Grounding Steel Support Posts or Unistrut

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teejer

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I work for an electrical cabinet manufacturer and I want to be able to give the propper instructions for instlaling our equipment. Our products are installed outdoors and a they get buried a minimum of 2 feet into the ground. Sometimes for extra support of the enclosure, we sell customers a steel post similar to Unistrut that they bolt to the enclosure. The bolt holes in the enclosure are factory provided and are powder coated, thus there is no metal to metal contact, which would technically prevent bonding between the post and the enclosure. The enclosure has a ground lug which can be connected to a ground rod and grounding system by the installer. The post is galvanized steel and completely buried, and the bottom of the post extends 4 feet below the ground level, but I am concerned that the post would not have an adequate path to ground if it were accidentally energized separately from the enclosure. Is there anything in the NEC about what is considered propper bonding of steel support posts like unistrut? Would anyone suggest connecting a grounding terminal to the post and then connecting it to the enclosure ground rod and grounding system? Thanks in advance for your replies.
 
teejer said:
. Is there anything in the NEC about what is considered propper bonding of steel support posts like unistrut? Would anyone suggest connecting a grounding terminal to the post and then connecting it to the enclosure ground rod and grounding system? Thanks in advance for your replies.
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Article 250.136(A) requires the equipment on the rack be effectively grounded to the rack. A jumper from the equipment to a clean contact would be effective.A ground rod would most likely be required if considered a seperate structure.

250.136 Equipment Considered Effectively Grounded
Under the conditions specified in 250.136(A) and (B), the non?current-carrying metal parts of the equipment shall be considered effectively grounded.
(A) Equipment Secured to Grounded Metal Supports Electrical equipment secured to and in electrical contact with a metal rack or structure provided for its support and grounded by one of the means indicated in 250.134. The structural metal frame of a building shall not be used as the required equipment grounding conductor for ac equipment.
Rick
 
I have had some experience with equipment like this. Service pedestals made by Milbank? I'm kinda sure. utilize the same "foot" method and I have not seen a proper installation yet. Most install units too low and make-up box ends up below grade.

Are your products tested and listed by a NRTL? That is where I would start.
 
Thanks for the replies everyone. Bonding the support with the enclosure looks like the way to go and I will reference that NEC section in our installation instructions. The enclosures are listed by an NRTL and I will contact them for more input. We are not Milbank, but I like the comment about never seeing a propper installation of one of these enclosures when they have the "foot" installed on them. The bonding principles here apply to the foot as well.
 
teejer said:
The bolt holes in the enclosure are factory provided and are powder coated, thus there is no metal to metal contact, which would technically prevent bonding between the post and the enclosure. The enclosure has a ground lug which can be connected to a ground rod and grounding system by the installer.
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Why not just use a short jumper from the enclosure lug, either inside the enclosure to bond the cabinet to one of the mounting bolts, or outside the enclosure to a clamp or lug on the supports?
 
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