Charting the S&P 500’s range-bound, but bullish, (unofficial) summer start | Lrd12 Overload Relay

Varistors, also called metal-oxide varistors (MOVs), are used to protect sensitive circuits from a variety of overvoltage conditions. Essentially, these voltage-dependent, nonlinear devices have electrical characteristics similar to back-to- back Zener diodes.

I was mainly thinking about the diff between high vs. low RMS AC voltage but the discussion of AC vs DC has been interesting as well.

A mains isolation transformer. wdwd [GFDL], via Wikimedia CommonsAn isolation transformer isolates the mains supply from the earthing system. This does not change any of the risks inherent to the mains voltage or other high voltages in your device, but it does provide you with some level of protection should you accidentally provide a path to earth from a live component.

During service calls, being able to identify undersized conductors can help resolve compressor start issues or intermittent trips of breakers or fuses. Knowing appropriate and inappropriate breaker and conductor sizes will save you and your customers time and money.

So a 20 amp breaker is designed to take the load shift on startup. A 15 amp breaker will carry the nominal load, but that surge on startup will kick it every time. In the days before switching supplies the input voltage would vary from 108 to 115VAC where I did work. This occasionally caused breaker trips on the unprepared circuit. I learned to spec high enough to minimize that issue and keep a safety factor in play.

Agreed. I work in electronics as a profession. High voltage electronics no less. Industrial size high voltage power supplies. Everything about them up to maintaining them down to component level. The comments here from people are scaring me shitless from the lack of knowledge to the over the top over complication of the problem.

the scariest thing I have ever seen/been around was in a fuel terminal at an oil refinery. I couldn’t figure out why we had printers, plotters, Apple II’s and monitors dropping like flies.

I to have worked with high voltage systems. My point was that it needs to be treated with a bit of respect or it WILL kill you even if not immediately. My friend was an electrician of many years. And sure, I hear lots of stories of how people get away with this and that, but that is just that they gotten away with it so far. They could be dead tomorrow.

The key is to reference NEC NFPA 70 Table 310.15(B)(16) to find the ampacity of a conductor and size that conductor according to the MCA listed on the unit label. When this is done, the conductor will be properly sized according to the NEC.

Agreed. I don’t see us revisiting the war of the currents. Interties between independent grids make sense, but there’s a reason that AC won, and I don’t think time and advancing technology has significantly changed that.

Once got electrocuted from a computer monitor though, that a relative thoughfully gave us without a case. I was reaching underneath to adjust the brightness or something. Touched something live. The monitor was on the floor, with the 8-bit computer (a Spectrum). My hand touched the live PCB, jerked away, bounced off the floor, and back up to the PCB again. Eventually my sister switched it off at the socket. Bit stupid really, I wouldn’t let kids near something like that, but…

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