Tagged Questions

*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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0
votes
3answers
62 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 ...
0
votes
4answers
69 views

Are unearthed metal cases actually unsafe?

Take a look at this picture: It shows that if there is a fault with a device, current will flow from Live to Earth, hence you don't feel an electric shock. However, I don't completely understand ...
2
votes
0answers
35 views

IEC 60079 Explosive Atmospheres Compliance

I'm wondering whether anyone has some experience with designing electronics for compliance to IEC 60079 Explosive Atmospheres. I have designed a device to be installed in silos facilities which are ...
0
votes
1answer
30 views

Safety advice for best EMF detector and body shielding for UHF RFID reader

I've got a UHF RFID detector (860 to 960 MHz). I'm just getting into configuring the power output but I think I've been testing it at about 20dBM, I might want up to 30dBM. I'm concerned about my ...
1
vote
2answers
163 views

The safety of the capacitor

I saw this material for making capacitors (http://www.capacitorfilm.com/web/enproduct.aspx?ch=64). It said capacitor with the material is very safe, does anyone know what is the principle under which ...
0
votes
4answers
104 views

Can a current be induced in an HDMI cable that runs parallel to a 120v AC cable for 15 feet?

I just went to go unplug an HDMI cable and got shocked from the end of it! The only possible causes of this that I can think of are that the receiving or sending end of the long (50ft) HDMI cable is ...
2
votes
1answer
46 views

Is there anything besides power factor that determines the max CFL that can be used in a socket compared to the max incandescent for that socket?

When shopping for lamps recently, I've noticed that the sticker on the socket says something along the lines of "To reduce risk of fire, use maximum 60 watt incandescent or 13 watt compact ...
1
vote
1answer
55 views

Current Leakage calculations regarding shock hazard. A complete picture?

There is a quantity called current leakage which has always confused me. By reading various definitions, it seems to be the current flowing through the ground circuit of a device (whether this be an ...
1
vote
1answer
69 views

USB current limiter and under/overvoltage protection

I know recent motherboards already provide these, but lately USB ports are also available in many different gizmos (smartphone chargers, TVs, standalone players, etc.), which I am often tempted to use ...
0
votes
0answers
30 views

Needed help on earthing grid mat installation

I needed knowledge about earth mat installation for underground metro. I am not sure if a test reference electrode could be used for two earth mats. We have limited space and I want to cut off some ...
1
vote
1answer
123 views

How to measure current leakage in Macbook Pro and the long term impact of using a laptop with such a problem

I get a tingling/numbing sensation in my hand after using my new MacBook Pro for an hour (I only use the laptop when it's running on battery). The sensation sometimes travels to my arm. When I first ...
0
votes
1answer
103 views

Winding a Toroidal Transformer

I have a toroidal ferrite core which has an outer diameter of 15 cm, inner diameter of 11 cm and height of 4 cm. I want to use it to make a transformer which takes in mains voltage (240V) and outputs ...
2
votes
2answers
57 views

Actual/theoretical benefits of round or flat outlet prongs

What might be the reasoning for European connectors having rounded prongs while USA and UK connectors are primarily flat pronged? Please correct any mis-tagging.
10
votes
6answers
2k 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 ...
1
vote
0answers
75 views

Can I determine a formula for fuse disconnection times?

This is the first time I have used this stack site so am not 100% sure this question is on topic (based on the tags I couldn't find) but thought someone may still be able to help me. For those not ...
1
vote
1answer
107 views

Unregulated AC-DC adaptor voltage response

This is my first post. I'm a long-time computer programmer but new to this field of hobby electronics. I bought a 12V 800mA AC/DC adapter to feed my circuits. Seems it's unregulated since the ...
-1
votes
1answer
87 views

Manuals vs certification plates

If a device manual with a stated model reads 220-240V 50/60 Hz must the certifcation tag match? Is this different on a per country basis? (In this case Germany) For example this manual excerpt: ...
11
votes
1answer
1k 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 ...
1
vote
1answer
138 views

Volts and frequency worldwide

If an electrical certification tag reads 220-240V 50/60 Hz can the device be used on both 220V 50 Hz and 240V 60 Hz?
1
vote
1answer
36 views

Checking my understanding of “branch in parallel current” warning

A datasheet for a power connector I was looking at tonight has this warning: Note: Do not branch in parallel current which exceeds the rated current. If branched in parallel, current ...
1
vote
1answer
75 views

Battery power in the home: Fire Safety

I would like to use 12v LED tape powered by an 8 x AA battery holder and switched with a motion sensor. This will be connected in my home 24/7, so I would like to know what precautions (if any) I ...
4
votes
2answers
93 views

Safety concerns over generic switching power supply units

I'm looking for a more stable power supply for my 3d printer. I've recently come across the following kinds of switching power supplies. They seem to come in all sorts of different sizes and ...
1
vote
2answers
64 views

How to handle / dispose of spent lithium primary cells [closed]

Disclaimer: This is a material safety question and not electrical. But it is electrical engineers who generally decide which type of battery to use when designing a system and other electrical ...
3
votes
3answers
136 views

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 ...
16
votes
3answers
2k 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 ...
0
votes
0answers
69 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 ...
1
vote
1answer
165 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 ...
0
votes
1answer
165 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 ...
15
votes
3answers
2k 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 ...
2
votes
2answers
129 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 ...
1
vote
3answers
166 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 ...
4
votes
4answers
570 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? ...
0
votes
1answer
73 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 ...
1
vote
1answer
129 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 ...
2
votes
5answers
595 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 ...
1
vote
2answers
382 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 ...
-3
votes
1answer
54 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, ...
1
vote
4answers
693 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 ...
0
votes
1answer
48 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 ...
1
vote
2answers
80 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 ...
0
votes
1answer
139 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, ...
3
votes
2answers
160 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. ...
5
votes
2answers
711 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 ...
2
votes
1answer
293 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 ...
0
votes
2answers
104 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. ...
3
votes
1answer
75 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 ...
1
vote
4answers
420 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 ...
1
vote
2answers
83 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 ...
0
votes
2answers
118 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? ...
2
votes
2answers
114 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 ...