grouding electrode requirements. Wire from metal fuel tank also ties into the ground rods. Legal? Does distance between each item or generator size have any relevence to this?
Generator and fuel tank grounding.
- Thread starter iowa
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petersonra
Senior Member
- Location
- Northern illinois
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- engineer
I once asked a similar question on this forum and never got an answer. IMO, the rules do not state you must have a separate GES for each structure, just that there be one.
rkrieger
Member
General information
General information
I can't address specific NEC issues, but on similar installations, we designed very similar parts/pieces.....This may seem like "overkill", but when the central tank is re-filled, a grounding jumper is always attached between either fuel truck or portable cans being used and the storage tank. Can't be too careful. Sounds like you have it pretty much covered. :smile:
General information
I can't address specific NEC issues, but on similar installations, we designed very similar parts/pieces.....This may seem like "overkill", but when the central tank is re-filled, a grounding jumper is always attached between either fuel truck or portable cans being used and the storage tank. Can't be too careful. Sounds like you have it pretty much covered. :smile:
bphgravity
Senior Member
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- Florida
I don't understand why the fuel tank is involved?
Grounding the frames of the generators to the same electrodes is not a code violation, nor is likely that grounding of the generators was required at all.
Why is there a 'wire' running to the fuel tank and connected to the ground rods?
Grounding the frames of the generators to the same electrodes is not a code violation, nor is likely that grounding of the generators was required at all.
Why is there a 'wire' running to the fuel tank and connected to the ground rods?
petersonra
Senior Member
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- Northern illinois
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- engineer
because the fuel tank is probably required to be bonded.bphgravity said:
see 250.110
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- Bremerton, Washington
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- Master Electrician
Are the generators a SDS?
IE do they power loads via a transfer switch and if so is the neutral switched?
IE do they power loads via a transfer switch and if so is the neutral switched?
Pierre C Belarge
Senior Member
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- Westchester County, New York
Typically, the generators are not required by the NEC (250.32) to be grounded. It is usually the installation instructions that require some form of grounding at the generator [110.3(B)]
250.32 does not apply to generators, as the generators are not supplied by the building. that is if the generator is not separately derived which the preponderance of generators are not SDS.
250.32 does not apply to generators, as the generators are not supplied by the building. that is if the generator is not separately derived which the preponderance of generators are not SDS.
frizbeedog
Senior Member
- Location
- Oregon
Hold on a sec.
Hold on a sec.
Exactly. Is the neutral switched.
Soars Book on Grounding and Bonding 9th ed. pg. 225
"Where the generator is not a seprately derived system, the neutral bonding jumper must be removed from the generator, and the neutral must not be grounded at the generator or at any point betweent the generator up to the service."
Do your generator's have a neutral bond jumper?
Follow the path of current and you might have a problem having both generators connected to the same ground rods.
Hold on a sec.
tom baker said:
Exactly. Is the neutral switched.
Soars Book on Grounding and Bonding 9th ed. pg. 225
"Where the generator is not a seprately derived system, the neutral bonding jumper must be removed from the generator, and the neutral must not be grounded at the generator or at any point betweent the generator up to the service."
Do your generator's have a neutral bond jumper?
Follow the path of current and you might have a problem having both generators connected to the same ground rods.
Generators are hooked to a 4 pole transfer switch. I don't know the specifics on if they would be considered a seperatly derived system. They are the only source of power. We have any where from 100KVA to 1800 KVA. I am tieing the fuel tank in with these two ground rods because they also are required to have a ground rod. In esscense I am trying to kill 3 birds with one stone but want to make sure I am doing it correct and can defend it.
frizbeedog
Senior Member
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- Oregon
More info?
More info?
If you say that the generators are the only source of power what is the tranfer switch for? Can you clarify your installtion some more?
No utilty service at all?
More info?
iowa said:
If you say that the generators are the only source of power what is the tranfer switch for? Can you clarify your installtion some more?
No utilty service at all?
Iowa,
You are switching the neutral with the 4-pole switch, therefore by the NEC defintion you have a SDS. Bond the neutral to frame (ground) on both generators, sized per 250.66 and converted to metric. Connect both generators to your grounding electrode system (2 ground rods or more).
As far as the fuel tank goes, per our elite electrical engineers over here, the fuel tank ground is a "static drain" and should not be connected to the generators GES. They say under a fault you wouldn't want any current possibly flowing on the tank. Makes sense to me.
I have found a fuel tank that was energized because it was tied to the Gen GES and the Gen had no N/G bond. That's not good.
You are switching the neutral with the 4-pole switch, therefore by the NEC defintion you have a SDS. Bond the neutral to frame (ground) on both generators, sized per 250.66 and converted to metric. Connect both generators to your grounding electrode system (2 ground rods or more).
As far as the fuel tank goes, per our elite electrical engineers over here, the fuel tank ground is a "static drain" and should not be connected to the generators GES. They say under a fault you wouldn't want any current possibly flowing on the tank. Makes sense to me.
I have found a fuel tank that was energized because it was tied to the Gen GES and the Gen had no N/G bond. That's not good.
So do you guys have to do ground resistance readings on the fuel tanks to then. If so I would assume that they would fall under something other than the rules talked about in Art. 250. Is the electic dept there responsible for installing and testing the ground rods for the fuel tanks.
FYI I just got a CMIP from QAQC because I have two ground rods at each generator. I think I have won that part of it. But on the rest since it says "Are ground resistance readings documented and maintained on site" This not so smart QA guys says that since I don't have actual numbers I am not in compliance. Even though I am with the two ground rods. Just about time for me to go home. These people are out there. The biggest reason there pushing this is because they believe it to be a safety issue. We need some serious help here man.
ground rod resistance testing
ground rod resistance testing
You are NEVER going to get out of the 25 ohm thing. It's in the contract. There are scenarios where it is a safety issue, so I have found it best to think of it in those terms. Just keep saying the Yes, the grounding is important but we still have to pull the required EGC. I have found it easiest to run an "external" EGC ran with the circuit conductors.
But back to the resistance testing. If you guys, like us, use a clamp on meter to check the resistance you are not checking much. Read the manual, it's for a utiltity-fed system. If you drive two ground rods connect a wire between them and clamp that thing on it will check the resistance between those two rods. I don't know what that tells ya. To check a single rod you need to use a different tool. (3-point tester). I would suggest you contact the engineers and tell them your dilemma with getting the 25 ohms, If they want it I say they design it.
I think whenever those testers register a "good" reading there is a closed loop system, ie: the ground wire is connected to the fuel tank twice or in a "loop" of some sort and the meter simply reads the resistance of the wire/steel in that loop. I highly doubt there is a single ground resistance test done that means anything in all of theater. Just my opionion
ground rod resistance testing
You are NEVER going to get out of the 25 ohm thing. It's in the contract. There are scenarios where it is a safety issue, so I have found it best to think of it in those terms. Just keep saying the Yes, the grounding is important but we still have to pull the required EGC. I have found it easiest to run an "external" EGC ran with the circuit conductors.
But back to the resistance testing. If you guys, like us, use a clamp on meter to check the resistance you are not checking much. Read the manual, it's for a utiltity-fed system. If you drive two ground rods connect a wire between them and clamp that thing on it will check the resistance between those two rods. I don't know what that tells ya. To check a single rod you need to use a different tool. (3-point tester). I would suggest you contact the engineers and tell them your dilemma with getting the 25 ohms, If they want it I say they design it.
I think whenever those testers register a "good" reading there is a closed loop system, ie: the ground wire is connected to the fuel tank twice or in a "loop" of some sort and the meter simply reads the resistance of the wire/steel in that loop. I highly doubt there is a single ground resistance test done that means anything in all of theater. Just my opionion
So then what says we have to have ground rods installed at generators? Thats where I am getting all my numbers from. I haven't got things to the point where there at the buildings? Would be funny if I am getting CIMP on the things I don't have to do, but am not on the areas I should be doing:grin:
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