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Pub. 42004-195F
GAI-TRONICS
®
CORPORATION
A HUBBELL COMPANY
Model 491-204
Mine Dial/Page Telephone
Confidentiality Notice
This manual is provided solely as an installation, operation, and maintenance guide, which contains
sensitive business and technical information, that is confidential and proprietary to GAI-Tronics.
GAI-Tronics retains all intellectual property and other rights in or to the information contained herein,
and such information may only be used in connection with the operation of your GAI-Tronics product or
system. This manual may not be disclosed in any form, in whole or in part, directly or indirectly, to any
third party.
General Information
The GAI-Tronics Mine Dial/Page Telephone system combines the convenience of a telephone station
with paging capabilities in gaseous or dusty locations that are too hazardous for standard telephone
equipment. The system is rated as “permissible” for use in gassy coal mines by the Mine Safety and
Health Administration (MSHA) of the United States Department of the Labor (Approval Number 9B221).
The system is used in conjunction with a touch-tone (also known as dual-tone multi-frequency [DTMF])
operated public telephone exchange or a private branch exchange (PBX). Each station in the system is
made up of two components:

Mine Dial/Page Telephone

Interface assembly mounted outside the hazardous area
The interface assembly is electrically connected between the station and the telephone switchboard. Each
interface assembly is connected to a separate line of the telephone exchange.
GAI-Tronics Corporation 400 E. Wyomissing Ave. Mohnton, PA 19540 USA
610-777-1374  800-492-1212  Fax: 610-796-5954
VISIT WWW.GAI-TRONICS.COM FOR PRODUCT LITERATURE AND MANUALS
Model 491-204 Mine Dial/Page Telephone
Pub. 42004-195F
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Features
The GAI-Tronics Model 491-204 Mine Dial/Page Telephone system is designed as an alternative to the
mine pager system and other communication systems (such as the “Pager” or “Loud-Speaking
Telephone”) that lack privacy and multiple conversation capabilities. The GAI-Tronics Mine Dial/Page
Telephone system includes the following features:

Each station has a separate line. The number of independent, simultaneous conversations is limited
only by the number of stations and the capacity of the PBX.

Stations inside the hazardous area can call any telephone outside the area, as well as any other Mine
Dial/Page Telephone station within the area.

Automatic circuits in the Mine Dial/Page Telephone “answer” incoming calls and permit the calling
party to page the desired person using a self-contained horn-type loudspeaker. This voice page is
preceded by a distinctive tone and is accompanied by a flashing light to assist in locating the
telephone in dark areas. The flashing light also gives visual notice of the call in high-noise areas.
The flashing light complies with Virginia and West Virginia MSHA regulations.

A person initiating a call can page someone at a specific location without disturbing personnel at
other locations.

The All-Call function pages all of the stations simultaneously while also reaching those stations using
the system for normal conversations.

