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Topic: Battery disconnect switch, POS or NEG side?

Posted By: babalu87 on 05/24/09 05:28pm

Which side makes the most sense?
After reading about the current drains I'm definately installing it this week, two brand new batteries and I want to keep them that way.

Have a switch right here that I never installed in an old truck.

Thanks


TV 2006 Tundra Crew-Cab
TT 2003 Nomad 248 Lite XL



Posted By: PapPappy on 05/24/09 05:32pm

Positive side.....with that shut off, there can't be any grounds that might cause a current drain.


Bill & Claudia / DD Jenn / DS Chris / GS MJ
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Posted By: babalu87 on 05/24/09 05:34pm

Thanks, that was my thinking exactly. Though I would like to know about/find any bad grounds that could become a nightmare.


Posted By: tvman44 on 05/24/09 10:11pm

Positive!!!!


Papa Bob
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1* 2008 Brookside by Sunnybrook 32'
1* 2002 F250 Super Duty 7.3L PSD
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Posted By: Tee Jay on 05/25/09 12:07am

Well, the local battery guy told me to put the disconnect on the negative or ground side. Dueling opinions.


Posted By: QCMan on 05/25/09 06:06am

Take the "local battery guy" and throw out his number and purge your memory of where he is located. It doesn't matter if it is AC or DC you are interrupting but it is ALWAYS the hot leg that gets disconnected. There are some devices that will open both sides but they are mostly for industrial purposes.
It is simple - no hot = no chance of any current going anywhere.


2004 Starcraft Aruba 25RS, 2004 Dodge Dakota SLT extended cab. Just the two of us, a Jack and a desire to roam!



Posted By: GuyM on 05/25/09 06:35am

The reason the “local battery guy” said to disconnect the negative side is to prevent accidents. If the positive side is disconnected and somebody is working around the battery and thinking, “I’m safe, it’s disconnected, nothing can happen,” and they somehow make a metallic connection from the positive battery post to the metal frame of the camper you will have a spectacular fireworks display, maybe even an explosion. If the negative side is disconnected and somebody shorts either the positive or negative post to the frame nothing will happen.

I have caused fireworks myself and witnessed an exploding battery from about ten feet away. On a negative ground system you should always disconnect the negative side first.

My disconnect switch goes on the negative side as the “local battery guy” said.

Guy


Posted By: kschitoskey on 05/25/09 07:05am

I put mine on the positive side - seems to me one source of electrons, but many potential destinations. Lots of things can ground a trailer, thus making a path for the electricity. That is my reason for wiring my trailer that way.


2012 Keystone Cougar 293 SAB; steady fast stabilizers, golf car batteries
06 Dodge 3/4 T Mega Cab 5.9 ISB - Pacbrake air bags, B&W Companion


Posted By: EVT0005 on 05/25/09 07:10am

I recommend installing the disconnect on the POS. side. Breaking the ground side can sometimes cause problems with sensitive electrical equipment on the travel trailer, i.e.: radios, fancy chargers, etc. I installed a disconnect on my TT on the positive side and it works fine.


1998 Fleetwood Wilderness 26H
2003 Chevy 2500 HD 6.0L


Posted By: barbjohn on 05/25/09 08:18am

There is also published safety concerns here. In semi-enclosed spaces, flooded cell lead acid batteries contain hydrogen and oxygen, two gasses that could ignite and explode. Removing the ground potential will avoid introducing arcing in the event that a load is still present. This method is used in large industrial applications.

In the real world of RVing, either will probably work without issue. Once either side is removed, the voltage potential is as well. Just understand where you are working and what you are working with.


Posted By: GuyM on 05/25/09 08:23am

As stated in the two above posts, it's a "safety concern."

Let me try and clarify my earlier post. The main reason for putting the battery disconnect on the “grounded” or negative side in most modern applications, is for safety when working around the battery. The reason I said “grounded” is those of you who work on old vehicles or are close to my age will remember the day when some vehicles had the positive post grounded. Now I’m giving away my age.

I have been an electronics technician for over 35 years before retiring. When your goal is to prevent discharge of the battery through hard wired components, putting the disconnect on either side of the battery will work equally well. Putting it on the negative side will not harm electronic components. It takes current flowing through a component to do damage and breaking either side will stop the current. Hence no damage from breaking either side. When ever I took the time to read an installation manual they stated to “disconnected the grounded side of the battery” before installing the equipment.

