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Questions tagged [safety]

*Your* health and safety while working on electrical devices, and designing devices that will not shock, set fire to, or otherwise harm the user of the device.

71
votes
8answers
12k views

Can a bird, previously at earth potential, get electrocuted by landing on a powerline at high-enough voltage due to the initial “equalization charge”?

At the voltage levels of typical overhead transmission lines in the US, a bird can land on one and be just fine (as long as it doesn't do something like spread its wings and touch a tree or something ...
62
votes
8answers
347k views

How much voltage/current is “dangerous”?

Related: Safe current/voltage limit for human contact? From what I've heard: 110 V (or 220 V; household voltage pretty much) is dangerous (i.e. can kill you) I think there's consensus on this, ...
60
votes
3answers
94k views

How is using a transformer for isolation safer than directly connecting to the power grid?

How is using a 1:1 transformer safer than using the mains straight off? Is it because you can limit the current coming from the transformer whereas straight from the mains its not current limited? I ...
51
votes
13answers
10k views

What kind of components in a computer power supply can explode loudly?

Today I heard a loud bang that tripped the circuit breaker in my server room. It must have been really loud because I could hear it 2 rooms away through 2 heavy doors and it was like a firecracker ...
51
votes
7answers
10k views

Does a dangling wire really electrocute me if I'm standing in water?

We've all seen this scenario in movies; somebody has to cross a room half filled with water and there is a dangling electric wire that shoots sparks everywhere. The poor person has to cross the room ...
49
votes
5answers
156k views

How much current can I draw from the Arduino's pins?

What's the maximum amount of current which I can draw from each of the Arduino's pins without tripping any of the internal fuses? Is there a limit per pin as well as an overall limit for the whole ...
44
votes
9answers
28k views

How safe is 48V DC?

In many Power over Ethernet (POE) setups the transmission voltage is 48V or slightly more. While higher voltage has obvious efficiency advantages, how safe it is? Is there any risk of electrocution ...
38
votes
1answer
2k views

What is / how can I get a student-safe power supply for electronics projects?

What is / how can I get a student-safe power supply for electronics projects? I'm looking for a student-safe power supply for solder less breadboard. I'm developing a course to teach electrical ...
31
votes
4answers
44k views

Safe current limit for human contact?

What's the point below which electrical current is generally considered safe for "casual" human contact? Is either voltage or amperage more "dangerous" (e.g. high voltage / low amperage vs. low ...
29
votes
11answers
14k views

Multimeter exploded during ACV measurment - What did I do wrong?

simulate this circuit – Schematic created using CircuitLab A DT-830B meter. I bought a new transformer, and I was trying to measure the output voltage. I plugged the probes on 'VΩmA' (not 10 A)...
26
votes
5answers
15k views

Why are Edison screws allowed to be used? [closed]

Why are the Edison screws allowed to be used? They seem unsafe. Why are they designed that way? They require a complete grounding system to ground devices for the rare situation where the hot wires ...
26
votes
10answers
15k views

Is it safe to sleep in the same room with a car battery?

I sleep in the same room with 2 car batteries. I'm not a battery person so I don't know what type they are. I tried looking for voltage but didn't find it printed on the battery. They're standard acid ...
25
votes
2answers
6k views

What is an “XY” rated safety capacitor, exactly?

Please help me understand this. In a prominent, 480v, 6kW AC servo drive, across three input phases, three 22mm "XY" class 10nF caps are placed for EMI suppression. Also, from these three phases, ...
23
votes
5answers
75k views

Fuses: What are the practical differences between Ceramic and Glass cartridge fuses

What are the practical differences between ceramic and glass tube cartridge fuses? I am trying to find new fuses for a piece of consumer electronics. The original fuses are going out of production. ...
22
votes
2answers
5k views

Why do condors get electrocuted by power lines?

Plenty has been said about why birds are safe to land on power lines. But condors, apparently, are not. The linked article explains that condors are electrocuted often enough and endangered enough ...
22
votes
8answers
24k views

Why are some AC outlets and plugs polarized?

