Under very carefully controlled and specified conditions, electricians do run multiple conductors to carry current. Sometimes, when dealing with a large number of fluorescent lighting fixtures, we do use multiple neutral wires. Also, it's common practice to run parallel service entrance conductors on a large service. However, in general practice, it's a bad idea to run parallel conductors hoping that the two smaller wires will work the same way that one larger one does.
There's a few OT cars that have the main electrical center less than 12" away from the alternator. The normal routing for the cables on these is battery to starter lug with starter lug to alternator and starter lug to the main electrical center. Some times they have an additional electrical center or 2!! That's a lot of cable when the battery is on the opposite side of the engine bay as the alternator and a boat load when the battery is under the back seat and an even bigger fuck load of cable if the battery is in the truck. These vehicles are prone to drivability problems and very goofy electrical quirks if anything is just slightly off, very unforgiving and intolerant. (For example, rolling the window down causes a stall at idle and many more head scratching oddities ) The fix to this is to run a 12" cable from the alternator directly to the main electrical center. Some gear head tuners did this first in order to eliminate voltage drop to the fuel pump and increase fuel volume . What they found was that they didnt suffer from any of the quirks.
For fluorescent lighting, it's not multiple neutrals, it's separate neutrals. You used to be able to 'share' neutrals but with the advent of electronic ballasts, these put weird harmonics into the neutral and caused heating issues in the wire and panels. Took the engineers about ten years to figure that one out.... Parallel service entrance conductors (or for very large loads) are used where it's impossible/impractical to use a single wire large enough to carry the load. The smallest size allowed in parallel is 1/0.
Yeah, I was struck by the amount/location of much of the electrical gear on my '13 Mustang; clustered very close to the battery. As to running an additional cable, they might be literally playing with fire. If the 'original' cable fails and the jumper is undersized, you could have a nasty fire pretty quickly....
My bad for not mentioning it, (forgot it is 101 haha) but there is a fusible link in the cable and its usually made from #6 or the same size that's feeding the center from the starter lug- which ever is bigger. Not only is it the same size but its usually around 80% shorter ( 12" vs 60")
Steve mentioned about grounds in post 84. On planes the most grounds we can put at one ground lug is 4. That is the most, but not exactly the best. 2 or 3 grounds is the preferred way. AC and DC grounds do play together very well. Have a separate ground for AC and one for DC. As we all should know by now, use the frame and body to carry the ground back to the battery. So as implied, your ground wire should be as short as possible, just like the power wires.
I would think the alternator creates a lot of noise, and if there are any connectivity problems it can fry your electronics. Alternators have coils just like your ignition so when the current is suddenly interrupted they can produce very high voltages. One time a charge wire broke on my (not computerized) diesel truck and it instantly burnt out both headlights. It's safer to have a separate wire for the alternator. Sent from my Verizon 4G LTE smartphone
I can't read all this good information fast enough!! Awesome info. Posted from the international space station & powered by the Full Custom H.A.M.B. App!
Agreed - fusible links are good for this though. I just bought a little roll of it for $4. Cheap insurance. Shorts ARE pretty scary. Sent from my Verizon 4G LTE smartphone
A fuseable link should be 4 numbers larger than the wire fused. A 10 gauge would need a 14 fuseable link.
