by John E. Galetzka(last update 04JAN2001)
by John E. Galetzka
(last update 04JAN2001)
Introduction
The advent of the Santa Ana Winds and the first rainstorm of the 96/97 wet season led to power
outages across the region. At several continuous GPS stations we had an annoying
phenomenon occuring: ground fault interrupter (GFI) receptacles, which feed power to the
station, kept tripping or "breaking circuit". This phenomenon occured at
stations which contained a surge suppressor (used to prevent power spikes and surges from
reaching the GPS receiver) plugged into a GFI (installed by us at our exterior equipment
enclosures to provide safe power to maintenance people). A solution was achieved after
reviewing station maintenance logs, comparing problem stations with healthy stations, and
talking to electrical specialist at LA County Public Works and Allied Signal. This problem
was probably related to frequent eletrical problems we had at our Table Mountain, CA
station (TABL) this summer.
This document is designed to inform the GPS community how to recognize and solve problems of using GFIs and surge suppressors at continuous GPS sites.
Symptoms RESET button on GFI trips, causing a circuit break. Station fails to respond via telephone connection--no AC or DC power to receiver or modem. Area power outages or "dirty" power supply (power service with frequent surges and splikes).
Cause
AC Power was supplied to the equipment enclosure (ie. NEMA box) through a GFI outlet. A
surge suppressor (rated to handle 1200 joule spikes) was plugged into the GFI outlet,
followed by the GPS receiver, modem and battery charger plugged into the surge suppressor.
Apparently a power surge or spike would come through the GFI and get shunted to ground by the surge suppressor. The GFI would probably see this as a current leakage and break the circuit. The only way to reset the GFI is to physically go to site and push the RESET button, which could be a very coslty trip if the station is a distant one! There are better ways...
Solutions Wire a four-receptacle outlet to be GFI protected on two receptacles, and unprotected on the other two. Plug the surge suppressor into the non-GFI protected side. This configuration provides safe power for people to plug into on the GFI protected outlet, but does not protect people from faulty electrical devices downline of the non-GFI protected receptacles. ORRemove the GFI and replace with a normal outlet. Plug the surge suppressor into the outlet. Plug a plug-in GFI into the surge suppressor, then plug your power supply into that. This should protect maintenance people when they work on any electrical device down line of the GFI without tirggering the GFI. A one-receptacle plug-in GFI costs around $15; a three-receptacle costs around $30. OR Choose not to use a GFI at all (this is the decision we made...no injuries to report!)
This report is preliminary and has not been reviewed for conformity with U. S.
Geological Survey editorial standards. Any use of trade, product, or firm names is for
descriptive use only and does not imply endorsement by the U. S. Government.
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