DSC MX920 Line Isolator - Install Guide - R002

*29011140R002*
MX920 MX Digital Loop Line Isolator
Module Installation Guide
29011140R002 2
MX920 MX Digital Loop Line Isolator Module Installation Guide Safety Note
Note:
Read the safety information before you install the equipment. This equipment must
be installed by a skilled person only. A skilled person is an installer with appropriate technical
training. The installer must be aware of potential hazards during installation and measures
available to minimize risks to the installer and other people.
Introduction
The MX920 Line Isolator Module is designed to be used on MX addressable controller loop circuits.
The module monitors the line condition. If it detects a short circuit, it will isolate the affected section
while allowing the rest of the addressing circuit to function normally. The module ensures that on a
looped addressable system, no short circuit fault can disable more detection devices than would be
lost on a conventional non-addressable fire/burg circuit.
Mechanical Specification
Table 1:
MX920 overall dimensions:
Height:: 87mm
Width: 148mm
Depth: 14mm
Weight: 100g
Figure 1:
MX920 Fitted to Cover
REV
10
20
30
40
50
60
70
REV
1
2
3
4
5
6
7
LIM800 PCB
125.165. 455. ISS A
ASSY 125.585.931
TB6
L+
L-
S+
S-
R+
R-
LED2
Environmental Specifications
•
Operating temperature: 32°F to 120°F (0°C to 49°C)
•
Humidity: up to 93% relative humidity at 90°F (32°C)
Electrical Characteristics
•
Addressable circuit voltage: 40VDC max with addressable waveform (polarity conscious)
•
Max series resistance (isolator normal): 0.25 ohm
• Equivalent Capacitance: 0.5nF (0.25 ac units)
•
Maximum wiring resistance monitored circuit: 10 ohm.
•
Use a 10K resistance for ground fault testing.
•
Current loading: Input current 90μA max (normal)
•
Isolator Tripped: 6mA into zone (10mA into isolator), 16mA total
3
MX920 MX Digital Loop Line Isolator Module Installation Guide •
All wiring is supervised and power-limited
Mechanical Construction
The MX920 is contained in a double sided Printed Circuit Board (PCB) which is fitted into a custom-
built fascia plate designed to be mounted onto a standard dual-gang MK box (refer to Figure 2).
The MX920 can be ordered already fitted onto the fascia plate. The MK box is surface mounted.
Suitable holes must be drilled into the box for the electrical connection. A cable gland is required
for MICC cable and conduit use. The PCB is mounted on the back of the fascia plate with a
protective plastic cover being fitted over the PCB leaving only the connection terminals exposed.
The PCB is fitted with a yellow LED which extends through the front of the fascia plate and provides
indication of unit operation.
Figure 2: Fascia Plate and Dimensions
148
87
14
Operation
The switches on the MX920 are normally closed. If a short circuit is detected on the spur circuit,
both switches open. If a short circuit is detected on the left hand side, the left hand side switch
opens. And if a short circuit is detected on the right hand side, the right hand side switch opens.
Figure 3:
MX920 Operation
L+
R+
S+
S-
L-
R-
Cabling and Wiring
One pair of terminals is used to provide a spur circuit (S+/S-) and two pairs of connection terminals
(R+/R- and L+/L-) are provided on the terminal block. These terminals are used for connecting the
MX920 MX Digital Loop Line Isolator Module Installation Guide
4 module to the HSM3105 MX Loop Card. Refer to the HSM3105 MX Loop Card Manual for loop circuit
ratings. Only one cable (max 2.5mm
2
) can be connected at any one terminal.
1.
There are no user-required settings (such as switches or headers) on the MX920.
2.
All conductors to be free of contacts to earth.
3.
Connect loop wiring. For MX920 typical wiring configurations refer to Figure 4.
4.
Verify the correct polarity of the wiring before connecting the MX920 to the addressable loop
circuit.
Figure 4: MX920 Wiring
R
L
L
1
L
2
R
L
L
1
L
2
TB6
L+
S+
S-
R+
R-
L-
LED2
REV
10
20
30
40
50
60
70
REV
1
2
3
4
5
6
7
LIM800 PCB
125.165. 455. ISS A
ASSY 125.585.931
+
-
FOR SPUR
CIRCUIT
REMOTE
INDICATOR
MX DIGITAL
LOOP CARD
OR PREVIOUS
DEVICE
TO NEXT
DEVICE OR
MX DIGITAL
LOOP CARD
Loop Wiring Verification
Note:
Do not merger loop wiring when the isolator lines modules are connected.
The MX920 is not designed to work with line voltages above the specified maximum 40VDC, which
means that continuity testing of the loop wiring when MX920s isolators are connected must be
done using a voltage between 20-40VDC. The resistance measurement range on conventional
voltmeters use low voltage only. Therefore, to confirm wiring you must connect a power supply
capable of providing 30 - 40VDC with a 300 to 600mA current limit to one end of the loop (in correct
polarity) and connect a voltmeter to the other end of the loop or any base along the loop. If there is
no voltage out at any measured point, this may be due to:
1.
Loop open circuit - wiring incomplete in part of the loop.
2.
