Safety

Risks

AC kills you, fire kills your family.

Please ask for someone's help, if it's outside of your comfort zone. They will probably be glad to do so rather than you risking your life.

Keep the AC side isolated from physical access
Never work on the AC side without unplugging the power cable
Keep a fire extinguisher on hand
Turn power off and don't hot plug jumpers or cables
Do not leave your printer unattended for long periods of time
Let someone know you are printing, have a camera, VPN access and a backup system such as a smart smoke alarm connected to a remote relay
Don't be ignorant

Test how your system's design prevents or mitigates unsafe consequences of the system's failure
Think of how the system will react to fast or slow failures
- A slow discharged short though a resistance which won't trip fuses
- MOSFETS and SSRs failing in a closed circuit causing a thermal runaway
- Short circuits on high voltage sources
- Accumulated heat on improper connectors with high resistance
- Software safety systems freezing or becoming offline

Do not insert tinned wire into screw down terminals. Crimp ferules or twist the bare copper wires.
Do not leave any AC bare wires exposed
Do not insert ferules or tinned wires into WAGO type connectors
Check your spade connectors fitting tightness and check the surrounding temperatures after a couple of minutes of operation
Ensure that cables are secured with strain reliefs
Ensure that appropriate cables and are chosen for motion applications
Look for points of potential wear and drag fatigue damage

Cutting, drilling, or sanding carbon fiber or glass fiber has to be done in a well ventilated space and wearing a respirator mask. Wetting the surface helps to minimize the airborne particles.
Please research the safety recommendations regarding processing carbon fiber, or other composite materials.

Note: These are common sense tips based on my personal experience, and are not coming from an authorized professional.