Power to cargo area - what guage wire?

[grinchy]

There's a ground behind the cover on the right (US passenger side) (I hooked a subwoofer amp to this one, so it's definitely there). I think there is one on the left (US Driver) too. The inverter is back there so I think there's a ground. Look about a foot up from the tailgate at the very back.

 

[CharlieS]

Yes, chassis ground points on both sides, at least on the '13, so I suspect on all of them.

 

[radman]

Yes, chassis ground points on both sides, at least on the '13, so I suspect on all of them.

Right, I know they are back there. Just want to discuss using that vs running a dedicated ground back to the battery. Advantages/disadvantages?
@TeCKis300 said it was advised not to run all the way back.

 

[CharlieS]

I followed guidance from people here on 'mud and ran my cargo area ground to those ground points at the rear.

 

[TeCKis300]

I just ran a 4awg wire from the main battery to the rear passenger cargo area. I was prepared to run a dedicated ground along the same path, however, I came across this post and wanted to double check.
The main purpose is to power a 18amp Victron DC to DC charger (up to 25 amps). I have the wire ready to go, but should I just grab a ground from the chassis area?

Yup, still best practice to use chassis as ground. There's no advantage to running a dedicated ground for this application.

 

[sdnative]

Yup, still best practice to use chassis as ground. There's no advantage to running a dedicated ground for this application.

I don't claim to be an expert, but what are you basing this on?

Using chassis as a low current return for non critical loads like lights, USB chargers, etc is perfectly fine but for significant loads like a DCDC charger I would definitely run a dedicated return.

 

[FrazzledHunter]

I don't claim to be an expert, but what are you basing this on?

Using chassis as a low current return for non critical loads like lights, USB chargers, etc is perfectly fine but for significant loads like a DCDC charger I would definitely run a dedicated return.

Not disagreeing but why?

 

[TeCKis300]

I don't claim to be an expert, but what are you basing this on?

Using chassis as a low current return for non critical loads like lights, USB chargers, etc is perfectly fine but for significant loads like a DCDC charger I would definitely run a dedicated return.

If you reflect on all the vehicles you've ever had, you'll likely note that almost universally there's only a single major ground tied to the actual battery post. Many on the positive post, but only a single large gauge wire to the negative.

Best practice is to use the chassis which is a giant conductive lump of very low impedance material, almost halving the wires in the system for reliability, weight, cost, and likely others.

But it's actually bad practice to ground any accessory directly to the battery post for safety reasons too. It's not so uncommon in a cars life for the battery post ground to fail for whatever reason - they get loose, ground strap to chassis gets undone, corrosion, etc. If you had an accessory wire tied to the battery that all of a sudden became the path of least resistance - 100+ amps worth of current of the entire vehicles electrical system may just choose to route itself through your accessory ground. Potential recipe for letting the magic smoke out, or fire at worst.

 

[prharper]

Not disagreeing but why?

Great post.

FWIW - Switch Pro user.
I ran #8 x 2 and #6 down passenger side to rear. (Fridge, Blue Sea Panel, and future)
Also ran #8, and #10 and other various smaller gauge wires on driver side. (roof lightbar and future)

All are connected to Switch Pro. << All the switch controlled devices are grounded to body.
Power is 125 AMP fuse to secondary battery.

Switch Pro manufacturer states for power unit: :
"Connect the black ground wire directly to the Negative terminal of the battery. DO NOT connect to frame
ground studs or ground distribution studs." <<< Probably more for reliability and warranty purposes.

Anyway, wish I had run #2 to rear for an inverter (not wired to Switch Pro, future use ~ 2k watts peak) but it would be on very limited occasions and I've gone with a different wiring approach for that req.

 

[FrazzledHunter]

Great post.

FWIW - Switch Pro user.
I ran #8 x 2 and #6 down passenger side to rear. (Fridge, Blue Sea Panel, and future)
Also ran #8, and #10 and other various smaller gauge wires on driver side. (roof lightbar and future)

All are connected to Switch Pro. << All the switch controlled devices are grounded to body.
Power is 125 AMP fuse to secondary battery.

