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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What is the risk when floating oscilloscope and DUT?
As far as I know the best practice for doing high voltage measurements with an oscilloscope is either using HV differential probes or connecting the DUT to an isolation transformer while having the ...
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Are MLCCs really suitable for safety isolation (Y-cap) use?
I am looking at a ~1nF capacitor for Y1 safety use.
I am aiming for SMT so as to avoid a THT step.
I see various MLCCs that fit the bill, for instance the following :
SCC4012X102K8C2TS , ...
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Do I really need a fuse to bypass a tube light ballast?
The electrical diagram for a GE type b LED T8 says that after removing the ballast they recommend I should add an inline 1A fuse. Is this just them covering themselves or is it really important that I ...
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How to safely use a 110 VAC Solenoid Valve in a water system?
I am using 110 VAC solenoid valves linked here, to control the water flow in my system.
https://www.electricsolenoidvalves.com/1-8-110-120-volts-ac-electric-brass-solenoid-valve/?gad_source=1&...
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Which Li-Po batteries to use?
I am working on my own handheld device and I would like to use a Li-Pol battery in the range of 1000mAh. I can get one of the li-po pouches with protection circuit in them and wires out, in which case ...
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Why is the Y-capacitor named so?
I guess X-caps are named so since they are connected across the Line and return. Similarly is there any reason for naming Y-caps, which are connected between L/N and GND ?
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Any evidence of real-world risk from someone else lead-soldering your devices?
I appreciate this is likely neuroticism, but a luthier has recently worked on a couple of guitars of mine. He uses lead-based solder (entirely reasonably), but obviously that involves handling the ...
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Can I replace this resistor (in USB adapter that plugs to mains) with this other resistor?
I would just test this instead of asking here, but because this goes to mains, dangerous voltages and all that, I prefer to be safe than sorry.
An old USB adapter stopped working, and I finally took ...
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User safety when touching tone controls in vacuum tube preamplifier
Images taken from: "Designing tube preamps for guitar and bass" - Merlin Blencowe. Pg-244,247. Published by author, 2009, 2nd edition.
I intend to use these circuits in a guitar preamplifier....
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ISO 13849-1 Cat 3 Architecture in safety sensors
Context > In ISO 13849-1 CAT-3 architecture, you need 2 redundant I-L-O (Input-Logic-Output) channels and there has to be a cross monitoring between two redundant logic units. Refer to the image ...
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Safety in industrial embedded system
I have just started working at a startup that specialises in imaging equipment in an industrial environment (based in Europe). I have just started a body of work looking to improve the safety ...
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Are inductors in resonant circuits dangerous? They produce very high voltages
A simple series LC resonant circuit has theoretically infinite voltage in the middle between L and C, if we assume 0 ESR and exact resonant frequency:
\$V_{at LC junc} = V_{in} \frac{X_{C1}}{X_{C1}-...
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Safety considerations for designing Mains Voltage Sensing Circuit
I'm looking to design a circuit to measure AC mains voltage and current for protection purposes. I'm considering using the ADS131E0 ADC by Texas. The IC is made with power-line monitoring in mind.
On ...
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How can a Class E Power Amplifier be built and experimented with safely?
Given that Class E RF amplifiers, even those that generate less than a few watts, can easily generate voltage spikes approaching (or exceeding) 100 V, how can they be homebrew built and experimented ...
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Does it improve safety to make a capacitative dropper symmetric?
Here's the most basic capacitative dropper circuit I could find with ten seconds on Google. Allegedly the voltage across the load will be about 5V. (I say "allegedly" because I couldn't ...
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Are there safety concerns with hooking an inductor to a MOSFET and generating 85V spikes from a 9V source?
Are there safety concerns with hooking an inductor to a MOSFET and generating 85V spikes from a 9V source?
Looking at the circuit below, I can generate this from a 9V battery. Is this safe? It's on a ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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, ...
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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 ...
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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 =...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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).
...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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" ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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....
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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 ...
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