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05-25-2017, 10:10 AM
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#1
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Senior Member
Join Date: Jul 2014
Posts: 409
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Negative or positive
I have decided to put a switch in between my battery bank and inverter as well as a switch inline on the coach side. General consensus seems to be to switch the negative line, but the switches show to break the positive side.
Just wondering thoughts from others.
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05-25-2017, 10:16 AM
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#2
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Senior Member
Join Date: Dec 2009
Location: Out there, somewhere
Posts: 9,941
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Quote:
Originally Posted by will stevens
I have decided to put a switch in between my battery bank and inverter as well as a switch inline on the coach side. General consensus seems to be to switch the negative line, but the switches show to break the positive side.
Just wondering thoughts from others.
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Manufacturers have been switching the negative on many components for decades. Heck, my fuel injection injectors (say that three times fast) were negatively switched, way back in '89. I'm no expert on this but, there's a reason for switching the negative. I maybe think it has something to do with less arcing inside the switch on a negative than a positive, not sure. But, I see no issue in switching either side but, again, no expert.
Scott
__________________
2004 ITASCA HORIZON 36GD, 2011 GMC Sierra 1500 4x4 Toad '20 Honda NC750X DCT
 2018 Goldwing Tour DCT Airbag
Retired-29.5 yrs, SDFD, Ham - KI6OND
Me, Karla and the Heidi character, (mini Schnauzer)!
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05-25-2017, 02:16 PM
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#3
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Senior Member
Join Date: Oct 2015
Location: Brighton, MI
Posts: 775
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Typically battery disconnects are on the positive side but the current really doesn't care where you break the circuit so either side will work. As far as arcing in the switch, either side will be the same. Electrons flowing from the negative terminal to the positive can't really tell what color insulation the wire has and any current flowing on negative side has to be equal to the current flowing on the positive side.
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Hank & Lynda
2003 Winnebago Adventurer 35U, Workhorse W22
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05-25-2017, 02:28 PM
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#4
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Senior Member
Join Date: Jan 2016
Location: So Cal
Posts: 168
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Quote:
Originally Posted by will stevens
I have decided to put a switch in between my battery bank and inverter as well as a switch inline on the coach side. General consensus seems to be to switch the negative line, but the switches show to break the positive side.
Just wondering thoughts from others.
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My motor home switches the positive 12 volts at a solenoid that kills all 12v. Does yours? If so, for your application, I would stick with switching the positive side so that wiring is consistent.
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Kevin
2004 Tiffen Allegro 31DA, 2015 JKUR toad, Ready Brute Elite tow bar/brake
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05-25-2017, 05:59 PM
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#5
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Senior Member
Join Date: Mar 2016
Posts: 107
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Quote:
Originally Posted by will stevens
I have decided to put a switch in between my battery bank and inverter as well as a switch inline on the coach side. General consensus seems to be to switch the negative line, but the switches show to break the positive side.
Just wondering thoughts from others.
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In the auto industry everything is ground switched. Less arcing on the contacts. I would do ground side switch.
__________________
1998 Fleetwood American Tradition 40VS
Cummins C8.3 300 HP Mechanical Injection Pump
Allison Transmission
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05-25-2017, 06:54 PM
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#6
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Senior Member
National RV Owners Club Florida Cooters Club Freightliner Owners Club
Join Date: Mar 2013
Location: Salt Springs, FL
Posts: 453
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For safety when working with DC voltage, open the negative (ground). For safety when working with AC voltage, open the hot(s) first.
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Jack & Beverly
1999 National Tradewinds 7371; Cat 3126; 6 Speed Allison; 7.5 KW Onan; MS-2012,
2014 Jeep Patriot on a EZE Tow
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05-25-2017, 06:58 PM
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#7
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Senior Member
Join Date: Jun 2011
Location: FL
Posts: 11,452
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Hot side is fine. However if something is dropped across the positive terminal you have a real problem. If you have the negative removed, shorting the negative to the frame will just make things come alive.
A good disconnect switch is fine on the positive and done every day in the RV industry.
