[RFI] Vibrating Ferrite Chokes on Service Line

[Jim Brown]

On Sun,7/12/2015 7:00 PM, Aaron Kreider wrote:
> So I finally got around to putting monster chokes on the service line 
> that feeds my house and several neighbors.  3 chokes on each line 
> (positive, negative, and neutral) with zero turns 

One pass through a core is one turn.

> (as the wire is too thick).  It decreased my noise on 492 khz from 50 
> uV to 42 uV (*probably - there is some uncertainity as the level of 
> noise varies presumably due to electricity usage  -- currently it is 
> at 62 uV*).
>
> The 492 khz is a 9th harmonic of the 49.5 khz fundamental rfi source.
>
> The unexpected thing was that the chokes vibrated and made a loud 
> buzzing noise that can be heard 40 feet away (even over modest street 
> noise).  This was very concerning at first, until I looked it up 
> online and found that this is normal behavior.

They should vibrate -- you're hitting them with lots of current! This is 
NOT a proper application of ferrite chokes.!
>
> Jim Brown - you might want to include information about choke 
> vibration in your very informative guide.  I searched it for "vibrat" 
> and didn't find any mention of this phenomena.
>
> Anyways, I removed the chokes - because I'm concerned that the 
> vibration would damage the insulation on the service lines.

I need to add advice not to put chokes on individual lines. :)

When all three conductors go through the chokes, the net flux is near 
zero. When only one goes through the choke, the flux can be HUGE, and 
probably saturates the core.

>
> The chokes also became strongly magnetized, making them harder to open.
>
> The choke on the neutral line vibrated a lot less than the others.

Yup, because it usually carries much less current.

>
> Is it safe to have the vibrating chokes on the service lines? 

No.

73, Jim K9YC