Temporary Ground

[CCCI]

Hi, I am installing a temporary transformer outside of our office for parties and special events this will be a 75KVA transformer on wheels for large lighting and Audio/Video loads. How should I install my Grounding Electrode?
We have a large open area and it could be used and many different places. Do I need to keep the Grounding Electrode next to the transformer, or how would it effect the Ground if it is ran with the Main feed from the building. We are in the Orlando, Fl. area and a good Ground is hard to get, so moving the ground rod with the transformer would not work very well.

 

[iwire]

In my opinion there is no relief of the electrode requirements for a temporary SDS

You will have to provide something.

There are no limitations regarding the distance you can run it.

IMO it will become a choice between cost of the GEC vs the PITA factor of driving a rod.

 

[bphgravity]

There is really no such thing as "bad ground". Systems are either grounded or thear are not grounded. The "quality" of the ground is of little significance. Follow the general rules for grounding a separately derived system SDS, and you will be all set.

 

[zbang]

I don't think you have a choice- wherever you put the transformer, there goes the ground rod (or, at least, reasonably close to there). This is also a check-with-the-AHJ situation; I've see the inspector require a second rod for a temp transformer, but only one for a temp service.

How/how far are you planning on running the HV to the transformer? In many situations, renting a generator is much easier than running multihundred feet of 480v feeder.

BTW, 75kva is not very large for lighting/production loads; 150kva is only maybe mid-sized .

 

[iwire]

I don't think you have a choice- wherever you put the transformer, there goes the ground rod (or, at least, reasonably close to there).

There is no NEC limit to the length of the GEC or how far a ground rod can be placed from an SDS if building steel is unavailable.

If I wire a 5 story brick and wood building, the GEC from an SDS on the fifth floor will run to the basement.

This is also a check-with-the-AHJ situation;

It should not have to be.

I've see the inspector require a second rod for a temp transformer, but only one for a temp service.

Both require two rods if you can not prove 25 ohms or less.

 

[zbang]

There is no NEC limit to the length of the GEC or how far a ground rod can be placed from an SDS if building steel is unavailable.

The original question was:
Do I need to keep the Grounding Electrode next to the transformer, or how would it effect the Ground if it is ran with the Main feed from the building.

There may not be a limit, however I could easily see being required to use the closest available dirt, not the dirt 100+' away (in a five story building, all the dirt is a long way off). Code or not, these things happen. (I've also seen an inspector require conduit for listed entertainment feeder cable, which is normally just laid on the ground.)

Re multiple rods:

Both require two rods if you can not prove 25 ohms or less.

My comment is directly from the situation where there was a temp 100a 120/208 service installed next to a temp 100kva stepdown transformer. The inspector required the transformer to have two rods, but only one for the service (same dirt, same 8'+ rods). Both were installed by the public works dept of the city.

The reality of it is that many inspectors don't have experience with temporary power outside of construction sites. When they run into a street fair, music festival, carnival, film shoot, etc, the lazy ones often start to make things up. (I have nothing but praise for the ones that don't have the experience but are willing to ask "is it safe?" before making arbitrary decisions.)

As always, Your Mileage May Vary.

 

[iwire]

The original question was:
Do I need to keep the Grounding Electrode next to the transformer, or how would it effect the Ground if it is ran with the Main feed from the building.

There may not be a limit, however I could easily see being required to use the closest available dirt, not the dirt 100+' away (in a five story building, all the dirt is a long way off).

There is no NEC limit, it can not be required without a local amendment.

Code or not, these things happen.

What things?

Inspectors requiring more than the code requires?

The answer is there is no NEC requirement.

If the OP does not know the actual NEC requirements they have no chance of disputing an inspectors wishes if they so choose.

You know what they say....knowledge is power.

(I've also seen an inspector require conduit for listed entertainment feeder cable, which is normally just laid on the ground.)

Kind of odd to say the least, perhaps if the person running the cable pointed out 525.53(L) (2002) to the inspector they could have avoided the conduit.

The reality of it is that many inspectors don't have experience with temporary power outside of construction sites. When they run into a street fair, music festival, carnival, film shoot, etc, the lazy ones often start to make things up.

Yes inspectors can make mistakes, sometimes more than a mistake.

The answer is not to simply give up and take it, the answer IMO is to learn the actual rules and discuss them with the inspector.