Battery disconnect wires
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URL: http://www.rpod-owners.com/forum_posts.asp?TID=14407
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Topic: Battery disconnect wires
Posted By: Camp town usa
Subject: Battery disconnect wires
Date Posted: 18 Feb 2021 at 3:57pm
| I'm a new pod owner and have a dual 6V setup. I am preparing for summer and buying a battery disconnect switch. I have already bought wire gauge 4, but am not sure what the actual rpod unit gauge wires are. Can anyone confirm what should be used - or to what degree it matters if not the same? I believe i should use the same gauge across all items. Meaning connecting the 6V in series as well as the disconnect itself. Secondarily, I was wondering for installation of the switch, do i connect to the ground wire directly or just use the available ground wire to connect to the switch terminal then to battery? I understand there might be directive on both approaches. |
Replies:
Posted By: offgrid
Date Posted: 18 Feb 2021 at 8:07pm
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4 gauge is more than capable of handling the current to your 12V loads . The wiring to the electric panel is going to be 8 gauge as there are 40 amps fuses in that line. You are half right on using the same wire size. You can always go to larger conductors, never to smaller. In this case you are going larger so no worries.
Per the electric code you should never switch or disconnect the neutral (grounded) conductor, which is the negative. If you do then the whole electrical system will be floating with no chassis ground reference. So place your battery disconnect in the positive conductor. Be careful not to short out your battery positive terminal to the trailer frame while working on it, it’s best to disconnect the negative conductor temporarily first to minimize this. ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
Posted By: Toyanvil
Date Posted: 18 Feb 2021 at 11:16pm
| I think the electric code you are thinking about is for AC. DC batteries can be on negative or positive. If you Google "rv battery disconnect switch wiring diagram" you will see both ways. Here's a fun one for you http://https://www.hotrod.com/articles/kill-switch-positive-or-negative/ - http://https://www.hotrod.com/articles/kill-switch-positive-or-negative/ |
Posted By: offgrid
Date Posted: 19 Feb 2021 at 4:59am
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Like most things the real answer is complicated.
First, the National Electrical Code, (National Fire Protection Association or NFPA 70) covers both AC and DC circuit design. I’ve been designing solar power systems (which are of course DC) for 40 years and participated in writing the NEC Article on solar installations. So for sure the NEC applies to DC circuits. Just ask any solar installers who have failed their electrical inspection. So if you design a DC electrical system for your house (regardless of voltage) you need the follow the currently approved version in your city/county (not all are on the same version) and have the Authority Having Jurisdiction (AHJ- typically your county building department) approve it. Where the confusion comes in is that an RV is not a house nor is it a motor vehicle. There is a section in the NEC specifically for RV electrical installations (Article 551). But an RV moves around so who is the AHJ? To solve that jurisdictional problem the RV industry association (RVIA) worked with the NFPA to produce NFPA 1192 specifically for RV safety. So it covers propane, ingress/egress, etc. It also covers electrical by referencing NEC Article 551 for all electrical systems. So again, the NEC applies to RV’s. However, it also references another standard, ANSI/RVIA LV specifically for low voltage electrical systems. I’m too cheap so far to drop the $45 to buy that one (all the current NFPA docs including the NEC are available on the NFPA website for free viewing if you want) so I don’t know what’s in it. But I can tell you that a basic rule in electrical system design is to maintain a solidly grounded neutral at all times and place all fuses, breakers, and switches in the ungrounded line so that when you open circuits they are dead and you can’t accidentally reenergize them by creating a connection to ground somewhere else. There are rare exceptions mostly for industrial applications but we don’t need to get into that here. So the summary is tha the NEC applies to both AC and DC systems and to RV’s. There is another standard I don’t have access to for RV low voltage electrical systems that also applies. And good electrical design tells us to install disconnects, switches, and fuses in the ungrounded (positive) conductor. Sorry it’s so complicated. ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
Posted By: JR
Date Posted: 19 Feb 2021 at 7:27am
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Thanks OG good information and well explained. Should help a lot of us novices. ------------- Jay 179/2019 |
Posted By: Camp town usa
Date Posted: 19 Feb 2021 at 8:17am
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Thanks for the background. Lots of information out there and some gray areas dont make it easy for newbs. I will connect the switch on POSITIVE. My last question was more for the switch itself and because i am not savvy enough. Without having my RPOD available due to storage, when i connect am I taking the available positive lead and connect to the switch, then switch to battery? I bought 2, 4 gauge wires but am visioning maybe i only needed one and can use the available positive line itself. I hope this makes sense what I'm trying to get at. I otherwise have a 2 gauge wire which i will connect the dual 6V in series. I have no problem getting same sized wires across the set up but if it doesn't impact anything then i will keep as i already have.
