[Top] [All Lists]

Re: [TowerTalk] Fwd: shack wiring

To: "" <>
Subject: Re: [TowerTalk] Fwd: shack wiring
From: Grant Saviers <>
Date: Mon, 02 Aug 2010 10:16:08 -0700
List-post: <">>
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.


TowerTalk mailing list

<Prev in Thread] Current Thread [Next in Thread>