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In a DC circuit, are there any reasons for wiring overcurrent protection such as fuse, pptc, etc.... PHYSICALLY near the load(or inside it)? By wiring "physically near", I mean in the power wire going to the load, but near the end of the wire physically closest to the load.

As to an example of what prompted the question: Any wires exiting body controller of Tesla's model 3 are left exposed and vulnerable along the length of their run to the load and might need protection near the load as opposed to near the power source. Many such wires exit the body controller, in the form of wiring harnesses, and the body controller can selectively protect(from its end) any loads/branches by switching off the mosfet for that load. However, these mosfets are located INSIDE the body controller which leaves the load and remaining length of wire to the load vulnerable and unprotected. Consider what would happen if some other power source were to make contact along that length AFTER the mosfet switch and between the switch and the load; bypassing the protective mosfet switch. By protecting near the load as initially postulated this problem might be addressed.

So in a DC circuit are there any realistic scenarios where protecting physically near the load is worth the trouble/cost? How common are these problems? Doesn't have to be automotive related.

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  • \$\begingroup\$ Yes, when the environment demands it. \$\endgroup\$ – Solar Mike Oct 14 '18 at 6:24
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    \$\begingroup\$ Locating protection near the load might save a walk back to the source to reset the protective device. The cable still needs to be protected though. \$\endgroup\$ – Transistor Oct 14 '18 at 8:23
  • \$\begingroup\$ If one single cable supplies several loads with small as well as large currents, there should be a fuse for protection of the cable near the source and several fuses near each load. But if a thin wire is used to connect small loads to the thick cable, the fuse should be placed near the thick cable to protect also the thin wire. \$\endgroup\$ – Uwe Oct 14 '18 at 10:50
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You seem to be thinking that the protection is against external power sources, but I'm not sure why.

The far more common fault is unwanted loads, such as insulation failures leading to short-circuits. This is why you put the protection near the power source — so that it can protect itself from failures in both the load and the wiring.

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  • \$\begingroup\$ It's probably worth noting that in this automotive scenario uncontrolled power sources are limited (and fused in their own right) and so the body controller and modules like it will likely represent the 'other sources'. These modules need to remain functional to perform whatever remaining functions after a failure there are so protection from the source not only keeps the wiring protected but helps protect the source itself too. \$\endgroup\$ – hooskworks Aug 27 at 10:10

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