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In a 120V AC motor circuit, a capacitor is wired in series with the start/auxillary winding. I'm a beginner, but I think I have learned that the cap's function is to create a phase shift to enable start rotation. What is still unclear to me is where the cap should be located:

Is it:

Hot line voltage-----cap-------start winding-------Neutral.

Or

Hot line voltage----start winding------cap--------Neutral.

If the cap came after the winding, wouldn't the winding be energized a second time when the cap discharged its saturated negative plate when line voltage oscillated through zero? But maybe this is what DOES happen. Can someone explain?

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  • \$\begingroup\$ Google is your friend - just type in a few words and look at the images produced. Refine words and get to the solution. \$\endgroup\$
    – Andy aka
    Commented Jan 9, 2016 at 16:47

2 Answers 2

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Scott. This is a follow up to your previous motor question . I haven't finished the response to that yet (as I ran out of lunch-break) but will do.

To answer this question, no, it doesn't matter what order the series connected components are connected in as long as they are all passive components. Remember that the same current is flowing through them all.

I'll respond in full in the original question in a few hours.

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  • \$\begingroup\$ I would say that there is no restriction to passive components in the principle that component order doesn't mater. The principle is restricted to 2-port components, but more that 2 ports would not be a series connection. Of course, polarity is important with some components in DC circuits. \$\endgroup\$
    – user80875
    Commented Jan 9, 2016 at 17:18
  • \$\begingroup\$ I appreciate your explanations. Looking forward to the completion of your original answer. \$\endgroup\$
    – Scott
    Commented Jan 9, 2016 at 19:34
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In a series circuit there is no functional difference in the order in which the components are connected. That is an important fundamental circuit principal. The order of connection can be influenced by such things as wiring connection convenience, connection of the case of a component to ground, and voltage rating of the insulation between a component and ground.

In all uses of capacitors in AC circuits the capacitor charges, discharges and charges with reverse polarity with every cycle of the applied voltage.

You are correct about the function of the capacitor in series with the start/auxiliary winding of a single-phase AC motor. It not only enables starting but also determines the direction of rotation.

Hot and Neutral

It appears that you may have some difficulty understanding "hot" and "neutral" in an AC circuit. Functionally, there is no difference between a "hot - hot" supply and a "hot - neutral" supply. This has been addressed in numerous other questions. I think the following one is closely related:

What does hot and cold mean on an AC outlet?

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  • \$\begingroup\$ I very well may have all this wrong. But here is what my googling and study have got me: AC current enters my house via three wires, two"hot" leads bringing 220v and a "neutral" wire, between them so to speak, to allow 110v. In an electric dryer or stove circuit, the heater is energized at 220v, 120v on the first half of voltage oscillation and then 120v through the other half when voltage reverses. The motor, however, receives 120v on the first half only, but nothing when voltage reverses because the current is returning to source via neutral rather than returnin through the other 120v hot \$\endgroup\$
    – Scott
    Commented Jan 9, 2016 at 22:42
  • \$\begingroup\$ You are correct about how AC enters your house but wrong about the motor receiving 120v only on the first half of the oscillation. Both 120v circuits receive half of the amplitude of both halves of the oscillation of the 240v. In the USA, and I believe, in most other places that have this system, the nominal voltage at the meter is 240 rather than 220. That increase took place at least 50 years ago, but many people still refer to 220 rather than 240. Look at the other question at the link I provided. \$\endgroup\$
    – user80875
    Commented Jan 10, 2016 at 0:59
  • \$\begingroup\$ The wiring diagram indicates that one leg of Line voltage 1 enters the appliance and feeds one side of both the motor and the heater. The wire exiting the motor runs to N. The wire exiting the heater runs to Line voltage 2. Motor is receiving 120v once from line 1 and nothing from N, but the heater gets it twice, once from line 1 and again from line 2. I picture it as 120v sloshing back and forth through the heater bringing 120v from Line1, again from Line2, but motor gets 120v on first half of wave, but doesnt get second slosh coming the other way because it's wired to N, not Line 2. \$\endgroup\$
    – Scott
    Commented Jan 10, 2016 at 15:11
  • \$\begingroup\$ I will say again. There is no functional difference between hot and neutral. Any load connected to hot and neutral behaves exactly as it would behave when connected to two hots. You need look at diagrams like the one in that other question for which I provided a link and study what ever resources you can find until you understand it. \$\endgroup\$
    – user80875
    Commented Jan 10, 2016 at 15:26
  • \$\begingroup\$ Thank you for the time you have taken and the knowlege you have shared. Will continue to study. \$\endgroup\$
    – Scott
    Commented Jan 10, 2016 at 16:01

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