*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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50 views

Does the following power supply configuration make my device a safe and legal PELV appliance?

A small disclaimer up front: I am fully aware that advice from this site is not a replacement for a safety evaluation by an expert. I merely want to check my understanding of the rules and potential ...
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1answer
76 views

current leakage in a laptop [closed]

Current leakage is apparently an issue with some aluminum Macbooks and other laptops. http://superuser.com/questions/462244/electric-shock-mild-vibrating-sensation-on-macbook-pro-when-charging Some ...
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1answer
97 views

Oscilloscope ground and unit under test ground issue

I am working with an instrument which has a supply of 230V AC or 400V DC. AC source is isolated at the input via 1:1 transformer and DC source is a floating supply. I have a Yokogowa DL1620 ...
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3answers
1k 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 ...
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2answers
93 views

Measure 230V mains with 300V CAT II probe?

I need to measure harmonic distortions on a 230V 50Hz AC mains circuit. The Tektronix P2220 probes I have for my scope are rated for 300V CAT II when set to 10X impedance. Are these probes safe to use ...
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3answers
95 views

How does a “break” in the neutral wire enable it to reach the full line voltage?

The answer to Is the neutral wire considered safe? states: When everything is working correctly, it should be at most a few volts from ground. However, and this is the big gotcha, if there is a ...
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4answers
324 views

What's the advantage of 'electrical tape' over 'regular' adhesive tape?

For covering copper wire and the like (whether it is carrying current or not), what's the advantage of applying electrical tape as opposed to 'normal' consumer adhesive tape (of similar thickness? ...
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1answer
43 views

Faster charging of Lithium Polymer battery possible?

I am designing a system which needs to run for 3 minutes, then charge as quickly as possible, then run for 3 minutes, then charge as quickly as possible, and so on. In order to reduce the charging ...
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1answer
90 views

Why does a mains appliance give a shock after it is completely unplugged

My wife has a food processor, bought a few weeks ago, powered directly from the A.C. mains, i.e. not via a "wall wart" power supply, and, after it has been switched off at the wall and fully ...
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5answers
583 views

User safety for battery powerd device against misuse of power supply

I want to design a safety circuit for a battery powered device which measures human body impedance. It is intended to be powered only by an external battery pack (5V) via a USB cable. But I want to ...
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1answer
160 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 ...
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1answer
48 views

Is this Li-Ion safe? [closed]

"TIANPENG li-ion 1300mAh 7.4V" is what the text on the battery is. Do you need internals of the charger? The battery 'case' (or whatever is holding packs of cells together) is cracked in some places, ...
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4answers
427 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 ...
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1answer
47 views

Downsides of using 5mm fuses in 6.3mm sockets

For my multimeter I need to replace a fuse. It is 6.3mm in diameter, 25mm long, rated 500mA/250V AC and 1500A interrupt rating. I have a couple of such fuses, but they are 5mm in diameter, and ...
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2answers
69 views

How does a GFCI breaker protect me if my device has no connection to ground? [closed]

I use a hairdryer with a 2-prong US plug (no ground). Suppose I plug it into a GFCI-protected outlet and drop it into a sink full of water. Will the GFCI still trip even though my hairdryer doesn't ...
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1answer
103 views

Laptop surface vibrating when rubbing over it [closed]

Because my previous HP laptop adapter stopped working, I got a new one. But if I use this one, I feel a kind of vibration when I rub over my laptop's surface. I don't have this if I work on battery, ...
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2answers
130 views

What makes a device intrinsically safe?

I work in possibly gas filled environments. As such safety recommendations are that I don't use my cell phone, camera and computer while touring around these areas that explosive gas may be present. ...
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2answers
628 views

What is the difference between “medical” grade and ordinary AC-DC power supplies?

Background My wife and I are expecting a baby soon and a family member has given us their previously-used, thoroughly cleaned electric breast pump. The pump came from the vendor with a "medical ...
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1answer
289 views

Can batteries conduct from their sides?

Back when I was younger, I used to take apart the old disposable cameras I'd take to camp to have fun playing with the parts and doing a bit of exploring. One year I ended up with a camera with a ...
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2answers
80 views

Isolation Transformer Safety

I recently purchased an armax 230 ISOTRAN Model 1521. I can’t find it on the web anywhere, and from what I understand it is an isolation transformer that takes in 115 VAC and outputs about 210 VAC. ...
2
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1answer
65 views

Power supply CE compliancy requirements

I'm dealing with an electrical equipment which should be compliant to the CE low voltage directive (LVD), following the EN60950 standard. The equipment is connected to the mains (220V) through an ...
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4answers
285 views

Is it possible to make a short-circuit detector for a battery power supply?

I have a basic understanding of electrical things myself, but semiconductors are not part of it. While pondering about some unrelated things, I came up with this question: Suppose I want to make an ...
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2answers
74 views

Human body and current flow effects

This is kind of theoretical question, but I hope that it will not bother anyone and it will not be reported or closed after a minute. In all basic electrical literature there is always information ...
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2answers
109 views

How to have a bad power supply fail safely? [closed]

I just read this article: iPad charger teardown: inside Apple's charger and a risky phony Basically I would like to see by myself the effects of a bad power supply failing. Can it be done safely? ...
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2answers
91 views

Obtaining O-Scope signals in a AC/DC supply - grounding issues

I need to check waveforms in the power supply from this design reference by Texas Instruments. I essentially built the supply, but it is not operating correctly - ie, no output current, but it has ...
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4answers
360 views

personal safety - preventing electric hazard

I usually have AC mains powered devices/circuit on my desk, and I rarely taste AC current by accident:) Could anyone suggest to me what kind of protection I should use for personal safety against ...
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3answers
851 views

How do I “cap” a wire so it doesn't short or electrocute someone?

