Ground rod at sub panel

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Mike Magoulas

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Would someone tell me where in the code book I can find where you do not need a ground rod at a sub panel unless it is located in a detached building???

Also is it bad to have a ground rod at the sub panel too???
 
Take a look at 250.32 for the first part. And yes you can have a ground rod at a subpanel even if it within the same structure. It would be called an auxiliary grounding electrode and probably won't do much.

Welcome to the forum. :smile:
 
The question I would ask is why? There is not benefit I can think of and in some cases can be detrimental.
 
infinity said:
Detrimental how?
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Actually at the panel, most likely no issues no different that the panel sitting on or being anchored to a concrete floor or steel structure. Driving exterior ground rods can cause issues when there are lighting strikes in the immediate area of the rod.

Minimal risk most likely, but if there is no benefit what would be the purpose?
 
infinity said:
Detrimental how?
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BECAUSE! That's why.

Seriously, I recognize that in some applications an auxiliary ground rod can be detrimental where, for example, at the end of a BC supplying a piece of machinery you ground the machine and can cause a difference of potential between where the machine is grounded and where the source is grounded. But I also can't think of a reason grounding a sub panel with an auxiliary ground rod could be detrimental.
 
say the service is at the north end of the building. sub panel at the south end. lightning or another anomaly happens outside at the south end of the building. your service ground just so happens to be the path of least resistance. you now invite objectionable current to jump across your system.
 
vinster888 said:
say the service is at the north end of the building. sub panel at the south end. lightning or another anomaly happens outside at the south end of the building. your service ground just so happens to be the path of least resistance. you now invite objectionable current to jump across your system.
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all the grounding electrodes present are required to be connected together. see 250.50
 
cpal said:
all the grounding electrodes present are required to be connected together. see 250.50
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Not if it is a auxillary electrode. See 250.54.

infinity said:
Take a look at 250.32 for the first part. And yes you can have a ground rod at a subpanel even if it within the same structure. It would be called an auxiliary grounding electrode and probably won't do much.

Welcome to the forum. :smile:
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JohnJ0906 said:
Not if it is a auxillary electrode. See 250.54.
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But! 250.54 requires the aux electrodes to conformwith 250.50 or 250.53(C).

Both of those sections are going to require all recognozed electrodes to bonded together ????
 
cpal said:
But! 250.54 requires the aux electrodes to conformwith 250.50 or 250.53(C).

Both of those sections are going to require all recognozed electrodes to bonded together ????
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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).​

Auxilery ground rods, being unneeded in the eyes of the NEC, do not have rules governing them so do what ever you want.

I heard MH say once "you can connect it to the equipment with CAT5 or rope or whatever you want".

​
 
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