JBD mentions the key point of the whole thread, which I should have addressed directly - yet once again I pulled a complete "Homer Simpson"...
and thus, let this be said:
"D'ohh!!!"
![[Linked Image]](https://www.electrical-contractor.net/ubb/eek.gif)
To elaborate more on the topic of L-G Voltage testing, via Medium and High input Impedance Meters; vs. Ungrounded AC Systems (Ungrounded Deltas, to be exact!), here are readings from two different Projects containing 480 VAC 3Ø 3 Wire Ungrounded Delta Systems, derived from PoCo Transformers.
Tests from L-G using three types of Meters:
<OL TYPE=A>
[*] 1 DMM with a "Medium" input Impedance / "Sort-Of Low" Loading Effect,
[*] 1 DMM with a "Higher" input Impedance / "Much Lower" Loading Effect,
[*] 1 Voltmeter with a Low input Impedance / High Loading Effect... a "Wiggy": the typical General Purpose Solenoid type Voltage Tester.
</OL>
Project location #1:Existing Building.
600 Amp, 480 VAC Service.
Apx. 100 Amp load total (Phase "A" around 90 Amps, "B" around 100 Amps, "C" around 95 Amps).
Apx. 200 Feet from Utility Transformers to Service Equipment (Apx. Feeder Length).
Tests taken at the Service Equipment / MDP between L-G (Grounded Metallic Enclosure).
Using Meter "A":
ØA to G: 245 VAC,
ØB to G: 260 VAC,
ØC to G: 230 VAC.
Using Meter "B":
ØA to G: 300 VAC,
ØB to G: 350 VAC,
ØC to G: 320 VAC.
Using Meter "C":
ØA to G: 0 VAC,
ØB to G: 0 VAC,
ØC to G: 0 VAC.
Project location #2:Existing Building.
400 Amp, 480 VAC Service.
Apx. 150 Amp load total (Phase "A" around 120 Amps, "B" around 100 Amps, "C" around 150 Amps).
Apx. 80 Feet from Utility Transformers to Service Equipment (Apx. Feeder Length).
Tests taken at the Service Equipment / MDP between L-G (Grounded Metallic Enclosure).
Using Meter "A":
ØA to G: 170 VAC,
ØB to G: 160 VAC,
ØC to G: 200 VAC.
Using Meter "B":
ØA to G: 375 VAC,
ØB to G: 400 VAC,
ØC to G: 450 VAC.
Using Meter "C":
ØA to G: 0 VAC,
ØB to G: 0 VAC,
ØC to G: 0 VAC.
BTW: I also "Clamped" the DMMs with the Wiggy for another test on each system, and brought the Voltage Readings down to near zero.
"Clamped" meaning connect the leads in Parallel during tests.
Each "Wiggy" test resulted in the "Typical Capacitor Discharge" reaction (transient reading of no more than 100 ms, then no solenoid or neon lamp reaction).
Lastly, I do not remember exact values recorded at the time of the tests (this was done several years back, and those papers have since been archived somewhere!), but the listed values above are "kind of" close to what was recorded AFAIR
(As Far As I Remember!)
![[Linked Image]](https://www.electrical-contractor.net/ubb/wink.gif)
Anyhow, that's my 2¢ contribution!
Scott35