How tools used for thorough testing practices prevent tragic accidents
By Tim Rzeszutek
Testing energized circuits, isolating them, confirming there is no voltage and applying LOTO is the foundation of what we do as electricians and how we go about doing our work safely. These principles of testing basic circuits 600v’s and below are driven home early in our apprenticeship and continue to be emphasized throughout our careers as professionals. Knowing the source you’re working on and selecting the proper meters, tools and PPE for the task is critical. I’m sure many of have heard the tragic stories of individuals selecting the wrong meter and essentially having the meter grenade in their hands, or the story where someone got distracted and missed a step. While this article is meant to discuss tools, I thought it was important to share and reiterate how important it is to write out and — most importantly — discuss with the team doing the work, the steps involved. This open discussion of steps and hazards most of the time reveals some additional steps or checks. We all know one missed step is all we need to have a tragic accident, or worse, a fatality.
While learning how to test AC circuits 600v’s and below is learned early on in our careers, learning how to test medium voltage (2400v-35,000v) circuits is not. This article will give you a very high-level understanding of how these circuits are tested and the tools we use to do so. This article is not intended to be training that would make you qualified to work on these systems.
Low Voltage circuits can be tested using contact and non-contact meters. Same goes for medium voltage circuits with one exception. Most medium voltage cables are shielded and cannot be tested with a non-contact tester unless tested at what we refer to as a “live front” termination location or at a “dead front” termination location through what is known as a capacitance test point. Refer to the image #1 for a live front termination gear and refer to image #2 for a dead front termination gear. For testing at live front type terminations, we use both contact and non-contact testers as there are exposed live parts to physically have meters touch. In the case of a dead front piece of equipment there are no exposed live parts.
Dead front equipment gets tested using a Salisbury 4744 URD non-contact voltage tester, or similar, as shown in image #3 below and brought to a dead-front termination capacitive test point shown in image #4 below. The test point itself has been circled in blue.
Removal of the test point cap is done via the use of a tested and inspected insulated shotgun stick as shown in image #5 below. Now, testing medium voltage circuits is pretty straight forward at termination points but when you get into vaults with multiple energized circuits it can be impossible to actually test for voltage via contact and non-contact methods. For these scenarios, we confirm cables that need to be cut into by using a CT or current meter. Medium voltage cables again cannot be tested with a non-contact voltage tester because of their shielding, but they can be tested with a current meter. Once the cable that we believe we need to work on is identified, we test for current. Once current is read on meter a breaker or switch would be opened which should drop current to zero. This process would be done several times to confirm. After circuits is confirmed, a remote cable cutters or hydraulic cable spiker would be used to cut or ground cables while personnel are well clear of area. Image #6 is an example of a remote cable cutter.
Again this article is not intended to be training session but hopefully you now have a better understanding of some of the testing practices associated with these higher voltage systems and the tools used to do so.