I got one for ya a 50 pr underground cable feeding one building to another aprox 200ft.
been installed 5 yrs sending a panasonic display phone and 3 single line phones. on panasonic phone here a loud buzz / hum . changed pairs same thing . on butt set monitor pairs some pairs have a loud buzz some faint buzz you can hear it and there is a lot of noise comming from my amp wand , any one got any ideas what is wrong. efi or rfi are there filters to take off this noise?

I will be you that your phone system is a KX-T or KX-TD system using hybrid ports. These ports are unbelievably sensitive to any kind of exposure to foreign currents, like those from even mild lightning storms. There's nothing wrong with the cable; the added resistance from the length of the cable amplifies the problem that might not be as noticeable right at the KSU. The ports might sound clean there, but the minute you add the resistance and capacitance of a cable run, the problem can be heard.

What has happened is that the port has been blown (well, not completely), but blown enough to where even a few dozen feet of cable result in cable pair imbalance. It doesn't matter if the cable is inside or underground.

You might be able to move to other port(s) to clear the problem. There really isn't any type of protector that will prevent this from happening again. Panasonic's hybrid ports put out enough ringing voltage where digital station protector modules can't be used. Regular CO modules (230 volt) allows too much exposure. These ports are just too sensitive for any, I mean ANY outside plant exposure.

The hum you are picking up with your butt set and probe are just simple AC induction and difference in ground potential between the buildings. This is perfectly normal and is not the cause for the noise you are hearing on the phones themselves.

Sorry to bear such bad news, but I have spent years chasing these problems with multiple Panasonic customers and many thousands of feet of outside plant cable. It's always come back to hybrid ports being knocked out of balance.

Hey Ed, ITW Linx (the people that now make the Panamax line) make a 66 block protector specifically for the Panasonic Digital system. It clamps at 100V. You could use it as secondary protection.

You know I'm not a Panasonic guy, buy I have used some of these, at different voltages, with good success.

Here is a link https://www.itwlinx.com/products/subcategory.asp?category=41&subcategory=4

I agree with you there, and we have tried using exactly the ones you described as secondary protectors, but for some reason, those Panasonic hybrid ports just can't seem to hold up to anything. We learned this from a bed and breakfast in the mountains with 20 remote cabins. Every time there was even a hint of a storm we would randomly lose ports. We changed out their system to another brand two years ago and haven't had a problem since.

ED,

What did you replace the PANASONIC with?
Yes the ports on the KXT-S are soft.

We replaced it with a Vodavi XTS (what a surprise).

What phones were in the cabin's?
I assume they were single line type 500?

We used Vodavi 2801 sets in the cabins because they wanted data ports and message waiting.

Previously, they were using standard 2500 sets on the Panasonic KX-T123211D.

Im impressed. Another fine outcome for VODAVI.
I think the single line ports are pretty strong on the lil STSe as well.