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kd87
(:

Registered: 11/05/11
Posts: 324
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Series circuit electrical question. Need help thanks
#26852115 - 07/29/20 03:26 PM (3 years, 5 months ago) |
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Ok this is for a series circuit
So 4 loads are connected in series across 120 volts and has a 3A current. One of the loads fails to operate. The voltage across the other devices is 40Volts. What circuit fault is indicated? And can you please explain this? Thanks y'all
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koraks
Registered: 06/02/03
Posts: 26,667
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Re: Series circuit electrical question. Need help thanks [Re: kd87] 1
#26853447 - 07/30/20 12:22 PM (3 years, 5 months ago) |
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The failed load has shorted. It's evidenced by the 40V drop across the other 3 loads.
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CaptainParanoid
Stranger Danger



Registered: 08/06/20
Posts: 74
Last seen: 1 year, 4 months
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Re: Series circuit electrical question. Need help thanks [Re: koraks]
#26866179 - 08/06/20 10:41 AM (3 years, 5 months ago) |
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If the failed load is the last in a series circuit it could have failed do to voltage drop and not be shorted. Like four lights wired in series. By the time power has passed to the last bulb the voltage drop is much higher. In your case it's 40v, if this were a 120v motor it would certainly not run.
If any of the loads fails open like a burnt bulb or open motor windings amperage draw would go to 0 as the circuit is open. A meter would read 120v across the failed device because none of the devices will be operating (open circuit) and no electrical energy being consumed (doing work) you will read the full potential of the circuit.
If the failed device shorted to ground the circuit protection device will trip and nothing will run.
But this sounds like one of those strange test questions that are way open ended. My answer would be voltage drop
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koraks
Registered: 06/02/03
Posts: 26,667
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Re: Series circuit electrical question. Need help thanks [Re: CaptainParanoid] 1
#26867539 - 08/07/20 12:20 AM (3 years, 5 months ago) |
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Quote:
CaptainParanoid said: But this sounds like one of those strange test questions that are way open ended.
I don't think it's strange or open-ended. The essential information is right there. Vtotal = 120V, and 4 devices attached in series. 3 loads have 40V each over them, which means that the 4th drops 0V. Total current draw is 3A, so from Ohm's law it follows that the 4th load as a resistance or 0R. We call that a 'short' in common parlance. It doesn't matter where the 4th (shorted) load is exactly in the chain - whether it's the first, the last or either of the two in-between. Electrically speaking it's essentially become a piece of wire.
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CaptainParanoid
Stranger Danger



Registered: 08/06/20
Posts: 74
Last seen: 1 year, 4 months
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Re: Series circuit electrical question. Need help thanks [Re: koraks]
#26867643 - 08/07/20 04:46 AM (3 years, 5 months ago) |
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Definitely a test question.
1) Wiring loads in a 120v series circuit is rare. It's even difficult to find new Christmas lights (the most common example given) wired this way. 2) Reading 40v across all three loads in total or individually? It's impossible to have the same or more voltage compared to the preceding load in a series circuit. 3) In the real world this example will result in a breaker trip.
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