Ground Ring for Bulk Storage Plant

[JDV]

Connecting Tanks and Pump bases to a ground ring? I have noticed some plants connecting their above ground steel tanks and pump bases to a ground ring. Why?
The only purpose I see would to bring the tank to earth potential. The motor for the pump requires an EGC from the service for ground fault protection. I scanned NEC Articles 250, 501, & 515 and cannot find any reason or requiremnent why this should be done and is it good practice.

 

[tshea]

Lightning is one possibility.

 

[hardworkingstiff]

NFPA has a publication (I forget which one) that recommends grounding tanks. I believe it said two ground rods on opposite corners (one at each of the two corners). I haven't read it in about 20 years or more.

 

[lile001]

Tank Grounds

Tank Grounds

NFPA has a publication (I forget which one) that recommends grounding tanks. I believe it said two ground rods on opposite corners (one at each of the two corners). I haven't read it in about 20 years or more.

NFPA 30 Flammable and Combustible Liquids Code. Paragraph 5-5.2.4 refers one to NFPA 77, Rec. Practice on Static Electricity. It goes on to say that all tanks and "equipment" (NFPA defines this word specifically) shall be bonded or connected to a ground. Additional codes on lightning protection also apply, and the requirements are more stringent for a tank farm with flammable and combustible liquids. I can't find anything in NFPA 30 that specifically requires two ground rods at a tank, but when we used to do these kinds of facilities we had very specific lightning protection details that ended in a grounding electrode and was of course bonded to everything else.

Static electricity is a big deal around flammable and combustible liquids!