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-   -   Negative or positive (https://www.irv2.com/forums/f84/negative-or-positive-341675.html)

will stevens 05-25-2017 11:10 AM

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.

FIRE UP 05-25-2017 11:16 AM

Quote:

Originally Posted by will stevens (Post 3615531)
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.

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

70ChevelleSS 05-25-2017 03:16 PM

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.

u04601 05-25-2017 03:28 PM

Quote:

Originally Posted by will stevens (Post 3615531)
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.

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.

badturks5 05-25-2017 06:59 PM

Quote:

Originally Posted by will stevens (Post 3615531)
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.

In the auto industry everything is ground switched. Less arcing on the contacts. I would do ground side switch.

LakeKerrGuy 05-25-2017 07:54 PM

For safety when working with DC voltage, open the negative (ground). For safety when working with AC voltage, open the hot(s) first.

YC1 05-25-2017 07:58 PM

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.

Starsekr 05-25-2017 08:17 PM

Positive grounds
 
I think I will take some exception to the statement that the auto industry switches the negative (ground side). :confused: 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.

twinboat 05-25-2017 09:11 PM

Quote:

Originally Posted by badturks5 (Post 3616128)
In the auto industry everything is ground switched. Less arcing on the contacts. I would do ground side switch.

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.

badturks5 05-26-2017 05:38 AM

Quote:

Originally Posted by twinboat (Post 3616299)
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.

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.

Sbrownstein 05-26-2017 06:03 AM

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.

winniman 05-26-2017 06:46 AM

I have manual disconnects on both my rv and my boat. Both are on the positive .

will stevens 05-26-2017 07:05 AM

So it looks like it really does not matter what side to switch.
Thanks everyone for input.

twinboat 05-26-2017 07:18 AM

Quote:

Originally Posted by badturks5 (Post 3616549)
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.

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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