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.

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60 views

Wiring a traffic light

So I have aquired 1 light of a traffic light that I salvaged from a local dump. I want to try and connect the light to use it like a lamp, however I am a little worried by it as the connector only has ...
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4answers
15k views

Is it Safe to Plug an Extension Cord Into a Power Strip? [closed]

Just a bit of context, I am a technology enthusiast. I love everything from software to hardware, Windows to Linux, Computer to Phone, and everything in between. So, I wouldn't be surprised is my ...
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3answers
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Connecting a higher-current power supply to a lithium-ion charger will damage the battery. Why?

I am not asking how the battery gets damaged, because that answer is straightfoward. What I am asking is why lithium-ion chargers allow batteries to be damaged by excessive charge current in the ...
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34 views

Product Safety Testing - EU

I was recently hit with the thought as to what safety tests a domestic electronic product has to go through before it is sold to consumers more specifically in the EU? I have been looking through ...
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2answers
822 views

Safely burning resistors - carbon film vs. metal film

Short: Are carbon film resistors and metal film resistors equally safe to burn? Long: I want to explain to children that they need to carefully calculate and check resistor values. I don't only ...
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4answers
714 views

Why not include a thermal fuse in electrical outlets?

I have found myself reading reports of fires lately, including some that started due to high-resistance connections in electrical outlets and switches. A load on a high-resistance connection can ...
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5answers
17k 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-...
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3answers
3k views

Making a device explosion proof

I am working on prototyping a gas leak detector device to be used in homes, it should have two small windows in the casing to allow sound to go out and the other window allows gas to reach the sensor. ...
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2answers
8k views

How do these safety relays work?

I've been trying to understand how these safety relays from Weidmuller work. But since I can't find any useful resource on the internet, it has remained unclear for me. Here is the link to data sheet: ...
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1answer
84 views

Is isolation between user accessible circuits and protective earth necessary for safety?

First let me say that I understand that this question is best answered by someone familiar with relevant standards (whatever those may be). Let me give some background. When I'm designing a board at ...
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1answer
101 views

Why not keep distribution transformers secondaries floating? Why do we need to earth them?

We use isolation transformers for many reasons, one of them is may be safety. So why not just keep the distribution transformers floating? If they're floating, then someone touches the live wire, I ...
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5answers
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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 ...
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1answer
147 views

Why is touching the live wire of a socket dangerous inside an apartment few stories up?

Let's say I touched the live wire of a power socket in my apartment that is located at the fourth floor of an apartment building. The current needs to flow through my body to ground in order for me to ...
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1answer
36 views

Fusing on dual voltage industrial device

Please forgive me if this question has been asked before. I am designing a heating device that will be sold to industrial consumers. In our past designs we have had multiple versions of the same ...
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2answers
1k views

What is the point of two fuses in series?

I've got a 12V power adaptor (3.8A). And it got two fuses in it (T3.15AL250V, 3AL250V, one of which (3.15A) has blown, along with mosfet, current sense resistor, 450V cap, and IC. I replaced all ...
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1answer
47 views

Can a power surge have a different effect on a led driver when floating?

I have a LED driver which has 3 connections on the AC side , L,N and ground. In the event of power surge, can there be a difference in effect if the GND connection of the LED driver is floating or ...
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0answers
107 views

How to line a Metal Melter secondary for higher safety

A Metal Melter is a kind of home-made low voltage (less than 40 volts, mine is 3v) welder (small-scale) made from a microwave oven transformer (MOT). I left the primary intact (the thicker wire, which ...
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Electrical safety measures in LED bulbs for the European market

Which electric safety measures are required to introduce LED bulbs on the European market? Which electric measures prevent that the plastic LED bulbs will melt down or ignite at the end of life? I ...
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3answers
138 views

Aluminum sheet as an underlay for electonic equipment

I am planning to build a NAS into a (sufficiently ventilated) closet. For flame protection and heat spreading, I mean to put a 2x700x550mm aluminum sheet under the equipment. Is this a good idea? ...
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1answer
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What are the tradition ways to signify/advertise that a potentially dangerous long-running test is in progress? [closed]

I frequently need to run long-term tests which have some potential for damage or harm if e.g. someone disturbs the test apparatus without being aware that it's running a test. Say for example ...
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1answer
2k views

Measured continuity between live and neutral

I was trying to get rid of the humming noise coming from my speakers in my hi-fi system. It is an old piece of equipment from back when the UK appliances did not come with the mains plug and you had ...
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1answer
370 views

Is this soldering iron and power supply combo grounded and if so, how?

I'm interested in a TS100 soldering iron as a decent starter iron and a light one that doesn't take up too much space. It doesn't come with a power supply though, presumably to keep it flexible as it ...
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1answer
63 views

LED current source circuit design concerns

TL;DR: Read the bulleted list below. I am designing a simple constant current source to power up some LEDs inside arcade buttons. My project consists of 20 of these buttons. Every button is ...
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1answer
987 views

What temperatures do resistors burn at?

