The length of safety system wires can cause a drop in supply voltage related to the current circulating. This voltage drop is due to sum of the currents circulating on the 0 Vdc feedback path of the electrical circuit. It is usual practice to double or triple the 0 Vdc wires.
In order to ensure the correct operation of the safety system (reactivation of relays) and a correct reading of diagnostic information, it is important that the voltage measured between terminals A1 and A2 be greater than 19 Vdc.
Cross-section of TELEFAST cables
Each TELEFAST ABE-7CPA13 terminal accepts bare wires or ones fitted with terminations, or spade or eye terminals.
The capacity of each terminal is:
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minimum: 1 x 0.28 mm2 wire without termination,
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maximum: 2 x 1 mm2 wires or 1 x 1.5 mm2 wire with termination.
The maximum cross-section dimensions for wires on the terminal block are: 1 x 2.5 mm2 wire without termination.
Calculation of cable length
The resistance of each safety system ((+) channel and (-) channel) must not exceed 75 Ohms. The maximum resistance of the channel between an SS ESD or PS and the corresponding input of the module must be ≤ 6 Ω.
Given the length and cross-section of the cable, its resistance can be calculated as follows:
Equation parameter
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Parameter
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Meaning
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R
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Cable resistance in Ohms
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Resistivity: 1.78 x 10-8 Ω.m for copper
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l
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Cable length in m
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S
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Cross-section in m2
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It is possible to wire the system so as to allow a greater distance between the SS ESDs or PSs and the module:
Standard wiring:
Optimized length wiring:
