If one is to run a feeder cable to a lighting panel located about 150 feet away to serve lighting in a wedding tent. Should a grounding electrode be installed at the tent? The panel is mounted on a free standing sheet of plywood along with 25 GFCI receptacles. All loads are cord and cap connected and there is a metal fence about 5 feet away from the panel. 120/240v. 3-wire w/ground.
If anyone sees a reason this is not safe- "Speak now or forever hold your peace"
First, is the tent a 'detached structure?' Well, is it temporary? If this tent is going up for a one time event, it's clearly temporary. If it will be up all year, then it's not a 'tent,' it's a structure.
The second detail is: how many circuits? Will there be a panel at the tent itself? A single circuit (really two, as a multi-wire circuit counts as one) doesn't require a ground rod be driven ... more does.
Or, look at it as you would a job site. A 'spider box,' which often has eight separate 20 amp circuits coming from it, doesn't need a ground rod .... simply because it's temporary.
If the source power is properly grounded, then a seperate ground rod is not required providing the tent panel is properly grounded through a 4-wire feeder. It appears to be a temp application so doesn't hurt to brush up on article 590.
From a practical sense, as long as everything is GFCI protected, this will not present many real hazards. I think I would follow John's lead. Just how temporary is this. If it is a one day event I think you can skip the ground rod. How are they protecting the feeder and the branch circuits on the line side of the GFCI? That is your hazard zone.
The tent and the loadcenter support are a 'structure'. No time limits or construction materials exempted in the definition. Temporary wiring doesn't exempt it. If more than one branch circuit (including a single multiwire)is provided then 250.32 requires the electrodes and bonding of the equipment grounding conductor run with the feeder thereto. If no electrodes exist at the site then they must be installed. Depending on the construction of the 'tent' there may be a need for bonding to the structural steel frame (should one exist).
Though the code text does not specifically elaborate, to consider an actual tent ... a temporary contraption covered in cloth ... to be a 'structure' makes as much sense as calling the Orkin Man a 'mass murderer.'
Then again, it's simply neither reasonable, nor possible, for any set of rules to spell out every possible variation. At some point, one needs to use some judgement.
Look at it this way: A local shopping center often has its' lot occupied by passing carnivals. While it's pretty hard to call the Ferris Wheel anything but a 'structure,' the parking lot remains intact - not completely torn up, as it would be if every ride was banging in ground rods.
Ditto for just about any job site. There may be a ground rod for that temporary power pole ... but the one for the building isn't there until construction is well under way. There sure are all manner of cords snaking about, though.
Now, I'm sure that. somewhere, there is a building official who is simply salivating over the prospect of selling permits the next time the Boy Scouts hold a jamboree .... imagine the permit fee income from all of those tents! ... but it's not going to happen.
To be fair, I have seen the term 'tent' used in different ways. For example, one of the casinos here has a permanent circus "under the big top." That roof may be canvas, but there's nothing temporary about this arrangement .... nor could anyone take it down with less than a month of labor.
That's why I focused on the true nature of the structure in my answer.
It really dosen't matter if it a tempory tent or permanent building (like a remodel). The panel IAW the OP is temporary that is fed with a feeder, not a drop or lateral therefore the service feeding the temp panel via a feeder, in theory is already grounded. Since the OP is being fed with a 3 wire with ground, presuming that it everything is properly connected, a ground rod is not required. Not to say one can be added but it need to be bonded to the service ground. The devil is in the definitions not the details.
Per NEC 252.2, a tent is explicitely considered a "Portable Structure" and Article 252 invoked as the prevailing code. Which means 525.21(A) is applicable, and the disconnecting means must be located within sight of and within 6' of the operator station. Does that mean the panel must be installed in the pulpit? And that it must be padlocked because the operator is an unqualified person? I'm confused!
Secifically to tents, 525.31:
525.31 Equipment Grounding. All equipment to be grounded shall be connected to an equipment grounding conductor of a type recognized by 250.118 and installed in accordance with Parts VI and VII of Article 250. The equipment grounding conductor shall be connected to the system grounded conductor at the service disconnecting means or, in the case of a separately derived system such as a generator, at the generator or first disconnecting means supplied by the generator. The grounded circuit conductor shall not be connected to the equipment grounding conductor on the load side of the service disconnecting means or on the load side of a separately derivced system disconnecting means.
No mention of 250 Part III anywhere in 525. In fact, it's completely silent on ground rods.