I have run a temp 30amp single circiut gfi protected circiut to a second building we are currently working on. The temp includes the hot, the neutral and a ground. In the second building I installed a small 8 circuit panel to redestribute the circiut to 3 breakers to control 3 different outlets at different loctions. The hot is connected to 1 of the phase lugs, the neutral is on the neutral bar and the ground is bonded to the panel under a lug. The neutral and the ground are NOT bonded together at this location. In this second building the shell of the entire building is up. My problem is that not being sure that the building is grounded I drove an 8' ground rod and connected a grounding electrode conductor to the building steel. I have made no other connections to the grounding electrode. My 3rd year apprentice says that I'm wrong in doing this. Does anyone else think that this is wrong? If I am, what exactly have I done wrong and why? In reading the 1999 nec 250-24 , Exception No.1& 2: I read that is not required to have a grounding electrode when only one branch circuit is used. This power is only being used for a few hand power tools for the next 3 weeks, we dont really have the need for any 208v or any heavy amprege. We have already taken voltage drop into consideration. My question is did I need to ground the steel in the building (I dont feel that a steel building sitting on concrete walls is well grounded structure) with a grounded electrode. Or did my running of the equipment ground with the branch circuit and bonding that to this panel cover it. My concern it that if there is a fault current on the building steel that it will have no where to go.
Is this maybe an apprentice looking for an answer on a journeyman practice exam? No? O.K., I'll take it at face value.
You're right in that a single branch circuit run to a separate building requires only a cutoff, not another grounding electrode system. But, by installing a loadcenter in the building, you're not running a branch circuit. You're running a feeder (because it's in front of the final OCPD).
The loadcenter, because it's serving a separate structure, is considered a service. Therefore, it has to be grounded at the building, using a made electrode system. The main reason, I think, is to bleed off a lightning strike.
Running an EGC is good, and required if there's any metallic path between the buildings. But it doesn't get you off the hook for installing a grounding electrode (i.e., two driven ground rods) at the second bldg. And if the building steel will be accessible in the finished bldg, you have to bond it to ground at the service. I'd bond it regardless.
Your apprentice is right. Look it up in Arts 250 and 230.
Best o' luck--
#22121 - 02/19/0312:35 AMRe: 2nd building temp power
Could you clarify what you mean by building steel? Is it structural steel, columns, beams etc., or is it just a steel siding/shell? A buildings structural steel is a preferred electrode when “effectively grounded.” There is no definition of effectively grounded but it is generally accepted that a steel superstructure standing on concrete footings is effectively grounded.
One thing you need to do that you didn’t is bond the grounding electrode system you set up to the equipment grounding conductor of your feeder at the panel. No need to bond the neutral in this case.
Amp-Man, One thing to note. A service can only be supplied by a utility so article 230 does not apply. (See article 100 definitions) Article 225 applies here although says about the same thing as 230.