I have come across several electrical schematics that use the shield of a twisted pair (16 AWG instrumentation wire) to ground a 120 VAC proximity switch (as an example) back to the plc. There are 2 main types of shields: braided (an actual copper conductor) or the foil with drain wire. I would assume that if the shield is a braided conductor sized to carry the current in the circuit, then it's OK to do? Is this acceptable practice? Please help. I never found clarification in the NEC.