mahmood Elnasser wrote:
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"Shields should only be connected at one end or you will have ground loops."
Why would there be ground loop while the shield is not connected to gnd, its only connected to the chassis of the equipment.

Because the potential at one end is not the same as at the other, by nano volts, or micro volts or millivolts or volts ! "Earth loops" form whereever a changing magnetic flux is surrounded by a conductor.


I actually sent my cables away to a specialised company to do the harnesses, they made them shilded at both sides. They manufacture harnesses for aviation industry and they make their cable shielded at both sides so i expect they know what they are talking about.

Not in this case, they don't ! As we have said it is bad practice so to do in most circumstances.

As others have said, your scope can be a bad source of problems while you try and fix the damned system. I have seen many people who were stupid enough to unground their scopes. It is VERY dangerous to do that. Much better to get a proper isolated differential amplifier. Thurlby-Thandar do a very nice one.

Steve