AFCI circuit breakers and the problem of ‘nuisance tripping’ | Circuit Breaker Parts

If you run a separate earth wire that is hard grounded at the sub and hard grounded at your house and nowhere in between. In this situation if you get a lightning strike at or near your house then the ground potential rises. This flows through the earth wire to the sub ground and can be a massive current, enough to make the network fail dramatically. This rise in ground potential can also be caused by other things such as a faulty insulator on an MV or HV tower (pylon) or pole. Even if insulators are good then you can still get this ground potential rise. You can easily measure it with a length of wire and two earth spikes, put one near a tower and the other a distance away and you can see a significant voltage. If you also have a separate wire called neutral running form the sub then the potential between that wire and the earth wire is unknown so you have a risk of lethal voltage between neutral and earth, a situation that is not expected and potentially extremely dangerous.

Of course in many parts of the world that’s not possible like it is here in the US where better than 60% of homes have access to NG

You also need to insure that the hot line is completely isolated from the neutral line other than via the intended switching and power supply paths. Insuring that is a hell of a lot easier when you use registered isolating components to do it.

I’m wondering why nobody is simply rectifying a 120vac input for dc wiring the secondary coil? It means you don’t have to swap the coil location or use a dc power supply. I have a trans with a secondary resistance of 82ohms. Putting 120vdc through it would be about 175watts (assuming I do a good job of determining wire size and 1.46amps is ok)

Yeah, dont use these. Use a relay instead. There is a reason all the high end stuff went away from the Triacs as they will float to full mains voltage when no load is connected and you get electrocuted when you mess with the circuit. AMX, Crestron, Lutron, etc all have moved away from pure Triac control due to this safety issue.

The second was in an industrial setting, working on repairing a 480v-supplied welder in a hard-wired installation. Plant electrician assured me the circuit was locked & tagged out. I trusted him. Sprayed some contact cleaner on the mains relay to start, and took 480v up the spray and into the can (and my hands holding it). That was an unusual sensation.

• Lightning: In fact, transients induced by lightning are not the result of a direct strike. A lightning strike creates a magnetic field that can induce large magnitude transients in nearby electrical cables. A cloud-to-cloud strike can affect both overhead and buried cables. The outcome also is unpredictable—a strike that occurs a mile away can generate 70 V in electrical cables, and another can generate 10 kV from 160 yards away. • Inductive-load switching: Generators, motors, relays, and transformers represent typical sources of inductive transients. Switching inductive loads on or off can generate high-energy transients that intensify in magnitude with increasingly heavy loads. When the inductive load is switched off, the collapsing magnetic field converts into electrical energy, which takes the form of a double exponential transient. Depending on the source, these transients can be as large as hundreds of volts and hundreds of amperes, with durations of 400 ms. Due to varying load sizes, there will be variance in wave shape, duration, peak current, and peak voltage of the transients. Once these variables are approximated, circuit designers will be able to select a suitable suppressor type. • Electrostatic discharge (ESD): This energy is the result of an imbalance of positive and negative charges between objects. It’s characterized by very fast rise times and very high peak voltages and currents.

Still can’t bring myself to install SSRs on “high current” applications, either. High quality mechanical relays.

i built the rig that day. I put an ammeter with max hold on a circuit, plugged the circuit into a known 20 amp connection, and put a load on the circuit that simulated the instrument. Turn it on, 22 amps max hold, 13 amps nominal.

They make “plate” heaters that are metal plate looking thing with a couple of stud terminals sticking out of them as well.

For the voltage setting, I thought that wattage equaled volts times amps? Shouldn’t the waste heat be the same regardless of whether it’s drawing ten amps at 120 or five amps at 240? Or is it more complex and nonlinear than that? I’m curious.

I’d like to say that if a circuit breaker is X-degrees over ambient, it’s a problem… but there’s just no hard and fast rule for this. I can’t say this.