Message Board Thread - "Inactive cable"

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Inactive cable mho 5/28/2004
Has anyone out there had any experience infrareding feeder cables in
manholes. What we're looking to do is to identify inactive cables as
opposed to cables carrying load in a manhole. Thank You
Re:Inactive cable Dan. M 5/29/2004
I'm not sure from your question if the term "inactive" means live but not in use or dead (no voltage). If these cables are of the medium voltage power distribution variety (7.5 K.V. or 13.8 K.V. for example) it is possible that at these high voltages, the live cable may have only 20 or 30 amps of load on them in use. I suppose by adjusting the level and span on an image, you could determine if it is live or not but there is ample room in this instance for errors which could prove to be disastrous.

Another point to consider is if the cables in question are part of a loop system or a redundant feeder system. If this applies to your situation, you may be shooting a live cable with no load on it. In both cases, you could be shooting a live cable that has little or no load and not know the difference.

The above response is to recommend that you not rely only on an infrared image to base your findings - the results could be deadly. I would recommend that you, with the proper protective equipment on, use a hot stick with a high voltage testing head to see if the cable is inactive but still powered up or inactive and dead.
Re:Inactive cable mho 6/2/2004
By inactive, I mean dead. We would ownly be doing this as a check, but ultimately we will be spearing the cable with a ground. To determine whether it is dead or alive at 27kv. Thank You
Re:Inactive cable Eric 6/3/2004
If you plan to detect if high voltage cables are energized or not, I would recommend that you use a more sound methods to accomplish this. The use of a hot stick as was mentioned in one of the response is not correct. A hot stick and high voltage tester will not tell you if your underground (in a manhole) cable is hot or not. This type of cable is insulated and therefore would not allow you the opportunity to measure its voltage. You can try to use an amp meter, but again this will only work if there is load on this cable.

The only way to check for sure if power is on a cable like this is to open it up. This, I know, is not something any of us like to do. However, they do make remote operated devises that will when activated push a nail or other sharp object into the cable grounding it out. This method however, is destructive in nature and should only be use as a last test before cutting into the cable.

I know this does not answer your original question, but I just wanted you to have a safe answer.
Re:Inactive cable Dan. M 6/5/2004
Eric, I have a Salisbury A.C. voltage tester that connects to the end of my hot stick and have successfully I.D'd live cables. However, I do know that this tester will not work if the cable is shielded. Also, MHO's original post did not specify nominal voltages.
Maybe I should have stopped after expressing the point that Infrared thermography by itself would not be a reliable means to determine if a cable is live. I was simply trying to point him to a more reliable way but do appreciate opposing views from others who may very well have more experience. Thanks.

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