Kommvia Field Notes – Incoming Line Voltage

Welcome to Kommvia Field Notes — real stories and lessons, straight from the field.

There are two kinds of telecom techs in the world:

1. The ones who have been hit by ring voltage.
2. And the ones who will be.

I joined group one a long time ago.

True story.

It was early in my career, back when I was still green enough to think that “voltage is voltage” and all of it comes from the same place. I was working on a phone line and made the rookie mistake of assuming the line was dead. No calls coming in, nothing ringing… so I grabbed it barehanded.

Right about then, someone decided to call that number.

Zap.

What is Ring Voltage?

For those outside the telecom world, ring voltage is the higher-voltage AC signal the phone company sends down a line to make the phone ring. In traditional analog systems, we’re talking 70–90 volts AC, sometimes peaking higher, riding right on top of the normal line voltage. It’s not constant. It comes in bursts, timed with the ringing pattern.

It’s different from the dial tone voltage, which is the steady DC voltage present when the line is idle . This is usually around 48 volts DC. That’s enough to get your attention if you short across it, but it’s the ring voltage that can really surprise you.

What It Feels Like

Getting hit by dial tone voltage is like a quick sting or mild tingle.

Ring voltage? That’s like someone smacking your hand with a live electric fence. It’s sharp, fast, and definitely wakes you up… but thankfully not dangerous in most cases.

For me, it wasn’t enough to cause injury. But it was enough to send my hand flying back and my heart rate into double-time.

The Lesson Learned

That day I learned the difference between incoming lines (the live feed from the outside world) and on-premise lines(wiring inside the building, after the phone system). On-prem lines can still be live if the system sends ringing internally. Incoming lines are the real wild card.

Now, before I touch anything, I check it. Every time. And I use a toner (a little tool that sends a signal down the line so I can trace it and verify it’s safe to handle). It’s faster, safer, and saves me from another unplanned handshake with Ma Bell.

Why This Matters

In our work at Kommvia, speed matters, but safety matters more. Knowing where the voltages come from and how they behave isn’t just a matter of comfort. It’s part of doing the job right, avoiding downtime, and keeping every install clean, labeled, and hazard-free.

I learned my lesson the hard way so you don’t have to.

Always check your lines. And remember… the call is coming from the outside.