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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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Feasibility of Using Xinya XY2500 4-Pin Pluggable Terminal for Three-Phase PCB

I am designing a PCB for a three-phase system and considering using the Xinya XY2500 4-pin pluggable terminal connector (pitch 5.08 mm, rated 15A @ 300V) to connect R (Phase 1), Y (Phase 2), B (Phase ...
Shubham's user avatar
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2 answers
47 views

Safety considerations when measuring an analog signal across an isolation barrier

I'm designing a PCB that is powered by 230V AC and switches 5 heating elements via 5 Triacs. As a best practice I included optotriacs for driving the main triacs and used a 230V to 5V buck converter ...
DreiDe's user avatar
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2 answers
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Can 3 power supplies safely share common ground?

I have a project with a DC motor @ 24V, an actuator @ 12V and an Arduino @ 5V. The motor and the actuator may draw several amps. The Arduino doesn't drive the motor nor the actuator, nor is it ...
MrSparkly's user avatar
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3 votes
2 answers
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My isolation transformer has its protective earth connected to the output neutral. How should I rewire it for my home lab for "DUT probing"?

I have a rather sturdy isolation transformer in my home lab and I just realized that the primary side earth is not only connected to the output side earth but also to the output side neutral. I don't ...
pipe's user avatar
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2 answers
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Understanding safety concerns with RGB modding hot-chassis TV

I'm in the US. I'd like clarifications on the safety of RGB modding an old, hot-chassis TV. I know it's not economically viable but I'd like to learn. While researching how to do this safely I ...
lwiseman's user avatar
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3 answers
91 views

Did Micro-USB have protection against "loops"?

I have an older USB power brick from a reputable, well-known company (i.e., not rock-bottom re-branded cheapest-as-possible). It has a female USB-A connector as output, and a female micro-USB ...
AnoE's user avatar
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Is EMT plenum rated? If I install EMT in a plenum and run general purpose wiring through it, does this violate NFPA 75?

I have a raised floor area with a few server racks on top, the under floor area is used to distribute HVAC to the racks. I have already run all the cables before learning of NFPA75's plenum rating ...
SherEEf's user avatar
15 votes
8 answers
3k views

Is there a standard which requires a high voltage warning label on a PCB?

If part of your PCB carries high voltages at certain nodes, is there a standard that requires some sort of silkscreen label or sticker to warn technicians when installing/uninstalling boards into ...
BobaJFET's user avatar
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2 votes
3 answers
373 views

Safely grounding 120V AC device

I'm pretty new to electronics. I'm building a device that has an aluminum enclosure, is powered by a 120V AC outlet, and requires roughly 520W of total power. My circuit is: AC input with a hot, ...
Sohil Sathe's user avatar
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1 answer
135 views

Infrared eye tracking - safe levels of infrared exposure on the eyes

I'm making an infrared eye tracker where an infrared light will be shone on one of the user's eyes, and a camera will capture the user's gaze, and I have a 940mm IR LED for this purpose. I have the ...
Joel Leung's user avatar
3 votes
2 answers
775 views

How to turn off a MOSFET in a case it fails and stays "ON"

how to turn a N-MOSFET (Q1) off, in case if fails and due to this error it remains in an "ON" state? My idea is to add a second P-MOSFET to have redundancy. I don`t want to use a relay. Vcc =...
theLastDay's user avatar
1 vote
1 answer
54 views

Undercurrent E-stop [closed]

what would be the effects of an emergency stop button rated significantly lower than the system's current draw? Say for example, an e-stop rated for 10A DC in a system pulling 20A DC. Would the e-stop ...
WafflesAndEggs11's user avatar
1 vote
1 answer
171 views

Should this Chinese power supply be earthed?

I recently bought a piece of equipment from China, and it came with a laptop-style power supply. I immediately opened the supply to check if it was electrically safe, because we all know how lax the ...
Sod Almighty's user avatar
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Need USB C cable / connector insulation voltage....and ESD on shield, will impact the internal signals

Any one know how much voltage the standard USB C cable insulation can withstand?..Also want to know shield to internal conductor insulation..If I apply ESD on the connector shield, will it impact the ...
NICEGUY NICEGUY's user avatar
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Ideas for protecting an sEMG system from external problems

I am designing a pcb to work as a human-machine interface. Here is the simplified schematic: The idea is to connect a custom sEMG acquisition system to esp32 and also a pcb to control vibrotactile ...
pedro ulhoa's user avatar
2 votes
3 answers
402 views

Should unused connector terminals be connected to ground?