Switch Pro manufacturer states for power unit: :
"Connect the black ground wire directly to the Negative terminal of the battery. DO NOT connect to frame
ground studs or ground distribution studs." <<< Probably more for reliability and warranty purposes.

Anyway, wish I had run #2 to rear for an inverter (not wired to Switch Pro, future use ~ 2k watts peak) but it would be on very limited occasions and I've gone with a different wiring approach for that req.

Interesting.

I had my Redarc DCDC charger installed professionally. The guy that did the installation and I had a LONG talk about wiring in general and grounds specifically. He recommended that the DCDC charger be powered by red/black lines from the main battery and emphatically said he would NOT recommend grounding to the frame in this case.

He gave these reasons:

1. He claimed he has seen Toyotas (not just Land Cruisers) sometimes throw trouble codes if you do not run +/- back to the battery. I have no idea what codes he was talking about or if that's just high current applications.
2. He also said, if you run high current sources grounded via the frame you can run the risk of exceeding the factory battery negative wire capacity. So, in some cases he upgrades that connection. That I can understand.
3. Running red/black pairs to the battery is usually more reliable. Well, maybe this is a gray area. I get that there are differences in resistance if you run your neg all the way back to the battery vs. the frame. Maybe issues with grounds on Unibody vs full frame vehicle like the LC?

FWIW, he did say that before he ever uses the frame as a ground he tests the resistance both ways - via the frame and straight back to the battery. I have no idea how he makes a decision based on those measurements, however.

I'm simply quoting what I understood this guy to have said. I'm not an expert in auto wiring by any means and do not have a thorough understanding of the gray areas.
That's why I hired someone that does auto wiring, amp & winch installs etc... for a living LOL!

BTW, I intend to connect #4 or #2 wire to my 2nd battery through the firewall to an Anderson SB-350 connector, location TBD. And when I do, based on his advice, I'll run a red/black dedicated pair from the 2nd battery to that Anderson SB-350 connector.

 

[mcgaskins]

Interesting.

I had my Redarc DCDC charger installed professionally. The guy that did the installation and I had a LONG talk about wiring in general and grounds specifically. He recommended that the DCDC charger be powered by red/black lines from the main battery and emphatically said he would NOT recommend grounding to the frame in this case.

He gave these reasons:

1. He claimed he has seen Toyotas (not just Land Cruisers) sometimes throw trouble codes if you do not run +/- back to the battery. I have no idea what codes he was talking about or if that's just high current applications.
2. He also said, if you run high current sources grounded via the frame you can run the risk of exceeding the factory battery negative wire capacity. So, in some cases he upgrades that connection. That I can understand.
3. Running red/black pairs to the battery is usually more reliable. Well, maybe this is a gray area. I get that there are differences in resistance if you run your neg all the way back to the battery vs. the frame. Maybe issues with grounds on Unibody vs full frame vehicle like the LC?

FWIW, he did say that before he ever uses the frame as a ground he tests the resistance both ways - via the frame and straight back to the battery. I have no idea how he makes a decision based on those measurements, however.

I'm simply quoting what I understood this guy to have said. I'm not an expert in auto wiring by any means and do not have a thorough understanding of the gray areas.
That's why I hired someone that does auto wiring, amp & winch installs etc... for a living LOL!

BTW, I intend to connect #4 or #2 wire to my 2nd battery through the firewall to an Anderson SB-350 connector, location TBD. And when I do, based on his advice, I'll run a red/black dedicated pair from the 2nd battery to that Anderson SB-350 connector.

That's how I've wired in the past with good results. This below post from a prior build shows a little bit of detail of running 6 gauge duplex wire from the battery to the aux fuse box, and I added a circuit breaker to kill power to everything downstream for times when I wasn't driving the truck for a while. I think it's a good addition for aux wiring except for the winch which I always wire directly to the battery since the draw is so high when being used. FWIW I haven't seen parasitic draw from the winch, so I haven't been concerned with isolating it.

Builds - mcgaskins' 2016 build thread - Ruby

As some of you may know, I had a 2014 that was built in the past, but I really liked the 2016 refresh and wanted to give the 8 speed a try to see if it worked better off road. Some pics of the 14: I found a decent deal on a 2016 in brandywine/terra in Minnesota and had it shipped to...

forum.ih8mud.com

 

[TeCKis300]

Great post.

