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Document: LT0273 MX4428 MXP Engineering / Technical Manual
Analog Loop Design Considerations
Issue 1.5 24 March 2006 Page 4-7
ELECTRICAL - Different construction/materials give different
REQUIREMENTS AC characteristics, noise immunity, etc.
(ii) CABLE WEIGHT
(i.e. gauge of wire used)
MECHANICAL- Does the application
REQUIREMENTS specification, or prevailing standards, call for a minimum gauge
(AS1670.1 specifies a minimum of .75mm² standard, for
instance).
ELECTRICAL - What is the minimum gauge wire that can be
REQUIREMENTS used without exceeding the maximum voltage drop for the
number of devices over the required loop length.
The four areas to be considered therefore are
• AC requirements
• DC requirements
• Mechanical requirements
• Noise immunity
4.4 AC REQUIREMENTS
4.4.1 GENERAL
All common types of wiring with a total length of up to 2000m may be used. Refer to section
3.2.3.
4.5 DC CONSIDERATIONS
4.5.1 GENERAL
A maximum voltage drop of 17V is allowed on the cable from the MXP to the most distant
device. This applies both where
• the cable is driven from the “left” end only.
• the cable is driver from the “right” end only.
Refer to the calculations in section
3.2.2.
4.6 MECHANICAL CONSIDERATIONS
Electrical considerations aside, the system design should take into account mechanical
aspects such as .....
• Need for fire rated cable.
• Need for mechanical protection.