The push button controlled, all-station page operation is activated automatically in the event of a
telephone switchboard failure.
A single pair of wires connects each Mine Dial/Page Telephone to the interface assembly. Each interface
is connected to the telephone switchboard with another corresponding pair of wires.
A person using a Mine Dial/Page Telephone station can access any station or any conventional telephone
connected to that switchboard. If the switchboard is tied into the public telephone system, an individual
can call out or receive calls from any public telephone.
Personnel in hazardous areas have direct contact to all non-hazardous areas with extension telephones
without the purchase of additional communications equipment for these non-hazardous areas.
In keeping with MSHA regulations, each interface cabinet must have at least one GAI-Tronics Model
491-204 Mine Dial/Page Telephone Station installed outside of the coal mine.
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Model 491-204 Mine Dial/Page Telephone
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Equipment Description
The GAI-Tronics Mine Dial/Page Telephone system can be configured to meet individual customer
needs. A single interface cabinet can support up to 80 Model 69001 Mine Dial/Page Telephone Station
Line Interface Cards within the Model 495-001 Mine Dial/Page Telephone Interface Cabinet. See Figure
1 for a typical system configuration and guidelines on cabling. Refer to Pub. 42004-198 for installation
and cabling of the Model 495-001 Interface Cabinet.
Figure 1. Typical System Configuration
The Model 491-204 Mine Dial/Page Telephone is contained within a corrosion-resistant, non-metallic
enclosure measuring approximately 13 H × 10 W × 7 D inches (330  254  178 mm), not including the
handset. The handset is located in a cradle mounted to the top of the enclosure. This cradle doubles as a
carrying handle.
The mounting and overall dimensions of the Model 491-204 Mine Dial/Page Telephone are shown in
Figure 2. This figure details many features of these stations such as the horn-loaded loudspeaker,
telephone keypad, emergency page push button, weatherproof seals, and stainless steel hardware.
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Model 491-204 Mine Dial/Page Telephone
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Figure 2. Mounting and Overall Dimensions of Model 491-204
A pressbar switch is built into the handset and must be pressed whenever the station is in use—both
talking and listening. This control replaces the conventional hang-up hookswitch, eliminating the
possibility of a user leaving the station off-hook and thereby unable to receive pages.
Most of the electronic circuitry is located on a single plug-in PCBA, GAI-Tronics Model 69491-401,
inside the Model 491-204 Station. The circuitry associated with the keypad and sidetone adjustment is
located on a small PCBA behind the keypad (Model 69491-002). All these circuits operate from a single
12 V NEDA 926 lantern battery also contained within the station. These internal components are shown
in Figure 3.
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Model 491-204 Mine Dial/Page Telephone
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Figure 3. Internal Components
For each Mine Dial/Page Telephone station, a GAI-Tronics Model 69001-001 Interface PCBA must be
used. This assembly is a plug-in printed circuit board measuring approximately 7.5 H × 4.5 W inches
(190.5 × 114 mm) and must be mounted in a non-hazardous area within a Model 495-001 Mine Dial/Page
Telephone Interface Cabinet.
Installation
Mount the Model 491-204 Mine Dial Telephone Station in a location where the handset can be reached
and where it is sufficiently visible. Four holes are provided for mounting to a wall or panel.
Wiring Connections
Connect the Model 491-204 Mine/Dial/Page Telephone to the card rack in the interface assembly as
follows:
1. Connect the L1 wire from the interface cabinet’s card rack to the telephone’s wide or silver-colored
terminal on the twist-lock plug.
2. Connect the L2 wire from the interface cabinet’s card rack to the narrow or gold-colored terminal. A
rubber boot with a twist-lock connector mates with the connector on the station. This boot is installed
to form a seal to the station enclosure.
While each underground station will have a telephone extension number, that number is associated with
the line rather than the actual station.
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Model 491-204 Mine Dial/Page Telephone
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For Example: If two separately connected stations at locations A and B are interchanged, the unit brought
from location B to location A will respond to the same telephone extension number as the original unit at
location A. Therefore, the telephone extension number should be marked at the location and not on the
unit.
Battery Installation
A NEDA 926 Battery (12 V) must be installed in the enclosure to maintain the unit’s MSHA intrinsic
safety rating. To install the battery, remove the battery hold-down bracket.
1. Connect the battery’s red wire to the positive terminal, and the green wire to the negative terminal.
2. Two brackets on the station are positioned so that the battery can only be installed in one direction.
The bracket terminal posts must be loosened to install the battery. When the battery is installed,
remember to re-tighten these posts.
3. Finally, reinstall the battery hold-down bracket.
Operating Instructions
Answering Incoming Calls
1. Wait until the “birdie” call stops, and allow the calling party sufficient time to announce the desired
person’s name.
2. Lift the handset from the cradle, and press the handset pressbar. Reply to the calling party. Do not
release the pressbar at any time during conversation, or the conversation will be terminated.
3. Release the pressbar to terminate the call. Return the handset to the cradle.
Initiating Calls
Calling Another Mine Dial/Page Telephone Station:
1. Press and hold the handset pressbar while listening for a dial tone.
2. Dial the desired telephone number.
3. Wait until the “birdie” signal stops, then page the desired person(s).
4. If no one answers after 30 seconds, terminate the call (the called person’s telephone connection returns
to ready condition after 30 seconds).
5. Release the handset pressbar to terminate the call.
Paging All Mine Dial/Page Telephone Stations (All-Call):
1. Press and hold the handset pressbar while listening for a dial tone.
2. Dial the special (PBX) page number.
3. Immediately page the desired person(s), giving the message and call-back instructions (the paged
person cannot answer directly).
4. Release the handset pressbar immediately.
5. Wait for the return call.
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Calling a Standard Telephone Station:
1. Press and hold the handset pressbar while listening for a dial tone.
2. Dial the desired telephone number.
3. Wait until the called person answers, then talk.
4. Release the handset pressbar to terminate the call.
Merge Mode
The system automatically transfers to this mode in the event of a switchboard failure.
1. Press and hold the handset pressbar; no dial tone will be heard.
2. Push and hold the EMERGENCY PAGE button.
3. Page the desired person(s).
