Electrical question

[HarryVanderpool]

If you want to listen to someone that REALLY knows this stuff, watch Mike Holt video:
217 NEC - Feeder Conductor Sizing [215.2], (18min:13sec) - YouTube

 

[buickanddeere]

Not true. His system is ungrounded. Without a ground there is no current flow to this metal surface. Any one leg can be grounded, but only 1. If you ground 1 leg them a second touches you get instant trip.

Even on a dead short/bolted short. A breaker still requires at least one AC cycle to trip, 17/1000 of a second absolute minimum. 40/1000 or more is a typical minimum.
For a wire just laying on the ground somewhere, the trip time will be at least a second and easily 5 even 10 seconds as the wire arcs, spits and spatters.

 

[buickanddeere]

I am quite aware of thermal overloads, They are listed as a 49 type device, and we test them frequently. I was fishing because there is a world of difference between a 240v table saw, and a motor on a 480-600V MCC with overload protection. I.E..."HEATERS"


I believe the OP was talking about residential single phase wiring. Does the 240V 100 amp breaker circuit you describe offer the homeowner thermal protection? Or should you fall back to the "Size the conductor to the FLA expected, and the breaker to protect the conductor?

Not trying to pick a fight Buickanddeere, but I believe your info is more for a business than a homeowner.

If home owner has a properly wired 10HP motor with thermal protection, the 50 amp cable and 100 amp breaker still stands .

 

[prichard]

Even on a dead short/bolted short. A breaker still requires at least one AC cycle to trip, 17/1000 of a second absolute minimum. 40/1000 or more is a typical minimum.
For a wire just laying on the ground somewhere, the trip time will be at least a second and easily 5 even 10 seconds as the wire arcs, spits and spatters.

True, not really instantaneous, but not delayed like the thermal overload part of the breaker.

 

[buickanddeere]

Your meter voltage is 240 volts whether or not you use 240, or 120 . Kwatts is 1000 voltamps... so using 240 on a pool pump means 1/2 the current. Ohms law states where resistance is constant, voltage and current are inversely proportional. So more voltage = less amps. Less amps = less kilowatts used. Amps are a measurement of electron flow.

Note I avoided the word POWER.. my explanations are bad enough without making it worse trying to equate it with work.., horsepower etc. If someone can explain it better, please do..I was terrible at physics.

Watts is watts and that is what you pay for. A 120V heater drawing 12 amps will cost you exactly as much to operate as a 240V heater drawing 6 amps.

 

[mbohuntr]

Watts is watts and that is what you pay for. A 120V heater drawing 12 amps will cost you exactly as much to operate as a 240V heater drawing 6 amps.

I stand corrected... I was always taught that 240 is cheaper to run, and to a point, that is true. But my statement about costing half as much is wrong. I made that assumption all on my own.

 

[mbohuntr]

If home owner has a properly wired 10HP motor with thermal protection, the 50 amp cable and 100 amp breaker still stands .

Not all motors have thermal overloads, and it requires the homeowner to understand that. Not a single motor I have used at home had thermal protection, Then again, I am getting old.
Those motors need to have conductor and breaker properly matched. Many people buy motors on craigslist..

 

[LD1]

I stand corrected... I was always taught that 240 is cheaper to run, and to a point, that is true. But my statement about costing half as much is wrong. I made that assumption all on my own.

The part about 240v being cheaper to run is partly true.....but its such a small savings the average person doesnt notice it on their bill.

240v is considered more "efficient" to run. There is less voltage drop in the lines (less waste via heat). And when sizing a motor to preform "work" a 2HP 240v motor is gonna pull half the amps as a 120v 2hp motor. Half the amps means a smaller breaker, smaller (cheaper) wiring, etc.

 

[SPYDERLK]

Watts is a unit of measurement that in it's simplest form equals Volts x Amps... 2000 watts / 240 volts = 8.33 amps used. 2000 watts/120 volts = 16.67amps.

Less amps = lower electric bill..

Rather,

Less WATTS = lower electric bill.

​

Watt hrs actually.

 

[SPYDERLK]

Why any difference if a live line grounds out on 120,240,277 or 347 ? Ever see how many sparks a 12V battery can throw ?

Wire for wire, much more Amps in a hi voltage short. Wires are resistors.