Hot fuse box

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Jadnashua

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Ideally, a CB or fuse is as close to a dead short when not blown or tripped. So, figuratively, if it was say 1-ohm at load, that equates to a high resistance. Since the heating coil of a dryer may only be 15-ohms (a quick guess, but in that order of magnitude), 1 ohm is a big part of it, and the fuse will generate a fair amount of heat.

High resistance in this case doesn't necessarily mean hundreds or thousands of ohms, which would drop the total current available so much, little heating would occur; even fractions of ohms on a high current circuit will cause significant heating.

Run the numbers yourself...
 

JWelectric

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Ideally, a CB or fuse is as close to a dead short when not blown or tripped. So, figuratively, if it was say 1-ohm at load, that equates to a high resistance. Since the heating coil of a dryer may only be 15-ohms (a quick guess, but in that order of magnitude), 1 ohm is a big part of it, and the fuse will generate a fair amount of heat.

High resistance in this case doesn't necessarily mean hundreds or thousands of ohms, which would drop the total current available so much, little heating would occur; even fractions of ohms on a high current circuit will cause significant heating.

Run the numbers yourself...

240/15= 16 amps
240*16= 3840 watts

Let’s add one more ohm of resistance

240/16= 15 amps
240*15= 3600 watts

According to the numbers we lose 240 watts of heat when one ohm is added to the circuit

Ohm’s Law simply states that an increase in resistance is a drop in amperage.

The heat produced by a lose connection has nothing to do with increased resistance. What causes the heat is the arcing which burns oxygen (an added fuel) which causes the heat not the resistance of the lose connection.
This is learned in Elec. 101 and you engineers should have this down pat by now.

This is the very heart of the arc fault debate. The arc fault devices today will detect a line to line arc which results in a low resistance path but do not detect a in-line arc which would be a high resistance arc.
The line to line or line to ground arc is a low resistance high amperage arc which is easy to detect but the in-line arc is a high resistance low amperage arc which is hard to detect.
 

Mikey

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You don't need an arc to produce heat.

Using your example, in the original case the entire 3840 watts is being dissipated in the dryer. However, if the resistance in the breaker, fuse contact, or a connection goes up to 1 ohm somehow, 225 watts (15A*15A*1ohm) will be dissipated there, and the remaining 3375 watts (15A*15A*15ohms) in the dryer. 225 watts is a lot of heat for a device to dissipate if it was designed for zero.

Having said that, the reason for the breaker, etc., to exhibit a 1-ohm resistance, rather than it's designed zero ohms, might well be due to arcing which resulted in the breaker terminals being oxidized.
 
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Jadnashua

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Your electric dryer or a soldering iron (or in this case a corroded connection acting like a resistor) create heat equally as well without producing arcing...
 

JWelectric

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225 watts (15A*15A*1ohm) will be dissipated there, and the remaining 3375 watts (15A*15A*15ohms) in the dryer. 225 watts is a lot of heat for a device to dissipate if it was designed for zero.

Yea What he said.

Iguess if I had been paying attention to what Jim has been saying instead of being so bull headed to get my point across I would have seen that he said the same thing.

A lesson to be learned; slow down and learn something.
 

Bob NH

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Yea What he said.

Iguess if I had been paying attention to what Jim has been saying instead of being so bull headed to get my point across I would have seen that he said the same thing.

A lesson to be learned; slow down and learn something.

See also Post #12 again. Same story.
 

BrianJohn

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If the resistance goes up wouldn't the amperage go up? If not, why do burned connections often cause so much heat that the insulation burns off the wires. Wouldn't it take high amps to burn insulation?

I did not read all the post sooo, if this was answered previously WELL IGNORE

VD, voltage drop. The voltage drop across a connection results in heat due to resistance and current. All which result in Watts (V*I=W).
 

JWelectric

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See also Post #12 again. Same story.

Yes you did but I was so engrossed in adding the total resistance that I wasn’t looking at the resistance being in series and also overlooking the drop across each point of series resistance.

This sometimes happens when we start looking at forest instead of the trees. As one student said on the phone this morning, “Mike was you looking at the picture and forgetting that your nose was in between you eyes and the picture?â€

Well I just don’t look at my nose every time that I look at something but yes this is exactly what I was doing.
 

hj

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circuit

If you hear a noise in the main panel, and it is getting hot, you have a loose, or defective, connection somewhere. If it is at or near the breaker it will overheat it and cause it to trip. A miswired dryer would trip the breaker immediately, although it might just affect one side and the other would allow the motor to run, which is why the breaker should be a linked pair so both HAVE to trip at the same time. Installing a 4 wire outlet and pigtail at the dryer would be useless since the wire to the outlet will only have 3 conductors.
 

BrianJohn

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If you hear a noise in the main panel, and it is getting hot, you have a loose, or defective, connection somewhere.

Not necessarily

If it is at or near the breaker it will overheat it and cause it to trip.

Not necessarily

A miswired dryer would trip the breaker immediately, although it might just affect one side and the other would allow the motor to run, which is why the breaker should be a linked pair so both HAVE to trip at the same time.

Not necessarily

Installing a 4 wire outlet and pigtail at the dryer would be useless since the wire to the outlet will only have 3 conductors.

Except this is required per the NEC for new installations dating back a few code cycles.
 
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