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Old 11-18-2009, 08:39 AM   #1
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serial or parallel?


Hi, I need some basic theoretical instruction here.

I have been puzzled:
1. are the two fuses that comes from the street and before the breaker box serial or parallel? Why?

2. are the breakers for 240V working on two 120V serial or parallel ? Why?

3. If we take one 240 line out of the breaker and add a fuse box before the appliance, the two fuses in this box are serial or parallel? Why?

Any background theories that i should learn about?

Thanks a lot.

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Old 11-18-2009, 09:18 AM   #2
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serial or parallel?


Check out this site

http://www.allaboutcircuits.com/

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Old 11-18-2009, 09:23 AM   #3
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serial or parallel?


serial or parallel have nothing to do with any of your questions. The two fuses are two separate out of phase 120V lines. Connecting a fuse box to an appliance would make no sense anyway. And again you are just adding an inline fuse to each of the separate 120V lines. This fuse is in series if you will.
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Old 11-18-2009, 09:44 AM   #4
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serial or parallel?


In each of these three situations (oversimplified to make the English sentences shorter), the elements or components described are in series.

In a really old fashioned or a miniature set of Christmas lights the current goes from one plug prong (through the wires) to one lamp and on to the next lamp and on to the next ... and back to the other plug prong. Should one light burn out, the others also go out (unless there is a special link inside the burned out lamp).

The typical current path for a 240 volt appliance is from one live wire out on the utility pole down to the fuse box (or breaker box), through one fuse (or breaker), then to the appliance, then back via the other live wire to its fuse (or breaker) and back out to the utility pole. The fuses must be in series with the appliance so that an overload will blow one or both fuses, breaking the circuit.

The typical current path for a 120 volt appliance is from one live wire out on the utility pole down to the fuse box, through one fuse, then to the appliance, then back via the neutral which goes dirctly back to the utility pole.

Now, parallel circuits.

Two or more household lights or appliances are always connected in parallel with each other, not in series. But together they are in series with the fuse. Current from the utility pole goes through a fuse, then has a choice of going through one appliance or the other appliance, then arriving at the neutral and going back to the utility pole. Considering just the portion of the circuit after the fuse, everything is in parallel. If the fuse blows, all the lights and appliances on that circuit go dead. If one light or appliance on the circuit is turned off, others stay on.

Connecting an appliance to its own fuse box.

(going into a little more detail) CUrrent comes from the utility pole down to the fuse box then goes through one main fuse (say 100 amp rating) then to a branch circuit fuse (say 20 amps rating) then to the appliance, then to neutral and back to the utility pole. The circuit described is a series circuit relative to the components mentioned. It is like having a separate fuse box for the appliance within the main fuse box.

Occasionally a smaller fuse box that is physically separated from the main fuse box is indeed found near an appliance such as a clothes dryer. This is classified as a subpanel.
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Stop wasting time re-adjusting the pattern. Have several lawn sprinklers, one for each pattern.

Last edited by AllanJ; 11-18-2009 at 09:51 AM.
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Old 11-18-2009, 05:12 PM   #5
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serial or parallel?


Fuses and circuit breakers are placed in series with the device they are protecting. Methinks your questions are misplaced for the concepts of parallel and series circuits.
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Old 11-18-2009, 05:45 PM   #6
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serial or parallel?


Quote:
Originally Posted by hohadcr View Post
1. are the two fuses that comes from the street and before the breaker box serial or parallel? Why?

2. Any background theories that i should learn about?
1. Paralleling fuses requires some assurance that the current will be shared equally. This requires each fuse to have a known and controlled resistance, in addition to contact impedances being known and controlled.

If a 30A fuse has 1/30 ohm of resistance, and contact impedance accounts for, I don't know, 1 milliohm, and these values vary all over the place, you could make a 60A fuse by putting each fuse in series with a 0.2 ohm. 1kw [or larger] resistor, and put these two assemblies in parallel.

You may be able to make the resistors out of short pieces of skinny wire that don't melt at 30A.

This current-sharing design may have downsides, depending on your application. For me it worked, to ensure current sharing between two 10A relay contacts when I needed almost 20A.

2. No, just practical concerns. In theory, you could parallel fuses.
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Old 11-21-2009, 10:28 AM   #7
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serial or parallel?


Thank you all very very much!

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