FWIW - Switch Pro user.
I ran #8 x 2 and #6 down passenger side to rear. (Fridge, Blue Sea Panel, and future)
Also ran #8, and #10 and other various smaller gauge wires on driver side. (roof lightbar and future)

All are connected to Switch Pro. << All the switch controlled devices are grounded to body.
Power is 125 AMP fuse to secondary battery.

Switch Pro manufacturer states for power unit: :
"Connect the black ground wire directly to the Negative terminal of the battery. DO NOT connect to frame
ground studs or ground distribution studs." <<< Probably more for reliability and warranty purposes.

Anyway, wish I had run #2 to rear for an inverter (not wired to Switch Pro, future use ~ 2k watts peak) but it would be on very limited occasions and I've gone with a different wiring approach for that req.

As I have a SwitchPros too and did run across that guidance...

It's useful to know that the SwtichPros ground wire isn't so much a load ground. As you stated, all accessories that it controls are ground directly themselves to the chassis. The SwitchPros ground is more of a sense wire as it doesn't support any appreciable loads other than it's own internal integrated electronics. It needs a well tied in ground for reference and low voltage disconnect functions. Consumers are bad installers. Lots of opportunity to hook-up a ground to the fender with paint, bad connections, etc. - leading to SwitchPros having to do a lot of customer support. Their guidance is to maximize customer experience and minimize installation pitfalls. Not necessarily for best practice.

I installed my SwitchPros ground to chassis.

Interesting.

I had my Redarc DCDC charger installed professionally. The guy that did the installation and I had a LONG talk about wiring in general and grounds specifically. He recommended that the DCDC charger be powered by red/black lines from the main battery and emphatically said he would NOT recommend grounding to the frame in this case.

He gave these reasons:

1. He claimed he has seen Toyotas (not just Land Cruisers) sometimes throw trouble codes if you do not run +/- back to the battery. I have no idea what codes he was talking about or if that's just high current applications.
2. He also said, if you run high current sources grounded via the frame you can run the risk of exceeding the factory battery negative wire capacity. So, in some cases he upgrades that connection. That I can understand.
3. Running red/black pairs to the battery is usually more reliable. Well, maybe this is a gray area. I get that there are differences in resistance if you run your neg all the way back to the battery vs. the frame. Maybe issues with grounds on Unibody vs full frame vehicle like the LC?

FWIW, he did say that before he ever uses the frame as a ground he tests the resistance both ways - via the frame and straight back to the battery. I have no idea how he makes a decision based on those measurements, however.

I'm simply quoting what I understood this guy to have said. I'm not an expert in auto wiring by any means and do not have a thorough understanding of the gray areas.
That's why I hired someone that does auto wiring, amp & winch installs etc... for a living LOL!

BTW, I intend to connect #4 or #2 wire to my 2nd battery through the firewall to an Anderson SB-350 connector, location TBD. And when I do, based on his advice, I'll run a red/black dedicated pair from the 2nd battery to that Anderson SB-350 connector.

Not trying to speak from a high horse but the reality is that many techs, AKA professional installers, are wrench monkeys learning from anecdotes. Anecdotes and experience are good things with the benefit of hard lessons learned, but sometimes can equally lead to false conclusions. There's a balance of best practice, theory, and experience.

To his points, not all grounds on the chassis are created equal. If one grounds a high power accessory to a bracket or component that itself is not well ground (substrate type, rust protection, paint, loctite, adhesive bonds, etc.) , that's a recipe for issues. Mix in the reality of varied vehicle examples, with wear and tear, loose grounds, etc., sure, I can see why he believes he needs to run a ground. To his credit, he tests resistance, that's a good thing. The other part of it is to consider that much of the current doesn't necessarily come from the battery. It comes from the alternator which a solid chassis ground has a stronger path to without additional loading of the battery ground connection.

Would I run a ground to battery...nope. But it is a reminder that one needs to consider where on the chassis one is grounding to. Taking steps to remove paint to ensure a solid metal to metal connection, particularly on high power draw accessories.