If you want to isolate the battery and be safe from accidental shorts when working around the battery put the switch on the “grounded” side. Either side will prevent discharge without harming equipment.

Happy Camping

Guy


Posted By: fncampn on 05/25/09 08:31am

When I was designing my inverter installation, I did a lot of research on wiring options. Every inverter installation manual I looked at had the battery cutoff switch located in the positive leg. The manufacturers must know something to recommend and publish these diagrams. So that's why I installed mine that way.

Check out this mod on battery switches:

Battery Cutoff Switch

There is a wiring diagram picture from Xantrex in that article which provides a good example. It's for the inverter model I installed and the wiring I followed.


'03 Cadillac Escalade ESV 6.0L Auto 3.73LS AWD
Camperless for the time being...


Posted By: Jacksons on 05/25/09 08:32am

Guy is correct,I also was an electronics tech before retiring


Posted By: gregputzer on 05/25/09 08:05am

I really doesn't matter.

If you use an enclosed (marine style) switch, you can do it on either side.

If you use an exposed, knife type switch, you MUST switch the negative side to avoid potential accidental shorts.

Greg


Posted By: shadows4 on 05/25/09 08:32am

GuyM wrote:

As stated in the two above posts, it's a "safety concern."

Let me try and clarify my earlier post. The main reason for putting the battery disconnect on the “grounded” or negative side in most modern applications, is for safety when working around the battery. The reason I said “grounded” is those of you who work on old vehicles or are close to my age will remember the day when some vehicles had the positive post grounded. Now I’m giving away my age.

I have been an electronics technician for over 35 years before retiring. When your goal is to prevent discharge of the battery through hard wired components, putting the disconnect on either side of the battery will work equally well. Putting it on the negative side will not harm electronic components. It takes current flowing through a component to do damage and breaking either side will stop the current. Hence no damage from breaking either side. When ever I took the time to read an installation manual they stated to “disconnected the grounded side of the battery” before installing the equipment.

If you want to isolate the battery and be safe from accidental shorts when working around the battery put the switch on the “grounded” side. Either side will prevent discharge without harming equipment.

Happy Camping

Guy


Excellent post Guy, that makes more sense to me than any other post on the subject I have read. Had a disconnect switch on previous TT on the positive side. I believe now I will install one on this TT on the negative side. Its getting old pulling the main fuse every time I put the TT in storage. Thanks, John


2003 4X4 F350,CC,SB,Lariat,7.3L diesel, 151,000 miles
2004 Coachmen 278 RKS Fifth-Wheel
Reese 15K slider hitch



Posted By: nny12972 on 05/25/09 04:50pm

GuyM hit it---a simple DISCONNECT SWITCH on the POS is good to prevent phantom discharge and disconnecting POS when you're adding/fixing things.....BUT ALSO using a 50A BREAKER SWITCH on the NEG will save you if there's short at battery---where the BIG AMPERAGE IS....I USE BOTH! MY setup works for shorts ANYWHERE, since I hard-wired both POS and NEG to battery throughout my TH...

Blue Sea Systems has my 50A breaker switch.....excellent quality, and either surface or flush mounting option....excellent insurance! It's too bad all mfgs. don't hard wire ALL NEG legs instead of going to the nearest chassis ground! But, that costs $$$$!!!
J


Posted By: robertbick on 05/26/09 12:39pm

Jacksons wrote:

Guy is correct,I also was an electronics tech before retiring

Negative side is the correct answer. The current flow is from the NEG terminal TO the POS terminal.


Bob
2008 Chevy Silverado 2500HD 4X4 LTZ
2010 Keystone Cougar 276RLS Pictures
PullRite Superglide 14K Hitch



Posted By: beemerphile1 on 05/26/09 01:02pm

Assuming that you intend to place the disconnect at the battery, here is something to consider that the retired electronics guys are not thinking of. Put the disconnect on the positive side and make certain that your breakaway switch bypasses the disconnect. Here is the reason; If you or the next owner inadvertently tows the trailer with the disconnect off you will still have operating breakaway brakes. If the disconnect is on the ground side, it is impossible for the breakaway switch to bypass the disconnect. It is a safety issue!

