I saw a video by ElectroBOOM where he wiretapped his home phone. So, apparently, there is around 40v coming through the phone line, with higher peaks when it rings etc. I have a few questions about this.

  • Firstly, is it legal to utilise this power for other uses (Australia)?
  • How much power can it provide?
  • 3
    \$\begingroup\$ The internet is not a good place to ask for any legal advice. Obviously it is legal to power your phones, and the power it can actually provide varies greatly. \$\endgroup\$
    – PlasmaHH
    Jun 13, 2018 at 9:56
  • 1
    \$\begingroup\$ I too watched that video and it was cool. However, he did mention there that check with your local laws. \$\endgroup\$
    – Parth
    Jun 13, 2018 at 15:53

1 Answer 1


The technology is explained here

In the United States, the telephone company guarantees you no lower current than 20 mA or what is known to your phone company as a "long loop". A "short loop" will draw 50 to 70 mA, and an average loop, about 35 mA.

As for legality, IIRC in the UK it was illegal to power other apparatus besides a phone. Largely this was because it was a battery backup based system that was expected to survive power outages. If everyone was sucking power all the time that survival would be in doubt.

  • \$\begingroup\$ Thx for the info \$\endgroup\$
    – skillz21
    Jun 13, 2018 at 10:17
  • 5
    \$\begingroup\$ If you draw more than a few microamps, the switch gear will think the phone is off-hook. It will send you dialtone and expect you to place a call. If you do not, after some time, it will send various alert signals down the line in an attempt to get you to hang up, after which, it will simply disable the line to eliminate the battery drain and file a repair request. \$\endgroup\$
    – Dave Tweed
    Jun 13, 2018 at 13:10
  • \$\begingroup\$ As a pre-teen, back in the day when land-lines are all there was, I fiddled around with my home phone lines a fair bit and can confirm that what @Dave Tweed says is easily verified experimentally. \$\endgroup\$ Jun 13, 2018 at 15:06

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