Hi Paul, Welcome back!!! [Linked Image]

In regards to the Delta thingee, the major concern was as you stated - some one mistakingly setting up an L-N circuit between the high voltage to ground line and the grounded center tap [AKA "Neutral"], with the intentions of driving a 120 VAC load.

This will result in two things:

<OL TYPE=1>

[*] 208 VAC impressed upon the load,
and

[*] Smoke leaving said load.
</OL>
<Just wanted to add some humor! [Linked Image]>

Anyhow, there are still many 4 wire Deltas in our area [I live near Scott "Electure"]. They can mostly be found in the older Commercial / Industrial areas, along with the areas zoned with Residential and Commercial / Industrial [again, older areas]. These systems are both flavors of Open and Closed configurations.

Funny thing is that the new company I work for, very few people have heard of - let alone worked on - a 4 wire Delta. I get some weird looks when mentioning them! Even weirder when I show the results of the "Orange Line To Ground" on my Wiggy.
P.S. a "Wiggy" is a Solenoid / Neon lamp type voltage tester which is usable from 120 to 600 Volts - AC or DC. They are the most common volt meters in the field. They have low accuracy [208 falls above the "240 VAC" markings!] and have a low input Impedance - which makes them useful as GFCI testers and when you run across an ungrounded Delta!

Lastly, my thinking on the 310 VAC [+/-] was that the tester is "Bridging" between two coils [one of 277 VAC potential, one of 120 VAC potential]- creating an Autotransformer / Reactor setup, similar to an HID Ballast.

I have seen readings like this. First was by use of a Wiggy, just to see what the voltage between Lines of 2 different panels [one 480Y277, the other 208Y120], the other[s] were with a DVM. I shunted the leads with a 22K Resistor to lower the input Z.

Felt nice to ramble again! Been really BZ [busy].

I'll be flying to San Fransisco on Monday, to do some surveys - then back to So Ca for a few days of work and colation, then back on Da Plane! again.

Scott S.E.T.

P.S.S. Looks like maybe next thursday our E-Mail address will change.
We are shooting for "stat113" at pac bell dot net. That will be confirmed later... [Linked Image]

Scott

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!