 

[sdnative]

Just because it is done on production vehicles does not necessarily make it best practice. Using the chassis as a return conductor is done for a few reasons, the largest being cost and weight savings (in that order I am guessing), neither of which are significant factors in our limited application.

From what I have seen, the chassis is a patchwork of structural metal substructures welded or bonded together, not a one piece steel structure. This could be to allow crumple zones or make manufacturing easier. It may not be as big of a continuous blob of steel as you may think. I have to assume the factory did testing to determine that this steel patchwork is acceptable to use as a DC return for the tightly integrated factory electronics. It is probably fine to add some additional DC load returns to the chassis given a design margin, but not sure I would want to extrapolate this as acceptable for many tens or even a hundred amps or more. High current through the vehicle chassis could potentially cause issues with sensors and ECU communications, cause galvanic corrosion, and intermittent behavior that may be hard to troubleshoot. If one of the critical ECUs lost communication it could lead to safety issues.

In my mind, adding a second auxiliary or house battery to our trucks for overlanding, traveling or limited off-grid purposes falls more under the recreational vehicle or boat application. In that case it would be good to reference standards and best practices for those applications. I know not required, but I tend to follow ABYC standard whenever possible when up-fitting my vehicle. There's also the ANSI/RVIA LV standard but I am not familiar with its guidance.

I know these are not boats (or maybe they are..), but I believe ABYC requires a return conductor. I don't know the size of the factory negative conductor from the chassis to the battery, but per ABYC a 8awg wire is limited to 80A, and 6awg is limited to 120A so that wire would need to be upgraded at least. ABYC also calls for voltage drop for critical loads to be <3%. I have not measured voltage drop on 80A when using the chassis as a return. I personally would not want to run a 50A DCDC converter or 1000W+ inverter through chassis.

Using the chassis could be acceptable practice, or possibly even a good practice in some cases, but I would be careful about saying it's best practice.

Feel free to use chassis as a return, but I will continue to run a separate return conductor. Like I said I am not an expert and could be wrong here, and will certainly entertain a convincing argument.

Good discussion!

 

[TeCKis300]

Just because it is done on production vehicles does not necessarily make it best practice. Using the chassis as a return conductor is done for a few reasons, the largest being cost and weight savings (in that order I am guessing), neither of which are significant factors in our limited application.

From what I have seen, the chassis is a patchwork of structural metal substructures welded or bonded together, not a one piece steel structure. This could be to allow crumple zones or make manufacturing easier. It may not be as big of a continuous blob of steel as you may think. I have to assume the factory did testing to determine that this steel patchwork is acceptable to use as a DC return for the tightly integrated factory electronics. It is probably fine to add some additional DC load returns to the chassis given a design margin, but not sure I would want to extrapolate this as acceptable for many tens or even a hundred amps or more. High current through the vehicle chassis could potentially cause issues with sensors and ECU communications, cause galvanic corrosion, and intermittent behavior that may be hard to troubleshoot. If one of the critical ECUs lost communication it could lead to safety issues.

In my mind, adding a second auxiliary or house battery to our trucks for overlanding, traveling or limited off-grid purposes falls more under the recreational vehicle or boat application. In that case it would be good to reference standards and best practices for those applications. I know not required, but I tend to follow ABYC standard whenever possible when up-fitting my vehicle. There's also the ANSI/RVIA LV standard but I am not familiar with its guidance.

I know these are not boats (or maybe they are..), but I believe ABYC requires a return conductor. I don't know the size of the factory negative conductor from the chassis to the battery, but per ABYC a 8awg wire is limited to 80A, and 6awg is limited to 120A so that wire would need to be upgraded at least. ABYC also calls for voltage drop for critical loads to be <3%. I have not measured voltage drop on 80A when using the chassis as a return. I personally would not want to run a 50A DCDC converter or 1000W+ inverter through chassis.

Using the chassis could be acceptable practice, or possibly even a good practice in some cases, but I would be careful about saying it's best practice.

Feel free to use chassis as a return, but I will continue to run a separate return conductor. Like I said I am not an expert and could be wrong here, and will certainly entertain a convincing argument.

Good discussion!

If there is a takeaway, the most important thing is to ensure a good ground/ground path and there's multiple solutions for that. A ground wire to the battery ensures that to some extent, perhaps as a crutch. With safety implications that the rest of the system may use that ground path if the primary ones fail for whatever reason.

