Two issues that are related.

Posted by Al Sekela (A) on December 18, 2006 at 10:53:29

In Reply to: outlet strap question posted by bkst140 on December 17, 2006 at 21:21:58:

It depends on whether the outlet is mounted in a steel, nonferrous, or plastic box.

For any type of box, the strap (very cheap outlets do not have one) is a steel or brass rod in the middle of the hot and neutral wires. Steel has a nonlinear magnetic response and acts like the core of a one-turn inductor. This inductor is in series with the AC voltage and causes distortion in the current from the nonlinear magnetic behavior of the steel. The magnet trick bartc mentioned helps by biasing the steel into a more linear region of its magnetic response curve, so that it produces less distortion. A better solution is to use an all-brass outlet.

For conductive boxes (steel or cast nonferrous alloy), the strap forms a conductive loop with the box that again is coupled to the hot and neutral wires because they pass on either side of the strap. This is a one-turn, shorted transformer, and a steel strap outlet in a steel box will have similar nonlinear response issues. A brass strap in a nonferrous alloy box will still have some effect. The simplest thing to do is to break the loop at one end of the outlet by using a Nylon screw and washer to prevent electrical contact and create a magnetic gap. The other end of the outlet should be fastened with a metal screw to properly ground the box, or you can wire a separate ground pigtail to the box.

The steel screws used on the outlet are also problems and should be replaced with brass or nonmagnetic stainless steel.

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Follow Ups Full Thread

Topic - outlet strap question - bkst140 21:21:58 12/17/06 (19)

Two issues that are related. - Al Sekela 10:53:29 12/18/06 (3)

Re: Material Madness - bkst140 19:49:29 12/18/06 (2)

Satisfy your Inner Maxwell (and Timoshenko)! - Al Sekela 21:27:21 12/18/06 (1)

Thanx a lot Al - bkst140 07:48:23 12/20/06 (0)

Re: outlet strap question - Mike B. 08:00:37 12/18/06 (5)

Re: outlet strap question - bkst140 08:26:41 12/20/06 (4)

Re: outlet strap question - Mike B. 09:00:39 12/20/06 (3)

Hysteresis affects the inductance in series with hot/neutral. - Al Sekela 14:50:34 12/22/06 (2)

Re: Hysteresis affects the inductance in series with hot/neutral. - Mike B. 19:13:10 12/22/06 (1)

The hot and neutral wire currents are equal in magnitude and - Al Sekela 14:49:56 12/23/06 (0)

I'd bet it does! - bartc 05:55:33 12/18/06 (8)

Re: I'd bet it does! - bkst140 20:30:47 12/18/06 (7)

Re: I'd bet it does! - bartc 06:02:00 12/19/06 (6)

Re: I'd bet it does! - bkst140 08:08:02 12/20/06 (5)

Ebay and your local hardware store - bartc 05:47:32 12/21/06 (4)

Re: Ebay and your local hardware store - bkst140 18:37:28 12/26/06 (3)

I can only pass on experience and info/misinfo! - bartc 19:41:47 12/26/06 (2)

Now it sounds more challenging - bkst140 16:47:21 12/28/06 (1)

Well, it isn't really hard but it isn't really easy either - bartc 21:03:35 12/28/06 (0)

Follow Ups

Two issues that are related. - Al Sekela 10:53:29 12/18/06 (3)

Re: Material Madness - bkst140 19:49:29 12/18/06 (2)

Satisfy your Inner Maxwell (and Timoshenko)! - Al Sekela 21:27:21 12/18/06 (1)

Thanx a lot Al - bkst140 07:48:23 12/20/06 (0)

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