Wiring Fundamentals: Star Point Earthing
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Star Point Earthing
02.04
| 00:00 | - The way we eliminate common ground paths from our power grounding system is to use a design technique called star point earthing. |
| 00:07 | This design entails defining only one physical location on the vehicle that is ground and all the power ground wires are run to this single point. |
| 00:16 | This is what gives the design its name as when a wiring harness diagram is drawn the single ground point ends up looking like a star. |
| 00:23 | With ground wires coming to it from all directions. |
| 00:26 | If we look at our starter motor example again, we can solve our problem by connecting all the power grounds of the system to only one star earthing point. |
| 00:34 | With the battery negative, the engine block which is the starter motor power ground, and the ECU power grounds all connected to only this one point, there's no possible way the large starter motor current can pass through the power ground wires of the ECU to get back to the battery. |
| 00:50 | If the connection between the engine block and the star earthing point becomes loose or corroded, the starter motor will either not function or be very slow to crank. |
| 00:58 | But the ECU power ground wiring will not be effected. |
| 01:02 | This is a much easier problem to diagnose and will not result in any permanent damage. |
| 01:07 | This of course raises the question of where do we define this star earthing point to be? Ideally we would analyse it for each EFI system we built a wiring harness for, but the reality is that there is one place that almost always ends up being optimal, and that is the engine block itself. |
| 01:22 | The engine block is so larger and thick that we can reliably assume that current can pass from one point on the block to another with no resistance. |
| 01:31 | Meaning the voltage we see at any point on the block is the same. |
| 01:34 | So from an electrical standpoint, we can consider it to be a single point. |
| 01:38 | Looking once again at our starter motor example, we have no choice but to connect the power ground of the starter motor to the engine block, as the current exits the starter motor via the motor housing itself. |
| 01:50 | We connect the battery negative to the engine block via a larger power cable and the ECU power grounds to the engine block via appropriately sized wires for the current that we expect them to carry. |
