What are the most common installation mistakes?
The most common mistakes: selecting the cross-section by current alone without calculating the voltage drop, placing the fuse more than 175 mm from the battery terminal, grounding to painted chassis, grounding the shield at both ends, running power and signal cables in the same conduit, and measuring with no load instead of under load. Each of these produces recurring faults that show up late.
The mistakes repeated in the field are surprisingly identical:
- Cross-section by current alone: the cross-section is calculated both for ampacity and for voltage drop, and the larger result applies. The formula is dU = 2 x L x I x rho / A, with rho = 0.0175 ohm x mm2/m for copper. At 12 V the 3 percent limit is 0.36 V, at 24 V it is 0.72 V.
- Fuse in the wrong place: every positive conductor connected to a battery, alternator or charging source must be protected within 175 mm of the connection point.
- Upsizing the fuse: raising the rating of a fuse that keeps blowing targets the cable, not the fault.
- Grounding to painted chassis: paint and rust are insulators; the surface must be cleaned until the metal shines.
- Grounding the shield at both ends: on a low-frequency analogue cable this creates a ground loop; the shield is bonded to the chassis at one end with 360 degree contact, and no pigtail is used.
- Running power and signal together: in practice, leave at least 15 cm of separation.
- Soldering in a vibrating environment: a fatigue fracture forms where the solder ends; use crimping.
- Measuring with no load: diagnosis is done under load; below 0.2 V is good, above 0.5 V is a fault.
- Neglecting sealing: a gland of the wrong diameter, an open hole, a missing drip loop and an enclosure with no breather plug.
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