I am using both male and female D-SUB connectors and about half their terminals are currently unassigned, unused and unterminated. They are not the crimpable versions, all the conductive terminals are ...
Tommy95's user avatar
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2 answers
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What's normal/safe behavior for a 48V/1200W switching power supply? [closed]

When I unplug my 48V/1200W switching power supply, with no load, it reads a full 48V at the output for 5 seconds before there is a "click", and the voltage starts to drop. It takes another ...
RaveTheTadpole's user avatar
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Creating a Class 2 circuit using a Class II ac/dc converter

I need a Class 2 circuit and I know that I can buy say an off-board DIN mount Class 2 power supply, but I am trying to put everything on a PCB board and looks like all the little converters are class ...
Spy's user avatar
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1 answer
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What's the difference in loading outcome with a 42 vs 48 V charger? [closed]

I have a Lithium-Ion battery for an ebike. The battery is 48V, and is rated 15 Ah, so that means 15V*15Ah = 720Wh, and as it says on the battery as well. Now it has a 48V charger (rated 2 amps). ...
Stefan Steiger's user avatar
1 vote
1 answer
62 views

Balancing high voltage and ESD safety for a work bench [closed]

I own various large stainless steel benches which I'm using to sit heavy equipment (200kg+ per bench). Some of this equipment will need new electronic components i'll have to wire up, such as 120vac ...
srb633's user avatar
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1 vote
4 answers
107 views

Risks of placing Varistor before Fuse for Mains Voltage

I have seen many questions on this and other forums asking about the best option to place the fuse relative to the varistor to protect it from mains voltage spikes and the answer was unanimous: The ...
Dinis's user avatar
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1 vote
2 answers
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Intrinsic safety (IEC60079-11) - assessing spark ignition of RLC circuit, but the L is placed before the zener barrier

My IS circuit contains an inductance, capacitance, and resistance. Shown below is the simplified schematic, with uncountable and countable fault applied, resulting in the most onerous condition: The ...
Never's user avatar
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2 answers
138 views

What is the purpose of these mercury switches?

I'm looking at a vintage wire recorder that won't even turn on. Examining it, the power leads (both of them) go through separate mercury switches and on to the main transformer, etc. The switch vials ...
noughtnaut's user avatar
0 votes
1 answer
66 views

Standard practice for storage of old / unused lithium ion battery cells prior to disposal

Is there a standard practice for storage of loose lithium ion battery cells that will be disposed of eventually? (in the timeframe of up to 1 year) Currently, prior to disposal, I have been storing ...
plu's user avatar
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2 answers
67 views

Surge Voltage Protection

I am currently working on designing a protection circuit for mains power. However, as a hobbyist rather than an expert, I am seeking assistance with this circuit. During my research, I came across an ...
M-125's user avatar
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4 votes
5 answers
2k views

Paintless (raw) aluminium enclosures connected to Earth: Bad practice?

I am producing a system with aluminium enclosures all connected to a central unit which is connected to Earth. All the enclosures of the system have their chassis ground connected together via cable ...
Tommy95's user avatar
  • 179
0 votes
1 answer
62 views

Is it okay to replace a 127 V indicator LED with a 110 V one? (Both are AC)

The available LEDs have no famous brand so they don't have a specific datasheet where you can search and look-up online. So I need a general answer to my question based on the "most common" ...
Michael George's user avatar
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0 answers
11 views

IEC61010 applicability for non-measurement category rated circuit?

I have measurement circuit that will be rated for CAT II 300V but do allow input voltage of over 300V up to 1kV. In IEC61010 6.7.3, "Insulation for secondary circuit derived from main circuits of ...
Cyclone1's user avatar
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2 answers
156 views

Power electronics on a PCI/PCIe expansion card

I'm not sure if its been done before but how feasible is the idea of building an computer expansion card (PCI/PCIe) that carries mains power on some areas of the expansion card being switched by ...
dazzleworth's user avatar
2 votes
1 answer
126 views

Is it safe to use 250V rated relays with UK mains voltages?

UK mains voltage is 230V (RMS) with a tolerance of -6% and +10%. That gives it an upper limit of 253V (RMS). Lots of relays are rated up to 250V: e.g. the Omron G5Q series has a "rated ...
Rob Gilton's user avatar
2 votes
0 answers
69 views

Philosophy of safety by Double Insulation

In a Class I appliance, when a fault occurs that brings dangerous voltage in contact with accessible conductive parts, the installation wiring fuse or GFCI will not only shut down the dangerous ...
tobalt's user avatar
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3 votes
3 answers
598 views

How safe is this TrueRife F-122 frequency generator?

A close friend bought a TrueRife frequency generator in hope of improving health.  I'm skeptical of the claimed healing powers, however let's put this aside for a moment;  if it helps - great!  The ...
Astrogator's user avatar
2 votes
2 answers
1k views

Difference between interlock and permissive

There seems to be somewhat differing and sometimes overlapping definitions of these terms. Below are definitions found in The Automation, Systems, and Instrumentation Dictionary, Fourth Edition by ISA....
ivvi's user avatar
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0 answers
49 views

How to interpret this wiki quote about connections between SELV and PELV circuits?

