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MP120
APPENDIX A - DIMENSIONING
CONNECTING CABLE DIMENSIONING
When calculating the lead section, you should consider the most critical power supply situation for the system, i.e.
no mains supply and booster batteries just above the "battery low" threshold (11.2 V-).
Under these conditions, at full load, at least 10.5 V- shall be guaranteed at the terminals of all devices.
It follows that the maximum voltage drop permitted on cables will be 0.7 V-.
Below is the formula used for calculation:
V
c
=
2
x
length
x
R
m
x
I
d
where:
V
c
: voltage drop (V)
length
: cable length (m) (single lead)
R
m
: cable resistance (
Ω
/m)
I
d
: current absorbed by the devices (A) (as detected from the respective specifications)
Below are the copper cable resistance values:
Section - mm
2
0.22 0.50 0.75 1.00 1.50
Resistance -
Ω
/m
0.0795 0.0350 0.0233 0.0175 0.0117
The diagram may help you identify the minimum cable section required.
Warning!
The diagram is used for preliminary evaluation: for accurate calculation, use the above-mentioned
formula. In any case, you should check, by means of a voltmeter, that the voltage measured at the terminals
of every single device is not lower than the supply voltage delivered by the control unit or auxiliary power
supply – 0.7 V-.
Cable dimensioning
(with max. voltage drop of 0.7 V)
Cable length (m)
Absorption (mA)
