Electrical Wiring in the Home/Wire size


QUESTION: What gauge wire should I use for a circuit carrying 30 amps at 12 volts DC(30 amp fuse)?

ANSWER: Ted,   with no length I cannot say, but below is a link to a chart,  that provides a DC 12 volt wire guage chart including lengths        one consideration is the type of load,   an inductive load,  or something that is anything but resistive, such as motor load, or conversion to some sort of AC, should be factored in,  but the chart has the parameters included and is easy to read, another consideration is the type of routing, is it buried, in free air, if so what is the average ambient,   heat dissipation is what they are looking for, so even the type of wire will be a consideration,          if you need to provide me the run length,  the type of load, the type of wire  and how it will be routed and I will help you with the chart if you need it,   

These things always seem simple, but a fuse or breaker in actually protects the wire, in most cases especially in AC wiring where the conductors are normally behind sheet rock and so on,     

For this DC application,  the chart should get you there with no problem, but if you are the least bit concerned,   let me know the exact data as above,      

Once in operation, if you can get to the wire,  make sure you have no to little heat,  a meter to measure the temp is better than hand touch  but hand touch to a hot outside cover is a warning the load is heavier than expected, or some other factor is creating heat,     

If you can get your hands on a clamp on amp meter, it always good to check the fully loaded current.

Any further questions let me know,


Will Babbitt    

---------- FOLLOW-UP ----------

QUESTION: Many thanks.

The wire will be less than 3' long.  It will run power to a motor which is used to change automate changes in seat position.  Ambient temp will be pretty warm since it will be under the hood.  Extent of use will be about 10 to 15 seconds per change.

ANSWER: 8 Automotive type wire would be fine,   they have packages of lengths at any parts store, auto duty wire is resistant to oils and fluids that deteriorate the insulation,   but unless it just coated with contaminates allowed to move around    it should last as long as the car     you can go to 6 but then it gets real bulky and hard to terminate,        

---------- FOLLOW-UP ----------

QUESTION: More info.  The wire is fused with a 30 amp fuse in a car.  There is no AC.  It runs to a motor which folds and unfolds the third seat in an SUV.  Thus the motor is a reversing motor.  The seat has three possible positions.  Control is through a relay.  The actual distance we will be wiring is less than 3'.  Ambient temperature is a consideration since the wire is under the hood.  The circuit is on very briefly, perhaps 10 to 12 seconds each time the position of the seat is changed.  The goal here is to add a switch into the motor circuit so that the mechanism can be shut down and not activate accidentally as has happened three times from accidental pushing of one of the activation buttons in the rear of the car.
Many thanks for digging in this deep.  You really are doing the job right.  The question was simple enough but asked in a vacuum it was impossible to give a viable response.

Ok   three feet to a switch is 1.5 to and 1.5 back,   3 feet to and back is 6 feet,  if this is just a switch in series to the fuse,  no issues,   6 wire will hold 30 amps constant duty, under 15 feet,   motors are a bit different load than say lighting because of the induction and inrush,  which is why there are different fuses,  slow blow dual element have two elements in parallel,  which allows for short duration peaks,   without opening the element,   

But you should be fine with 6 if you are jumping the fuse,  basically just opening the circuit and disabling the switch,      and I assume you have checked for recalls, or factory mod options, seems a bit inconvenient to open hood     or will three foot go through fire wall?

The ambient is not a factor at such short duty cycle.

Have you checked for mods such as different type switch,  locating a switch near the ezisting that can be a keyed switch,  or hidden,  some times the panels pop off, sometimes it is a major project to get access to the switch panel      so if works for you,   the wire is fine,  just open the common,

JC Whitney and others have tricky gadgets such as lock covers, and other devices to lock modify such things,   sounds like poor engineering from the factory,  

If you want to give me the year make and model I am happy to research the specific switch and see if there is a mod out there already,    or some hidden combination of existing door locks that lock the back seat,  but assuming you have investigated that already,     

Like our dual fuel stove, the supplier said to lock the burners we needed mechanical locks on each knob,  which seemed odd to me,  turns out,  it is nothing more than holding the OVEN Start button for 5 seconds and that locks the top burners,   

