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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.

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Proper Chassis Grounding

I'm starting to design things that run off mains voltage and I want to be sure that I have a proper connection from my chassis to earth ground. I've been reading a bit about proper grounding and have ...
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1answer
22 views

Can I simply add a 240V Neutral to SONOFF TH10 when replacing wall thermostat

So, I have purchased a SONOFF TH10 wanting to use it to replace my wall mounted thermostat. The thermostat has 2 connections: Always-Live and Switched-Live (which is activated of course by the ...
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2answers
26 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
491 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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0answers
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Why do some lamps have different power ratings for different kinds of bulbs? [migrated]

I had a lamp that broke recently after getting smashed against a wall by accident (there are now numerous exposed conductors, making it unsafe to use), so I went to the store to get a new one. I ...
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1answer
89 views

What precautions should I take to setup a home electronics lab? (Living in the UK) [closed]

I'm soon to be buying a house in the UK and would like to setup an electronics lab in the garage (attached to the house).The type of equipment I'll be using is nothing out of the ordinary: ...
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3answers
2k 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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1answer
57 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
92 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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1answer
61 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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3answers
72 views

Protecting against a SSR failing closed

In a project I'd like to control a heating circuit with an SSR, and I'd need a contingency plan for when the SSR fails closed, and the microcontroller cannot turn off the heating element, which would ...
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1answer
29 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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1answer
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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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97 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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0answers
39 views

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 ...
4
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1answer
66 views

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
61 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
47 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
40 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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2answers
71 views

Power tool safety: Grounding v/s Double insulation

OSHA regulation 29 CFR 1926.404(f)(7)(iv) states that electric power tools must be grounded except when they are double insulated. I quote from the Black & Decker rotary drill manual: "Do not use ...
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2answers
53 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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0answers
14 views

Substitutability of thermal fuse

I have had this SW-104T thermal fuse blow on me. I'm not in a situation where I can obtain an the exact replacement, so I am wondering about the substitutability of thermal fuses. If I match the ...
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1answer
137 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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2answers
70 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
85 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
53 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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1answer
83 views

Is it safe to measure 220Vrms@50Hz on DSO directly?

I borrowed my friend's DSO to complete my project(Hantek DSO5072), but on scope it says CAT II/400V. So is it safe to measure 220Vrms@50Hz with it?
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0answers
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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
95 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
94 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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1answer
73 views

Using a residual current device when there is an isolation transformer

In a system, currently there is no circuit breaker and RCD, but there is an isolation transformer as in the diagram below: simulate this circuit – Schematic created using CircuitLab As you see ...
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0answers
41 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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3answers
186 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
82 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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1answer
88 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
32 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
137 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
64 views

Bad Practice - Charging Lithium Batteries while powering circuit?

I'm using a 2s BMC to charge a 2s2p lithium battery pack (7.4v, ~6Ah). The output of the charging circuit is the same as the input - they're not separate. As a result, when I want to charge the ...
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2answers
111 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
80 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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0answers
34 views

Reference material for mains-interfacing circuit safety

I've designed a simple switch/timer circuit for the following environment: Residential installation for North America (technically only for Canada) Single-phase 120Vac Current of switched output ...
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1answer
120 views

100V “rated” wire on 220V supply [closed]

I am genuinely sorry for posting such a basic, basic, basic question. Moving to Thailand (220V) from Japan (100V). You cannot buy an extension cord in Thailand that is flush to the wall. Here in ...
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2answers
88 views

What is the purpose of galvanic isolation?

Is it correct to say that the primary reason to have galvanic isolation (ensuring minimum clearance and creepage distance for required voltage of power circuit between HV and LV) between the HV power ...
2
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1answer
54 views

Safety Relay Circuit

I am looking for a way to add a relay-based safety feature to my BLDC controller. In case of an emergency the user must be able to push an e-stop (probably consisting of an NC contacts) completely ...
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2answers
133 views

Protecting yourself with latex gloves

Would wearing white latex gloves(doctor gloves) protects you from getting shocked when repairing electronics? And is there a reason why you seldom see anyone wearing gloves when dealing with ...
19
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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 ...
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2answers
548 views

How to rinse container used for ferric chloride etching?

From what I have gathered online, after etching one stores the "used" ferric chloride (more specifically FeCl2 and CuCl) in some container which can then be taken to a waste disposal facility. What ...
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2answers
267 views

Safety design on mains detector

I've designed a simple mains detector which I have drawn below. The theory of operation is pretty simple. A capacitor is used to reduce the current so that my optocoupler can operate (represented by ...
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1answer
74 views

Is it appropriate to use a 300V RMS CAT I rated oscilloscope to measure 230V RMS of a power inverter?

Yesterday I decided to look at the waveform of my portable power inverter. The inverter specs are the following: Input: 12 V DC Output: 230 V RMS Rated power: 300 W I powered my inverter from a ...
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0answers
74 views

Out of limit Touch Up current - Servicing PE

My device may not be connected to PE during normal operation, but does require 230VAC mains input. I know I have to take the touch up current of any Y-caps into consideration when developing my ...