OT: Electrical Question Options

[McMark]

How many amps would the circuit below draw? What if they were 2 kW, 3 kW and 4kW?

Anyone care to explain how you found your answer? Electricity stuff makes me feel totally inept. It always feels like I'm on the verge of understanding things and then I realize I don't know anything. (IMG:http://www.914world.com/bbs2/html/emoticons/confused24.gif)

I'm trying to wire up the heat lamps for the paint booth and I need to know what size wire we'll need and what size breakers to use. (IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif)

EDIT: It's 220v.

[dmenche914]

You will have 6 kW going thru the total circuit. 2kW on each of the three legs of the circuit.

The 6 kW is power. To determine the amperage (electric flow rate) , the resistance of the circuit will need to be known, or the voltage.

One watt is equal to one amp going across one ohm of resistance.

One Volt is the potential between two points flowing one amp dissappated as one watt (accross an one ohm resistance)

Thus to get your answer, we need either the voltage, across the circuit, or the resistance of the circuit.

If it is 200 volts, then:

6kW = 6000 Watts at 200 volts means 30 Amps of current.

200 Volts x 30 Amps = 6000 Watts

if 220 volts, then it is 27.3 Amps

if 120 Volts, then it is 50 Amps

Note how the current increases for a given power, as the voltage is reduced. Higher voltage means less amperage to consume the same watts (power)

Thus a 240 volt circuit can on a 20 Amp breaker can supply as much power as a 120 volt circuit running 40 Amps! The total watts on each circuit is the same maximum of 4800 watts. Less voltage, means higher current to get same power.


if you are talking heaters, the bottom line is power to the heater. By using a higher voltage, a smaller breaker or fuse is required for the same wattage (power). with higher voltages, smaller currents mean a smaller diameter wire can be used to power the heater, as the diameter of the wire is selected based on current, not voltage (the insulation on the wire determines its voltage rating)

hope that helps.

dave

PS if the lamps are run on 110 volt, and if you have a 220 v supply, you could run half the lamps off one leg of the 220 hot to nuetral, that will supply half the lamps, and repeat on the other half using the other "hot" half of the 220 line to neutral. Thus you will have 110 volts to the lamps, and will need two 30 amp breakers, one for each leg, Or if you have 220 volt heat lamps, wire directly to the 220 volts, using one 30 Amp breaker

In each case you will have about a 10% margin on the breaker amperage. (you might want more)

Wire selection will need be based on the current you run (amps) which will be determined by the voltage you select. Also the length of wire must be considered in the determination of diameter. A longer run of wire will require an increase in diameter.

So armed with the current (determined by voltage) and the length of wire, you should be able to look up the correct gage of wire on a chart. I generally go one size bigger for extra robustness, or for future expansion room for add on circuit, so keep that in mind.

Same holds true with the breaker, the 27.3 Amps required could work well with a 30 amp breaker, but I'd likely up rate it to 40 or 50 amps. Just be sure that the breaker is no bigger than the wire it must protect. If your wire is only good for 40 amps, do not install a 50 amp breaker. The breaker must be rated less than the wire, and the wire must be rated to carry the planned load, plus any future expansion.