High Voltage Safety

Electricity doesn't give warnings. It doesn't care how careful you think you are. It kills in a fraction of a second.

This guide covers the specific safety procedures for builds that involve dangerous voltages. If a build uses a microwave oven transformer (MOT), CRT flyback transformer, capacitor bank, or any voltage above 50V AC / 120V DC, this guide applies.

Understanding the Danger

It's not the voltage that kills — it's the current flowing through your body. But voltage determines whether current can flow at all (it has to overcome your skin's resistance). Here's the reality:

Key fact: A MOT delivers 2,000V at 500mA-1A. It takes only 100mA through the heart to cause ventricular fibrillation (cardiac arrest). A MOT delivers 5-10 times the lethal current. There is no "minor shock" from a MOT.

Capacitor Discharge Procedures

Capacitors store electrical charge and can deliver it all at once — even when the device is unplugged. A charged capacitor is a time bomb sitting in your project.

Microwave Oven Capacitors

MOT capacitors are typically rated at ~2,100V and 1µF. They store enough energy (approximately 2.2 joules) to be lethal.

Discharge procedure:

1. Unplug the microwave and wait 60 seconds.
2. Build a discharge tool: Connect a 10k ohm, 50-watt resistor between two insulated-handle screwdrivers or probes. The resistor limits the discharge current, preventing violent arcing. A 10W resistor is NOT sufficient — peak power during discharge can exceed 400W momentarily, and an undersized resistor can fail open, leaving the capacitor still charged.
3. Touch both probes to the capacitor terminals simultaneously. Hold for 10 seconds. You may see a small spark — that's the stored charge dissipating through the resistor.
4. Verify with a multimeter set to DC voltage. Read across the capacitor terminals. The reading should be less than 1V. If it's higher, discharge again.
5. Short the terminals with a screwdriver (insulated handle) as a final safety measure. You should see no spark if the discharge was successful.

NEVER just short a capacitor with a screwdriver without the resistor. The instantaneous discharge can weld the screwdriver to the terminal, arc-flash, or damage the capacitor (causing it to rupture or leak).

CRT Anode Capacitor

The CRT tube itself acts as a capacitor. The inner coating (aquadag) and outer coating form the two plates, with the glass as the dielectric. The anode can hold 10,000-30,000V for weeks after unplugging.

Discharge procedure:

1. Unplug the TV and wait at least 5 minutes.
2. Build a discharge tool: Connect a 10M ohm, 25-watt resistor to a thick insulated wire, with one end clipped to the chassis ground (metal frame or the grounding strap on the CRT). Peak power during discharge can reach 10W, and a 5W resistor can fail — use a higher-rated resistor for safety margin.
3. Wearing insulated gloves, slide the other end of the wire under the rubber anode cap on the side of the CRT tube. You should hear a loud SNAP — that's the stored charge.
4. Leave the discharge wire connected for 30 seconds to drain any residual charge.
5. Verify: Disconnect and reconnect the discharge tool. If there's a second snap (smaller), repeat. Some CRTs have "bounce back" — they rebuild a partial charge after initial discharge.

Capacitor Banks (Electromagnetic Can Crusher, Coil Gun, etc.)

These are the most dangerous capacitors in any build — banks of large electrolytic capacitors charged to hundreds or thousands of volts, storing tens or hundreds of joules. Enough energy to cause severe burns or cardiac arrest.

Rules:

• ALWAYS have a physical discharge mechanism built into the device — a high-wattage resistor (or bank of resistors) that can be switched across the capacitor bank to drain it safely.
• Verify voltage with a multimeter before touching anything, every single time.
• Treat every capacitor as charged until you personally verify it's discharged. Don't trust someone else's word. Don't trust that you "already discharged it."
• Bleeder resistors: Install a permanent bleeder resistor across the capacitor bank. This slowly drains the charge over time as a passive safety measure. It does NOT replace active discharge procedures.

The One-Hand Rule

When working on or near high-voltage circuits:

Keep one hand in your pocket or behind your back.

This is not a joke. This is standard practice in electrical engineering labs, power companies, and any environment where lethal voltage is present.

