Safety

Safety is competency 1.0 for a reason — it comes first. The Associate CET exam expects you to know how electricity injures, how to work on equipment safely, the fire classes, and how to respond to an incident. These are high-yield, memorizable facts; this page collects the ones the exam draws from. Sections 7–16 cover the rest of competency 1.0: first aid, fuses, the NEC and OSHA, arc flash and NFPA 70E, meter CAT ratings, RF exposure, fiber, tools, ladders and service vehicles. Section 17 is job practice.

How electricity injures — it's the current

The single most important safety concept: current, not voltage, is what harms you. Voltage is what drives current through your body, but it's the amount of current and its path that determines the danger. As little as 100 mA through the chest can cause ventricular fibrillation — the most common cause of death by electric shock.

The figures are OSHA's, for a one-second, 60 Hz shock from hand to foot, drawn from NIOSH's 1998 report on worker electrocutions. Other texts round them differently; the order of the effects is what matters.

Reducing the risk

Because current depends on the path and on body resistance, the practical rules all aim to keep current from flowing through you:

One hand behind your back when probing live circuits keeps current from crossing your chest hand-to-hand. Discharge capacitors before working — a charged filter capacitor in a power supply can hold a lethal charge long after power is removed. Use a GFCI on bench outlets, keep one hand in your pocket, remove rings and watches, and never work alone on dangerous equipment.

Lockout / Tagout (LOTO)

Lockout/Tagout is the procedure for making sure equipment stays de-energized while it's being serviced. You physically lock the energy-isolating device (a breaker or disconnect) in the off position and attach a tag identifying who locked it and why. Only the person who applied the lock removes it.

1. Notify everyone affected that equipment is being shut down for service.
2. Shut down the equipment by its normal stopping procedure.
3. Isolate the energy source (open the disconnect/breaker).
4. Lock and tag the isolating device in the off position with your own lock.
5. Release stored energy — discharge capacitors, bleed pressure, block parts that could move.
6. Verify zero energy: test that the equipment won't start and measure that voltage is actually gone.

Fire classes & extinguishers

A technician must know which extinguisher fits which fire — using the wrong one can make things worse (water on an electrical fire is a shock and spread hazard).

ESD — protecting the components

Not all safety is about protecting people — Electrostatic Discharge (ESD) protects the parts. A static spark you can't even feel (hundreds of volts) can destroy or weaken sensitive devices like CMOS chips and MOSFETs. Control it with a grounded wrist strap, an ESD mat, anti-static bags, and a humidity-controlled bench.

Where static comes from (competency 1.5). Charge builds by triboelectric charging: when two materials touch and then separate, electrons move from one to the other. Walking across carpet is the classic case, and dry air makes it far worse. The ESD Association lists about 35,000 V for walking on carpet at 10–25% relative humidity, against about 1,500 V at 65–90%. Humidity lowers the charge but never removes it. Ordinary plastics, foam cups and packaging charge easily and have no place on an ESD bench.

How it damages parts. The discharge current can punch through the thin gate oxide of MOS and CMOS devices and burn out junctions and metallization. Some parts die at once, a catastrophic failure that testing usually catches. Others are only weakened: they keep working, then fail early in service. There is no practical screen for these latent defects (TI calls them "walking wounded"), so a part that still works after careless handling is not proof that it is undamaged.

Responding to a shock incident

First aid and emergency response

Competency 1.2 asks why first aid matters so much to people who work on electrical and electronic equipment, and what an untrained helper must and must not do. Competency 1.14 asks for the emergency response to each hazard on this page.

A shock can stop the heart or breathing, and help has to start before the ambulance arrives. OSHA's power-line standard shows how seriously that is taken: 29 CFR 1910.269, which covers electric power generation, transmission and distribution work, requires people with first-aid training, which includes CPR, wherever its crews work on exposed lines or equipment energized at 50 V or more: at least two at a field location with two or more workers, and at a fixed site such as a substation, enough that anyone exposed to shock can be reached within 4 minutes. Most bench work falls under OSHA's general first-aid rule instead: 1910.151 requires a trained first-aider when no clinic or hospital is close by, and eyewash or drench facilities wherever corrosive material, such as battery acid, can reach the eyes or body. Telecommunications work, including two-way radio field installations, also falls under 1910.268, which requires first-aid training that includes instruction in artificial respiration (1910.268(c)(3)).

