The Stack Overflow podcast is back! Listen to an interview with our new CEO.

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.

Filter by
Sorted by
Tagged with
64
votes
9answers
358k 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, ...
64
votes
3answers
96k 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 ...
31
votes
4answers
45k 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 ...
54
votes
5answers
170k 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 ...
22
votes
8answers
25k 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 ...
13
votes
8answers
59k views

Why is it dangerous use a coiled extension cord

What aspect using a coiled extension cord makes it more dangerous than using an unrolled power cord. Many fire safety websites reference that an extension cord should not be used while coiled. Is ...
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 ...
7
votes
2answers
1k views

Why are typically fatal currents non-lethal when they pass through your body for a short time?

I've been reading up on electrical safety, and the commonly cited controversial quote "it's not the volts that kills you, it's the amps". What I have gotten out of these sources is that it is in fact ...
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 ...
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 ...
19
votes
4answers
32k 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 ...
2
votes
1answer
834 views

Self Checking Circuit

I was reading the specs. of an electronic module used in process-safety applications & came across this note: Self-Checking (Circuitry): a circuit with the capability to electronically verify ...
10
votes
4answers
58k views

Calculating current load for a switch?

This SPST switch is labelled on the box as "Rated 10A at 125VAC or 6A at 250VAC". Is there a calculation as to the amperage it will handle at 12V DC? (update) As JYelton points out, a naive ...
20
votes
4answers
41k 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 ...
6
votes
2answers
1k views

Using 240v mains on/off as input to microcontroller

I have a light switch that switches 240v (UK) mains. Instead of using that to directly control a light, I want to use it as an input to a controller board so I can also automate the lighting. (It's ...
4
votes
4answers
12k views

At what current and voltage do typical resistors explode?

I don't have an explosion chamber, so I cannot test critical values. If you explode resistors with too high current-voltage combination, does it damage your equipment, such as multimeter and DC-...
2
votes
1answer
4k views

Putting two wall-warts in series?

I'm helping a friend make a 48 inch hot-wire foam cutter. He would like it to be as economical as possible, so I'm giving him two 15V 1.1A wall wart power supplies that I have sitting around. I don't ...
2
votes
2answers
3k views

High side switch and Low side switch

I wonder what is the difference between high side switch and low side switch. Basically it work the same way (electrically speaking) but I don't know if one is better than the other. Is there any ...
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 ...
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 ...
16
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 ...
9
votes
2answers
14k views

How to attach (safely?) an o-scope to various sources

I've heard of course that probing mains can ruin your oscilloscope, so that is out of the picture. There are a few situations I do not quite understand however: Is probing an i.e. 10:1 transformer ...
6
votes
3answers
659 views

Add ground earth to a Chinese music player [closed]

I have this Chinese Portable Rechargeable Mp3 player. It has a two pin plug connector behind that is used to recharge it and some generic rechargeable non removable battery inside it. It has the ...
3
votes
3answers
3k views

Mobile phone battery charger

I would like to know about the workings of mobile phone battery chargers. I know the basic principle, you take a transformer to bring it down to 9/6/3.7 volts then a bridge rectifier circuit and a ...
15
votes
3answers
30k 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 ...
12
votes
6answers
4k views

What makes mains voltage safe in homes?

When I started learning about electrical engineering, one of the most important safety guidelines that I learned was that voltages over 36V can be dangerous. As my circuits professor put it, 120VAC ...
10
votes
2answers
7k views

What is the recommended way to protect a circuit from non-transient overvoltage?

I'm designing a 12V battery-operated portable lighting controller, and frequently am asked about improving the run time. The simplest way is to add a second battery in parallel, but I often worry that ...
20
votes
3answers
13k 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?
9
votes
3answers
9k views

ICs with humidity or moisture sensitivity - bake recommendations

I purchased some ICs recently that included something I'd not seen before - a moisture 'sensor' on a paper strip with color indicators for a few specific levels of humidity. Once the paper reaches a ...
7
votes
8answers
2k views

Basic Training for working with 120V AC

I'm planning to build a digitally-controlled light dimmer circuit. I'm not trained in electrical engineering, and I don't want to do something that an electrician would immediately recognize as ...
6
votes
3answers
9k views

USB Fuse to protect USB ports?