4. Release the button, and wait for an answer.
NOTE: Conversations are NOT private; any number of persons may use the party line simultaneously in
the same conversation.
5. Release the handset pressbar to terminate the call.
Flashing Page-Indicator Light
Automatic circuits “answer” incoming calls and permit the calling party to page the desired person using
a self-contained horn-type loudspeaker. This voice page is preceded by a distinctive tone and is
accompanied by a flashing light to assist in locating the telephone in dark areas. The flashing light also
gives visual notice of the call in high-noise areas. The flashing light complies with Virginia and West
Virginia MSHA regulations.
The flashing light circuitry connects to the mine dial/page telephone circuitry at only four points—the two
battery binding-posts and the two loudspeaker connections. The audio signal at the speaker does not
control the light. The dc level on both loudspeaker lines, with respect to the positive battery terminal,
controls the light.
Specifications
Line voltage ........................................................................................................................................12 V dc
Supervisory current ........................................................................................................ 20 mA dc maximum
Audio impedance, input ......................................................................................................... 200 Ω, nominal
External controls (2) .............. Push-to-operate switch (in handset)/Emergency Page push button (on panel)
Internal controls (2)........................................................... Speaker volume adjustment, sidetone adjustment
Microphone ............................................................................................................Dynamic, noise-canceling
Speaker........................................................................................................................ Dynamic, horn-loaded
Power supply............................................................................................... Internal dry cell battery, 12 V dc
Page-indicator Lamp (optional) ........................................................ 66 flashes per minute, 6.6% duty cycle
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Model 491-204 Mine Dial/Page Telephone
The table below defines the cable size with cable characteristics necessary to achieve increased operating
distance and is dependant upon the type and quality of the cable utilized, optimum cable line installation,
and PBX.
Table 1. Typical Cable Characteristics
Capacitance
(conductor to conductor)
Maximum
Cable Length
Maximum 0.20
µH/foot
Maximum 35 pF/foot
15,750 feet
(~3 miles)
7.1 ohms per
1000 feet
Maximum 0.20
µH/foot
Maximum 35 pF/foot
31,500 feet
(~6 miles)
2.8 ohms per
1000 feet
Maximum 0.20
µH/foot
Maximum 35 pF/foot
63,000 feet
(~12 miles)
Cable Size
DC Resistance
Inductance
No. 22 AWG
16.5 ohms per
1000 feet
No. 18 AWG
No. 14 AWG
Replacement Parts
Part Number
Description
10415-101
Handset Assembly
12502-101
Replacement Receiver Kit
12504-012
Keypad Replacement Kit—Model 491-204
12506-003
Speaker Replacement Kit
12567-001
Page Switch
61507-009
Harness Assembly/Subset
69491-002
Keypad Amplifier PCBA
69491-401
Speaker Amplifier PCBA
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Warranty
Equipment.
GAI-Tronics warrants for a period of one (1) year from the date of shipment, that any
GAI-Tronics equipment supplied hereunder shall be free of defects in material and workmanship, shall
comply with the then-current product specifications and product literature, and if applicable, shall be fit
for the purpose specified in the agreed-upon quotation or proposal document. If (a) Seller’s goods prove
to be defective in workmanship and/or material under normal and proper usage, or unfit for the purpose
specified and agreed upon, and (b) Buyer’s claim is made within the warranty period set forth above,
Buyer may return such goods to GAI-Tronics’ nearest depot repair facility, freight prepaid, at which time
they will be repaired or replaced, at Seller’s option, without charge to Buyer. Repair or replacement shall
be Buyer’s sole and exclusive remedy. The warranty period on any repaired or replacement equipment
shall be the greater of the ninety (90) day repair warranty or one (1) year from the date the original
equipment was shipped. In no event shall GAI-Tronics warranty obligations with respect to equipment
exceed 100% of the total cost of the equipment supplied hereunder. Buyer may also be entitled to the
manufacturer’s warranty on any third-party goods supplied by GAI-Tronics hereunder. The applicability
of any such third-party warranty will be determined by GAI-Tronics.
Services.
Any services GAI-Tronics provides hereunder, whether directly or through subcontractors,
shall be performed in accordance with the standard of care with which such services are normally
provided in the industry. If the services fail to meet the applicable industry standard, GAI-Tronics will
re-perform such services at no cost to buyer to correct said deficiency to Company's satisfaction provided
any and all issues are identified prior to the demobilization of the Contractor’s personnel from the work
site. Re-performance of services shall be Buyer’s sole and exclusive remedy, and in no event shall GAITronics warranty obligations with respect to services exceed 100% of the total cost of the services
provided hereunder.
Warranty Periods.
Every claim by Buyer alleging a defect in the goods and/or services provided
hereunder shall be deemed waived unless such claim is made in writing within the applicable warranty
periods as set forth above. Provided, however, that if the defect complained of is latent and not
discoverable within the above warranty periods, every claim arising on account of such latent defect shall
be deemed waived unless it is made in writing within a reasonable time after such latent defect is or
should have been discovered by Buyer.
Limitations / Exclusions.
The warranties herein shall not apply to, and GAI-Tronics shall not be
responsible for, any damage to the goods or failure of the services supplied hereunder, to the extent
caused by Buyer’s neglect, failure to follow operational and maintenance procedures provided with the
equipment, or the use of technicians not specifically authorized by GAI-Tronics to maintain or service the
equipment. THE WARRANTIES AND REMEDIES CONTAINED HEREIN ARE IN LIEU OF AND
EXCLUDE ALL OTHER WARRANTIES AND REMEDIES, WHETHER EXPRESS OR IMPLIED BY
OPERATION OF LAW OR OTHERWISE, INCLUDING ANY WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Return Policy
If the equipment requires service, contact your Regional Service Center for a return authorization number
(RA#). Equipment should be shipped prepaid to GAI-Tronics with a return authorization number and a
purchase order number. If the equipment is under warranty, repairs or a replacement will be made in
accordance with the warranty policy set forth above. Please include a written explanation of all defects to
assist our technicians in their troubleshooting efforts.
Call 800-492-1212 (inside the USA) or 610-777-1374 (outside the USA) for help identifying the
Regional Service Center closest to you.
(Rev. 10/06)
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