Fuses and circuit breakers

Competency 1.4 asks for the fusing and breaker rules and the reasons for the different fuse types. A fuse or breaker protects the wiring and the equipment from overcurrent. It does not protect you: a 15 A breaker is built to carry 15 A, and the 100 mA that can stop a heart is less than 1% of that. Protection for people comes from GFCIs, which trip at about 5 mA of leakage, and from safe practice. Every fuse carries four ratings:

That is why there are different types. A motor, a transformer or a capacitor-input power supply draws a large inrush current at switch-on, so a fast-acting fuse there blows every time the unit starts: it needs a time-delay fuse of the same current rating, with a voltage rating equal to or greater than the circuit voltage. A load with no inrush, or parts that can't survive even a short overcurrent, gets a fast-acting fuse. A meter's current input is the extreme case: use only the high-energy fuse its maker specifies. If you must pull or install a fuse whose terminals are energized, OSHA requires fuse-handling equipment insulated for the circuit voltage (1910.335(a)(2)(i)(A)).

Codes and rules: the NEC and OSHA

The NEC (competency 1.3). NFPA 70, the National Electrical Code, is the installation rulebook. NFPA revises it every three years (the 2026 edition replaced 2023), but an edition has legal force only where a state or city adopts it, and adoption varies: in 2026, Texas and New York enforce the 2023 NEC while Pennsylvania enforces 2020. The local authority having jurisdiction (AHJ) inspects the work. In practice a technician complies by knowing which edition and local amendments apply where they work; by using listed equipment and installing it as its listing instructions say, which the NEC makes mandatory (110.3(B)); by using the cable listing the space requires (plenum or riser, see Cabling); and by never altering overcurrent protection to make something work.

Other OSHA rules (competency 1.10.3). OSHA sets the legal minimum for US workplaces. The rules a technician meets most often:

Arc flash and NFPA 70E

An arc flash is the sudden release of electrical energy through the air when the insulation or spacing between conductors breaks down (NIOSH). Arc temperatures have been recorded as high as 35,000 °F; the light and heat cause burns, and the arc can heat the air so fast it makes a blast that throws molten copper and aluminum. Competency 1.10.1 asks for the protective equipment (PPE) this needs, and cites NFPA's Table 130.5(C).

That table comes from NFPA 70E, Standard for Electrical Safety in the Workplace. The current edition is 2024 (as of 2026); a 2027 edition is in development. Employer electrical-safety programs are built on it alongside OSHA's rules. It is a copyrighted standard, so this page teaches its ideas and does not reproduce its tables. Its first rule is to remove the hazard: put the equipment in an electrically safe work condition (disconnect it, lock and tag it, test for absence of voltage, and ground it if needed). Energized work is allowed only when de-energizing would create a greater hazard or is infeasible, the same test OSHA uses in 1910.333.

Testing for absence of voltage is the step that turns "switched off" into "safe to touch"; the method is called live-dead-live. NFPA 70E has you use an adequately rated tester on each phase conductor or circuit part, phase to phase and phase to ground, at each point of work. If no live source is nearby (up a tower, for example), a battery-powered proving unit can serve as the known voltage.

Meter CAT ratings

A meter's CAT rating (its measurement category under IEC 61010) tells you where on the power system it is built to survive a transient, a short high-voltage spike that can arc across inside an under-rated meter while it is in your hands. The rule of thumb: the closer you measure to the utility source, the more fault current is available and the higher the category you need. OSHA requires test instruments and their leads to be rated for the circuits they connect to, and inspected before use, and only qualified persons may do testing work on electric circuits (1910.334(c)). This supports competencies 1.10 and 8.3.

The voltage and the category both matter. Within one category, a higher voltage rating means a bigger test spike. A step up in category matters more, because the test comes from a lower source impedance. In Fluke's comparison, a CAT III 600 V meter is tested with a 6,000 V impulse from a 2 Ω source and a CAT II 1000 V meter with the same 6,000 V from 12 Ω. That is a peak of 3,000 A against 500 A, so the CAT III 600 V meter is the safer choice in a panel despite its lower voltage number. The voltage rating must still cover the circuit: a CAT III 300 V meter does not belong on a 480 V panel. Test leads carry their own rating, and the set is only as good as its lowest-rated part. Look for the mark of an independent testing lab (UL, CSA, TÜV); a CE mark is the maker's own declaration.

