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Shielding Question

EFI Wiring Fundamentals

Discussion and questions related to the course EFI Wiring Fundamentals


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Hi HPA team! Let me take the opportunity to say thanx for the course! I guess a lot of people were involved to make it that level, - so thanx a lot to all of you.

My question is re Shielded cable section, particularly at 00:30: ".. Its critical that it is shielded at one end, if the shielded braid is grounded at both ends you will certainly violate or stop the earting rules.."

So could you plsease be more specific about that. Lets take the particular case, - imagine we have a GM E67 ECU (it has no dedicated shielding pin) that recieves its groung from the engine block (thats clear and not discussable). Crank position sensor is wired using a 3 wire shielded cable. Shielded cable has a shield that has 2 ends :) one at the ECU side, that is definitely connected to the ECU ground (which respectively goes to the engine block), another one at the connector side. So all the game it happening at the connector side. There are several options:

1) Leave it unconnected

2) Ground shield at connector side to Engine block

3) Run a separate wire connected to shield at the connector side back to ECU and connect it to ground there (both ends would be grounded at ECU side)

Option 1 - is what Zak is saying. Options 2 and 3 are the two side termination and i would greately appreciate if you could comment what's wrong with these.

The question is mostly due to my curiosity, but it was also triggered by this article:

http://pdb-media.leinelinde.se/media/file/9700/Shielding_connection_eng.pdf

Hope the question is not that much stupid..

Tks in advance

Rgds

R

The reason you only want to ground your shield at one end is that if you ground it at both ends, to different ground points, it will give a path for current to flow between these two ground points that might not be considered in the design. Large transient current events can cause spurious current to flow along the shield, which can actually induce noise in the wires below, if large enough. Grounding the shield at either end is likely to be fine, but still steer away from grounding it at both.