Here is a third option; My trailer has the disconnect between the converter and the fuse panel inside the electric closet. When off all interior 12V wiring is dead but the charging system can still function as well as my tongue jack and breakaway.


A poor man seeks riches, a rich man seeks power, but a wise man seeks contentment.

2006 Weekend Warrior FK1900/1998 Ford E150 4.6L = 8MPG
2009 Aliner Sport/2009 Pontiac Vibe 1.8L = 22MPG



Posted By: babalu87 on 05/26/09 01:21pm

beemerphile1 wrote:

Here is a third option; My trailer has the disconnect between the converter and the fuse panel inside the electric closet. When off all interior 12V wiring is dead but the charging system can still function as well as my tongue jack and breakaway.


That may be the best option as the switch will be inside.

Who wants to be that there isnt enough slack in there to cut and crimp a switch in when I get around to it.................


Posted By: Jacksons on 05/26/09 01:31pm

beemerphile1 wrote:

Assuming that you intend to place the disconnect at the battery, here is something to consider that the retired electronics guys are not thinking of. Put the disconnect on the positive side and make certain that your breakaway switch bypasses the disconnect. Here is the reason; If you or the next owner inadvertently tows the trailer with the disconnect off you will still have operating breakaway brakes. If the disconnect is on the ground side, it is impossible for the breakaway switch to bypass the disconnect. It is a safety issue!

Here is a third option; My trailer has the disconnect between the converter and the fuse panel inside the electric closet. When off all interior 12V wiring is dead but the charging system can still function as well as my tongue jack and breakaway.

I would not tow with the battery disconnected, I also run my refrig will traveling and I need 12v for that


Posted By: smkettner on 05/26/09 01:36pm

All the other switches and fuses are on the positive side.
I would continue with that convention. Mine is on the positive.

If you are disconnecting a battery cable or using an uninsulated terminal switch then I think I would use the negative side.


2001 F150 SuperCrew
2006 Keystone Springdale 249FWBHLS
675 watts solar
Send a PM if I missed something


Posted By: mguerrasr on 05/26/09 01:44pm

Negative side


Posted By: whjco on 05/26/09 02:23pm

Guy is dead on with his advice. From another electronics technician who is not retired, if all you're trying to do is to disconnect the battery, it makes NO DIFFERENCE whether the disconnect is on the positive or the negative pole. You must complete a circuit between the poles of the battery to induce any current flow. If either pole is isolated with a disconnect switch, then it is impossible to induce any external current flow.


Bill J., Lexington, KY
2006 Starcraft 2500RKS 25' Travel Trailer
2000 Excursion Ltd. 7.3 PSD
2000 Ford E350 7.3 PSD


Posted By: Perrysburg Dodgeboy on 05/26/09 02:42pm

Install on the ground side.

LINK TO THIS INFO
I believe the switch should be inserted in the ground path, IE, between the battery post and body (ground) for four reasons —
Switched Positive Ground
Switched Negative Ground
1) It is the easiest method of insertion as you don't have to cut or make joints in any of the wires
2) If for some reason the switch wires happen to touch the body, nothing will happen as this would be the normal connection anyway. You would be able to tell by turning on the lights. If the lights come on and the switch is off, then your wires are touching the body somewhere near the switch.
3) The switch is located right at the power source. This is important — you want to know that the power is turned off at the source and not at some other location.
4) If you install the switch in the “power” wire then you have to cut the wire and attach it to the switch. Depending on where you locate the switch, you may not have enough length. If not, just how are you going to safely join the wires?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I have always been told that you should break the ground side. Think about it if you wire the disconnect to the ground wire and for some reason the wire breaks it's not going to short out. But if you use the positive wire it could short out!

Hook it to the ground side!

Don


On Sunday Jan. 26,2014 Toledo Fire department lost two Hero's in a fire.
God Speed Privates Stephen Machcinski and James Dickman. We will take it form here my Brothers.


Posted By: fncampn on 05/26/09 08:48pm

For all the "negative" posters (lol), why do all of the inverter manufacturers' wiring diagrams show disconnect switches and battery bank switches in the positive leg of the power supply? I understand it really makes no difference aside from convenience, but the manufacturers must have a reason...


Posted By: pete42 on 05/26/09 09:18pm

There you have it.

Wire the darn thing anyway you want, half of the posters will thing you wired it wrong.






