A 0.1uF capacitor has a reactance of around 15 ohms at 100KHz and if you
bridge your two phase lines with it, you should resolve the problem. At
50Hz the reactance is 16000 ohms and so only a few milliamps of line
current will be bridged, even if the two phases are not the same (i.e
two phases from a 3 phase source, for example).

The capacitor should be rated (X or Y, I think, from memory) for
continuous mains usage, and if the two phases are indeed different
phases from a 3 phase source, the voltage rating must be sufficient to
cope with the peak-to-peak voltage expected. You should assume the
worst-case peak voltage could be the total peak-to-peak swing of the
line - this is 672V for a 240V line. 1000V would be prudent, especially
if you have any reason to believe voltage surges may occur.

A potential hazard is introduced if the capacitor bridges the main feeds
after any fuses. If one feed is disabled by pulling the fuse or breaker,
it is important that current induced through the capacitor does not
appear on that feed line from the other phase. Therefore you must bridge
the phases before the fuses. I would also put a small 100mA picofuse in
series with the capacitor, to protect in the unlikely event that a short
occurred, or a surge sufficient to rupture the capacitor's insulation.
Use heatshrink tubing rated for 600V isolation to encapsulate this fuse,
then encapsulate the entire assembly in heatshrink tubing. If all this
is done, I believe you will meet all regulatory requirements, but I
would check, nonetheless, if I were you. Finally, label the switchboard
to ensure that any service personnel are aware of the wiring change you
have made.

> ----------
> From:         Martin R. Green[SMTP:elimar@NOSPAMBIGFOOT.COM]
> Reply To:     pic microcontroller discussion list
> Sent:         Wednesday, January 14, 1998 12:13 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      [OT] Carrier Current Query
>
> This is not exactly about a PIC, but I know that some of you out there
> have done some carrier current and/or X-10 stuff, so maybe you can
> help me.  I have some carrier current intercoms that work quite well
> as long as they are on the same half of the 240V circuit in my house
> (BTW, I live in Canada, 120V 60Hz, 240V feed to the house).  The
> problem is that many of the AC outlets I want to use are not on the
> same side of the wiring.  I know that a similar problem shows up with
> X-10, and I believe it is solved by placing a small value capacitor
> across the two halves of the 240V line, but I don't know exactly what
> type of cap, or what size to use.
>
> The intercoms use one of 3 carrier frequencies (FM modulation, 1KHz
> deviation) at 200KHz, 230KHz or 260KHz.  Can anyone suggest a suitable
> device to link the two halves of the circuit at carrier frequencies,
> tell me exactly where to put it (no cracks pleez), and alert me of
> anything I should look out for (I have done quite a bit of AC wiring
> in my 40 years - tomorrow - so I'm not a neophyte in that area).
>
> TIA - Martin.
>
> PS. maybe you should reply directly to me via email, this is quite
> off-topic
>
> Martin R. Green
> elimar@NOSPAMbigfoot.com
>
> To reply, remove the NOSPAM from the return address.
> Stamp out SPAM everywhere!!!
>