RF exposure and MPE

Competencies 1.8 and 1.10.2 cover RF transmitter hazards and MPE, maximum permissible exposure. Strong RF heats tissue. The eyes and testes are the most vulnerable, because they have little blood flow to carry heat away (FCC). Touching metal in a strong field (a guy wire, a fence, a vehicle) can also give an RF shock or burn; NIOSH found exactly that hazard at a high-power VLF transmitter site. Three documents set the limits:

Controlled vs uncontrolled. The FCC's occupational/controlled limits apply to people exposed because of their job who are fully aware of it (they have been told about the exposure and trained to control it) and can exercise control over it. Everyone else gets the general population/uncontrolled limits, including workers who aren't aware or can't control their exposure. Controlled limits average over 6 minutes, uncontrolled over 30 minutes.

Why the limit depends on frequency. The body absorbs RF most strongly near its whole-body resonance, about 70 MHz for a standing, ungrounded adult, so the limits are tightest from 30 to 300 MHz. From 300 to 1,500 MHz they rise in proportion to frequency, and above 1,500 MHz they are flat:

Fiber optic hazards

Competency 1.9 lists the hazards of optical fiber to the skin and eyes. There are three, and the Optical & Fiber guide covers handling.

Tool hazards

Competency 1.6 asks for the hazards of the tools you use in the shop and in the field. OSHA makes the employer responsible for the safe condition of every tool, including ones the employees bring (1910.242(a)). Soldering burns and fires are competency 5.1, on Soldering.

Ladders and working at heights

Competency 1.11 covers ladder handling (the ANSI A14 standards) and OSHA's working-at-heights rules: 29 CFR 1910.23 in general industry and 1926.1053 in construction.

Service vehicle safety

Competency 1.12 lists service-vehicle concerns: securing ladders and loads, flying objects, and driver screens. It matters because motor-vehicle crashes are the leading cause of work-related deaths in the US (NIOSH).

On the job: three walk-throughs

Job practice, not exam content. These show how the rules above fit together on real work. Your employer's procedures and training come first; these are illustrations, not a qualification.

1. Lockout and live-dead-live at a radio shelter. You are replacing a hard-wired rectifier fed from a 240 V breaker in the shelter's panel.

1. Find every source. The breaker, but also the battery plant, a generator or UPS, and any backfeed. OSHA's test must also catch induced voltage and backfeed.
2. Open and lock. Open the breaker, then lock and tag it with your own lock.
3. Pick and check the meter. At a branch panel and fixed equipment you need CAT III, with a voltage rating of at least 240 V. Inspect the meter and leads for damage.
4. Live. Prove the meter on a known live source: a live circuit nearby, or a proving unit.
5. Dead. At the rectifier's terminals, test each conductor to each other and to ground.
6. Live again. Re-prove the meter on the same known source. Only now treat the circuit as de-energized.
7. Stored and other energy. The rectifier's output capacitors and the DC battery plant are still live: discharge or isolate them, and wear battery PPE.
8. Restore. Clear tools, tell the people affected, and remove your own lock yourself.

2. Choosing the meter for the measurement. Match the category to where the probes go, and the voltage rating to the circuit.

3. A rooftop RF check before you work. Before you step in front of anything on a roof or tower:

1. Know the antennas. Read the RF signs and the site's exposure information, and find every antenna that can transmit near your work spot.
2. Know your tier. The controlled limits apply only if you have been informed and trained and can control your exposure. An untrained helper is in the general-population tier.
3. Compare. At 851 MHz the limits are 2.84 (controlled) and 0.57 mW/cm² (uncontrolled). A measured 1.4 mW/cm² at your spot is within the controlled limit but over the general-population one, so the untrained helper should not stay there.
4. Reduce. Stay out of the main beam, keep your distance, keep your time short, or arrange a power reduction or shutdown with the site owner.
5. Don't touch or look. Never look into an open waveguide, avoid grabbing metal that may carry induced RF, and report any RF burn or shock.