This will show my naivety when it comes to alternating current... but why are some plugs and sockets on AC outlets polarized (one prong is taller than the other)? (See this question on DIY.) (Or this ...
20
votes
3answers
12k views

Is it OK to solder a power cord?

A few people have advised me to never solder a power cord directly to a PCB, but they couldn't explain why not. Why can/can't I solder it directly?
20
votes
3answers
11k views

How to water-protect my Arduino?

I am building a watering system with an Arduino. Basically it runs on a track with a hose that drips water down on plants a couple of times every day. Its outside, and water might sometimes get from ...
19
votes
6answers
8k views

How did I survive this shock? [duplicate]

When I was about 10 years old playing with lamps, I accidentally picked up a wire completing a circuit for a lamp plugged into the wall (120 V AC U.S. standard). I'm not sure if it was the hot or ...
19
votes
11answers
4k views

How to safely discharge oneself

At work I have the problem that I seem to collect a lot of static charge as soon as I leave my desk and return. I am not quite sure why this happens. Strangely enough the effect is stronger the ...
19
votes
13answers
4k views

Path for a child to learn electrical engineering

What are some paths for a child (7-year-old) to learn electrical engineering (in a safe way)? I do not want to saturate (or frighten away) the child with lots of concepts, I want that my son learn ...
19
votes
3answers
3k views

How could using an ungrounded appliance with a grounded extension cord be a fire hazard?

My local fire department, @Barrie_Fire, recently tweeted (then subsequently deleted) this: Don’t even THINK about using a 2-prong plug in a 3-hole slot! Use only the required number of slots in ...
19
votes
4answers
30k views

How much current can Solderless Breadboards handle?

I'm working on a project with a few stepper motors. I want to breadboard them so I know the circuit works well before creating a physical PCB. Each of the three motors is rated 2A, but I'll be ...
18
votes
6answers
11k views

How does earthing work when earth is dry?

Earthing is meant to provide reliable contact of an electric appliance to earth so that if there's an insulation fault current goes into earth instead of through a person's body. This requires ...
18
votes
3answers
33k views

Are UV LEDs really dangerous?

I just bought some UV LEDs I bought them for testing banknotes and identity papers. I read the documentation and saw some warnings about UV light in which the vendor advises not to look directly at ...
18
votes
3answers
2k views

Health risks of exposed contact to a capacitive sensor

I want to make a wearable metal trinket with the ATtiny85 chip acting as a capacitive sensor (with the same technique that this Arduino library uses), so it can detect when it's being worn. Are there ...
18
votes
4answers
37k views

Guidelines for determining shock hazard of capacitors

I'm looking for guidelines on how to identify capacitors which have the potential to cause pain, injury or death due to electrical shock if not handled correctly. I recently purchased a "getting ...
17
votes
3answers
8k views

Electrocution in rubber swimming pool?

This doesn't immediately look so good, but if you think about it, why shouldn't it be? If the extension cord drops in, why should the electricity choose to flow through any of them, instead of just ...
17
votes
3answers
4k views

What operation could cause the inductor or the capacitor to explode?

In really early days of electronic school, the teacher used to say something about not unplug power too quickly at an inductor or capacitor and we were used to slowly turn the voltage generator from a ...
17
votes
5answers
16k views

How to safely dispose of a damaged lithium ion battery?

I replaced a lithium ion battery in a device and the old battery is swollen/bulging but no otherwise damaged. My municipality (NYC) requires many retailers to accept batteries or devices containing ...
16
votes
5answers
11k views

Is this true: “At over 700 Hz, current simply flows over your body”?

I have heard this in a movie clip. I was just curious to know, is this really true? Because the one thing that I do know, is that at a high voltage, the current decreases, so that it doesn't harm a ...
16
votes
7answers
4k views

What if I overload a cheap AC adaptor?

I'm experimenting with PIC microcontrollers and various related circuits both on plugboards and simple homemade PCBS. I'd like to use various old AC power adaptors I have lying around to power my ...
16
votes
2answers
3k views

Why are caps configured this way in EMC filters?