System Design Part 5. Branch Circuit Design. Ok, hopefully at this point you have a 'worksheet' showing what size wire you need for each circuit. You took the calculated load, multiplied that by 125% to get the fuse size, selected the smallest 'standard' sized fuse equal to or larger than the calculated size, then selected wire by ampacity @ 60C, again equal to or larger than the fuse size. Plug in the wire size, load, wire/circuit length, and voltage into the voltage drop calculator (I used 13.5 volts) and this will give you voltage drop. If that's what you did, you'll find that the drop on most (if not all) circuits will be well under 5%, probably under 3%. Here's the 'worksheet' I did for my 'example' car.... It may be a bit hard to read (my scanner is busted), but left to right you have: circuit, load, fuse size, circuit length, wire size, and voltage drop. Lengths are in feet, so don't forget to divide them in half for the calculator. These lengths are just rough guesses, don't use these for your car. If you get a result of more than 5%, go up on the wire size until the drop is under 5%. By being very conservative on the voltage drop, this helps you in another way. Remember all those 'derate' factors? By doing it this way, this gives you 'headroom' when/if you need to derate. Here's an example; let's say one circuit is a #12 wire with a 16 amp load. If you've 'bundled' your wires and kept 'continuous' load wires in the bundle to three or less, you don't have to derate for that. If the wire goes into an area of higher temps, if you route the wire so the maximum temp it sees is 140F, the derate factor is .71. Remember that #12 wire is rated for 30 amps @ 90C (194F) in a 60C ambient, so multiplying 30 X .71 = 21.3 amps, or still well above the 16 amps needed. If bundling more than three continuous wires together but the ambient stays within 60C, again applying the derate will still give enough ampacity in the individual wires. This underscores the importance of planning the system layout and wire routes to keep bundling and high temp exposure to a minimum. Now up to this point we've assumed that each branch circuit will come from its fuse, maybe go to a switch, then continue out to a single load. But that's not the case for some circuits, particularly lighting. Let's talk about those.... Headlights. This can vary depending if you have two or four lights, but the principle will be the same for both. My example car has four, so let's look at that. That 20A load actually represents the high beams; all four will be lit on high beam. But once you hit the first light, the load will drop by 5A at each light. So you could drop to #14 after the first light to the third light, then #18 to the last one. Or can you? Again, #14 is rated at 25 amps @ 90C, if the ambient is 60C or less you can do this because your fuse rating isn't bigger than the wire ampacity. You can't drop to 18 for the last light as the fuse size exceeds the wire rating. If ambient is higher, then go up a wire size. Calculate the low beams the same way. While the circuit current will be much lower (could be anywhere from 6.6 to 9.1A), you still need to stay with #14 at least because of the fuse size. I will note here that the 5A value I gave may not be right for your actual headlamps; after doing some research, I found that lamp ratings have changed over the years. The incandescent headlights of the past were generally rated at 38/40 watts low beam and 50 watts high beam, or 3.2 and 4.2 amps. Modern 'sealed beam' halogen replacements can be between 38 and 55 watts on low beam, and as much as 65 watts on high. This can significantly change the circuit amps, so make sure you check this and take it into account. If you're using replaceable lamp non-sealed beam lights, check the lamp rating. Failure to check this can cause serious issues.... Brake/turn/emergency flasher lights. This is another problem area. Most typical vehicles 'share' these lights, with the brake lights also working as turn/emergency flasher lights. The power supply wire for each circuit will go to the turn signal switch, at this point you'll have individual wires going to each light. Do these as individual branch circuit calculations, but keeping in mind you can't drop wire size below the fuse size. In this case, the emergency flasher circuit uses the largest fuse, so size your wire to the lights so as not to overfuse them. This will limit you to no smaller than #14 wire because of the 20A fuse. One more thing about the rear lights before moving on; if you're planning on towing anything, add on the anticipated lighting load to the brake/turn/flasher circuits, as well as the taillight circuit. This will probably require larger fuses and wire sizes, but failing to add this will cause problems. The last circuit that may give you issues would be power windows. The problem here is you need to reverse the power to the motors so that the windows will go both up and down. Not an issue with seats generally, as the switches are built into the seat as a rule. But with windows, the switches could be many different places, and you may have a 'master' switch (all four controls in the drivers door for example). From each control switch, you'll need two wires to the motor it controls. While the load will be reduced (in my example, each motor may only draw 4 amps; 16 divided by 4), you still need to size the wire not to exceed the fuse size; in this case, #14. If you have some of these circuits, it will pay to do a worksheet on just these, treating each 'piece' as a separate circuit then making sure that all wire is rated correctly for the 'overall' circuit. One more thing I'll note. You'll find that you really won't end up with many circuits that can use wire smaller than 14 in most cases. I'd recommend not using anything smaller than that; the price difference in the wire won't be much, and eliminating having to buy additional terminal sizes in minimum quantities may make up the difference. Another thing is the 16/18 wire has less mechanical strength, the 14 is just more durable, making your system more reliable. Any questions on any of this? Next up, I'll talk about component selection; switches, relays, etc....
