iso transformer and ground

[turls]

I recently installed a 25 kva xformer using it as an iso trans to take 240 to 120/240, deriving a neutral. (This is for a new sound system, which required iso ground receptacles as well, in a church.)
From the existing panel I fed the new xformer with two lines from a 2-pole 100 amp breaker. From the xformer I had the two lines and neutral feeding the new 100 amp panel. The ground came from a copper water pipe, came into the panel and landed it on the ground bar. The neutral was bonded to the same bar. I then took two #4 green with yellow tracer wires from the ground bar up to the isolated (insulated) ground bar.
Another jw had to install one more circuit at a later date, he called my boss saying I dont know what im doing, he then "unbonded" the neutral from ground, and took the ground electrode conductor and connected it straight to the iso ground bar and removed the jumpers connecting the iso ground to the solid ground bar. Now I have 15vac between the neutral and iso ground, and 3 vac between the sg and ig. Which way is correct?

 

[don_resqcapt19]

The neutral is required to be bonded at the transformer or the first OCPD. Note that the grounding electrode conductor to the copper water pipe is required to run back to within 5' of the point where the water pipe enters the building.

 

[GoldDigger]

There is no requirement, though, that the neutral from the secondary be tied directly to the primary/service neutral. They will be connected indirectly through their connection to the common GES.

 

[ActionDave]

I recently installed a 25 kva xformer using it as an iso trans to take 240 to 120/240, deriving a neutral. (This is for a new sound system, which required iso ground receptacles as well, in a church.)
From the existing panel I fed the new xformer with two lines from a 2-pole 100 amp breaker. From the xformer I had the two lines and neutral feeding the new 100 amp panel. The ground came from a copper water pipe, came into the panel and landed it on the ground bar. The neutral was bonded to the same bar. I then took two #4 green with yellow tracer wires from the ground bar up to the isolated (insulated) ground bar.
Another jw had to install one more circuit at a later date, he called my boss saying I dont know what im doing, he then "unbonded" the neutral from ground, and took the ground electrode conductor and connected it straight to the iso ground bar and removed the jumpers connecting the iso ground to the solid ground bar. Now I have 15vac between the neutral and iso ground, and 3 vac between the sg and ig. Which way is correct?

Your original install sounds correct. Bonding the XO in the panel is perfectly acceptable, leaving it floating is not. I would everything back the way it was and make sure to run the GEC back to the first five feet of the water pipe like don_resqcapt19 said.

The other guy sounds like he was trying to achieve an isolated ground but is going about it poorly.

 

[Sparky3141]

250.68 (C) (1) Exception: In industrial, commercial, and institutional buildings or structures, if conditions for maintenance and supervision ensure that only qualified persons service the installation, interior metal water piping located more than 5 ft. from the point of entrance to the building shall be permitted as a bonding conductor to interconnect electrodes that are part of the grounding electrode system, or as a grounding electrode conductor, if the entire length, other than short sections passing perpendicularly through walls, floors, or ceilings, of the interior metal water pipe that is being used for the conductor is exposed.

You might still be able to use your grounding electrode. Depending on length and route it might be worth checking in to.

But the other dude removed your system bonding jumper so you will never clear a ground fault. And solidly (earth) grounded your iso ground bar which effectively isolates the grounding electrode's purpose for being there. The only reason for an isolated ground is to isolate it back to the panel that the circuit came from not to isolate it from clearing a fault. Otherwise, why even install it?

I think it might be beneficial for you 2 to draw it out on paper and look at how you intend to clear ground faults on both grounds. They BOTH have to be bonded to the system via the grounded conductor either at the transformer or at the first OCPD.

 

[SparkyHC]

You were correct...

You were correct...

Another jw had to install one more circuit at a later date, he called my boss saying I dont know what im doing, he then "unbonded" the neutral from ground, and took the ground electrode conductor and connected it straight to the iso ground bar and removed the jumpers connecting the iso ground to the solid ground bar. Now I have 15vac between the neutral and iso ground, and 3 vac between the sg and ig. Which way is correct?

if you have voltage between neutral and ground then, there is no longer a connection from the ground back to the source, so a fault to ground will not clear...this is a hazard, no?
250.30 is the section of the code I think will prove your case.