Why: If you touch a high-voltage source with both hands, the current path goes hand-to-hand THROUGH YOUR HEART. This is the most lethal shock path. If you touch it with one hand only, the current path goes through that arm to ground — still dangerous, still painful, but much less likely to cause cardiac arrest.

Practice this every time you're near energized high-voltage equipment. It should become automatic.

Required Equipment for HV Builds

High Voltage Builds — Voltage Table

What to Do if Someone Gets Shocked

If They Are Still in Contact with the Electrical Source

1. DO NOT TOUCH THEM. You will become part of the circuit. You will also be shocked.
2. Cut the power. Flip the kill switch, unplug the device, or turn off the circuit breaker. If you can't reach the power source safely, use a DRY non-conductive object (wooden broom handle, dry rope, thick rubber mat) to push the person away from the source.
3. Call 911 immediately.

After They Are Free from the Source

1. Check responsiveness. Call their name, tap their shoulder.
2. Check for breathing and pulse. If they are not breathing or have no pulse, begin CPR immediately. Electrical shock causes cardiac arrest — CPR can save their life if started within minutes.
3. Call 911 if you haven't already. Tell them: "Electrical shock, [voltage if known], [person is/isn't breathing]."
4. Look for burns. Electrical burns occur at the entry and exit points of the current. These may look minor on the surface but can be severe internally. Cover burns loosely with a clean cloth.
5. Do not move the person unless they are in continued danger (near fire, ongoing electrical hazard).
6. Keep them warm and comfortable until emergency services arrive. Shock victims can go into physical shock (low blood pressure, cold skin).

Preventing the Situation

• Always use a kill switch within arm's reach.
• Never work alone on builds above ⭐⭐⭐.
• Make sure your helper knows where the kill switch is, what to do if you get shocked (DO NOT TOUCH, cut power first), and to call 911.
• Have a charged phone nearby — not across the shop, not upstairs.

Electrical Fire Safety

Electrical fires are Class C fires. Standard rules:

• NEVER use water on an energized electrical fire. Water conducts electricity — you'll be shocked.
• Use a Class C rated fire extinguisher (CO2 or dry chemical). ABC-rated extinguishers are also safe for electrical fires.
• If possible, de-energize first. Once the power is off, it becomes a Class A fire (ordinary combustible) and water is safe.
• Capacitor fires: If a capacitor ruptures and catches fire, the electrolyte is flammable. Keep distance. The burning electrolyte produces toxic fumes. Ventilate the area.

Specific Component Warnings

Microwave Oven Transformers (MOTs)

• The secondary winding outputs ~2,000V at 500mA-1A. This is 5-10x the lethal current level.
• MOTs are intentionally designed to deliver high current — they are NOT current-limited like neon sign transformers.
• The secondary winding is often connected to the core (chassis ground). Touching the core while touching the secondary output = shock.
• Always remove the magnetic shunts intentionally if you want more power, but understand that this makes the transformer even more dangerous.

Capacitors

• Treat EVERY capacitor as charged until you personally verify it's discharged with a multimeter.
• Oil-filled capacitors (MOT caps) can rupture and leak carcinogenic PCB oil (in older units). Dispose of properly.
• Electrolytic capacitors can explode if connected with reversed polarity or charged beyond their rated voltage. The explosion sprays caustic electrolyte.

CRT Tubes

• The anode holds charge for weeks. Discharge EVERY time, even if "you just discharged it yesterday."
• The tube is under vacuum. A broken CRT implodes, sending glass in all directions. Handle with extreme care. Wear goggles.
• The phosphor coating contains toxic compounds. Never break the screen intentionally.

Neon Sign Transformers (NSTs)

• Lower current than MOTs (typically 30-60mA) but much higher voltage (2,000-15,000V). Still dangerous and potentially lethal.
• NSTs are current-limited, which makes them slightly less dangerous than MOTs, but "less dangerous" is not "safe."

The Golden Rules

1. One hand at a time. Always.
2. Discharge first. Always.
3. Verify with a meter. Always.
4. Kill switch within reach. Always.
5. Someone knows what you're doing. Always.
6. When in doubt, don't. Always.