Posted By: nny12972 on 05/27/09 08:48am

fncampn wrote:

For all the "negative" posters (lol), why do all of the inverter manufacturers' wiring diagrams show disconnect switches and battery bank switches in the positive leg of the power supply? I understand it really makes no difference aside from convenience, but the manufacturers must have a reason...


First, all inverter mfgs specs I've viewed specify a DC disconnect switch AND fusing, OR a disconnect/circuit breaker, of appropriate rating---on the POS leg ...NOT JUST A DISCONNECT SWITCH! This is to protect both the inverter and attached AC appliances, NOT THE RV 12V DC ELECTRICAL SYSTEM! (LOL)

(Most DIY inverter installs I see have no shutoff or circuit protection between battery and inverter!!!)

Second, most RVIA/licensed electricians I know also strongly reccommend a second DC discconect/circuit breaker on the NEG leg at/close to the battery due to often confined spaces, and the high risk of simply dropping a tool or other metal object across battery terminals during disconnect & servicing procedures---which effectively breaks the DC ground connection and eliminates high-current surges throughout the RV electrical system which can fry DC fuses, and/or switches, wiring, meters, and/or sensitive electronics & appliances!

Third, while installation of a simple, accessible DC disconnect switch at/in/on the battery box located OUTSIDE the trailer on the tongue is the "shortcut" many, if not most DIYers do, it is easily subject to "unauthorized" shutting down of the entire 12V DC supply to the trailer! Even an "innocent kid" can shut down your fridge, furnace, etc. without anyone else knowing 'til it's too late!

Bottom line is, a "secure" quality DC disconnect with fuse or circuit breaker in the POS leg is minimal protection...a second disconnect/breaker on the NEG leg completes the protection "loop."
J


Posted By: jblz51 on 05/27/09 05:03pm

The way I teach this to my students is that a battery gives or loses (hence "-") off its' energy through the "negative" side of the battery. The "positive" side of the battery is where energy flows back into the battery (hence +). The signs + and - show you what happens at that terminal to the battery. Hope that is helps.


Josh
2001 Chevy Tahoe
1991 Jayco Eagle 220


Posted By: Perrysburg Dodgeboy on 05/27/09 09:48pm

jblz51 wrote:

The way I teach this to my students is that a battery gives or loses (hence "-") off its' energy through the "negative" side of the battery. The "positive" side of the battery is where energy flows back into the battery (hence +). The signs + and - show you what happens at that terminal to the battery. Hope that is helps.


So what side would you tell your students to install a disconnect?

Don


Posted By: fncampn on 05/27/09 09:58pm

nny12972 wrote:

fncampn wrote:

For all the "negative" posters (lol), why do all of the inverter manufacturers' wiring diagrams show disconnect switches and battery bank switches in the positive leg of the power supply? I understand it really makes no difference aside from convenience, but the manufacturers must have a reason...


First, all inverter mfgs specs I've viewed specify a DC disconnect switch AND fusing, OR a disconnect/circuit breaker, of appropriate rating---on the POS leg ...NOT JUST A DISCONNECT SWITCH! This is to protect both the inverter and attached AC appliances, NOT THE RV 12V DC ELECTRICAL SYSTEM! (LOL)



Well...I didn't say that a fuse shouldn't be used. My question why do inverter wiring diagrams show disconnect switches in the positive leg? I am quite familiar with how inverters are installed and wired having done many installations myself. I always go by the recommendations of the manufacturer. They designed it so they must know something.

Here is a diagram from Xantrex that I'm referring to:




Posted By: nny12972 on 05/28/09 06:19am

"This is to protect both the inverter and attached AC appliances, NOT THE RV 12V DC ELECTRICAL SYSTEM! (LOL) "
J


Posted By: GuyM on 05/28/09 07:43am

Some posters are confusing the issue here.

The original poster wanted to isolate the battery to prevent accidental discharge. As I and others have stated earlier, the best place for that disconnect switch is on the "grounded," usually negative, side of the battery as close to the battery as possible.

Other electrical components are not installed at the battery. They are installed elsewhere, some distance from the battery. The fuse or disconnect switch that the manufacture shows is to protect that item and that item only. That is why it is shown on the "ungrounded," or positive side on the battery.

We have two different issues here.

To protect individual components the fuse, circuit breaker, switch, etc., is placed on the "ungrounded" side of the battery and usually at a central location some distance from the battery.