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Certified Senior Electronic Technician, Telecommunications Engineer, Telecommunications repair Service Center Owner, Original owner HR 2008
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05-25-2017, 07:17 PM
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#8
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Senior Member
Join Date: Feb 2014
Posts: 381
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Positive grounds
I think I will take some exception to the statement that the auto industry switches the negative (ground side).  Many accessory items have their return path to the negative battery terminal through a body connection or through a lead (wire) to a common ground point. The fuses are connected to the battery through the positive terminal, and if a ground switched device shorts out, there is no circuit protection.
One of the most well know positive ground cars was the early VW Beetles. They changed to negative ground around in the mid 1960's. Search Positive Ground cars on Google for more info.
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Jim and Valerie, 2005 Winnie Adventurer 37B, 2014 Subaru Forester Toad, hitches, brakes, anti-sways, autopilot, gourmet food on a Social Security budget.
"Wave as you go by."
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05-25-2017, 08:11 PM
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#9
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Senior Member
Join Date: Jul 2014
Posts: 35,446
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Quote:
Originally Posted by badturks5
In the auto industry everything is ground switched. Less arcing on the contacts. I would do ground side switch.
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Very little in the auto industry is ground switched. Door jamb switchs and a few other thing maybe, but that's about it. Even the starter relay is on the positive cable.
Electric current takes a circular route and the arching would be no different in any section of the flow.
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05-26-2017, 04:38 AM
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#10
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Senior Member
Join Date: Mar 2016
Posts: 107
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Quote:
Originally Posted by twinboat
Very little in the auto industry is ground switched. Door jamb switchs and a few other thing maybe, but that's about it. Even the starter relay is on the positive cable.
Electric current takes a circular route and the arching would be no different in any section of the flow.
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All modern electronics are ground switched. it has been like that starting way back in 1990's. System protection is almost always on the hot side. Turning something on and on the hot side can and will cause a high voltage spike. switching on the ground side reduces the voltage spike and that helps protect the electronics. I was a 30 Master GM auto Technician. The ground switching is done using the main computer ecm, vcm pcm, bcm tcm or whatever they want to call it. Cannot have any voltage spikes in the computer. With almost everything being computer controlled that's why its ALL now ground switched.
__________________
1998 Fleetwood American Tradition 40VS
Cummins C8.3 300 HP Mechanical Injection Pump
Allison Transmission
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05-26-2017, 05:03 AM
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#11
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Senior Member
Ford Super Duty Owner
Join Date: Dec 2010
Posts: 1,799
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This whole thing about ground switching causing less of a surge totally perplexes me. This is simple DC and what goes in one end comes out the other. It makes absolutely no difference. This is an old myth that continues to perpetuate.
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Scott Brownstein
Palm Island, Florida
2015 Georgetown 335DS
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05-26-2017, 05:46 AM
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#12
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Senior Member
Join Date: Jan 2013
Location: Muskoka Ontario Canada
Posts: 3,142
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I have manual disconnects on both my rv and my boat. Both are on the positive .
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 2000 coachmen santara 370 5.9 cummins isb
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05-26-2017, 06:05 AM
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#13
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Senior Member
Join Date: Jul 2014
Posts: 409
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So it looks like it really does not matter what side to switch.
Thanks everyone for input.
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05-26-2017, 06:18 AM
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#14
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Senior Member
Join Date: Jul 2014
Posts: 35,446
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Quote:
Originally Posted by badturks5
All modern electronics are ground switched. it has been like that starting way back in 1990's. System protection is almost always on the hot side. Turning something on and on the hot side can and will cause a high voltage spike. switching on the ground side reduces the voltage spike and that helps protect the electronics. I was a 30 Master GM auto Technician. The ground switching is done using the main computer ecm, vcm pcm, bcm tcm or whatever they want to call it. Cannot have any voltage spikes in the computer. With almost everything being computer controlled that's why its ALL now ground switched.
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That may be the case in computer chip micro circuits, but when I need to troubleshoot a circuit in brake, tail, head and marker lights, AC compressor clutch, fan, wiper, pump and seat motors, along with most other 12 volt components, I take my test light and connect one end to ground ( negative ) and use the probe to find switched hot ( positive ).
If they switched the ground on a dual filament bulb with the common 3 wire connector, how would you control which filament lit with a single ground wire ?
Do reversible DC motors arch more, switching in one direction than the other ?
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