Shielding for power cords?

I understand there is a difference of opinion about shielding interconnects. Twisting the wires tightly together (Cat6 Ethernet, Morrow, and others) is said to provide noise rejection without shielding.

But what about power cords? I have always assumed (perhaps wrongly) that power cords are more likely to give off EMI due to the higher voltage they carry and so should be shielded. Is that right?

I think the general consensus is that if you shield a PC (and the shield is grounded) it should only be connected to ground on one end.


I have used copper foil and conductive carbon fabric mesh over aftermarket cords it is most effective with antenna RF drain to male ground pin. Thus noise external and internal RF is removed.

One can easily hear improvements before and after in lowered noise floor and better fidelity across the spectrum. Cords with addition of an internal silver wire RF drain also improve. Foil is fragile but results over weave address shorter wavelength frequencies better.

No, no and no on SPG, Single Point Antenna grounds - Cable Shield Grounded At One End Only - EMC Standards

SPG are RESONANCE circuits and NOT a RF ground that attenuated RF. The reason people think they work is when a terrible earth ground differential (ground loop) mitigated at the EXPENSE of RF shielding not the other way around. Fix your broken ground to remove the ground loop and this also allows true RF shielding.

Transfer impedance, SEED and absorbing clamp or any RF shield test require a total and complete GROUND and at both shield ends to attenuate RF for ingress or egrees. Power cords are not “high-voltage” and if RF is an issue at the IEC outlet it is RF being inductively or capacitively couple to the outlet and into the cable (egress). Most all modern devices include low impedance ground path to RF.

The FCC has class A and B RF limits on equipment that use “open” IEC connectors. If it passes the UL antenna field tests, no special cord is needed. If it FAILS you need a special design cord that is CAPTIVE to the device (no open IEC socket).

## FCC Class A vs. Class B Emissions Standards
Because they’re designed for use in commercial and/or industrial settings, Class A devices are permitted to have higher levels of radiated emissions. These environments have less potential for interference with residential electronic equipment. Class B emissions standards are more stringent. Devices in this class are intended for use in a residential setting.

The rationale behind the stricter standards for Class B emissions is that home devices are more likely to interfere with radio or television reception — as well as other electronic devices, such as personal computers — if they output an excessive amount of emissions. - What Are FCC Class A Emissions? - Compliance Testing

This is REALLY how it works. A shield has to have BOTH ends grounded to be a RF shield, or you are building a resonance circuit that is usually WORSE at removing RF, never better (see the sourced paper). An open ground end breaks a ground loop that is from a broken ground system and is NOT to be confused with RF shielding, ever.

Another place to go on shields is in here; Technical Papers: Iconoclast Cable
Shields and Grounding.

I know the science is hard and can take decades to learn, but it is what it is. Myth is easy, the truth can hurt. Do the hurt!



Thank you!