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Posted By: Toyanvil
Date Posted: 19 Feb 2021 at 8:30am
| I will just add this, I do know about Article 551 and it is for the 120 AC in RV's. Here's a link you should read before installing on the positive side. It is written by Mike Sokol who is an electrical and professional sound expert with 40+ years in the industry. here's his book https://www.amazon.com/No~Shock~Zone-Electrical-Safety-Michael-Sokol/dp/0990527913/ref=as_li_ss_tl?ie=UTF8&qid=1476457526&sr=8-1&keywords=no+shock+zone&linkCode=ll1&tag=sokol0d-20&linkId=c5e922130b3d838f0529618eef806015&language=en_US - RV Electrical Safety For more info on Mike’s qualifications as an electrical expert, http://www.rvtravel.com/rv-electricity-12-volt-tech-battery-disconnect/ - http://www.rvtravel.com/rv-electricity-12-volt-tech-battery-disconnect/ |
Posted By: pedwards2932
Date Posted: 19 Feb 2021 at 8:50am
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Not sure if this helps but here is the thread where I installed my switch. http://www.rpod-owners.com/forum_posts.asp?TID=14096&KW=battery+switch&PID=137055&title=battery-shutoff-and-hayes-sway-control#137055 - battery shutoff and Hayes Sway control - R-pod Owners Forum - Page 1 (rpod-owners.com) I used 8 gauge wire and a 40 amp breaker at the battery output. You could use the 4 guage wire....I would recommend a breaker in case of any short out. It probably won't trip because all the wires connected to the battery switch have a fuse or breaker so it is just an added safety feature
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Posted By: Camp town usa
Date Posted: 19 Feb 2021 at 9:17am
| Pedwards, Thanks for sharing your install. I cant tell how the lines are connected through the switch. Can you describe the line connections from battery to switch and then to positive? Are there more lines attached to the switch at each switch terminal? |
Posted By: pedwards2932
Date Posted: 19 Feb 2021 at 9:37am
| I connected the line from battery thru circuit breaker to one side of switch terminals. I took all the wires that were formally on the battery + and put them on the other terminal on the switch. If you turn the switch off it kills all the DC to the trailer. I have noticed if you plug the trailer into A/C power the convertor seems to supply 12 volts to some circuits not sure which but I know the refrig fan comes on even if the battery switch is off. |
Posted By: Toyanvil
Date Posted: 19 Feb 2021 at 10:02am
| You should install the switch on the ground side of the battery, and it is a lot easier to do. |
Posted By: Camp town usa
Date Posted: 19 Feb 2021 at 10:28am
| Thanks again Pedwards, but one last question (maybe). In buying the disconnect switch i didn't also get a breaker to insert in between. What size breaker do i need? Is there any preference otherwise on type? |
Posted By: pedwards2932
Date Posted: 19 Feb 2021 at 10:54am
| I used to work on boats which are essentially RVs on water.....never saw 12 volt shut off use the ground always used the positive. I suspect the worry is it would be easier to accidentally ground the system...not sure. The circuit breaker I used is a 40 amp and the one I got easily fit in the battery box and is easily resettable. I used the circuit breaker because there is no protection between the + side of battery to switch. |
Posted By: Camp town usa
Date Posted: 19 Feb 2021 at 12:55pm
There's a lot of options, of which I'm not sure which is appropriate. Does it matter automatic or manual reset? Can you simply point me to the applicable breaker I should order?  ...I'm almost there! |
Posted By: offgrid
Date Posted: 19 Feb 2021 at 1:29pm
Yes NEC Article 551 discusses ac circuits. But that does not mean the NEC does not cover dc circuits. That is simply incorrect. Article 690 covers solar which is dc and article 480 covers battery installations, which are obviously also dc. In fact essentially all of the NEC is applicable to dc as well as ac systems. All the sections covering grounding, fuse and circuit breaker selection, conductor ampacity are equally applicable and need to be followed say for an off grid home to pass an electrical inspection. The reason it is better to first manually connect and disconnect the bolted battery negative terminal for maintenance purposes is because you can’t inadvertently short your tools to ground if you disconnect that first, then the positive. That maintenance activity has nothing to do with where you install a permanent switch like a battery disconnect. The article you are referring to claims that placing the disconnect in either positive or negative works “equally well”. I disagree. Every other switch, fuse, and circuit breaker in the trailer is in the positive leg, because FR is following the Code and good practice. That way you know that the grounded conductor (negative) is solid and any open circuit is in the positive leg. Why should the disconnect switch be any different? No explanation other than there might be a fuse block in the positive line which could make disconnect switch placement there inconvenient is given a a reason for placing the disconnect in the negative line. That is certainly not the case in an rpod, and even if it was inconvenience is not an excuse for violating code. I’d love to be a fly on the wall if an electrician tried that in on his local inspector. 