Let’s continue with our discussion on Electrical meters and examine “other reasons” why this is such an important subject. The NFPA 70E states that Only a Qualified Persons are allowed to use test equipment. That person is trained to recognize and avoid the hazards associated with this task. Too often, technicians, electricians, engineers are severely burned when performing what we call sometimes an “easily task”, because we fail to use the equipment correctly or the test equipment fails. Both, Donnie Johnson and Mark Standifer of “Other Reasons” were metering the circuit or had a broken meter and failed to perform a zero energy tests.
NFPA
205.1 Qualified Persons. Employees who perform maintenance on electrical equipment and installations shall be qualified persons as required in Chapter 1 and shall be trained in, and familiar with, the specific maintenance procedures and tests required.
This is stated in many locations thru out the NFPA 70E, also in OSHA1910.269 just to mention two.
That being said, please allow me to talk about the risk of performing voltage readings on a live bus. Stop and think that when you place, (connect) a foreign object (your meter) onto a live circuit, that live circuit is extended to the terminals of the meter via the test leads. I ask you to consider this:
- Is the meter rated for the expected voltage and fault current? Many times, we think about the voltage rating but we do not consider the fault rating of the meter thus CAT III or IV.
- Is the meter your using working?
- Are the test leads rated?
- Are we wearing the proper PPE?
- Do you have a location to place your meter in a safe condition to make sure it does not fall or rip lose, or is that person you got to hold the meter for you, (not such a good idea), Qualified and wearing the proper PPE?
- Can you see the meter face without having to place yourself in a dangerous position too close to the live circuit?
Many hazards are present when performing zero energy test and you must realize the danger and take nothing for granted.
So when you place your meter on that bus, ARE YOU READY?????
I mentioned some things to consider when using a full contact meter, how about the non-contact detector?
Please note that I called the instrument a detector and not a meter and there is a big difference in the way they function. As I said in last week’s blog, non-contact testers/detectors do not tell you the level of voltage, they only tell you energy is present.
Only use voltage detectors if the following conditions are met:
- Verify that the voltage detector is working properly.
- Use the detector to test a known live circuit both before and after you test an unknown circuit, and make sure it gives you the proper response.
- If there is any doubt in your mind about whether the circuit is truly live or dead, use an additional method to verify the test results.
- This should be done for both contact meter testing and detector use.
- Ensure that the voltage detector you are using is appropriately rated for the measurement environment you’re working in and is within the voltage range you’re testing.
- Industrial environments are generally CAT III or CAT IV. Not all voltage detectors are safety rated, however, and they’re not equally sensitive.
- Some detectors will read small levels of voltage that others won’t detect at all. Don’t assume that the detector you’re using now will perform the same as others you’ve used in the past.
- Know the limitations of your voltage detector and know that capacitive voltage detectors have certain limitations.
- Correct operation depends upon the capacitance between the detector’s barrel and ground (normally through your hand and body). If this path is broken for any reason, the detector probably won’t work. For example, if you’re standing on a wooden ladder, the capacitance between your body and ground will be much less than if you were standing on a concrete floor.
- To help avoid incorrect detector readings, find an installation ground that you can touch when using the voltage detector.
- Note that the detector cannot detect live conductors inside a grounded metal conduit. For best results always hold the detector by the body and remember to keep your fingers away.
Getting safe, reliable readings from voltage detectors requires the right kind of detector for your work environment, as well as adhering to safety ratings and procedures. Ultimately, your voltage detector is only as safe as the procedures surrounding its use.
I hope this gives you some things to consider and this discussion was based on voltages 1000V and below. I will next week talk about the Medium Voltage detectors and full contact meters used. I would hope that by todays methods and technology, we have found better ways of determining zero energy.