The wiki page about SELV circuits says: A SELV circuit must have [...] simple separation from other SELV systems, from PELV systems and from earth (ground). Assume I have a SELV Class III device ...
tobalt's user avatar
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1 vote
0 answers
89 views

Class III appliance with metal chassis connection

I am designing a SELV/Class III appliance (lab/industry type, IEC 61010), supplied via two-pin isolated DC power. For mechanical reasons, the chassis has to be metallic. As a result, there are going ...
tobalt's user avatar
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1 vote
1 answer
97 views

Is it safe to disable the write-protection of registers all the time in a microcontroller? [closed]

Because the hardware write-protection feature is given only for few registers while there are many other critical registers are left unprotected in a typical microcontroller (For example in Renesas ...
user3214692's user avatar
0 votes
1 answer
125 views

Safety of unplugging while device is switched on [closed]

Help resolve a debate: is it less safe to switch off devices at the wall socket rather than using the off button on the device? He says it’s equally safe to just switch on and off it even just unplug ...
ruth shaw's user avatar
1 vote
2 answers
73 views

Have I replaced the power supply in this radio safely?

Preface: I know little about electrical engineering, I mostly used a multimeter to diagnose and measure and to make sure I made nothing obvious wrong. But I know nothing about circuits, reading ...
Lennart's user avatar
  • 113
4 votes
5 answers
1k views

Emergency stop switch loop to shut down possibly many equipment items

I need to design an E-stop system - any number of normally closed switches, anywhere from one to possibly as many as 30 identical pieces of equipment that all need to be informed of a switch opening, ...
jasonharper's user avatar
3 votes
2 answers
690 views

How to connect PE lead of oscilloscope?

I just bought my first oscilloscope. It's a Rigol DHO804. Quite happy with it, but I have 1 question. It is powered by a USB-C adapter and comes with a seperate PE lead. I can plug this in the back of ...
Luuk256's user avatar
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9 votes
3 answers
1k views

What causes self-charging of foil capacitors?

High-voltage foil capacitors are shipped with shorting brackets to prevent the buildup of dangerous charge. But once in a circuit that is not energized, such a safety shunt will be an awkward ...
tobalt's user avatar
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0 votes
3 answers
161 views

Why are capacitors more dangerous than batteries?

It seems decent size capacitors can electrocute you when it's charged. Somewhere I read capacitors don't have internal resistance therefore, current is NOT limited unlike the batteries with internal ...
nmr's user avatar
  • 123
2 votes
1 answer
66 views

Non-contact powering of LED indicator from a high voltage cable

We manufacture fireproof power plugs for high-voltage transformers used in mines. The way it works is we take the incoming single-phase cable and epoxy it into the plug and attach it to the ...
Mark Coetzee's user avatar
2 votes
0 answers
99 views

Determining if white LEDs are eye safe for direct eye exposure

I am looking at buying lots of LEDs for a signboard hobby project. This is my first project using LEDs and I wanted to make sure (and learn) that I am making a safe project. The LEDs I am looking at ...
JustHeavy's user avatar
  • 301
0 votes
0 answers
49 views

Using both safety PLC and safety relay

I am in the process of designing a robotic cell. This contains a safety door and several e-stops. I want to use the safety PLC from siemens S7-1200F. I need to have two roller tracks with 8 24V motors ...
user357063's user avatar
5 votes
3 answers
2k views

How to understand schematic circuit diagrams in functional safety

I'm having a hard time understanding the kind of diagrams which frequently appear in literature relating to ISO 13849. Are there relevant instructions or guides on how to understand this kind of ...
lightweight's user avatar
0 votes
1 answer
102 views

How to charge capacitor bank safely?

I am making a project that needs a capacitor bank. I have six 250 V rated capacitors, a 120 V - 240 V step-up transformer, and a bridge rectifier. Is it safe to charge these using a wall outlet (I am ...
toomanyfeet's user avatar
1 vote
3 answers
200 views

In aircraft power supply, why is the neutral not connected to chassis GND unlike household utility power?

Usually the chassis of any household equipment is connected to earth ground for safety. Part of the culprit is neutral being connected to Earth ground. (Reasons are mentioned in this post.) My ...
Dynamic_equilibrium's user avatar
6 votes
1 answer
2k views

Which wire is hot?

I have an analogue oscilloscope that had its power cable head chewed off by something. Before I replace the cable, I want to be 100% sure which side of the cable is hot and which is neutral. This is ...
zuzomuzabi's user avatar
3 votes
0 answers
68 views

Ground to L1 in 3-phase have almost 0 V potential

I am in Peru and was helping check ground rod to line and neutral and see higher than one leg to ground voltage. This is at a plant with 3 phase power 220/440 volts. The local utility doesn’t provide ...
Dososo56's user avatar

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