Electrical testers and meters are diagnostic tools that let you know if the wires you are working on are hot, if an electrical device is functioning, and if a receptacle is wired properly. I for one in safety NEVER EVER leave home for the field without my tester. BUT NEVER EVER NOT FOLLOW RULE NUMBER ONE WHICH IS KNOW AND FOLLOW YOUR COMPANY OR CLIENT LOCK OUT TAG OUT CODE OF PRACTICES and that includes filling out the necessary safety permits first!
Rule TWO its is meter supported by a power supply like a battery!, Before you test anything what is your bench test or quality control test control before testing any circuits or items. Your electrical test meter is ON and you’re ready to work. But is your meter ready? Is it safe? Before work commences, taking the time to analyze the status of your meters–both from a safety and an operational perspective—is an important step before any measurement work begins. Here are best practices:
- Inspect your tools
National Fire Protection Association (NFPA) Standard 70E states that test tools must be visually inspected frequently to help detect damage and ensure proper operation.
- Check for broken case worn test leads or faded display.
- Inspect test leads and probes for frayed or broken wires. Be sure your leads have:
- Shrouded connectors.
- Finger guards.
- CAT ratings that equal or exceed those of the meter.
- Double insulation.
- Minimum exposed metal on the probe tips.
- Use the meter’s own continuity testing function to check for internal breaks. Check test lead resistance by:
- Inserting leads in V/Ω and COM inputs.
- Selecting Ω, touching probe tips and being sure the leads are 0.1 – 0.3Ω.
- Ensure independent testing and certification
Be sure to find a multimeter that is independently tested. Rather than getting independent certification, some manufacturers simply state that their products are “designed to meet tough standards” for safety ruggedness and durability. It’s critical to find one that has been independently tested by a third party verification lab such as:
- International Electrotechnical Commission (IEC) the standard setting organization for multimeters.
- Underwriters Laboratories, Inc. (UL), US -based safety organization.
- Canadian Standards Association (CSA), certification entity for the European community.
- ETL Testing Laboratories, Inc. (ETL) for US and Canada.
- TÜV SÜD (TUV), a safety agency based in Germany.
- Use only IEC-rated test tools
NFPA 70E also requires the use of IEC (International Electrotechnical Commission) rated test tools. These tools should meet the meet the following guidelines:
- Look for 600 volt or 1000 volt, CAT III or 600 volt, CAT IV rating on the front of meters and testers, and a “double insulated” symbol on the back.
- Check the manual to verify that the ohms and continuity circuits are protected to the same level as the voltage test circuit.
- Make sure that the amperage and voltage of the meter fuses meet specifications. Fuse voltage must be as high or higher than the meter’s voltage rating.
- Use the meter’s own test capability to ensure that the fuses are in place and working right.
- Step 1: Plug test lead in V/Ω input. Select Ω.
- Step 2: Insert probe tip into mA input. Read value.
- Step 3: Insert probe tip into A input. Read value.
- Verify the meter and accessories are appropriately rated and designed for the system and equipment to which they will be connectedby looking for the following elements:
- DMM category rating.
- Test probes ratings.
- Are any components double-insulated?
- Is DMM NRTL listed?
- Are voltage and current probes NRTL (Nationally Recognized Testing Lab) listed?
- Is a magnetic hangar or other device needed to support the multimeter during use?
Using properly functioning tools is vital to help protect yourself from possible injury and death. Tools that have not been inspected for the above elements or that fail a pre-work inspection should be replaced with new tools from a leading manufacturer.
Rule three you must know a few critical definitions
Continuity- Continuity means that current can flow. When an ohmmeter is placed across a closed circuit it will read ohms this means that the circuit has continuity.
Closed-When the term closed is used in relation to an electrical circuit it means that current can flow or it has continuity.
Open-When the term open is used in relation to an electrical circuit it means current cannot flow or no continuity.
Infinity ohms-This is what an ohmmeter reads when placed on an open circuit. On an analog meter infinity ohms is when the needle doesn’t move at all and on a digital meter infinity ohms is 1 .
In direct current (DC), the electric charge (current) only flows in one direction. Electric charge in alternating current (AC), on the other hand, changes direction periodically. The voltage in AC circuits also periodically reverses because the current changes direction.
Rule 4 can be a deal breaker or life taker without!
PPE is a combination of protective clothing, helmets, goggles, or other garments or equipment to protect eyes, head, breathing, and the full body from splashes, vapors, loose objects, and chemical penetration through personal clothing. The level of protection depends on the level of exposure in the working environment.