50A in my mind doesn't begin to approach the threshold that most any chassis ground would have a problem handling. Stereo amps at hundreds to thousands of watts, no big deal. Winch, at potentially hundreds of amps, that one is more critical that there is a clear and short ground path.

That said, don't forget the battery is the secondary source of power. The alternator is the primary, especially for super high load inverter/winch stuff. Electrons actually flow from negative to positive. By putting super high draw stuff at the negative battery terminal would mean power transmission comes from alternator, over engine block, over block to chassis ground straps, over chassis, over chassis to battery ground strap, then to your high draw stuff. The battery strap may be an extra hop. With battery acting as sort of a capacitor too. Question is whether the typical 4 gauge battery chassis strap sized to your big accessory?

There's more to this than meets the eye. Takeaway again is to have a considered and solid ground to begin with, without introducing new complexity and failure modes.

 

[radman]

another stupid question: My understanding is that breakers/fuses are intended to protect the wires. My 4awg is rated at 160amps (per ABYC); however, the Victron is the only thing that i'll be connecting to it, which will peak at 25amps. What size breaker should I put in the engine bay at the stock battery? I'm thinking one of these so I'll be able to switch on/off as needed.

looks like my options are 36, 60, or 90 apms

Amazon product ASIN B000THNMGS

 

[grinchy]

another stupid question: My understanding is that breakers/fuses are intended to protect the wires. My 4awg is rated at 160amps (per ABYC); however, the Victron is the only thing that i'll be connecting to it, which will peak at 25amps. What size breaker should I put in the engine bay at the stock battery? I'm thinking one of these so I'll be able to switch on/off as needed.

looks like my options are 36, 60, or 90 apms

Amazon product ASIN B000THNMGS

I"m horribly conservative with wiring, so I'd do a 125 amp fuse/breaker on the wire, and the recommended fuse (and type if they want a slow blow) at the service location for the Victron.

105DegC is way too hot for a wire in my vehicle

 

[radman]

I"m horribly conservative with wiring, so I'd do a 125 amp fuse/breaker on the wire, and the recommended fuse (and type if they want a slow blow) at the service location for the Victron.

105DegC is way too hot for a wire in my vehicle

even at max 75C, would that 125 breaker ever even trip if the victron peaks at 25amps?

 

[eatSleepWoof]

another stupid question: My understanding is that breakers/fuses are intended to protect the wires. My 4awg is rated at 160amps (per ABYC); however, the Victron is the only thing that i'll be connecting to it, which will peak at 25amps. What size breaker should I put in the engine bay at the stock battery? I'm thinking one of these so I'll be able to switch on/off as needed.

looks like my options are 36, 60, or 90 apms

Amazon product ASIN B000THNMGS

Size the breakers to be ever so slightly larger than the maximum expected current draw. The wiring should be able to handle that same current, but if the wiring is "overkill" for the current, there's no harm in it.

If your device peaks at 25amps, a 30amp breaker would be a good option. 36amp is not too far off and I wouldn't hesitate using it.

 

[radman]

Size the breakers to be ever so slightly larger than the maximum expected current draw. The wiring should be able to handle that same current, but if the wiring is "overkill" for the current, there's no harm in it.

If your device peaks at 25amps, a 30amp breaker would be a good option. 36amp is not too far off and I wouldn't hesitate using it.

thanks, this is what I was thinking... I had a typo above - Options in that breaker line are 25/30/40/50/60

 

[sdnative]

another stupid question: My understanding is that breakers/fuses are intended to protect the wires. My 4awg is rated at 160amps (per ABYC); however, the Victron is the only thing that i'll be connecting to it, which will peak at 25amps. What size breaker should I put in the engine bay at the stock battery? I'm thinking one of these so I'll be able to switch on/off as needed.

looks like my options are 36, 60, or 90 apms

Amazon product ASIN B000THNMGS

I am using a 50A breaker for that setup. Look for a bussmann 185 or 285 series breaker. Cheaper than the blue sea labeled one. Amp rating from 25A and up.

I don't think you need the heavy duty 187 series but it's your money.