Safety guidelines for building electronics equipments

This document intends to give you some guidelines how to to make your homebuilt electronics equipments safe. I have tried to make those guidelines to be as caaurate as possible. However, I do not assume, and hereby claim, any liability to any party for any loss or damage, direct or consequential, caused by errors in those guidelines.

The safety requirements refer mainly to the 230V mains voltage and European electrical safety requirements.


Equipments must be designed and built so that they do not cause danger to the operator or the environment in the normal operation or in case of equipment damage. Especially take ce of the shielding against electrical shocks, high temperatures, explosion and fire.

There are two classes of insulation:

Class I characteristics

Class II characteristics

If you are designing electronics product you should aim for making your products class II. They are easier to sell abroad. If you need to provide the equipment as class 1 you should be very clear in the installation instructions of the correct methods for wiring the equipment to a supply.

Practical considerations on building safe equipments


The fuse is to prevent overheating or fire hazard in case of a short. The protection for user is not by fuses, instead the ground bonding for the class 1 and double/reinforsed insulation for class II would be to ensure the protection of user against electrical shock.

Mechanical construction


Special details on building Class II equipments

When the power switch is not required ?

Power on/off switch is nit required if the power consumption of the equipments is less than 10W or if the equipment is intended for continuous use.

An on/off switch not in the mains circuit is allowed if the transformer has isolated promary and secondary coils and power consumption in "off" position is less than 10W. There must be a visible indication that the equipment is plugged in.

Information sources

Some additional tips when operating with line powered electronic circuits

Three rules when working with line powered electronics equipments

That way you live longer when you work with mains powered equipments. Failing to follow all 3 rules may shorten your life span.

Additional safety tips when operating with mains powered equipments

Tomi Engdahl <[email protected]>