Personal Protective Equipment categories
Always abide by the limits of use and minimum working distance. The following PPE categories are described by the National Fire Protection Association (NFPA) Standard 70E. The greater the electrical hazard, the higher the personal protective equipment arc rating must be to withstand an arc-flash incident. Please note that the following chart is a summary only. For a complete list of NFPA standards see NFPA 70E Table 130.7( C)(16)
As the PPE categories increase, so do the arc-rating clothing requirements. The lists may seem similar in some cases, but the variances between categories are significant.
Before you start to test did you cover—do you understand—has supervisor covered?
****Underestimating the dangers of lower voltage levels****
“It’s only 120 volts (or 208 or 480).” The only difference between low and high voltage is how fast it can kill you. High voltage kills instantly; low voltage may take a while longer. A 120 volt shock, for example, can lead to death up to 48 hours after the initial exposure. Take appropriate safety precautions.
When testing for absence of voltage, understanding the difference between backfed and induced voltage is crucial. If a worker tests their meter and it seems to work, and he tests the circuit for the absence of voltage and it appears deenergized, he can be severely injured by the presence of remaining voltage. Injuries from erroneous absence of voltage testing can be caused by:
- Broken leads.
- Unverified test equipment.
- Lack of PPE based on absence of voltage assumption.
- Unmarked or not clearly marked circuit breaker or fuse.
- Look alike equipment (deenergized equipment in same area as energized).
Induced voltage (also known as “ghost voltage”) is often understood as occurring only in outdoor, high-voltage substations. This is incorrect. While that circumstance poses the biggest danger, low-voltage circuits run in cable trays and can also induce voltage into deenergized cables that are in the same tray. The solution is to apply a static ground to the circuit and dissipate the voltage, since an induced voltage does not have any short circuit current capability.
Backfed voltage often originates from another circuit or part of the equipment, but backfed through indicating lights, CPTs, or resistors in equipment. Unlike induced voltage, backfed voltage does have a generation source feeding it and will arc if it is connected to ground.
The solution to both scenarios is to use a combination of test instruments in order to determine whether the voltage is backfed or induced, and then verify the initial results. If you find a circuit that shows voltage when there should be none, be careful what you do next. Creating an arc is an unsafe act and could result in severe injuries. Therefore, when testing for absence of voltage, determine whether the voltage is induced by nearby energized cables or if it is being backfed from an unknown source.
A multimeter is an electronics testing device that, um, tests multiple things, including resistance, voltage, and current. Using certain multimeter models, you can test to be sure that components — such as diodes, capacitors, and transistors — function properly. You can also troubleshoot your circuit to see where current is failing and pinpoint the problem spots.
Voltage testers, circuit breaker finders, continuity testers and receptacle analyzers all detect the presence or absence of electrical voltage.
Voltage testers detect the presence or absence of electrical voltage in cable, wires, circuit breakers, light fixtures, outlets and switches.
Use these to be sure the power is off at an outlet or other device with which you will be working.
- Non-contact voltage testers provide a reading on the wires or devices being tested without needing to touch the wires. They emit a sound or give off a light when voltage is detected, but do not provide a numerical reading of any voltage that’s present.
- Electronic voltage testers measure alternating current (AC) and direct current (DC) and give a numerical reading of the voltage present. Some electronic voltage testers also measure continuity.
Circuit breaker finders identify the circuit breaker that controls an outlet. They consist of two parts: a transmitter and a receiver. The transmitter is plugged into the outlet in question and the receiver is passed over the circuit breakers in the breaker panel.
- When the transmitter passes over the correct breaker, it emits a sound or lights up, making it easy to know which circuit breaker to turn off before you work on an outlet.
- Some circuit breaker finders include a light socket adapter for finding the circuit breaker that controls a light fixture.
Continuity testers are used to determine if a light switch is malfunctioning. They measure whether an electrical circuit is open or closed.
- A light switch circuit is closed when the light is on and open when the light is off.
- Open circuits cannot conduct electricity while closed circuits have continuity and conduct electricity.
- Be sure to turn off power to a circuit before performing a continuity test.
Receptacle analyzers plug into an outlet to tell you whether that outlet is working properly and safely. Some analyzers test both ground fault circuit interrupter (GFCI) outlets and standard outlets. Different lights will glow to show you when the outlet is working, grounded and polarized.
While there are several meter types, a multimeter is the most economical as it performs several functions in one unit.
One multimeter can take the place of a voltmeter, which measures voltage; an ammeter, which measures current; and an ohmmeter, which measures resistance.
- Multimeters come with black and red lead testers, probes attached to the ends of wires, that can be held against battery terminals or inserted into outlets for testing.
- More advanced models measure continuity, temperature and more.
- Digital multimeters display measurements as a number and offer the most reliable readings.
- Analog mulitmeters display measurements across a bar.
- Auto-ranging meters are available that do not require you to manually set the expected voltage range.
- Professional multimeters include features such as backlit displays, work lights, high safety ratings, magnetic mounts and more.
