1

I want to invest in a high-quality fish tape and I’m doing some research on them. One of the biggest selling points of many fiberglass fish tapes is that they are non-conductive, for safety. But when would a fish tape bump into a bare live wire?

4 Answers 4

8

When fishing into an electrical panel

In most cases, there will be live terminals (at a minimum, the service connections on the main breaker) in a panel you are fishing wires into. While new panels have what are known as IP20 terminal shields that make the service terminals finger-safe (i.e the live parts are no longer poke-able with a finger), these shields are not complete protection, and are only found on very recent panels anyway. In addition, many times when you are fishing into a panel, branch circuits not proximate to the rest of the work are left live, for obvious nuisance reasons.

2
  • Yet another reason I like my intermediate junction boxes a foot from the panel. Fish to the intermediate box after deenergizing all the circuits in it, then just poke the wires through the last foot carefully. Commented Jul 3, 2018 at 3:25
  • 1
    Another reason I would go for the fiberglass is their excellent flexibility and drag coefficient through the conduit. Commented Jul 3, 2018 at 15:46
2

Commercial buildings regularly have shared conduits with live circuits. Many old circuits that have yet to be replaced with new cables. A string should always be left behind, but that doesn't always happen. Some of those conduit penetrations are not always penetrations you want to, or are allowed to, recreate.

Metal tape is still metal, as "smooth" as it can be, and rubbing against just insulated wiring can cut into it. Among the fact there could be already exposed wiring from some sort of existing damage you could run into. Coated tape could cause a little more friction and burn cables, but that's completely controllable by speed. Both of which are heavily alleviated by using dielectric grease, they sell large bottles of the stuff for fishing. Technically it should insulate the metal tape from shorting a little, but I still wouldn't rely on it for that.

This especially applies more to Ethernet/LV applications. Fish tape is regularly used in live conduits. And nowadays communications is generally considered critical infrastructure so even more so have to be very careful of damage. Among the fact it can now carry substantial amounts of wattage and voltage through PoE++. Being class 2 it, and you, are pretty protected against a truly dangerous short, but it's again not something to play around with and can still damage some very expensive equipment doing so.

There's also some frankly cool types of the coated tapes that allow you to pull it all the way through the reel and out, so it becomes effectively a massive push rod. So you can just attach a string/head to the back and pull straight through in one go, without needing to first back-feed a string and then pulling the cable. Which for structured Ethernet/communications, some paths don't give you a choice which end to really start at. And junctions for communications are very improper and to be generally avoided. Among the need to locate the end of conduits in the first place, which you could also then pull through in one go with such a thing.

1

If you are fishing through stud/joist bays in an old home there is the possibility of contacting live knob-and-tube wiring where insulation or connectors are damaged or missing.

There is always the possibility of contacting a live wire that was incorrectly left in a wall with just some tape or a wire nut and no junction box. Fish tape can find its way into these incorrect splices and caps and become energized.

1

The one important point left out in the other answers is:

you need a non conductive tape when pulling a new wire in with live wires.

metal tapes square edges (although rounded some) can cut through the insulation and create a short to ground if metallic conduit, or cut through multiple wires insulation and create a short that way.

The live terminals in a panel are obviously an important place to use caution.

I have had a metal tape find a Nick in the wire insulation at a point the pipe was not properly reamed instantly welding the tape to the pipe.

The damaged insulation from the original work allowed the metal tape to become a conductor but I have heard of electricians pulling and have the metal tape slice the insulation and cause the same problem.

I have had a few 100% non conductive tapes break and become brittle over time, I now purchase nylon coated metal, it holds up better for the heavy use I put them through,

For really heavy work we only use the fish tape as a guide to pull a string/rope through when a mouse cannot be “blown through”.

2
  • Why would you (or anyone) be pulling through live wires? Seems a recipe for problems, no matter what you're pulling/pushing with.
    – Tim
    Commented Jul 19, 2022 at 16:16
  • 1
    @Tim Wires in the pipe that are live it is very common in the electrical world to use a pipe for multiple circuits. You don’t get to turn off circuits that are in use to pull new ones in commercial work.
    – Ed Beal
    Commented Jul 19, 2022 at 17:46

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.