how to best protect 6 gauge 30 Adc power and ground under truck

pluton

Adventurer
My rules for routing battery cables under the truck, the one time I did it 8 years ago:
1. Run it along or near the top of the frame if possible...out of harm's way.
2. Make sure it can't move... and use split loom where it might, especially where IF it broke loose it could start some trouble.
3. Never run it near, and especially not above the exhaust.
 

DaveInDenver

Luddite
My rules for routing battery cables under the truck, the one time I did it 8 years ago:
1. Run it along or near the top of the frame if possible...out of harm's way.
2. Make sure it can't move... and use split loom where it might, especially where IF it broke loose it could start some trouble.
3. Never run it near, and especially not above the exhaust.
I like using plenty of those rubber-cushioned stainless clamps with decent chemical-resistant and appropriately high temp insulation.

Split loom or something similar where abrasion is a concern. I've used lengths of old garden hose and bicycle tubes to protect cables going through bulkheads and firewalls over the years.

Otherwise it seems to me Liquidtite, conduit and what-not is unnecessary if you can route it in protected places and support it well. I try to avoid secondary protection like conduit (particularly that interrupts air circulating) since you might need to derate the current capacity of the wire when you use it.

Not to mention that anything rigid, metal or even hard or stiff plastic might itself be an abrasion risk to the wire inside or fatigue problem.
 
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krick3tt

Adventurer
I used the flexible tubing from a discarded shower hose to protect the wiring under my M416A trailer. It is plastic inside and metal outside similar to romex house wiring.
 

Superduty

Adventurer
@ramblinChet I meant to comment that the split loom that you chose is a very good choice. Electriduct is my go-to supplier. There are many brands out there that are cheap and poor quality. The one you chose is excellent. They also sell one with a gray stripe that is also great quality.

Sent from my SM-G973U using Tapatalk
 

llamalander

Active member
Re. Flexible metallic conduit, it is designed and used to protect wires running to motors or other vibration sources, I've never taken apart a system that had damage from the conduit that wasn't caused by either the unprotected ends or destruction of the conduit itself.
Any cable running between two power sources should be fused at both ends, with the conduit as a ground, you are sure to blow a fuse in the event of damage.
Derating wire is done to grouped wires where the net heat generation is greater than the the insulation can stand. For one wire, it is not generally an issue when housed in a conductive body.
For more than one wire you should follow the derating schedule of the NEC or the boating codes Blue Sea references, regardless of the sheathing material--Plastic traps heat as well.
As to near or over the exhaust? That was something I decided to experiment with because of the difficulty of routing such a large cable from one corner to the other.
4 years and 30k+ miles it has held up well. I took a look last year and found no damage to the insulation, from heat or abrasion, and there is no measurable voltage drop across the run, so it seems like a successful experiment.
One thing I did learn from not burning my truck to the ground was that a big unshielded power cable running too close to to the truck's main computer can inspire some some pretty bewildering symptoms and expensive repairs.
Grounded metal conduit adds a good deal of shielding... but moving the wire works even better!
As for overkill? I have plenty lying around, which is how most of my truck gets modified.
'Suppose if you all wanted another laugh I could show you all the Unistrut I've used...
 
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DaveInDenver

Luddite
Re. Flexible metallic conduit, it is designed and used to protect wires running to motors or other vibration sources, I've never taken apart a system that had damage from the conduit that wasn't caused by either the unprotected ends or destruction of the conduit itself.
Any cable running between two power sources should be fused at both ends, with the conduit as a ground, you are sure to blow a fuse in the event of damage.
Derating wire is done to grouped wires where the net heat generation is greater than the the insulation can stand. For one wire, it is not generally an issue when housed in a conductive body.
For more than one wire you should follow the derating schedule of the NEC or the boating codes Blue Sea references, regardless of the sheathing material--Plastic traps heat as well.
As to near or over the exhaust? That was something I decided to experiment with because of the difficulty of routing such a large cable from one corner to the other.
4 years and 30k+ miles it has held up well. I took a look last year and found no damage to the insulation, from heat or abrasion, and there is no measurable voltage drop across the run, so it seems like a successful experiment.
One thing I did learn from not burning my truck to the ground was that a big unshielded power cable running too close to to the truck's main computer can inspire some some pretty bewildering symptoms and expensive repairs.
Grounded metal conduit adds a good deal of shielding... but moving the wire works even better!
As for overkill? I have plenty lying around, which is how most of my truck gets modified.
'Suppose if you all wanted another laugh I could show you all the Unistrut I've used...
If you're going to use the NEC as authoritative then it's Article 310 where the statement for conductors to be derated comes from. Table 310.15(B)(16) give ampacities for not more than three current carrying conductors bundled or in a raceway or duct in ambient of 30°C. One cable fits the "not more than three" criteria. It also says if ambient is not 30°C to follow the conductor derating in Table 310.15(B)(2)(a). The alternative would be to design based on a single conductor in free air, e.g. a cable not in a raceway, duct or bundle, which is followed in Table 310.15(B)(17).