I wanted to make a mini 12V heating element using 12 2 ohm resistors in series. What temperature will it be safe to heat it up to ? It is housed in acrylic housing which starts to melt at around 600 C
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2answers
620 views

Amperage rating of thermal fuse

Consider this SW-104T thermal fuse. It has a current rating of 10A. Does this mean that in addition to its thermal fuse capabilities (blowing at a certain temperature profile), it also behaves as a ...
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2answers
90 views

Symmetrical power supply: Rail fuses useful or dangerous?

I'm designing/testing power amp stuff with symmetrical power supplies (43V-0-43V). In the next future I'm planning to control all safety/healthy stuff (like over current / over voltage / temperature ...
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9answers
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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 ...
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6answers
249 views

Why can closing a circuit breaker into a short circuit result in an arc flash?

NFPA 70E 130.6(M) states: After a circuit is de-energized by the automatic operation of a circuit protective device, the circuit shall not be manually re-energized until it has been determined that ...
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4answers
63k 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 ...
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1answer
3k views

Is it safe to use my multimeter to test UK wall outlet voltage?

From the question it should be clear I'm no expert. Just want to learn. I have a digital multimeter. If I connect the multimeter to hot+ground & hot+neutral on the 240v 50hz (max ~30A) AC wall ...
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4answers
47k 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 ...
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2answers
495 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 ...
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2answers
160 views

Why do we have “live” and “neutral” wires? [duplicate]

Our house wiring is AC. I thought that AC means we have current flowing from Wire 1 to Wire 2, after 1s/Frequency it flips and current flows from wire 2 to wire 1 and this goes on and on. I heard ...
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3answers
253 views

Do 240V AC switches only need to open the active wire?

I want to add a simple inline switch to a small, mains powered lamp (~240V AC, 10W Max). It's earthed; it has a typical 3-core cable with a 3-pin plug. I bought a bunch of switches, expecting ...
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1answer
54 views

Safety Rule: Sum of wire lengths over two phases may not exceed X. What is this for?

Everybody knows various flavors of the rule "don't connect too long electrical lines to an outlet / generator / whatever". They sometimes come in the form of "don't chain your extension cords". As far ...
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0answers
90 views

Is this safe? Wiring for power relay jqc-3fc(t73)dc5v

I have an ac relay jqc-3fc(t73)dc5v that I am trying to use with a atmega and drive with 5v. Is the wiring as shown in the picture a good idea? Considering that ac and DC need to be very close ...
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1answer
513 views

Can a magnet cause a microwave oven to unsafely radiate energy?

I've already successfully warped the colors on a large old CRT Television by setting unshielded speakers on top of it. If I understand correctly, this was due to the deviation of the electro-magnetic (...
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1answer
104 views

How much current does it take to injure me? [duplicate]

I'm building a 5 V and 4 A circuit that will be in contact with the body. How can I know if this amperage, in case something goes wrong, will not be a problem for my health or my life?
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2answers
10k 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, ...
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4answers
3k views

Can I use a switch rated as 250VAC 25A to switch 50VDC 25A?

I am looking for a switch that can handle 25A continous current, the voltage will be maximum 50VDC, most often about 46VDC, and it will be used to switch on two dc-dc converters that have no load ...
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0answers
55 views

Why are contactor coils connected to two different safety relay outputs?

When looking through a manual for a safety relay, I began to wonder why the coils of the load contactors (K3 and K4 on pages 14-15) are always connected to two different NO contacts of the safety ...
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2answers
105 views

Use of relay in a gas sensor (safety issue)

I have developed an MQ-5 based LPG gas sensor which uses a relay. Is the relay itself a fire hazard (while switching) if gas is in the vicinity ? Thanks.
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10answers
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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 ...
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3answers
1k views

Can 10-100mA kill a person / be deadly? [duplicate]

According to various sources something as little as 0.01A = 10mA can be painful, at 0.1A = 100mA you can expierence * "ventricular fibrillation of the heart". "an uncoordinated twitching of the walls ...
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2answers
178 views

Powering two 3-LED lamps with battery/Battery pack - Multiple questions

I have seen many questions along these lines but I don't think any is an exact match (if that's incorrect, please just point me to the right match, that would be great and save everyone some time). ...
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1answer
421 views

How can a Live-Neutral transformer fault cause 2000 Ampere to flow?

In this critique of an ELV PSU design, it is suggested that a "Live-Neutral" fault could result in a fault current of thousands of amps. It says: Fire – (d) the plastic had a UL94-HB rating ( ...
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1answer
97 views

How (not) to set the house on fire? [closed]

With a recently renewed spark of interest in electronics, I’m now starting to solder stuff and build more permanent devices than before with breadboards. But with great power comes great ...
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1answer
50 views

Can you bridge off of a 240 V Breaker Box that connects to an Intermatic Timer?

I have an Intermatic T104 Timer drawing power from a Homeline Breaker Box for a home swimming pool. I'm wondering whether it would be considered safe to use the knockout in the timer enclosure to ...
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2answers
163 views

Laptop fried from spark while connected via USB to a battery system

EDIT 10/11 9:40am Central: I learned from my partner on this project I got the order of events wrong. I have edited the post accordingly. I am working on some custom electrical hardware for ...
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1answer
107 views

Safely housing a power supply

I'm building a 3-d printer, which will be driven by a smoothieboard. This needs a 24V power supply. I've bought the one shown below: What I don't know is how to house this safely. I think there's ...

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