I went to check out the power to an AC unit that had been blowing fuses repeatedly. Its disconnect had a burnt fuse clip. I also got some nasty voltage readings to ground. 235, 234, and 0. Not good for an ungrounded 240 delta. Rooftop EMT was kicked apart all over the place, and liberal doses of tar had been applied. Lovely
I got the keys from a tenant, and headed for the electrical room.










I was fortunate to find that the circuit I was after was in the C-H board in pic 3.


Now the dilemna would be to find the ground in the system. The only way I can think of is to shut everything off, take voltage readings, and turn services and feeders on one by one until the ground is located, then follow it up the line. I don't think that those old circuit breakers stand a very good chance of turning back on once they're shut off
Any ideas besides the obvious? (Bulldozer, Gas & Match, or maybe just wait for a ground on another phase)


(i forgot a "/")

[This message has been edited by electure (edited 06-16-2006).]

I have not worked on ungrounded delta but I though the normal way was to turn feeders off one at a time till the readings are right than work that feeder back toward the branch circuits.

Of course that assumes you only have one same phase ground.

Bob

Dang, Scott - you sure get some Hellish things to shoot trouble on / Job walk fun!
But this is the "Glamorous Life" of the Project Manager, so we grin and bear it (ugggh!).

Anyhow, you have the right idea on tracing out the Ground Fault(s).
Hunt and Peck away on de-energized Branch Circuits until your Continuity Tester yells "Bingo", then search for the Fault, or Faults
(might need the Mounties to assist on this one, so call for Dudley Do-Right ...)

You will definitely want to isolate the Circuitry from any PoCo Line Side stuff, or anything connected to Customer Owned Transformers (like the one in the second image), as these items may inaccurately show L-G connections.
(if this sounds odd, post a "Whaddaheck???" message for explanations).

Seeing how many older roof top conduit runs are found in an "Accordion Fashion", it's an easy bet that you will find a few Ground Faults up there.

Those Ground Faults on Grounded Systems are really fun - especially when the Equipment Bonding means back to the Panelboard has an "Unintentional Impedance" placed in series (poor connections), and when the OCPDs for Branch Circuitry has an Inverse-Time Trip Characteristic which allows blazing Faults to continue "much too long"

Got to see this a few times, and "Funny" was not the overall general feeling everyone had!
They were quite interesting, though!

So, to sum things up - Ring the Branch Circuitry out until no _Solid_ Ground connections exist (on Circuits which should not have a solid ground connection), then do a "Smoke Test".

BTW, are you sure the system is an Ungrounded Delta?
Although the Ungrounded flavors do exist in a 240 VAC version, I have seen a high majority of the 240 VAC Deltas being Corner Grounded, and nearly all the 480 & 600 Volt Deltas to be Ungrounded.

Just a thought.

Scott35

edited tew git shed of baad speeellinn

[This message has been edited by Scott35 (edited 06-17-2006).]

Ungrounded delta system and NO "Ground indicator lights"???

A.D

Bob, your idea is a good one. If it is shut off until the ground "disappears", it might result in less trouble.

Scott, there's no evidence of intentional grounding at the service. All 3 legs are fused and the conductors are black, red & blue (no white) It might be an even worse chore to correct it if it were a corner grounded delta.
Oh, I don't want to do this

BTW, all that junk in the 2nd pic except for the starter in the center is hot. I didn't touch any of it. 1993 newspaper and pile of beercans in front of it added nice touch.

Double check that it is not a corner grounded delta. Some electricians have been known to fuse the grounded leg, even though it shouldn't be fused.
Alan--

If the phase to phase voltages were OK then it sure appears corner grounded to me. Might not have the corner ground connection in the service equipment. Have seen one where it was done on the utility transformer connections but not in the building.

That's kinda why I thought I'd turn everything off and check the voltage ahead of the service disconnects first

Crikey Scott,
You really struck oil here, mate!.
What a mess from start to finish.

[This message has been edited by Trumpy (edited 06-21-2006).]

One word, "DYNAMITE!!!"
(More power! More power! More power!)

Ian A.

Fuses in the main would tend to indicate an ungrounded system as they are not permitted here in a corner grounded system. We probably all know what an assumption like that can lead to.

I agree with others on double checking what the POCO is supplying. I would call the POCO and ask them to verify that their XFMR is not corner grounded. If it is then you have some more work to do.

Scott, that room you posted pictures of reminds me of one of ours that I was in some time back. I thought they might be the same, but yours is actually messier (I hand't thought it possible).

I'm emailing you 2 or 3 pics of our room - many of the same hazards but slightly less clutter. No 1993 newspaper, or beer cans. This is out in the SF Valley.
Radar










[This message has been edited by electure (edited 07-25-2006).]

Well, it's somewhat better.


.

The ground is on the utility side of the service equipment.

Some derelictrician had gone back and reenergized the abandoned service.....by connecting it up in the CT cabinet (seen in pic1). Meter? What meter?. This reenergized all the abandoned wiring, too.

The Bad part? I only had 2 days approved to fix it, and this place would take much more time to really repair.

The Good part? The building is scheduled for DEMOLITION.

Definate improvement !
From the readings I was sure you had a corner grounded regardless of the fuses in the grounded leg.
Glad you got it straightened out, so they could demolish it.
Alan--

Woo hoo! I was right for once!

Ian (Dynamiter) A.