2 Ground Rod Used

[GrobinsonLUI]

Hello All. I'm a newbie here but I have a question. Hopefully its an easy one.
I have a client that is "demanding" a dedicated ground rod for his home electronics racks. I believe that I once heard/saw in the NEC that this is against code unless they are bonded together and at least within 6' of each other. Now I can't seem to find this info. Can anyone help me out with this?
Thanks in advance.

 

[rcarroll]

If I understand your question, your customer wants a supplementary grounding electrode. If you have an '05 NEC, look at 250.54.

 

[winnie]

See 250.54 of the NEC.

You can have supplementary ground rods, and they can be wherever you want them, but they must be bonded back to the building grounding electrode system. Having a separate _isolated_ grounding electrode is unsafe, a code violation, and would also make the customer's equipment a receiver for any currents flowing through the soil (say caused by a nearby lightning strike).

-Jon

 

[charlie b]

250.50 says that all available grounding electrodes shall be used, and shall be bonded to each other. That eliminates your client?s notion of having a separate electrode for electronics racks.

Ground rods are more effective if they are further apart. I think the ?6 feet? limit you are thinking of comes from 250.56. It says rods must be at least 6 feet apart.

 

[rcarroll]

See 250.54 of the NEC.

You can have supplementary ground rods, and they can be wherever you want them, but they must be bonded back to the building grounding electrode system.

-Jon

The supplementary grounding electrodes need only be connected to the equipment grounding conductors.

 

[roger]

A supplementary ground rod may be used in addition to the required Equipment Grounding Conductor but it can not be used in place of the EGC.

250.54 Supplementary Grounding Electrodes
Supplementary 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).

The following is from Mike Holts training material

A supplementary electrode is an electrode that is not required by the NEC. This electrode is not required to be bonded to the building or structure grounding electrode (earthing) system. Figure 250?103

The supplementary electrode is not required to be sized to 250.66, and it is not required to comply with the 25 ohm resistance requirement of 250.56. Figure 250?104

The earth cannot be used as an effective ground-fault current path as required by 250.4(A)(4).

Author?s Comment: Because the resistance of the earth is so high, very little current will return to the electrical supply source via the earth. If a ground rod is used as the ground-fault current path, the circuit overcurrent protection device will not open and metal parts will remain energized.

CAUTION: The requirements contained in 250.54 for a ?supplementary? electrode should not be confused with the requirements contained in 250.53(D)(2) for the underground metal water pipe ?supplemental? electrode.

Author?s Comment: Typically, a supplementary electrode serves no useful purpose, and in some cases it may actually create equipment or performance failure. However, in a few cases, the supplementary electrode is used to help reduce static charges on metal parts. For information on protection against static electricity in hazardous (classified) locations, see NFPA 77, Recommended Practice on Static Electricity.


Roger