Many threads in diyAudio Forum deal with mains connected equipment and/or equipment capable of producing dangerous voltages and powers. This page is here to tell you about the safety rules you need to know about before you embark on your “DIY adventures”.
Electronic equipment is dangerous. Every person is responsible for deciding if they are willing to risk their life, and for ensuring that whatever information they receive is correct. This forum and it's members accept no responsibility for any death, injury or property damage that result from any of these suggestions; your safety is your own responsibility
Before worrying about how safe your electronics are (this is just as critical, but it comes later on in the cycle), you need to consider your own personal safety while working with your electronics projects.
Several members of this community can tell you stories of people who have been killed whilst working with electricity. In some cases, these were people who knew the rules and, because of a mere moment's carelessness [they lost the fear] they left friends and families to mourn them.
This is serious stuff. Too much fear is better than not enough.
How Much (or How Little) Will Kill You?
"It's mils that kills and volts that jolts"
It always is milliamps of current that will kill you. The general rule of thumb is that voltage will give you a jolt; it's what gives you the tingles or causes your muscles to contract.
Current is what kills you and it doesn't take much; a few milliamps (mA) running through your body, for a just a few seconds, can stop your heart.
You can actually withstand a considerable amount of voltage as long as the voltage doesn’t travel a long distance through your body such as from the front of your finger to the back of your finger (or between the probes on a tazer).
The Best Way to Learn
The safest way to learn electrical safety is by spending time around experienced people. Never work alone.
If you intend to work with high voltages (1000V+) all of the rules are different and you would be INSANE, no, SUICIDAL to tackle that kind of project without the direct supervision of someone who experienced in that field.
The following best practices are not applicable in these cases. You really do need to learn from people who know what they are doing as there are just so many ways that high voltage systems can electrocute you (like arcing through the air just because you are standing too close to them).
What is electrical safety?
The European Standard “IEC 60950-1” defines that electrical safety relates to protection from:
On top of that, there are many other normative reference that stipulate rules and regulations dedicated to electronic equipment safety, such as fire hazards, risk of injury, etc.
Mains Power Safety
Use a wall-wart supply!Whenever possible, it is recommended to use commercially available and approved (UL, VDE, KEMA) power supplies to power your equipment. These power supplies are tested for safety by independent institutions, they are readily available and usually quite cheap as well.
Safety ClassificationsIf it is necessary to build a mains-connected application, protection against electric shock can be provided in two classes:
Class I equipment uses basic insulation; its conductive parts, which may become hazardous if this insulation fails, must be connected to the supply protective earth. Examples are computer power supplies and kitchen appliances.
In summary, Class I isolation requires adequate insulation between mains and any user accessible part, capable of withstanding a test voltage of at least 2120V peak. An isolation distance of at least 3 mm must be maintained between any user accessible part and mains carrying parts. Furthermore, any conductive, user accessible part must be adequately connected to the safety ground.
Class II equipment uses double or reinforced insulation for use where there is no provision for supply protective earth. Examples are power tools, hair dryers and cell phone chargers.
The double insulation requirement means that the insulation between mains and any user accessible part is capable of withstanding a test voltage of at least 4240V peak. An isolation distance of at least 6 mm must be maintained between any user accessible part and mains carrying parts.
In practice, it is recommended to separate mains carrying parts and user accessible part as much as possible, but never less than required (see above).
When building a power supply, the use of a Class II insulated transformer is preferred, but note that when this is fitted in a Class I equipment, this does not, by itself, confer Class II status on the equipment.
When the mains enter your projectIt is always recommended to use an approved mains entry with an integrated fuse holder and switch. If this is not possible, you should do the following.
Safety GroundAnyone constructing a Class I equipment, must pay special attention to proper safety grounding:
Source: Elektor Construction and Electrical Safety Guidelines (Dutch, English)
!!! DO NOT MESS WITH MAINS !!!
Threads of interest
The following are other threads where safety in certain situations have been discussed.
* Safety Practices: General and Ultra-High Voltage
* Safety First
* 83 safety rules
* Safety issues and CE Certification
* Document on electric safety
* Auto Transformer - safety advice
* On soft start circuits and safety
* Power Supply Safety
* Safety Question about Capacitors
* Electrical safety with pcb mount transformer
* Question regarding 3rd wire grounding and safety
* Building a class II PSU (double insulated, no safety earth)
* Workbench safety practices?
* one safety question (Painting components)
* Safety question concerning ground loops
* Safety with high volts: 101
* Safety when testing headphone amp for muso's
* SMPS -- "safety and the 5 cent zener"
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