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| Subject - voltage drop again | |
| cs409 |
how would you figure voltage drop for a circuit which has 40feet of #12 and 140 ft of #10? 120V 2 wire circuit, with 10amps....would you do a voltage drop cal. for #12 and then one for #10 ,then add and div. for ave? are is there another math formula? |
| JimmyDee | Use the figures (this assumes AC circuit) 3.1 ohms per 1000 feet for #14, 2 ohms/1000 ft for #12 and 1.2 ohm/1000 ft for #10. Be sure to double the length of your circuit because it has double the wire (out and back) Calculate the total number of ohms of resistance, then just use Ohms Law. Jim |
| cs409 | your going to make me break out the side rule  yes, this is an AC circuit..... |
| JimmyDee | 40' x 2 = 80' x .002 ohms/ft = .16 ohms 140 x 2 = 280 x .0012 ohms/ft = .336 ohms Total ohms = .496 ohms x 10 amps = 4.96 volt drop @ 10 amps You can put your slide ruler back. However, 3.6 volts is the 3% allowed.Jim |
| Ryan_J | quote: Allowed by what? Also, make sure you use a #10 EGC to satisfy 250.122(B) |
| JimmyDee | A theoretical old myth (it was code at one time when I was a little boy and is still a good rule of thumb) that 3% is an acceptable voltage drop for a branch circuit. 5% with feeders. Jim |
| JimmyDee | quote: Still need to do if this is an existing circuit? Jim |
| Ryan_J | quote: I think if you were to replace some of the conductors to satisfy a voltage drop issue then you would have to. If you aren't changing anything, then I would say you are OK. |
| JimmyDee | Thanks Ryan. Jim |
| cs409 | this question doesnt refer to any job am working on. it was just a question that popped into my head as to if there was a formula for 2 different wire sizes...i have always just did the 2 different VD cal, using the uglys book or an online VD calculator....have made notes to add to my how to list! thanks..... |
| cs409 | Heres a good question.......why do you think a 100amp service with #4 wire will blink, with some very slight of hand dimming more of a big eye wink but more than just a blink! but with #1 wire u will hardly ever notice a slight blink and never a dimming big eye wink! this is the same service with just the wire size changed...service wire lenght is 20ft. major items in house, 3ton central AC,,,standard free standing electric stove, electric dryer... diswasher, disposal......refridge, freezer.....blinking/dimming happens with #4 when the AC comes on....oh, 50ft. of #10 feeding the AC unit....now for this question forget all the bad neutral, poor utilities,,,this is alll the worlds best in top shape and tested, retested and goood..all in the meter can is top notch, panel the same... |
| cs409 | Heres a good question.......why do you think a 100amp single phase service with 3 #4 wires will blink, with some very slight of hand dimming more of a big eye wink but more than just a blink! but with 3 #1 wires u will hardly ever notice a slight blink and never a dimming big eye wink! this is the same service with just the wire size changed...service wire lenght is 20ft. major items in house, 3ton central AC,,,standard free standing electric stove, electric dryer... diswasher, disposal......refridge, freezer.....blinking/dimming happens with #4 when the AC comes on....oh, 50ft. of #10 feeding the AC unit....now for this question forget all the bad neutral, poor utilities,,,this is alll the worlds best in top shape and tested, retested and goood..all in the meter can is top notch, panel the same... |