That's why I used the word "might" because is being put in a split loom really like a raceway or duct? I think so but it's just an opinion. Plus derating above 30°C for a conductor isn't linear. At 35°C you only have to derate ampacity 4% for a 90°C insulation. At 45°C you have to reduce by 13%, at 55°C it's 25% and so on. At the top end of 85°C ambient for a 90°C cable you will have to derate by 70% (e.g. 0.29 correction).

Take an arbitrary ambient, perhaps 75°C/167°F under the frame probably isn't that hard to justify with still air around the cable inside a conduit. That's the 50% point where a 6 AWG with 90°C insulation goes from 75 amps to 38 amps.

Is any of this realistic? Maybe, maybe not. That's just what the NEC is suggesting, the responsibility is the designer's to decide what to do. It's also why the SAE, ABYC and other standards have been developed to try and give guidance as what to do on vehicles.

The SAE for their part in various places say to assume a maximum of 125°C on the chassis normally and up to 150°C near heat sources. But that's for electronics not harnesses. Unless you're running a wire right over an exhaust manifold under the hood or next to a catalytic converter that's unlikely a real worry.

As far as FMC I know the NEC has several restrictions but I don't actually know that vibration is one of them. Wet locations, exposure to gasoline, subject to physical damage and a 6 foot maximum distance are, though. It's not really an expectation that it's used this way but they're also concerned with it from a higher voltage standpoint and relative to ground and neutral for safety. Liquidtite would be appropriate perhaps, I could see that.
 
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llamalander

Active member
Thanks for the in-depth explanation of derating--
Not totally approachable to folks uninterested in arguing points of syntax.
Luckily, Blue Sea makes a pretty good app/ charts for illustrating acceptable resistance when you design DC circuits
that covers the interplay between amperage, voltage drop, ambient temp. wire grouping and insulation quality.

I do appreciate the part about the responsibility of the designer, in my case it's me.
It may be worth mentioning that working on a Nissan (needing turbochargers, seat-lifters, bed stiffeners, and all manner of aftermarket add-ons to make it run like a Toyota)
left me thinking that OEM maybe isn't always the be all and end all of material choices for non-standard applications--Sometimes you might need... more.

For that I try to start with the NEC and look over the ABYC codes and go rooting around my basement for something to bolt onto my truck.
Then if I find something that fits I cross my fingers, fill up with volatile liquids and go careening down the highway like a proper test pilot.
In my case I used FMC, an inexpensive material on hand that fit all my criteria for protection, heat dissipation, ease of installation and grounding--
turns out it works just fine for my purpose: running a heavy cable over the exhaust pipe. Though it shouldn't be done and it can't be done
and there's no reason to do it (except IED's) someone on the internet posted a picture of it, so there you go.

This isn't a suggestion to skip the hard parts and casually risk a fiery death because of something you read on the internet.
Rather, assess your needs, see what fits your criteria, try it out. See if you were right, check to see how durable it is, keep an eye out for unintended consequences, that's all.
 
D

Deleted member 9101

Guest
...left me thinking that OEM maybe isn't always the be all and end all of material choices for non-standard applications--Sometimes you might need... more.
OEM is a good starting point so long as you know what the limits the manufacture designed it for.
 