Every EMC filter I've seen has capacitors between the AC lines and earth, configured like this: simulate this circuit – Schematic created using CircuitLab Why are the caps not configured like ...
15
votes
9answers
5k views

Safety of making PCBs

I've been making a few hobbyist PCBs at home and note that the photoresist developer and ferric chloride etch solutions are both pretty nasty chemicals that come with all kinds of warnings. So I've ...
15
votes
3answers
29k views

What does it mean when there is a voltage difference between ground and neutral?

Between ground and hot there's approximately 120V as expected. I had expected the voltage difference between ground and neutral to be 0v, but instead it's 0.4V. Why would this not be the case? Is ...
15
votes
3answers
22k views

Safety Guidelines for Ultraviolet LEDs?

I'm interested in using some UV LEDs to light some projects. Specifically, painting some designs on RC aircraft with florescent paint and illuminating them with UV light for night time visibility. ...
14
votes
12answers
2k views

What Workbench Safety Improvements Have You Made?

What was your worst electronics workbench accident involving equipment, voltage, soldering irons, chemicals, or whatever else, and what changes have you made to prevent that type of accident from ...
14
votes
7answers
9k views

How can a faulty USB charger kill you?

This question relates to this incident here, where a women in Australia died from a faulty USB charger that allowed the full 240V mains voltage through the USB cable. Now from my understanding you ...
14
votes
5answers
5k views

Is it safe to connect an Arduino to the human body?

I want to create some project which uses an Arduino to collect and display ECG data. It uses two electrodes which are attached to the body (on the chest). The signal is then transmitted through op-...
14
votes
3answers
3k views

Strange symbol on PSU label

I have a PSU (wall wart) with a symbol on the label that I don't recognise. I'm curious as to what it means. It's probably some safety symbol of some form, but not one I have ever seen before. I'm ...
14
votes
2answers
22k views

Is it safe to disassemble an unpowered PC power supply?

Once a typical PC power is unplugged, is there any danger of receiving a shock while disassembling it? Are there typically high voltages stored that one should be aware of? context: removing a ...
14
votes
2answers
5k views

I just blew a capacitor. Now what?

We worked two years on and off on this project at my friend's place. Finally we finish, I take it home. There's a power supply unit but it can't be connected directly to mains, it expects some lower ...
13
votes
4answers
3k views

At what level of complexity should I consider UL listing my widget?

I am interested in making a widget to sell, but it will probably have a small market and small volume. At what level of complexity should I consider UL listing (or otherwise certifying) my widget? I ...
13
votes
4answers
13k views

How do I choose a fuse? Fusible Links vs Polyfuse?

I realise this is an extremely broad subject area but I need to know how to choose a fuse to protect a circuit. Recently, a cheap PSU of a friend's blew up quite spectacularly (the two primary ...
13
votes
7answers
55k views

Is soldering wires directly on a NiMh battery safe?

I'd like to know if soldering two wires directly on a NiMh battery is considered as safe or not. My fear is that battery would explode (right in my face) because ...
13
votes
2answers
85k views

Hazards of puncturing lithium-ion batteries?

I was doing some electronics repairs, and accidentally punctured a small (mobile phone capacity) lithium-ion cell battery with a metal spudger. At first, I hadn't realised I punctured the batteries - ...
13
votes
1answer
3k views

Why is Ethernet not intrinsically safe?

I understand from a training session that ProfiBUS is considered intrinsically safe, while ProfiNET is not. Some googling indicates that ProfiNET can never be intrinsically safe, because Ethernet can ...
13
votes
1answer
2k views

Can Arduino operate under water?

I have an idea for an automated small toyish submarine. Can I use the Arduino for this? Does it behave well under the ocean surface? I think I'll need some kind of casing with silicone around it, and ...
13
votes
1answer
827 views

Safety when experimenting with large currents

I am experimenting with large currents from ultra capacitor discharge. For example with 500 A (at 2.8 V) you get a very impressive demonstration of the magnetic field of a straight conductor using ...
13
votes
4answers
4k views

Solder Fumes - Activated Charcoal vs Outside Venting

Like probably everyone else here I do a ton of soldering. When I setup my current workshop I built a fume extractor that actually goes in a window near my bench. Basically just a length of dryer duct ...