Clamp meters are used primarily to measure current, though many models will also function as multimeters, measuring voltage, temperature and more. While clamp meters are similar to multimeters, they offer the advantage of measuring the current in an electrical conductor, such as a wire, by letting the wire be threaded through the clamp opening, avoiding having to disconnect the wire.
Low-voltage meters are used to test for good connections, opens, shorts and cross connections in cat5, cat5e, cat6 or coax cables, which run phone lines, computer networking cables, home automation networking cables, television signal cables and audio/video distribution cables. These meters also test the connections that keep your home office or home theater equipment communicating.
The test of one’s procedural knowledge Non-contact voltage tester
This is the safest tool to confirm that electrical power is off, even before you touch a wire.
The two most important safety steps to take before opening any electrical box are:
- Turn off the electrical power to that outlet at the main panel.
- Double-check the outlet to make sure you turned off the right circuit. A non-contact voltage tester is the best tool for this job. With this tool, you don’t even have to touch a bare wire. The tester will flash and/or chirp whenever it comes close to a hot wire. It’ll even detect voltage (a hot wire) through the wire’s plastic insulation. However, it’s not reliable when testing wires covered by metal conduit or metal sheathing.
This tester is powered by small batteries, so make sure it works before using it. Shove the tip into the slots of a receptacle that’s live, hold it near a plugged-in lamp cord or hold it against a light bulb that’s on. With most testers, you’ll see a series of flashes and hear continuous chirps that indicate voltage. Testers may flash and chirp at other times, but without the continuous pattern that indicates a hot wire.
This is the most reliable tool to tell if a circuit is complete.
The two-lead circuit tester shown here also tests for voltage. When you touch a live hot wire (black or any other color except green and white) with one lead and a neutral (white) or ground (green or bare copper) with the other, the neon test lamp should light . It confirms that the power is on and that you have a complete (good) circuit. If the light doesn’t come on, either the power is off or you have a bad circuit.
To test a ground wire, follow these five steps:
- Turn the power off to the switch (confirm with the non-contact voltage tester) and uncap the neutral wires (they can remain in a bundle).
- Disconnect the two switch wires and spread the bare ends so they don’t touch one another (Photo 1).
- Turn the power back on and identify the hot wire with the non-contact tester.
- Confirm that the circuit tester is working by carefully touching the hot wire with one lead and a neutral wire with the other. The tester will light if it’s working.
- Touch the hot wire with one lead and the ground wire with the other. If the tester lights, the ground wire is good and you can use it.
Follow a similar procedure when working with metal boxes in which no ground wire comes into the box. In this case, you want to find out whether the metal box itself is grounded (through conduit or another method) and will therefore serve as the required ground.
How a multimeter works
A multimeter has a set of leads: a black one and a red one. You attach these leads to the component or portion of the circuit that you’re testing, and a digital readout provides the results. You adjust a knob to set the test you wish to perform such as resistance, voltage, or current as well as the range to test. Note: Some multimeters have an auto-ranging feature that saves you the trouble of setting the range.
Test leads that typically come with multimeters use simple cone-shaped tips. You can buy test clips that slip onto the cone-shaped tips to make it easier to clip them onto the leads of a component. This makes testing much easier, trust us.
The two things you’ll probably test most often with a multimeter are resistance and voltage.
The problem with resistors is that manufacturers seem to expect you to memorize the color code that identifies the resistance rating. Here is an easier way:
- Clip your test leads onto the resistor leads.
- Dial your multimeter to the resistance range you think the resistor fits in.
- Read the value.
If your multimeter reads 1, you guessed too low of a value. Move the dial to the next range up until you get a valid reading. If your multimeter reads at close to 0 (zero), you guessed too high of a value. Dial to the next range down until you get a valid reading; if you get to the lowest range and the value is still 0, whatever you’re testing has zero resistance.
Testing switches or relays is another common use of the resistance-testing feature of your multimeter. You can clip your test leads onto the lugs of an SPST switch to verify that it’s working. (Hint: Occasionally, they don’t work.) When the switch is open, you should get a value of 1, meaning that the resistance is higher than your meter can measure. When the switch is closed, you should get a low resistance — close to 0 (zero) ohms. You can also test SPDT or DPDT switches or relays to make sure which lugs are connected in which switch position.
To run a test to measure voltage, you connect the red multimeter lead to the positive side of the battery or circuit that you’re testing and the black lead to the negative or ground side and set the dial to the voltage range you expect.
Consider checking the voltage at the contacts of a battery pack. To do this, touch the red lead to one of the battery pack outputs and the black test lead to the other. With a 4-battery pack loaded with fresh batteries, you should get a reading of about 6 volts. (If you get a reading of -6 volts, don’t worry: Just reverse which lead you are touching to which battery pack output.) When batteries get old, the voltage drops. If you get less than 5 volts from a 4-battery pack, it’s time to get new batteries.
