Just having a look at some of the posts and decided to once again add something different. This post is a contribution from Ron Columbine and I decided to post it exactly as Ron wrote it. Thanks for the contribution Ron, I agree with you, Safety is Essential in our trade.
As maintenance electricians there are a number of things that need to be remembered and checked before working on any equipment. The most important pieces of equipment you have is your test equipment. Your life may depend on your equipment when it comes to checking for no power before going to work on any equipment. The following is a list of things that I do on a regular basis with my test gear.
1 – Your meters and test equipment need to be checked and tested before each use to ensure they will tell you if there is power present or not.
2 The first thing to do is check the meter leads for damage or bare spots. A bare spot on the positive lead especially will cause a short to ground if connected to the power source.
3 Make sure the meter leads are rated for the power available. You can get class 3 or class 4 leads for most meters. If your meter can only read to 600 volts either lead is OK. Some meters will read to 1000 volts but can be shipped with 600 volt leads. Always make sure you know what your voltage is.
4 If you are using test equipment such as an oscilloscope that requires power to operate it should be powered from an isolation transformer.
5 Always make sure you know what you are checking for and that your meter is set to the proper scale. You do not want to be measuring 600 VAC with the meter set to ohms or amps. As well you need to know if it is AC or DC you are measuring.
6 A lot of people like to use the Tic Tracer to check for power. I use one only for a quick check to see if there is power. When It comes to isolation to perform maintenance I think you need to use a digital or analog volt meter so you can see what the voltage level is.
7 With the Arc Flash regulations now it is important that you are wearing the proper PPE for the job you are doing. I helped build an OSB plant in Oklahoma in 2003 and we went totally Arc Flash compliant in the mill. The mill supplied all the electrical team members the required clothing (shirts, pants and tee shirt) to work on the 600 VAC switchgear. Each Electrical room had a safety locker with the face shields and hot gloves to be used when the MCC bucket doors were open and the power was still on. As well each electrical room had what we called a Sheppard’s pole that could be used to remove a person from contact with power if required. Our procedure was that two electricians would suit up until such time as the power could be turn off and locked out. The other level of PPE was to cover everything up to the supply voltage of 25 KV. Again two people would suit up until such time it was confirmed that all power was off and locked out.
8 As well we had written procedures and check sheets for working on all the equipment in the mill. A FHRA was filled in and signed by all involved at the time of isolation. It might seem like a lot of extra time but in fact it was faster and totally safe.
9 The following is kind of a check sheet we used for troubleshooting and repair of electrical equipment.
- Physically check the meter to be used for damage. Check the leads for an signs of damage. A good way to check for continuity of the leads is to put the meter on resistance test and touch the leads together. You should get zero ohms.
- The meter should then be checked on a known voltage preferably the same as the MCC.
- Check to make sure you are wearing all the required PPE to open the MCC bucket.
- Turn off the MCC disconnect switch and lock it open.
- Open the MCC bucket door and check for power on the top of the breaker. Unless you have isolated the MCC supply from somewhere else there should be voltage on the top of the breaker. Then check at the bottom of the breaker for zero volts. In the case of three phase breakers you should always check each phase to ground. I have seen breakers where one phase did not open and by checking phase to phase it would read zero volts everywhere. When it was checked phase to ground there was one phase with power on it.
10 Power systems are called the SILENT KILLER because you cannot see the voltage that is present so your life depends on the reliability of your test equipment and your knowledge of the proper use of it. You quite often don’t get a second chance.