How much AWG do I need for my circuit wires knowing that the current can vary 10 to 20A with 12V supply  And what is the cheapest and safest way to join 2 wires together ?
109087
I've been working on providing power for high current applications for my project. I'm working on a project with high current (or at least compared to what I'm used to...)  What a lot of people point to online is tables that you can look up the resistance for AWG per foot, and then you can calculate the current drop of your wire. However, with that current drop, how much of  a voltage drop will make my wire "too hot" and risk a fire? Am I looking at this the wrong way? How do I calculate the temperature of the wire and decide when it'll be too hot, and I should use a thicker wire?
106216
I've noticed mains voltage tends to be 120V +/- 10% for 108-132VAC.  How would you go about building a regulated AC-to-AC power supply which works off of mains and outputs 120VAC with a much lower (less than 1%) variation?  The output must be a sine wave at 120Vrms.  Edit: For those asking, the output would be fairly low, 1.5A - 2A, 2.25A max.  Circuit to be powered:  Expected input: 0V-5.5KVrms sine wave at 60Hz  Simulated output: +/- 0-100KV DC.  The objective here would be to connect components in the order:  mains --> power conditioner --> variac --> 1:46 center-tapped transformer insulated for high voltage --> Cockcroft Walton Multiplier outlined above.  To achieve a variable 0-100KV DC (effectively 0-200KV DC with both channels factored in) power supply.  I am not certain the power conditioning stage is the way to go but assumed it would be since it is much easier to stabilize low voltage (120Vrms) than it is to stabilize high voltage (5.52KVrms.)  Relatively minor ripple of 5% will grow into +/- 10% by the end of the CW stage at full power, yielding around 20KV off of the expected value - not an insignificant amount.
6581
Is it possible in circuit design to split like say a temperature sensor line reading into 2 wires, and read by 2 different system/circuitry? My motive is to tap the signal line in a safe way without affecting or disrupting the other system functioning.
13535
My father-in-law is a builder. He has put in 20 amp and 15 amp breakers, and ran 12-2 as the home runs to the switch's and the first plug to make them hot. He then ran 14-2 to feed the rest of the plugs, lights, and ceiling fans.   Is it okay that he used different gauge wires on the same circuit?
87085
I have a sub panel on back of house. From main in garage is three wire.  2 hot one neutral.  NO GROUND WIRE.  Sub has a single bar used as neutral and grounds.  Its bonded to case (Screw in).  I will add a ground only bar, a ground to earth rod and wire them together.  I cannot get the snake all the way through the conduit to pull a ground wire.    Can I run a separate ground wire alongside the conduit to the sub?  ===========================================================================  Update/clarifications:  Thank you Speters.  ArchonOSX, I understand there should be a common ground back to the main, I do not have that. Currently (pre-existing),  I have a 3wire 50 amp gfci breaker for a spa in this SUB.   Its the only circuit. I was advised to Isolate the neutral bar and add a ground bar, bonding it to earth;  Where new circuits utilize the ground bar. In this config would I be protected and no SUB/main panel metal become  energized if a short occurred?
50914
I have 3 12VDC/40A automotive relays () that I want to use with my Arduino. Based on the tutorial I am following () I need transistor, resistor, and diode. I am not an electrical engineer therefore I am unsure about the parts and calculations I made. For the start, relay coil resistance is 90+-10% Ohm per datasheet. So I proceed by calculating the current flow.  Voltage=Resistance*Current Current=Voltage/Resistance Current=12V/90 Ohm Current = 133mA  For the transistor I can get 2N3904 or 2N4401. At this point I have to calculate resistance for the base of transistor. In tutorial its as following  hfe = Ic / Ib Ib = Ic / hfe Ib = 0.03 A / 75 Ib = 0.0004 A =&gt; 0.4 mA R1 = U / Ib R1 = 5V / 0.0004 A R1 = 12500 Ohm  2N3904 datasheet states the H(fe) is 30-300 when lc = 100mA (mine is 130mA) and Vce = 1V. At this point I have no clue what is going on, thus I need help. Edit: Here is what I ended up with. RLY1 in the picture is 12VDC/40A ()
111626
I am wondering how to read the numbers on electrical wiring separated by slashes such as 12/2. What do the numbers refer to? What other numbers should I watch out for when purchasing wires to be run within the walls and sockets of a home? P Thanks.
73081
I'm trying to make a welder-like transformer, but I'm having the problem that apparently I'm drawing too much current from the primary side of the transformer as the variac I'm using to supply about 10V is getting too hot. The variac is a chinese model rated for 20A, and unfortunately I have a 30A circuit and 30A fuse installed so the variac is smoking and trying to catch fire instead of fuse-blowing.   How can I limit the current on the primary side to 20A?  I did some calculations on the reactance of that coil and determined its current limiting capability is a very high current limit (293A, 0.001 H). The formula I'm using is 2 x PI x 60Hz x L = Ohms impedance. Whats puzzling to me is that this formula doesn't account for the magnetic permeability of the core or anything. Or is that already accounted for in the L reading? I measured the L via an LCR gauge across the coil wound around the transformer.  Another thing I'm wondering about is will an increase in current on the secondary side of a transformer (due to low resistance) cause an increase in current in the primary side?  I know the ratio of turns is inversely related to current (high voltage, low current : low voltage, high current), but isn't current determined by resistance of the load? Does a high current on secondary from low resistance cause a proportionately higher current on the primary?  Is a transformer like a set of 3 gears, with gear size being turns/voltage, the middle gear being flux, and the speed of the first and last gear being current? I like to visualize electronic components like water or physical machines.  Sorry for all the questions but this will sure help me out a bit.  My current course of action is to get an AC welding transformer and rewind the secondary with thick wire (2 ga) for high current output. I'm hoping that the primary's inductance is high enough to limit primary current to 20A (same as the welder's spec).   Thanks
89492
This is subjective per say. But I am looking for other peoples experience.  If I am going to screw eight wires into daughter relay board's terminal block, is there a benefit or advantage to tinning the copper end before?  The environment that the units are to be installed is not near the coast and is not normally damp/wet. Rather dry and hot.
