Two conductors in a magnetic field, canceling each other’s EMF


If two conductors are in a changing magnetic field, oriented the same in the field, and they induced equal EMF's, can their wiring be oriented in a way that they can cancel each other's induced EMF?

So that that $$\epsilon_t= \epsilon_1 – \epsilon_2$$

Similar to twisted pair concept.

Best Answer

Yes, this is one of the things coaxial cable and twisted pair cable try to do. Ideally, each conductor sees the same magnetic field and thereby has the same EMF generated end to end. This affects the common mode voltage, but not the differential mode voltage. Systems that use such cables are usually designed to use the differential voltage only, and allow for some common mode offset.

Twisted pair ethernet is a common example of this. The ends are transformer coupled, so only the differential mode voltage matters. The common mode voltage can be up to whatever the insulation of the cable and the transformers at each end can handle. If I remember right, the ethernet standard requires ends to be able to handle 100s or volts of common mode offset, or maybe 1000 volts. I don't remember the exact number, but it's enough to allow one device riding on a 240 V power line with the other device tied to ground.