To isolate the battery from the entire system and prevent accidents, the best place for that disconnect switch is on the "grounded," usually negative, side of the battery as close to the battery as possible. If you're worried about vandals or other accidental switching use a keyed switch, one where the key can be removed in either position.

Lets go camping


Posted By: whjco on 05/28/09 08:00am

I think it depends on whether you're towing with a gas or diesel TV


Posted By: kearlms on 05/28/09 09:25am

If there is this much concern and confusion as to what side to disconnect, then why not just put a disconnect on both sides and then you are fairly safe. I have seen someone drop the dreaded wrench on the battery making contact and melting posts. Just try to be safe as you possibly can and keep in the back of you mind that there is always a risk when dealing with batteries.


Posted By: Perrysburg Dodgeboy on 05/28/09 12:01pm

Angus_NB wrote:

But which side do I disconnect first?


Always Ground side first, that way if you drop or touch the positive cable to the frame it won't short out!


Posted By: smkettner on 05/28/09 12:05pm

Angus_NB wrote:

But which side do I disconnect first?

You will need to team up and disconnect simultaneously on the count of three.


Posted By: whjco on 05/28/09 05:01pm

smkettner wrote:

Angus_NB wrote:

But which side do I disconnect first?

You will need to team up and disconnect simultaneously on the count of three.


But what if I can't count that high?


Posted By: dyb on 05/28/09 06:39pm

Why not pull the main blade fuse ??


2005 F 250 5.4, 4.10 Gear, Tow/Haul, TorqShift Tranny 8ft. Box
Built in Break Controller
Super Duty super cab 158" wheel base
Eagle 320 rlds 2008
Raised Oct, 1988
Reese Dual Cam


Posted By: rw62 on 05/28/09 07:29pm

whjco wrote:

smkettner wrote:

Angus_NB wrote:

But which side do I disconnect first?

You will need to team up and disconnect simultaneously on the count of three.


But what if I can't count that high?


It might be time to buy a tent.


Posted By: Camper G on 05/28/09 07:53pm

On the negative side, for all of the reasons posted prior.


2000 Ford Expedition Eddie Bauer, 4x4, 5.4L Triton V-8 with factory heavy duty trailer tow package & Load Leveling Suspension, Tekonsha P3 Brake Control, 1989 Skyline Layton model 75-2251,


Posted By: Learjet on 05/28/09 08:33pm

wow 5-pages again on what side. The correct answer it all depends on the set up, but in the end it does matter. FYI...I did the Neg. side on mine... hahaha


2013 Ford F250 XLT 2wd Crew Cab 6.2 and 3.73 rear
2006 KZ Frontier 2303P-F
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Equal-i-zer
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sold* 2001 Hurricane 30Q Chevy workhorse
sold* 2006 Nissan Titan CC with tow package



Posted By: jblz51 on 05/28/09 08:38pm

Perrysburg Dodgeboy wrote:

jblz51 wrote:

The way I teach this to my students is that a battery gives or loses (hence "-") off its' energy through the "negative" side of the battery. The "positive" side of the battery is where energy flows back into the battery (hence +). The signs + and - show you what happens at that terminal to the battery. Hope that is helps.


So what side would you tell your students to install a disconnect?

Don


The negative side. No short possible if flow of electrons is prevented.


Posted By: babalu87 on 05/28/09 09:28pm

I'm putting switch on the NEG AND THE POS


Posted By: whjco on 05/28/09 09:43pm

jblz51 wrote:

Perrysburg Dodgeboy wrote:

jblz51 wrote:

The way I teach this to my students is that a battery gives or loses (hence "-") off its' energy through the "negative" side of the battery. The "positive" side of the battery is where energy flows back into the battery (hence +). The signs + and - show you what happens at that terminal to the battery. Hope that is helps.


So what side would you tell your students to install a disconnect?

Don


The negative side. No short possible if flow of electrons is prevented.


No short is possible if it's on the positive side, also. If there's no reference to the opposite pole of the battery, the flow of electrons is not possible.


Posted By: Angus_NB on 05/28/09 10:31am

But which side do I disconnect first?


2008 Toyota Tundra 5.7L 4x4 DC
2009 KZ Spree 261RKS
Reese Dual Cam HP / Prodigy P3
2 Black Labs - Lucy (Her) & Tosha (Him)



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