😜 As for installing the switch, you can also just cut the existing positive conductor and install an inline switch if you have enough slack and you want to do it that way. Pedward’s suggestion to use a circuit breaker is a good one, that also will protect the conductor from the battery to the panel. Any 12V taters 40A breaker should work but do gets manual resettable one so you’re not waiting around for an automatic one to decide to reset. ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
Posted By: pedwards2932
Date Posted: 19 Feb 2021 at 1:50pm
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Here is the one I used: https://www.amazon.com/gp/product/B07FF8TDSS/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 - Amazon.com: STETION Car Audio 40 Amp Resettable Fuse Circuit Breaker Car Protect for Audio System Fuse 12-24V DC for Car Audio Amps Overload Protection Fuse (40A): Automotive
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Posted By: Camp town usa
Date Posted: 19 Feb 2021 at 2:11pm
| ordered, thanks! |
Posted By: Toyanvil
Date Posted: 19 Feb 2021 at 3:34pm
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offgrid, I was only trying to show there are two ways of installing a switch. I am a building engineer and am familiar NEC code book and have not seen a code that would apply here. Article 480 covers storage batteries, like the ones in my UPS systems and Article 690 provides the circuit requirements for PV systems (solar photovoltaic) I too would like to know what code an inspector would refer to for a 12 volt DC switch on an RV. |
Posted By: pedwards2932
Date Posted: 19 Feb 2021 at 3:39pm
| I was just going by how all the boats i delt with were wired as all the larger ones have battery switches and they are always wired from the positive terminal......I just figured a TT would be similar. |
Posted By: Toyanvil
Date Posted: 19 Feb 2021 at 4:33pm
| Both ways work the same and are good, it sounded like it would work better for the OP to switch the ground side of the battery without a lot of work and that's how I would do his. The funny thing is, I have dual 12 volt batteries and my switch is on the positive side. Only because my switch has 1-2-both or off setting so I have no need to install a disconnect only switch. |
Posted By: offgrid
Date Posted: 20 Feb 2021 at 6:20am
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Toyanvil, I only pointed out sections of the Code that explicitly deal with what are obviously dc circuits to show that they are covered. I was not suggesting they were the only sections covering dc circuits. The way the NEC works is that it’s prescritive, meaning that unless there is an exception noted you have to do what it says. There are no such general exceptions for say 12V dc circuits so you have to follow all the applicable Code articles for those systems just like you would for 120Vac. So that means if you are wiring up an off grid home at 12 or 24Vdc you need to maintain a contiguous grounded neutral and place all your disconnects and over current protection in the hot line, just like in a grid powered building.
That is for an off grid residence. If that residence is subject to electrical inspection then it would be reviewed for code compliance just as if it was ac powered. I have seen many such systems installed by my solar customers rejected for not following the NEC. As for what an electrical inspector would say about an RV, most likely he’d just say he doesn’t have jurisdiction over it and wouldn’t look at it. That leads us back to NFPA 1192 and the RVIA low voltage standard which I am too stingy to drop $45 on. That and the NEC are going to be the most appropriate US standards for electrical systems in RV’s. If anyone wants to “crowd fund” me to get the standard and review it I’ll be happy to 😄. Your current 4 way switch in the positive battery leg is a good example of why the battery disconnect should be in the positive line. By keeping everything that can open the circuit in the ungrounded (positive) line you always keep a solid ground reference (negative) and can manage multiple sources without inadvertently connecting things together that shouldn’t be or disconnecting things that should stay connected. When you get into more complex circuits with multiple sources like solar, generators, grid supplied chargers, inverters, multiple battery banks, etc etc you can easily find where they hid the smoke unless you keep a common ground reference. ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |