Generator grounding

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arnettda

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I have searched back posts and have most of my answer but when grounding to the supplied lug on the frame of a 20kw generator can I just drive one ground rod or do I need two? The generator directions said follow nec requirements. So I need two?
 
I believe 250.30 is the section you're looking for. A ground rod is required for a separately derived system generator. Personally speaking, for the extra $10.00 and a few minutes time I usually drive the rod just so I don't have to delay the job and argue with an uninformed inspector.
 
Note carefully what Chris said. In a vast majority of the installs I see, the transfer switch does not switch the neutral so the generator is not a SDS. In those cases, generator grounding is accomplished by an equipment grounding conductor run with the generator feeds and the only reason far a ground rod is to satisfy manufacturer specs.
Therefore, if their spec call fro "a" rod, so be it.
If, in the rare situation the TS does switch the neutral, then you need to establish a grounding electrode at the generator that satisfies 250.30
 
chris kennedy said:
You just need 1 to satisfy 110.3(B). (Unless your transfer switch switches the neutral)
Click to expand...

I disagree; I ask just why we are driving the rod in the first place. If we are driving the rod as an electrode then this electrode must meet the requirements for an electrode.

If we are driving the electrode to keep the genset tied down so the wind don?t blow it away then it up to our own discretion.

There is this concept that there is an electrode at the service. In the event that feeders were supplying a remote building one could argue that the electrode system is already installed at the service so why install another at the remote building. The same holds true for the genset which is the same thing as the remote building.

In the 2011 code cycle there was language added to state that in no case could an EGC be used to connect any grounding electrode.

250.121 Use of Equipment Grounding Conductors.
An equipment grounding conductor shall not be used as a grounding electrode conductor

5-259 Log #4526 NEC-P05
C:\Users\Owner\AppData\Local\Temp\msohtmlclip1\01\clip_image001.gif
Final Action: Accept
(250.108 (New) )
_______________________________________________________________
Submitter: Phil Simmons, Simmons Electrical Services
Recommendation: Create a new Section 250.108 as follows:
250.108 Use of Equipment Grounding Conductors.
An equipment grounding conductor shall not be used as a grounding electrode conductor.
Substantiation: This new section will clarify that grounding electrode conductors and equipment grounding conductors serve a different purpose in the electrical safety system, are sized differently and have different installation requirements. Equipment grounding conductors do not normally carry current while a grounding electrode conductor may normally carry current since it is often in parallel with the neutral conductor.
Panel Meeting Action: Accept
Panel Statement: The panel notes that this new section is to be located in Part VI and suggests it be numbered as Section 250.121.
Number Eligible to Vote: 16
Ballot Results: Affirmative: 16


So to say that the equipment grounding conductor between the genset and the service connects to the electrode system for the service just don?t fulfill the requirements of the NEC.
 
I agree with Chris and Augie. The use of the rod is to satisfy the instructions that are part of the listing of the generator. Almost all 20 kw gen sets are not SDS's since they do not switch the neutral with the transfer equipment. The rod is an auxiliary electrode therefore only one is required.

250.54 Auxiliary Grounding Electrodes.
One or more grounding electrodes shall be permitted to be connected to the equipment grounding conductors specified in 250.118 and shall not be required to comply with the electrode bonding requirements of 250.50 or 250.53(C) or the resistance requirements of 250.56, but the earth shall not be used as an effective ground-fault current path as specified in 250.4(A)(5) and 250.4(B)(4).
Click to expand...
 
jwelectric said:
I disagree; I ask just why we are driving the rod in the first place. If we are driving the rod as an electrode then this electrode must meet the requirements for an electrode.

If we are driving the electrode to keep the genset tied down so the wind don?t blow it away then it up to our own discretion.

There is this concept that there is an electrode at the service. In the event that feeders were supplying a remote building one could argue that the electrode system is already installed at the service so why install another at the remote building. The same holds true for the genset which is the same thing as the remote building.

In the 2011 code cycle there was language added to state that in no case could an EGC be used to connect any grounding electrode.

250.121 Use of Equipment Grounding Conductors.
An equipment grounding conductor shall not be used as a grounding electrode conductor

5-259 Log #4526 NEC-P05
C:\Users\Owner\AppData\Local\Temp\msohtmlclip1\01\clip_image001.gif
Final Action: Accept
(250.108 (New) )
_______________________________________________________________
Submitter: Phil Simmons, Simmons Electrical Services
Recommendation: Create a new Section 250.108 as follows:
250.108 Use of Equipment Grounding Conductors.
An equipment grounding conductor shall not be used as a grounding electrode conductor.
Substantiation: This new section will clarify that grounding electrode conductors and equipment grounding conductors serve a different purpose in the electrical safety system, are sized differently and have different installation requirements. Equipment grounding conductors do not normally carry current while a grounding electrode conductor may normally carry current since it is often in parallel with the neutral conductor.
Panel Meeting Action: Accept
Panel Statement: The panel notes that this new section is to be located in Part VI and suggests it be numbered as Section 250.121.
Number Eligible to Vote: 16
Ballot Results: Affirmative: 16


So to say that the equipment grounding conductor between the genset and the service connects to the electrode system for the service just don?t fulfill the requirements of the NEC.
Click to expand...

I agree here, if Genset is not SDS, then the equipment ground is all that is necessary for grounding the unit. Grounds rods are not required for outdoor HVAC equipment, why would one be required for a standby generator.
 
elohr46 said:
I agree here, if Genset is not SDS, then the equipment ground is all that is necessary for grounding the unit. Grounds rods are not required for outdoor HVAC equipment, why would one be required for a standby generator.
Click to expand...

I agree, but I'm not sure that you're agreeing to what Mike said in his post. He's saying that the gen-set is the same as a separate building and would therefore require it's own GES. Mike please correct me if I'm wrong. :)
 
infinity said:
I agree with Chris and Augie. The use of the rod is to satisfy the instructions that are part of the listing of the generator. Almost all 20 kw gen sets are not SDS's since they do not switch the neutral with the transfer equipment. The rod is an auxiliary electrode therefore only one is required.
Click to expand...
It is not a SDS. Thanks for all the information.
 
infinity said:
I agree, but I'm not sure that you're agreeing to what Mike said in his post. He's saying that the gen-set is the same as a separate building and would therefore require it's own GES. Mike please correct me if I'm wrong. :)
Click to expand...

You are correct, I miss read his intention. However, he is incorrect. Soares book on g&b(2008) has a good illustration on page 228, figures 12-17 & 12-18.
 
Even if it is a separate structure, it is likely only supplied by a single branch circuit and would not trigger the grounding electrode rule in 250.32.
 
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