64324
I have an older home where some of the house has updated electrical and some doesn't.  In a few rooms I still have several of the 2 prong outlets with no ground wire in the box and I want to replace them with 3 prong tamper proof outlets with proper grounding.  If I had an easy way to run a new line from the panel I would not be wasting your time, but I live in a split level home and several of these rooms have their lines fed from below, in-between floors, so I don't have any way to run a new line easily.   I know I can add GFCI outlets for some human protection but I want to do better.   I need to know if it is safe and/or legal to run a ground wire from a junction box in my attic (there are several) down the wall to use as ground when I replace the 2 prong with a 3 prong.  The junction box likely leads back to a different circuit but it is all originating from the same panel (I only have 1)
92286
So I've gotten myself into a healthy, educational Facebook discussion.  if you're a member of that group.  When I thought about it, everyone defines wire capacity by current only. The voltage only comes in when talking about wire insulation.  However, I've always thought about a wire's capacity by total power transmitted, not just the current.  Assuming arcs and corona discharges aren't a problem, could I transmit say 10 kW via a #40 AWG wire at 10mA, 1MV DC? The ampacity isn't , but that doesn't look right for wire that's around the width of a hair.  I'm aware of the math behind it (5th year Electronics engineering student) and I can judge what voltage/current I need for X watts versus safety/other constraints, but wires being rated by current only hasn't bothered me up until this point.
41014
I am working on a double leaf bascule bridge and installing a PLC I/O rack on the farside. The power transmission between the two piers (nearside and farside) is via a single submarine cable (installed 1987). Unfortunately, the submarine cable is made up of #10 AWG xhhw-2 control wires and no ethernet cables. Would it be possible to use 8 individual #10 AWG wires to make up the "4-pair" cable required for PLC communication? I would like to avoid wireless communication, and modifying existing/installing a new submarine cable is not an option.
105693
I am replacing an old 4-wire oven with a new Kitchen Aid 4-wire oven. I have 3 wires in the outlet box (black, white, bare (ground)).  The old oven was connected the following way: From the oven the white wire and the bare (ground) together were connected to the bare (ground) in the box. The black wire from the oven was connected to the white wire in the box and the red wire from the oven was connected to the black wire. There was a lot of black electrical tape wrapped around the white wire in box about 3 inches from the connection point. Not sure what that means? I was planning to connect the same way, but see some instruction on the internet to connect the same way, except black goes to black and white goes to red. Confusing and  conflicting information and not sure which is correct way. Or does it not matter since each wire, black and the white are hot each supplying 110V for a total 220V?
62375
I'm curious how much current it is safe to pass through a 0.1" pitch pin header. I'm sure it will depend on the gauge and stranding of the wire attached to it as well, but assuming that is not the limiting factor how much could be safely passed?
90038
I am a hvac tech, but my question is I have 2awg stranded and my plug is 6awg, will it matter much if I cut some strands to fit my plug? the plug is 60amp 250vac for a piece of kitchen equipment if the matters.
96921
I need to pull a neutral wire to my light switch for a smart switch.  It's presently switching an outlet that I don't need switched, and the other side of the outlet already has unswitched power.  My plan is to use a smart switch, which requires neutral, to control a different device wirelessly.    I can't feasibly run a new wire, because the wires aren't run through conduit.  Instead, my plan is to repurpose the switched wire to get neutral from the outlet.    The switch, which controls an outlet has two wires, one black and one red.  The switched outlet has a white neutral wire, plus the red and black wires that I assume run directly to the switch.  I've completely disconnected the red and black wires from the outlet and the switch.  The black wire is measuring 120V AC when measured against ground using the box as ground, both at the outlet and at the switch. Using my DMM, the red wire is measuring 24V AC with respect to the box/ground at both sides.  I assume this is a  caused by induction from the charged black wire over to the floating red wire.    Our house is ~100 years old and this particular switch seems to be run using armored cable (note the paper wrap around each wire.)  There are literally only two wires in the switch box; no wire nuts.    If relevant, we do have some old knob and tube wiring active, but I'm pretty confident there's none on this circuit.  Is there some way I can determine with enough confidence that the red wire isn't connected elsewhere such that I can know it's safe to connect the red wire at the outlet to netural?
33165
I'm tying into an existing outlet box to provide power for a new electrical outlet. The existing outlet already has 2 lines connected to it - one from "upstream" (to the fuse box) and one downstream to more outlets. The existing lines are connected to the "quick connect" holes in the back of the outlet, leaving 2 open terminals on each side of the outlet. Is it okay to connect the third new line to the side terminals, and the new ground wire in with the other two grounds?   So the new setup would consist of this:   2 lines (2 white + 2 black wires) connected through the backwiring holes 1 line (1 white + 1 black wire) connected via the side terminals (black on "long" side, white on "short" side). all three lines' ground wires pigtailed, with the pigtail connected to the one ground terminal on the outlet.