Up To Speed: Should You Test a New Spool of Cable? Here’s the Why & How.


Up To Speed Graphic Thin Version

Up To Speed is a concise, technical blog compiled by industry veteran Mark Reeder. It provides an interesting fact, answers a thought-provoking question, or offers a cliffhanger from an actual site visit by one of our world-class Field Service Engineers.

Cable Spools

This tip is all about being proactive.

The scenario: Cable spools generally come pre-tested from the manufacturer. And in general, cable is tough—very tough. But accidents happen. For instance, let’s say a new spool of cable falls off the back of the truck, gets hit by a forklift, or some object gets dropped on the spool. Or, let’s say you have an older, used spool you’re thinking about reusing. In either case, you want to make sure the cable is undamaged before it goes downhole…not after.

So, how can you be sure the cable isn’t damaged? Simple—test it first.

“Yes, brand-new wire always comes pre-tested, but it could get damaged—typically the outside wire of the spool, the first part that goes down into the well,” Franklin Electric Field Service Engineer Dave Bumbalough said. “Sometimes this damage is difficult to detect visually and not discovered until it’s far downhole.”

Dave recently used the following technique to discover a nick in a large spool of drop cable. By testing the spool of wire in the shop before visiting the job site, he was able to detect the compromised insulation, ultimately saving time and money.

To conduct this test, you’ll need:

  • A body of water large enough to submerge the entire spool of wire. The body of water could be anything from a 55-gallon drum cut in half, to a washout pan, to a large bucket or even a horse trough.
  • A megohmmeter, or insulation tester. A megohmmeter (sometimes referred to as an insulation tester or megger), can measure ohms in the millions and can find damage in this type of circumstance.

Megger FINAL
To conduct the test, submerge the cable in water. While submerging the cable, make sure to keep both ends of the cable dry and out of the water. Since air acts as an insulator and water is partially conductive, if there is a breakdown in insulation in the wire cable, electricity will leak into the water and can be detected by a megohmmeter.

Place one probe in the water, and another probe on one of the ends of the wire. The readings should result in very large numbers. If not, the electricity is being leaked into the water, likely from a nick in the installation.

So, what’s a high ohm reading?

With the megohmmeter set to either 500 or 1000 VDC output, normal insulation resistance readings for drop cable and a motor (if attached) should read two-million ohms or more. If the reading is below two-million ohms, it is not recommended to use this wire. Reference Franklin Electric’s AIM Manual and AIM Manual App (available on both the Apple® App Store and Google Play Store*) as needed for insulation resistance readings.

Instead of spending time, money, and energy dropping hundreds of feet of cable into a well and finding there’s a breakdown in insulation, test it at the shop first. It only takes a few minutes, but could save a lot of time in the field.

Now, you’re up to speed.

*Google Play and the Google Play logo are trademarks of Google LLC.