house wired wrong?

[Brian H]

Yes using the capacitor is not always the best thing to do.
Most would add it inside the breaker box and would be a code violation.
I did at one time ad I used a AC Power Line rated one. Made for AC Power Line use by UL and a few other authorities.
I would not trust a 600 volt one most say to use.

[JeffVolp]

A .1uF capacitor has a capacitive reactance of 13 ohms at 120KHz.  The 18uH inductor cancels that out, providing a low-impedance path for the 120KHz signal.  I use .22uF and 8.2uH in the XTB for the same function.

I agree with Brian that capacitors rated for 250VAC across line operation are the best for this application.  However, a metalized polyester capacitor rated for 600 or 630VDC should also be safe.  The ones I use from CDE are rated 630VDC / 250VAC.

FYI:  Unless they changed it recently, the capacitor in a 4816H SignaLink is only rated 400VDC.

Brian is also correct that a capacitor should not be installed across two breakers in the distribution panel as it will violate the electrical code.

The point I was trying to make earlier is that the SignaLink is a very inexpensive coupler in a convenient package.  The XPCP made by X10 is a much more elaborate unit with twin tuned circuits and complete isolation between them.  That coupler is code compliant when installed in a standard electrical box adjacent to the utility panel.

Jeff