The MGN system isn't used in my neighborhood (Santa Clara County, CA).
The poles and undergrounds are 3p delta so each pole pig hangs across
one pair of the three wires. Local ground is the center-tap of the
secondary. This avoids the MGN fault current/voltage to ground problem
and thus seems a better way to go from that perspective but causes a
problem if one phase is lost (happens much more than it should).
Connected loads feed back into the faulted phase at some indeterminate
voltage (40 to 80 volts measured). One thing we've learned is to have
phase fault/reversal detectors on all 3p motors not monitored (eg pumps,
wells, HVAC, etc.) so they don't try to start. We actually had a phase
reversal once after an outage - how did they do that??
In my inspections of several commercial buildings in SiVly, most all had
PG&E provided 3p delta 240 or 480v at the service entrance and a local
transformers were used for 208/120 wye distribution to lighting and
utility outlets and service entrance direct to a separate panel for
240/480 delta for machinery. One older building had "stinger" phase
which split one phase of 240 delta and grounded the center tap to
produce 120/240 but the power company hates these because they load up
one phase and unbalance the distribution system.
PG&E wanted $35k to run the third wire (2 poles away) and put in a 3p
transformer for my ranch, so I make my own with a 40hp rotary converter
at 1/10 that quote. Works fine.
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