When a circuit doesn’t work, one of the first things to check is the voltage between the +V bus and the ground bus of the breadboard. Here’s how:
- Strip both ends of a 3″ piece of 22 gauge wire.
- Clip one end of each wire to one of your test leads.
- Slip the free end of the wire attached to your red test lead into any contact on the +V bus.
- Slip the free end of the wire attached to your black test lead into any contact on the ground bus.
Although you might not get a reading of the full 6 volts because of drain on the battery from the circuit, you should get a reading above 3.5 volts.
If you get a reading close to 0 (zero) volts, check to make sure that your battery pack and the wires from the battery pack terminal block are connected properly.
Important Safety Note in your Hazard Review
Fuses are often overlooked when it comes to electrical testing equipment safety. Yet as a protection against electrical shock and overheating wires, using the right fuse for the job is critical. Taking voltage and current measurements with a tester that does not have the fuse protection that was designed into the tester is extremely dangerous and can cause serious burns and possible death. Fuses matter to safety and picking the right fuse is crucial. Be sure to:
Use fuses the engineer designed into the testing equipment
- For your own safety you need to be sure the fuses you use are the ones the engineer designed into the tester. Always refer to the tester’s manual, or check with the tester manufacturer to ensure you have the correct fuse. Your safety is worth much more than the money it takes to purchase the proper fuse for which the tester was designed.
- Don’t make the beginner’s mistake of substituting inferior fuses once the originals fail, and don’t ever disable the fuse on a job.
Use high energy fuses approved by the meter’s manufacturer
- High-energy fuses are designed to keep the energy generated by an electrical short within the fuse enclosure, thus protecting the user from electric shock and burns.
- These high-energy fuses are designed to limit the length of time the energy is applied and the amount of oxygen available for combustion.
- In addition to the specially designed fuse element, the high energy fuse is filled with sand. The sand will not only help absorb the shock energy created by the exploding element, but the high temperatures (up to 10,000°F) generated by the energy will melt the sand and turn it to glass. The glass coats the element and smothers the fireball by cutting off the available oxygen, keeping you and the tester safe from harm.
- Not all fuses of the same amperage and voltage are the same.
Use fused test probes for additional protection
- A fused test probe has built-in replaceable fuses. Fused probes provide protection to those using multimeters that lack built-in fused protection.
- Fused test probes help protect against arc blast and fire when making voltage or current measurements, as well as against transients on a measured circuit when the transients exceed the capability of the instrument to withstand transients—such as when lightning strikes.
Use safety-rated fuses
- You don’t want a meter that uses just any old fuse. Specially designed high-energy fuses dissipate stray voltage before it reaches you and are designed to blow in time to get you out of harm’s way.
- If your digital multimeter meets today’s safety standards, that fuse is a special safety sand fuse designed to pop before an overload hits your hand. When you change your DMM fuse, be sure to replace it with an authorized fuse.
Manufacturers specify the required amperage, interrupt and voltage ratings for replacement fuses for a reason. If you select a fuse without these ratings you put your safety and the safety of those around you in jeopardy.
High Safety Risk Reminder TWO
Test leads are more than a means to connect your digital multimeter (DMM) to the unit under test; they’re an integral part of measurement safety. Poorly made, worn, or under-rated test leads can cause inaccurate readings and may pose a serious shock or electrocution hazard if you touch live wires that the meter has read, assuming they’ve been de-energized.
Here are some guidelines to ensure leads are safe to use in test measurement:
- Look for high quality leads made of good materials
- Leads made from poor quality, dissimilar materials can affect the readings recorded on the DMM.
- Be sure to use the leads that are rated for the appropriate category and voltage level
- Confirm that both the DMM and test leads are rated for the appropriate category and voltage level.
- The CAT rating on the leads should match or exceed the category of the DMM, and the two together are appropriately rated for the job.
- Ensure exposed metal matches the energy potential of a given measurement
- The higher the CAT rating, the less exposed metal is allowed at the tip of the test lead.
- Use retractable probes, probe tip covers or probes with shorter tips to avoid an inadvertent short.
- Inspect the leads
- Check to make sure insulation is not nicked or cracked and that there are no signs of gaps or cracks between the insulated wire and the molded banana plugs or probes at each end.
- Test the leads
- Conduct an ohms measurement to confirm leads are electrically reliable and able to carry a signal.
- To “ohm out” your leads, place your DMM in the resistance function, plug the leads into the meter and touch the probe tips together red to black. The meter should read about .5 ohms or less for good quality test leads.
Regardless of the quality of your multimeter, it’s only as good as the test leads you use with it. Taking a few minutes up front to confirm the leads you’re using are reliable and appropriately rated for the job are essential to ensure your electrical measurement safety.