System Design, Part 6. Component Selection, Part 1. What I'll talk about here is some of the parts you'll need to make the system work; specifically the switches, relays, and fuse panels. On some items any switch needed will be supplied or built into the device, like aftermarket heat/AC or a radio. And if you're reusing OEM components, the OEM switches for those will probably be the best choice. But for some, you'll need to select a switch and getting the right switch for the application can make a big difference in both how the system will be wired and the reliability of the circuit. Just like every other part of a properly-designed system, they do need to be rated for the intended use. Using a too-small switch will result in shortened switch life, and can cause fires and/or melt wiring without blowing even a properly-sized fuse. I will say that if you have a choice between a good OEM switch and an aftermarket unit, the OEM switches are usually higher quality. Switches. 'General' switches (basically, most 'on-off' switches and anything not designed for a specific purpose) should have their rating printed or embossed right on the switch. And it doesn't matter if the switch is AC/DC, AC, or DC rated, although for our use DC rated switches will usually be best. The difference is a AC switch has better arc-suppression capability, and a DC switch usually has heavier-duty contacts. So if you find a AC-only switch you just have to use, reduce it's current rating by 50% and you'll have no problems. Any switch you find rated in 'V-A' (volt-amps) will be too light duty for pretty much anything except energizing a relay; don't apply the actual load to it. If the switch is used to directly control a motor load, for long life and reliability derate the switch by 33% (GM actually recommends this). Unfortunately, some 'automotive' switches sold various places don't have any rating shown; what to do? Best bet here is to look at the screw terminals. Figure that a #6 screw is good for 10 amps, #8 for 20, and #10 for 30. This is still no guarantee that the switch is good for that, so finding a 'rated' switch will always be preferred. 'Specialty' switches. In most cases, a matching switch designed for the component will be available, so that's the best choice. If you're buying aftermarket parts, the vendor should be able to supply a switch if needed. But I'm going to go into detail about two switches that can have a large affect on how you circuit some wiring, and can affect fuse panel choice. The first one is your ignition switch. What you need here will depend in large part as to how your car is equipped. If you have a 'bare bones' car (lights, ignition, horn and little else), a simple 'on-off' with a start button or a 'off-on-start' switch will be fine; the only switched circuit will be the ignition. A 20A rated switch will be more than adequate. But what if you have additional accessories? Turn signals, wipers, heater, radio can be typical, maybe AC. Having those items on a separate terminal can simplify your wiring considerably as I'll show when I talk about fuse panels. You'll find that these types of ignition switches are usually rated for 30 amps total load. So if you have anything more than a bare bones car, I highly recommend a 'acc-off-on-start' type switch. Now all this above is if you're using a dash-mounted switch; what if you have a locking column and it has a built-in switch? The later OEM switches on most locking columns have two or more sets of contacts; a set for 'on-start' and a separate set for accessories. For these, I'd limit load to 20 amps for any set of contacts. When these came along, the factories had started using relays a lot more to reduce the load on the switch. I was unable to find an amp rating for these. Again, when I get to the fuse panels I'll talk about actual wiring. Headlight switches are the other switch that needs care in selecting. The OEM switches have evolved quite a bit over the years, going from little more than simple on-off switches to mini 'control centers' with multiple functions. Speedway sells a 'basic Hot Rod' switch that features 'off-park-low beam-high beam' positions and also has connection for tail and dash lights. This switch has several disadvantages IMO; one, you're forced to combine these circuits because there's only one power connection. So you need a larger wire and fuse, and this will likely be too big for the tail/dash light circuits. If you have a problem and lose the fuse, you have NO lights at all. You can install a fuse after the switch for the dash/tail lights which will improve safety, but it will have to be inline and probably not in the fuse panel. Next step 'up' would be a mid-50s/early 60s OEM-style switch. These also have a single power input, but now can feature a built-in circuit breaker for the headlights and have the fuses for the tail and dash lights built into the switch. Downside is these will be glass fuses, and being well up under the dash, hard to get to. These will also usually have a switch to turn on the interior lights as well as a rheostat for dimming the dash lights. Best choice (IMO) will be a late 60s/early 70s style switch. Same features as the one above, with a few important changes. The fuses are no longer on the switch (although the circuit breaker for the headlights is still built in) and these circuits have their own separate contacts so installing fuses in the panel is no problem. These switches are bulkier and require a specific plug for connection, but worth the trouble IMO. One change in operation is these usually leave the 'park' lights on even when the headlights are on, unlike the older switches. Now the above are mostly 'conventional' push-pull switches. But what about more late-model switches? Some of these will work also, generally wire more-or-less the same as the above, and may have a few more features, like a built-in fog-light switch. Some even have 'auto-on' and 'delay off' features. If you install the 'auto-on' light sensor in the top of your dash, you could completely hide the light switch and your headlights will come on at dark... Food for thought.... One caveat with the built-in breakers in most push-pull switches; if your car has two headlights, no problem. But if yours has four and you're using halogen lights, they won't be big enough; the high beams will have to be switched through a relay. Relays. These have become increasingly important over the years as more and more electrical items have been added to cars. Basically a way to operate a large load by using a small control circuit to operate the relay and remove the load from the switch; I'll talk more about this later on. So what to look for? First, any plug-in 'cube' type relay is only good for 30 amps max, period. Sure, you can find them from some vendors with claimed ratings of up to 80 amps. Not true.... The reason? You cannot buy a terminal for these any larger than for #10 wire and I looked - hard. Now, there are some 'legitimate' 40 amp rated plug-style relays available, and there are places where these should be used; just not at 40 amps continuous duty. I did find a few 'legitimate' plug-in relays rated above 40 amps. but these use a 'special' 3/8" wide terminal that's not easy to find, again only comes in a #10 wire size max, and interestingly enough, isn't UL-rated. But there's no reason to use a plug-in beyond 30 amps in any case. There's plenty of higher-amp relays with bolted connections available, all the way up to 200 amps. Most any industrial electronics supplier will carry these, even places like McMaster-Carr will have these (as well as the smaller ones; with accurate ratings...LOL). Search for 'high inrush DC rated relay' and you'll get results. So, how to select the right relay size? Here, big is good. There's generally little difference in price for the cube relays, so unless you have serious space considerations, using a larger relay will extend the relay contact life a lot. Motor loads? Again, size the relay at least 1/3 larger than the load, again to improve contact life. This can be the difference between a system that needs parts replaced regularly or has 'issues' and one that's trouble-free.