I'm repurposing a PSU that I recently replaced. I'm using it in a project that needs high current supplied. I don't need all the wires (as you could imagine), but I don't know how to seal them off ...
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3answers
142 views

Safety of this circuit (involving hand-to-hand current):

Note1: The voltage source in diagram is 3 lantern cells in series. Note2: Hands are placed on acrylic/plastic mesh so not directly in contact with metal trays. The hands would be submerged for ...
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0answers
54 views

Would electrified water hurt me? [duplicate]

Considering following scenario: What would happen, If electric plug went under water beeing powered, electrifiing water? I have two hypothesis, that I'm not going to test for obvious reasons :). ...
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3answers
159 views

Played with some lead solder without washing my hands for awhile, should I be concerned?

I was using some lead solder at work, and wasn't aware it was lead solder nor had anyone told me that it can be dangerous. For the most part I was just handling it. This was last week and I don't ...
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0answers
69 views

What regulatory and legislative requirements are important for avionics? [closed]

Lets say I was building a device that is designed to go into an international commercial airliner, e.g. a digital altimeter or a GPS device. What legislative and regulatory requirements, specific to ...
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0answers
72 views

PCB voltage and current

I am building new project, which I will power up the water tank heater from my smartphone. I have few safety though I want to ask here to get your opinion.. I am going to use AVR to run a relay, that ...
2
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2answers
168 views

Choosing the right Relay for the mission

I am building new project, which I will power up the water tank heater from my smartphone. I have few safety though I want to ask here to get your opinion.. I am going to use AVR to run a relay, that ...
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1answer
104 views

Choosing a transistor to Relay

I am building new project, which I will power up the water tank heater from my smartphone. I have few safety though I want to ask here to get your opinion. I am going to use AVR to run a relay, that ...
0
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1answer
49 views

Using Ground Off Another Circuit [closed]

I have a power outlet without a ground, but I have an electronic device which requires a real ground (can't use a GFCI protected outlet). Would it be okay to run an extension cable from an outlet ...
1
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1answer
64 views

Safety when working with CD burner laser

What kind of safety precautions should I take when working with a laser I've taken out of an old CD-RW burn drive? I'm making a small laser writer/printer to write on wood. Should I wear glasses? ...
2
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2answers
71 views

Safety concerns using metal switches near 300V (low current) lines?

I am building a nixie tube clock whose power supply in the best (or worst) case scenario will put out ~300V. This is obviously quite hazardous if not handled correctly. I need to use at least 1 spdt ...
4
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2answers
336 views

Explosion proof enclosure wiring

I am currently working on a device that is to be used in hostile environments. It needs to be explosion proof. Our team has decided to place our instrument in this housing shown here. ...
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2answers
134 views

Fault-current circuit breaker breaking on grounding neutral conductor?

I just put some lamps on and got the fault-current circuit breaker triggered. While skinning the earth conductor the knife touched the neutral. I was a bit puzzled: I thought that happens only under ...
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3answers
358 views

How did I survive a short hand-to-hand 230V shock? [closed]

About 5-10 years ago (can't remember when exactly), my father asked me to unplug a lawn mower from an ungrounded power outlet with no sunken part (the kind which had been outlawed by the EU for a few ...
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3answers
368 views

Giving shocks to students [closed]

My son's science teacher had 15 fifth grade students stand in a semicircle holding hands. The student at each end held an electrode connected to some kind of variable contoller. The teacher ...
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0answers
123 views

Would Beetee's electrocution plan work and kill the tributes in the lake? [closed]

I would like to understand the design of an electrical system to route the electricity from lightening into a salt water lake and to thus kill anyone in the lake. In its simplest form the design is a ...
0
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1answer
186 views

Safe to use 4.5v 300ma rated 'universal' ac/dc adapter with kids alarm clock that requires 5v 500ma? [duplicate]

Have a kids alarm clock that requires 5v 500ma for power supply option (but can also run on 3x AAA batteries). I have a universal adapter that can supply 4.5 or 6v (with the correct polarity) but it ...
1
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1answer
126 views

Safely discharging large value capacitor without blowing it up

This is related to my previous question. I have this circuit in which I discharge the capacitor by turning ON M2. The ON resistance of the MOSFET I have in mind (the picture shows the wrong MOSFET in ...
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0answers
27 views

What is the functions of Safety Interface Modules?

I read a manual of safety interface modules http://info.bannerengineering.com/xpedio/groups/public/documents/literature/62822.pdf I see "The Interface Module offers a series connection of normally ...
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1answer
197 views

How to safely use the power-socket ground for the anti static wrist strap?

I saw as practice to use the power-socket ground for the anti static wrist strap, I saw this done where there is no available specially designed ground for anti-static pads and bracelets, but this may ...
2
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0answers
121 views

Options for a simple over-temperature cut-off?

I am designing a heater circuit that will be used in a product to be produced in small to medium quantities (hundreds to thousands of units, not tens of thousands). This heater will be PWM controlled ...
2
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1answer
103 views

Wearing “conductive shoes” instead of heel grounders?

I've been looking into alternatives to heel grounders since they're kind of cumbersome to put on and take off often (not to mention being uncomfortable) and I'm considering buying a pair of ...
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0answers
41 views

ATX power supply repair intermediate power up testing

Hi I'm repairing ATX power supplies these days. I'm so newbie to the repairing business and I wants read some value of some test points when the device is active. How could I do this? Is it oky to do ...
3
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2answers
240 views

Are touch lamps safe?

I've used "touch lamps", where you turn it on and off by touching the lamp. As I understand it, this works by putting a small electrical voltage through the human body: touching the lamp completes ...