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Measuring and Explaining Inrush Current

5:27
8:33
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At 5:27 in

MASTER ELECTRICIAN DAD TEACHES SON HOW TO TROUBLESHOOT A 480 VOLT PANEL!

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What happens here

The technician performs a live test using the clamp meter to demonstrate the "inrush current" that occurs when the circuit breaker is re-engaged. He initially takes a reading of 0.66 amps before starting a piece of equipment. When the equipment starts, the meter briefly surges to 256 amps before settling down to 32 amps. He explains that this high inrush current, while momentary, is the cause of the "buzzing" and could eventually damage the 100-amp circuit breaker, even though it's not enough to trip it due to its short duration. The problem was not the circuit breaker itself, but rather an issue with the load it was connected to, likely on the roof.

Goal: Quantify the inrush current and explain its impact on the circuit breaker.

Tools and materials

  • 480-Volt Electrical Panel — The live electrical panel where current measurements are taken, Clamp Meter Unknown

What they say

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Okay. AC amps. Put my light on. Put my light on. >> Yep. AC amps min max. >> Mhm. >> And we're going to put it on and let's see what happens. 66. Watch what happens when it gets ready to start. >> 66 amps. >> No, it's 66 amps right now. >> Wow. >> Yeah. So, there's an issue with the load. >> Yeah. >> You see how much it surge is up to? more range right there. Here we go. So, what I've done, I've moved the decimal point over so we can see exactly what this thing is going to pull. 256 amps. 256 amps it pulled. >> Mhm. >> Ow. Oh, wait. It's a >> 256 amps on the 100 amp circuit breaker. >> Yep. >> How's that possible? >> Inrush current. That's way too high. That's what the problem is. Oh, how the >> How come the breaker didn't trip though? >> Because it's not enough to trip the circuit breaker. It's a It's a quick inrush. >> Okay. >> See what it's where it's running at 32 m. Yeah. So, that's what it is. So,

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