I can see the use of relays when a builder/MFG wants to use pretty little switches or save money on heavier ga wire. But let's say a builder is putting together a 1946 Dodge Power Wagon where weight and pretty isn't a concern but super reliability is. Wouldn't it simplify the system to just use heavier switches and eliminate the added circuit required for a relay?
I have a question: The original wiring on my 1959 Chevy pickup ran the generator charging wire thru the amp gauge, then on to the starter. Back in the 80's, I installed an internal reg alternator, & kept that same circuit (- the ext reg) All worked well - points distributor & FM radio. I'm redoing the electrical now, but I have more electrical stuff - MSD, 400w amp, H4/H1 lights, & a higher output alternator. I have it all wired correctly with the right sized wires. I want to keep & use the original amp gauge, but I'm concerned about running the entire load thru it. I think the original wire is a 10 gauge, or might be a 12. Can I keep the original amp gauge circuit, & run another wire between the alt to the starter? It will be a 6 gauge.
Nope.... If you run another wire parallel to the ammeter circuit (and particularly a larger wire), the ammeter won't read correctly or maybe not at all. And you're correct; the original ammeter probably won't take the load and will burn up. This is why ammeters have pretty much disappeared today, as running that high-amp circuit under the dash to the meter isn't all that safe, and finding an ammeter that reads that high isn't easy or cheap. Best bet if you want to retain the 'factory look' will be to have the ammeter converted to a voltmeter by someone who specializes in gauge work. Or just disconnect it and install a voltmeter under the dash.
One other thing I'll note; running those four halogen headlights through the OEM light switch. As I noted above, most of these switches had internal circuit breakers for the headlights but were only rated for the then-standard incandescent lamps of the day. What you'll find is the lights will all work, but if you run on high beam for a bit of time (5-10 minutes), the breaker will trip... no lights. As soon as the breaker cools a bit (seconds), the lights will come back on. But if you're still on high beam they'll go out again, and the 'on' interval will get shorter while the 'off' interval gets longer. Switching to low beam will break the cycle. I found this out the hard way.... losing all lights at 70+ mph on a dark night is not a fun thing....
Thanks. Thought that might be the issue with the amp gauge. Good idea about the conversion. Will look into it. The original headlight switch now will power up a couple of relays for the Cibie headlights. Great post. BTW, I did a little diagram of my trucks electrical so I can remember how I did it - hear it is (it is pretty much the same as my buddy's ski boat) http://www.jalopyjournal.com/forum/album.php?albumid=37341&pictureid=430267
A diagram and a parts list should be a must-do for any rewire... I love Cibie lights; I've upgraded almost every car I've owned with them, and most of my motorcycles too. As to the relays, those OEM switches will handle the low beams just fine... it's the high beams that does them in...
I was looking at Hella's, but the Cibie's look a little more OEM with the convex lens http://dsl.torque.net/images/146HCR.jpg Here are the flat E-Code Hella's on my vette for comparison http://carphotos.cardomain.com/ride_images/1/933/4641/2332320014_large.jpg?v=0
High-amp switches are fairly rare, bulky, and generally expensive. I'll get into relay use a little further on....
Not to hijack, but you can get some really nice USA made heavy duty switches and relays here. marine grade are the best http://www.colehersee.com/home/catalogs/ Note, they don't sell to the public. Just write down the p/n of the switch you want & google it for the best price
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