chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
If you have 20 mins to kill I highly recommend this......................................
5000A fuse failure
- Thread starter chris kennedy
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gadfly56
Senior Member
- Location
- New Jersey
- Occupation
- Professional Engineer, Fire & Life Safety
I watched this and wasn't overly impressed. They just hit it repeatedly until all the links failed. It was interesting to learn how really high amperage fuses were constructed.
synchro
Senior Member
- Location
- Chicago, IL
- Occupation
- EE
At first I was wondering why the two parallel cables jumped apart at 13:41 because they should attract each other if their currents are in the same direction. But after playing it at a lower speed, it looks like they came together and closed the small gap between them first and then they rebounded apart.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
How much does one of those cost? 
How much does one of those cost?
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
Such a deal- "This item ships free!"
kwired
Electron manager
- Location
- NE Nebraska
did not look, but shouldn't currents in same direction have same magnetic polarity and repel one another?
currents in opposite direction would have opposing magnetic polarity and be attracted to one another.
chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
That appears to be used.
Looks like the sell for around $2900
synchro
Senior Member
- Location
- Chicago, IL
- Occupation
- EE
The magnetic fields produced by the two conductors will encircle each conductor in the same direction because the currents are going the same way. However, the direction of the magnetic field on one side of its circular path around a conductor is opposite to its direction on the other side of that path. Here I am referring to the direction of the magnetic field in a tangential direction along its circular path. Therefore the polarity of the magentic field at conductor #1 created by conductor #2 will have an opposite polarity as the magentic field at conductor #2 created by conductor #1. Therefore, along the lines of your argument, opposites attract and the forces will pull the wires together.
Yeah, I don’t think he would destroy a brand new one, but what do I know..
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
When you have a bolted short circuit between two phase conductors of AC the currents will be in opposite directions and will repel. This is the situation most often encountered.
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kwired
Electron manager
- Location
- NE Nebraska
Magnetic fields around a conductor carrying current must not be quite same as they would be for simple bar magnets laying next to one another?
Multiple conductors of an AC circuit I get would have different polarity at different points in time, but a set of parallel conductors (with no other opposing circuit conductor in same vicinity) are like laying two identical magnets next to one another in same orientation - I think, shouldn't they repel one another?
synchro
Senior Member
- Location
- Chicago, IL
- Occupation
- EE
In both cases the attraction or repulsion is due to magnetic fields. But the orientation and path of the magnetic fields relative to the object that is creating the magnetic field is different. In the bar magnet the path of the magnetic field is lengthwise along the magnet then out one end and back around through the air to the other end. In a wire the magnetic field encircles the conductor, and so its direction is not along the length of the wire.
Below is an analogy that might help:
Say that you have two parallel wires with the currents flowing in opposite directions. Then the magnetic fields around them will be in opposite directions, one clockwise and one counterclockwise when looking down the wires. Think of these as gears rotating on the axes of the wires in opposite directions and with the edges of the gears in close proximity to each other. We could then mesh the gears (if they were slightly bigger) because at the point of contact they would be moving in the same direction. And so in our analogy, between the wires the magnetic field coming from one wire has the same direction (i.e., polarity) as that coming from the other wire, and so there will be a repulsion between them.
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- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Perhaps a better way to do a rough analysis is to know that energy is contained in any magnetic field. Where the two field lines on the facing edges of the wires are aligned bringing the wires closer to each other increases the magnetic field and hence the stored energy. So the tendency will be for the wires to move apart.
When the currents are in the same direction the magnetic fields will be opposite. Bringing the wires closer together will reduce the system energy, so the force will tend to move the wires together.
When the currents are in the same direction the magnetic fields will be opposite. Bringing the wires closer together will reduce the system energy, so the force will tend to move the wires together.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
They are somewhat similar if you orient the bar magnets correctly. For a CCC, the magnet field lines are circular around the conductor, while for a bar magnet, they are loops that go through the bar. So the arrangement that makes the fields most similar has the bar magnet perpendicular to the wire, tangent to one of wire's field lines.
Then for two wires with the current at the same polarity, the two side by side magnets would both have the N pole pointed, say, to the left, as you look along the direction of the wires. The poles facing each other are opposites, so the magnets attract, just like the wires would. For two wires with current of opposite polarity, flip one of the magnets around; now the same poles are facing each other, so the magnet (and wires) would repel each other.
Cheers, Wayne
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