Incorrect polarity - MX920 will appear as a short circuit.
3.
Loop short circuit - If this occurs between two MX920, it will isolate that section of the line,
which will then appear as an open circuit. If this occurs between the supply and the first
MX920, the supply output will go low due to the internal current limit.
The MX920 serves as a protection device against short circuits. It operates by isolating the section
of line containing the short circuit from devices on the line and from the rest of the line (refer to
Figure 3). Optimum operation requires the line to be wired as a loop so that a section of the line
with a short circuit can be isolated between a pair of isolator modules. A short circuit on the spur
connections will also cause the MX920 to open circuit the loop at that point. The current can pass in
both directions in order to enable the isolator's use in a looped circuit (Line IN to Line OUT or Line
5
MX920 MX Digital Loop Line Isolator Module Installation Guide OUT to Line IN). The operation of the MX loop driver means that there are effectively 2 operational
modes for the MX920.
1.
When the loop is first powered, if a section of the line appears as a low impedance (with an
equivalent resistance of less than 2k), the line isolator will restrict the power to that section of
line until the fault is cleared.
2.
If a short circuit is introduced onto the line when the loop is powered up, in most instances
the controller’s internal protection will switch in before the line isolator. The voltage is then
removed from the line by the controller, on restoration, the line isolator will isolate the low
impedance section of the line. In addition, the MX920 also isolates if the loop voltage is
degraded by a partial short circuit.
Note:
When a short circuit is detected, the LED lights up.
Ordering Information
Table 2:
Ordering Information
Components
Number
Line Isolator Module
MX920
FCC and ISED Canada Information
This information applies to the MX920 MX Digital Loop Line Isolator Module.
Modification statement
Tyco Safety Products Canada Ltd. has not approved any changes or modifications to this device by
the user. Any changes or modifications could void the user’s authority to operate the equipment.
Interference statement
This device complies with Part 15 of the FCC rules. Operations are subject to the following two
conditions: (1) This device may not cause harmful interference and (2) This device must accept any
interference received, including interference that may cause undesired operation.
This equipment has been tested and found to comply with the limits for a Class B digital device,
pursuant to Part 15 of the FCC Rules. These limits are designed to provide reasonable protection
against harmful interference in a residential installation. This equipment generates, uses and can
radiate radio frequency energy and, if not installed and used in accordance with the instructions,
may cause harmful interference to radio communications. However, there is no guarantee that
interference will not occur in a particular installation. If this equipment does cause harmful
interference to radio or television reception, which can be deter-mined by turning the equipment
off and on, the user is encouraged to try to correct the interference by one or more of the following
measures:
•
Re-orient the receiving antenna.
•
Increase the separation between the equipment and receiver.
•
Connect the equipment into an outlet on a circuit different from that to which the receiver is
connected.
•
Consult the dealer or an experienced radio/television technician for help.
MX920 MX Digital Loop Line Isolator Module Installation Guide
6 The user may find the following booklet prepared by the FCC useful: "How to Identify and Resolve

Radio/Television Interference Problems". This booklet is available from the U.S. Government

Printing Office, Washington D.C. 20402, Stock # 004-000-00345-4.
CAN ICES-3 (B)/NMB-3(B)
Trademark
The trademarks, logos, and service marks displayed on this document are registered in the

United States [or other countries]. Any misuse of the trademarks is strictly prohibited and Tyco

will aggressively enforce its intellectual property rights to the fullest extent of the law, including

pursuit of criminal prosecution wherever necessary. All trademarks not owned by Tyco are the

property of their respective owners, and are used with permission or allowed under applicable

laws. Product offerings and specifications are subject to change without notice. Actual products

may vary from photos. Not all products include all features. Availability varies by region; contact

your sales representative.
© 2022 Johnson Controls. All rights reserved. JOHNSON CONTROLS, TYCO and DSC are trademarks

of Johnson Controls. Toronto, Canada ∙ www.dsc.com Tech support: 1-
800-387
-3630 (Canada and
U.S),

or 1-905-760-3000 (International)
7
MX920 MX Digital Loop Line Isolator Module Installation Guide MX920 MX Digital Loop Line Isolator Module Installation Guide