DaveInDenver

Luddite
Sort of...
NEC Article 551 covers ‘line voltage” systems on RVs. But excludes DC circuits of the vehicle. I will guess those are covered by SAE and probably others such as DOT.
NFPA 1192 which covers all sort of RV systems. Probably has an elecrical chapter.
As aside, As its fairly recent development and never had to deal with professionally, I dunno what NEC or NFPA have to say about highvoltage traction systems of electric vehicles.
The NEC tells us their intention...
90.2 Scope.​
(A) Covered. This Code covers the installation of electrical conductors, equipment, and raceways; signaling and communications conductors, equipment, and raceways; and optical fiber cables and raceways for the following:​
(1) Public and private premises, including buildings, structures, mobile homes, recreational vehicles, and floating buildings​
(2) Yards, lots, parking lots, carnivals, and industrial substations​
(3) Installations of conductors and equipment that connect to the supply of electricity​
(4) Installations used by the electric utility, such as office buildings, warehouses, garages, machine shops, and recreational buildings, that are not an integral part of a generating plant, substation, or control center.​
(B) Not Covered. This Code does not cover the following:​
(1) Installations in ships, watercraft other than floating buildings, railway rolling stock, aircraft, or automotive vehicles other than mobile homes and recreational vehicles​
Informational Note: Although the scope of this Code indicates that the Code does not cover installations in ships, portions of this Code are incorporated by reference into Title 46, Code of Federal Regulations, Parts 110–113.​
(2) Installations underground in mines and self-propelled mobile surface mining machinery and its attendant electrical trailing cable​
etc, etc, etc
I think alot of people use ampacity tables from NEC as they are abundantly published, and fairly conservative values.
They are conservative but for smaller gauge (I'd say up to around 10 or 12 AWG or so) wire that's fine and in reality even if you do all the calcs yourself you'll probably arrive at about the same place as the NEC charts.

It's when you get larger than about 8 AWG and certainly by around 4 AWG or so the NEC approach makes less sense with respect to vehicles. They are coming from a standpoint that if you're hanging heavy cable it's because you're probably wiring a factory or substation but you're just doing intermittent use of a winch on a truck. That's not to say there's not overlap, such as supplying the DC-side of an inverter.

If you adhere to their capacity charts you'll end up with 1/0 where 2 AWG is very likely acceptable for your heating expectation. So while you err on the side of safe using a size or two larger you can factor in weight and cost to see what you *really* need. Which is where you'll find the...
OEM is a good starting point so long as you know what the limits the manufacture designed it for.
They follow down to the decimal point circuit capacity in current and time. They don't want to have you carry around one gram more copper and PVC than the circuit requires as the cost is MPG and profit for them. The main thing to understand is the OEM (SAE) was interested in being just safe enough when building millions of widgets.

So when we do our work we have to find a sensible balance between the two approaches. We're not bound by the need to gram shave like they did but being ultra conservative still has an impact on our space and money budgets.
 
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D

Deleted member 9101

Guest
They follow down to the decimal point circuit capacity in current and time. They don't want to have you carry around one gram more copper and PVC than the circuit requires for the cost is MPG and profit for them. The main thing to understand is the OEM (SAE) was interested in being just safe enough. So when we do our work we have to find a raesonable balance between the two approaches.
"Just safe enough" sums up most OEM specs...lol. Which is why replacing your alternator to battery wire with a thicker one often results in better charging and running larger wiring to your fuel pump will often make it push more fuel.

I learned a long time ago the OEM is designed for the masses....and not necessarily how I'm going to use it...lol.
 

drrobinson

Member
Good quality wire ( like the Anchor you chose) and then split loom the entire length. Zip tie every foot or so. If you pass through any holes use grommets.

Run it on top of the frame rail if you can. Much less likely to get damaged there. Especially avoid high heat areas (as others have said).
 
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roving1

Well-known member
Go look at some commercial trucks and how the wiring is done. It may not look pretty with split loom and zipties but the lifetime vibration cycle of these things would boggle the mind and they do just fine. I might do plating or inside of conduit in some area I thought might need extra abrasion protection but I would try awful hard to just not route the wire anywhere it would need extra protection.
 
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