MX4428 MXP Engineering / Technical Manual Document: LT0273
Device Information and Programming
Page 3-8 24 March 2006 Issue 1.5
It is recommended that the PC program F4000CAL is used for conducting the loop loading
calculations. However note that it does not include the isolator base loading, this must be
done manually.
3.2.2 DC LOAD
The total current available from the MX Loop terminals on the MXP is 400mA DC.
This must supply operating current to all addressable devices an the loop. This not only
includes the quiescent current required to power the device electronics, but also the
additional current drawn by devices in the ALARM state or by associated ALARM LEDs and
other loop powered outputs.
The sum of currents for all devices connected to the loop is calculated using the “alarm
current” values shown in
Table 3-2. Note –
1) The MXP limits the number of Alarm LEDs turned on at any one time to 5
(programmable at MX4428).
2) Remote LEDs must be allowed for at 7mA each. Remote LEDs programmed to follow
the detector LED will be limited by the number of alarm LEDs. However remote LEDs
programmed to operate on “Circuit Alarm” or “Relay” will not be limited in any way.
3) LEDs on relay output devices (SNM800, RIM800, LPS800) will operate when the
relay is activated, if the MXP is configured at the MX4428 to flash the LED on Poll
“Global Blink Mode”.
4) The 814RB, RIM800 and SNM800 relay load current must not be supplied from the
analogue loop.
The sum of all currents must not exceed 400mA.
Furthermore, the voltage drop in the cable must not exceed 16.0V, regardless of which end
of the loop the cable is driven from. This is in order to ensure that with the minimum 36V
voltage available from the MX Loop terminals on the MXP, the minimum voltage at any
device will be at least 20V.
If you have any LPS800 devices on the loop, you may need to design for a higher minimum
loop voltage and a lower voltage drop. Refer to section
3.23.2.
3.2.3 AC LOADING
Calculate the total of the “AC Units” shown in Table 3-2. The total must not exceed 250.
Also ensure that the cable length does not exceed the values in
Table 3-3.
Cable type Cable length
MICC 2L1.5, 2L2.5, 1H1.5, 2H2.5 1.8 km*
Steel Wire Armour (SWA) 1.8 km*
Fire resistant ‘foil and drain wire’, e.g.
Radox FR3013, FP200, Lifeline, Firetuff
2 km
BS6883 marine cable 2 km
Table 3-3 Maximum Cable Lengths
* Up to 2km of these cable types may be used on condition that the maximum AC loading is
restricted to less than 220 AC units per loop.
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