I've got an Archer C2300 router providing wifi for my house and its connected to a Ubee cable modem (Spectrum is the ISP).

I've been having intermittent internet problems; several times a day, most often at night, the cable modem will lose connection and have to reacquire.  Had the ISP tech come out and check all the outside cables, and everything seems good.  He uses a voltmeter and checks the cat-5 cable connecting the router to the modem and says that the cat-5 coming from the C2300 router is has a 70+ volt charge.  This is shorting the cable modem and causing it to reboot.  I'll be testing this hypothesis later today but first, I wondered if this was at all possibly true?  Is this working as intended?