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Designing single fault safety into class I device

You have the whole secondary circuit in an earthed, highly-conductive enclosure. There is no way any fault (or even multiple faults) inside it can produce an earth leakage current.
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IR LED Safety: Subtend Angle and Retinal Exposure Limit

I'll give this a shot. As the subtend angle gets bigger, the image becomes larger on the retina. However, the limit allows more power (flux?) with smaller images. This seems counter intuitive since ...
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1 vote

Power camping lantern with 12v AGM battery

I have a lot of LED experience that I can share from the last 20 yrs. Simple version Choose a Battery with adequate Ah capacity that is < 25% above the LED voltage if you would like to have a ...
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2 votes

Power camping lantern with 12v AGM battery

AGM batteries do require venting. No one would recommend using one in a low/no ventilation area/container, even if you are not charging it in that area. May be better off putting it in a box outside ...
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  • 70.8k
12 votes

Do neon signs emit x-rays?

High energy electrons produce x-rays when they strike atoms, usually metal. That's how a scanning electron microscope can detect elements. Basically, you need electrons accelerated with a high ...
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19 votes

Do neon signs emit x-rays?

Neon signs do not produce X-rays. Although they operate at high voltages, the gas within the tubes prevent electrons from gaining enough energy to produce X-rays. However, if one wants to split hairs, ...
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4 votes
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What prevents old (low current) USB cables from catching fire if used to Quick Charge modern devices (at high-current)?

As a generic answer, the USB specs, and QC specs. The USB specs require that a PD source detects the cable type from the plug. If the plug does not identify as PD capable plug then PD will not be used....
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  • 87.4k
4 votes

What prevents old (low current) USB cables from catching fire if used to Quick Charge modern devices (at high-current)?

First of all, an old cable has VBUS, GND , D+ and D-. This is only four wires. The full 100W power draw is only possible when using USB 3.0 compatible cables, which have 8 wires in them (two extra ...
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1 vote

Help designing a safety indicator for a high current transformer

Knowing if there's any current flow in the secondary (or the primary) doesn't really help much from a safety standpoint. Suppose there's nothing attached to the output, there would be no current flow ...
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  • 3,644
1 vote

Help designing a safety indicator for a high current transformer

There are several companies that make current sensing indicators using a mini CT and LED. These provide electrical isolation up to some point. Wiring it in the return wire on a grounded HV system ...
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2 votes

Help designing a safety indicator for a high current transformer

The most common indicator for a safety no-voltage/current is a low voltage Neon Indicator with 220k current limiting resistor or as desired. https://www.intl-lighttech.com/instrumentation-sensor-light-...
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Help designing a safety indicator for a high current transformer

The transformer primary current will be quite small if there is no load on the secondary (high voltage) end. Therefore it is sufficient (and much safer) to monitor the primary (120 V) current. So now, ...
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1 vote

Help designing a safety indicator for a high current transformer

On secondary side it is difficult because the insulation. Much easier it is on the primary side. No voltage on primary side => no voltage secondary.
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How can failure of Class Y capacitors lead to electric shock?

Due to the fact that earth-fault failure are a common type of dangerous failure, capacitors that connect active to earth must be Y-class. Earth-fault failures are a type of dangerous failure (1) ...
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7 votes

How can failure of Class Y capacitors lead to electric shock?

It would potentially lead into hazardous situations if an Y capacitor would fail into a short circuit. However, Y capacitors are special safety capacitors that are specifically designed to fail into ...
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4 votes
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How can failure of Class Y capacitors lead to electric shock?

In an ideal world a Y-Capacitor failing short would trip a safety device, either a fuse or a GFCI will trip. Sadly, your world is not ideal and a ground path has a lot of ways to be broken. It's a ...
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  • 1,516
-2 votes

Are touch lamps safe?

I have owned a touch-control lamp for years. Depending upon the measurement device, the lamp base generates between 2-3.7 milligauss field at 16 inches. At 8 inches, the magnetic field was measured at ...
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