I shorted by accident a circuit creating large voltage to my computer, luckily MBA has some sort of shorting protections -- yet this kind of thing should not happen. I would like to have a fuse ...
3
votes
5answers
938 views

Why do 0.02A fuses not protect a person? Why no protection from shocks?

I understand the user here so that fuses do not protect people from shocks. I am planning to put put fuses such as fast-blown fuses and PPTC fuses around all kind of positions such as computerUSB-...
14
votes
7answers
59k 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
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 ...
10
votes
7answers
11k views

How to hook up a mains voltage relay?

This will be my first attempt to control a 110v device (high voltage, by my standards!). Initial tests will be on a table lamp; eventual target may be a small 500W heater. How should I wire the 110V ...
10
votes
7answers
5k views

Mains Voltage on Strip Board

I need to prototype something quickly as a proof of concept. Is it safe to use mains (UK 230V) on stripboard? It will be going to a transformer so I can control some appliance. Or should I design a ...
9
votes
4answers
12k views

Which are the safety recommendations for soldering?

I was reading about tin alloys for electronics soldering and found it it has about 40% of lead in composition. Lead, everyone knows, it's very dangerous to breathe due to being a heavy metal. Also, I ...
6
votes
2answers
470 views

Electric shock from laptop due to capacitive coupling?

If a person touches an exposed wire (the wire has a ground-prong) on the 20V side of a power cable while barefoot, I heard that it is possible to receive a shock of higher than 20V due to capacitive ...
6
votes
4answers
2k views

Is it dangerous if I do not connect the ATX shield to ground?

I'm living in an Asian country and there isn't a ground connection provided on sockets here. There is only L (live) and N (neutral) so I need to use a 3-to-2 converter. It means that the ATX case does ...
3
votes
3answers
3k views

Any problems with “floating” an oscilloscope?

I have a Chinese scope with a two-pin power cord and a plastic body, and measure megaohms between its ground terminals and the actual earth, so I believe it has an internal isolation transformer (I ...
1
vote
1answer
462 views

Using aluminium enclosure as heat sink

Can I use the aluminium enclosure of my mains powered product as a heatsink? I'm thinking about mounting TO-220 transistors pressed against the enclosure, to get away with passive cooling by using ...
0
votes
1answer
558 views

Hacking DSLR battery to power camera from power supply [closed]

I would like to power my DSLR for long captures with a power supply. I know the voltage and inner structure of the official batteries. The battery has 2x 3,7V cells inside with a circuit. People ...
-2
votes
1answer
1k views

I want to build a portable railgun and I'm a complete rookie [closed]

I'd like to enter the world of electronic hobbies by making a railgun, and so far I know that I understand the basics of the device and that I need high amounts of direct current. However, I am ...
1
vote
1answer
479 views

Class II isolated power supply (wall wart) — referencing the output to mains neutral?

If you connect the negative terminal of a Class II (isolated) wall-wart-type power supply to the neutral of the mains circuit feeding the wall wart, will that cause any damage or hazards that I should ...
0
votes
1answer
3k views

Transformerless power Supply - 24VDC, 120V AC and 230V AC

I want to know if it is possible to design a power supply for a circuit that can operate from DC and AC using the same input terminals. Thus, the output should be xxV DC (5-24 or whatever is decided ...
44
votes
9answers
32k 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 ...
26
votes
2answers
8k 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, ...
19
votes
6answers
12k 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 ...
11
votes
5answers
15k views

Disposal of ferric chloride etchant

I've just got hold of a nice little PCB etching kit, which uses ferric chloride as the etchant. I know it's re-usable for at least a few etches (though the kit doesn't actually specify an estimated re-...
24
votes
5answers
78k 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. ...