But if you have been down the road on the specific vehicle this is a reasonable fix,  if you dont mind the lock out location,      

Glad to look into it,  if you wish,    but from what you are saying I am sure you will be fine,    

If anything comes up  you know where to find me,  
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Will Babbitt


Electrical issues of all types, wiring, control, appliances, components, specialty in Electric MOTOR or APPARATUS trouble shooting, electric motors, electrical problems, single phase, three phase, DC, capacitors, elevator MG-Sets, modifications, reverse engineering, VFD Drives, single to three phase convertors. Repair of most any electrical/mechanical/electronic apparatus, OEM, AC, DC, Industrial Applications, Three phase, single phase failure mode, determining the root cause of the equipment failure BEFORE failure repeats, Antique appliances, electric motors, fans, ceiling fans, base mount fans, poor equipment performance, Modifications, habitual failures, vibration, redesign, obsolete issues, collectible items restored, rewinding. Owner of EMR Repair Inc www.emrrepair.com More information on electric motors, under Engineering/Motors Ask about any electrical or mechanical problems in the home, office, or even at your work. B2B or business to business CONSULTING I can do but it would be a much more complex issue, that would require a significant amount of time. repair@mearservice.com from there we can discuss and begin work on about anything. Industrial electric motors, controls, troubleshooting, vibration, alignment, any type of industrial or commercial electric/electrcical equipment For the home owner, renter, apartment if you have odd things going on, describe to me, photos are normally very helpful, appliances, heating and air conditioning issues, light switches, installation, DIY PROJECTS FOR THOSE NOT EDUCATED IN ELECTRICAL, we can do some things, but for safety and sanity reasons, I may refer you to a local electrician, and help you find one, help you with pricing and even speak directly with anyone you hire if you have issues,


Over thirty years with a major repair and sales company, VP of Operations, and former owner of my own specialty repair shops, MEAR Services local to Kansas City Missouri EMR Repair Inc., located in Kansas City Missouri, 2014 sold both businesses to JCI Industries, Lee's Summit Missouri wbabbitt@jciind.com Evaluation and repair of electrical/mechanical apparatus. Electrical and mechanical repairs, trouble shooting including, vibration and balance issues. About.com provides this service, and the huge costs to provide help on about any subject. They provide the servers, the people to vet the experts, costs that would be the same as operating a good sized business, They should be appreciated for what they do, the huge costs and the great help they provide for free, Electric motor questions, can be answered here but there is a dedicated category that has other experts to help and add to a solution. Other common questions, are noises in the walls, breakers tripping, devices not starting or shutting down for no apparent reason, smoke alarms buzzing, thermostat change outs, or sizing wire or needing information for a new project, but anything can be resolved, anything, with enough effort and patience, DIY, with electrical is possible, but in most cases the use of a simple ohm meter or volt meter is needed, they can be purchased at any hardware store for a few bucks. If you have smoke, or smell smoke, don't be writing me, call 911 the Fire Department has no problem looking for smoke smells, better then spraying water on a blazing fire. DO NOT GET CAUGHT INVESTIGATING AND TRAPPED IN A BASEMENT LOOKING FOR A BLOWER FAILING< As to the tip jar, it is up to you, it is appreciated, every expert spends out of pocket that I know, we spend on IP time, computer wear, printing documents, books, and of course our time, but if we prevent a $400 service call, we did well,

Former IBEW, EASA, IEEE, UL, ..............


10 plus years, various Technical Schools, followed by Industrial College Credit and non Credit Courses, electronics courses, experience in most any electrical apparatus, electric motors and generators, AC OR DC, fractional to above 5000HP, other electrical apparatus, slip rings, sleeve [plain] bearings, lubrication, identification-no data plate, control components, service and sales. I have continued night schools for decades, the list is extensive. I have been in the business of repairing most anything with wires or mechanical parts for decades, I have some helpful hints and directions you won't have to dig up. Or hopefully not have to pay a huge service call invoice to find.

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