Is battery negative and 'ground' the same thing?

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Is battery negative and \'ground\' the same thing?

I'm installing a new chartplotter and GPS both of which have plus and minus 12V supply cables but in the case of the plotter (Raymarine E80) it says to connect the screen cable to ground and for the GPS (Furuno GP32) it says to connect the case stud to ground. I thought battery negative was always grounded? Can I just connect the ground cables to battery neg? Or should I run a wire to the keelbolt to which the mast to keelbolt lightning conductor cables are attached to act as a separate ground ?
 
Re: Is battery negative and \'ground\' the same thing?

[ QUOTE ]
Can I just connect the ground cables to battery neg?

[/ QUOTE ]Yes.
 
Re: Is battery negative and \'ground\' the same thing?

yes - you should find that the common earth bar has all the neutrals connected to it and a big fat black lead from the battery negative.
 
Re: Is battery negative and \'ground\' the same thing?

The short answer is yes, you can just connect the ground to 0 Volts.

Technically yes, it can make a difference to an antenna, and maybe even to shielding but (a) you may not notice it and (b) grounding lines should always be kept short, connecting to a distant keelbolt could even set up an earth loop which would actually make things worse.
 
Re: Is battery negative and \'ground\' the same thing?

When I installed my C70 I found a Raymarine technician in the yard and asked him the same question. He said to attach it to the same -ve as the 12v -ve (ie battery -ve) or even just leave it unattached and it would be fine.

I twisted the shield and the 12 -ve together and crimped into the same connector which went to the -ve busbar on the DC panel (and then to battery -ve). It works fine for me!

Jonny
 
Re: Is battery negative and \'ground\' the same thing?

Another answer to your question, perhaps a little old fashione dis 'No'!

Negative terminal on the battery will only be ground on a Negative earthed system.

Positive earth used to be fitted to cars....then the positive was the ground, of course...
 
Re: Is battery negative and \'ground\' the same thing?

The general consensus appears to be yes. But, as others have suggested, connecting to ground does not always mean connecting to the negative terminal of a power supply, which strictly speaking is 0V, so don't blindly follow the rule with everything you install, especially if you are installing radio equipment. It can lead to all sorts of problems such as ground bounce, and earth loops (which may be the same thing as ground bounce I'm not sure)
 
Re: Is battery negative and \'ground\' the same thing?

Even a lot of people have said yes IMHO it is not always true.

I have a steel yacht and the battery negative is not and should not be connect to the hull / earth.

I also have current meter shunts in the line between the each battery bank and the common ground point and if you connect any device to the battery terminal the amp meter will not show the current to that device.

IMHO all equipment negative cables should be connected to a common point negative buss bar as in my case
 
Re: Is battery negative and \'ground\' the same thing?

"IMHO all equipment negative cables should be connected to a common point negative buss bar as in my case"

But then that bar is connected to Bat neg, so what's the difference, electrically speaking?
(I'm not being a smartarse, honest, I would like to know if there IS any difference /forums/images/graemlins/smile.gif)
 
Re: Is battery negative and \'ground\' the same thing?

There is no ground in a boat - but thats being pedantic. /forums/images/graemlins/blush.gif

Because GRP doesnt conduct effectively, you need a return from any appliance and that runs to the battery negative. In a well built boat, you will likely have a nice solid bar of brass to which all negative wires can be connected. In practical terms the anodes , sea cocks etc may also be connected because most engine blocks and shafts are also connected.

You could connect the negatives to the hull in a steel boat just like you do with a car or motorbike, but steel isnt a brilliant conductor and I would have thought the compass might well be affected
 
Re: Is battery negative and \'ground\' the same thing?

Yes: apart from positive earth cars (and I once saw it on a boat - which was a nightmare!), the negative of a battery does not have to be grounded to earth and can be left 'floating'. This is not good in the 12v marine environment because it increases the risk of stray currents causing problems.

A 'floating negative' is quite common in AC applications and electronics. Continental mains for example has220v across the terminals, actually works at only 110volts above earth - but on both wires, unlike UK mains where the negative wire is effectively at zero volts.
 
Re: Is battery negative and \'ground\' the same thing?

With respect, I don't think you are answering the question I thought I was asking.

The neg cables are connected to a common point (bus bar), then that is connected to batt neg with another cable. What is different about that, compared to connecting them directly to the batt? (apart from the extra resistance, and safety issues of course)
 
Re: Is battery negative and \'ground\' the same thing?

I my case I have 3 battery banks. 1 engine start battery and 2 domestic. Each has an amp meter to show the current in and out of the battery bank. The shunt for each battery bank is in the negative side between the battery negative and the common negative connection. All the equipment negative's are connected to the common negative point. If any piece of equipments negative was connected directly to the battery the current for that device would not be indicated on the amp meter for the selected battery.

The reason for the shunts to be in the negative line is to keep the voltages on the DVM sense terminals that are connected across the current shunt as close to negative voltage as possible
 
Re: Is battery negative and \'ground\' the same thing?

Okay: Electrically speaking, a single busbar is exactly the same as individual negative returns to the battery. The only time this would not apply is in high frequency electronic circuitry where the physical position of the conductors may affect the function.

Single point return is standard in cars where the metal body acts as the negative return for most circuits, saving substantially on wiring. And we know what fun it can be on a complex wiring loom if the return point connectors start failing! Smaller boat wiring is generally less complex than a car, though as size increases they rapidly catch up, so a negative bus is quite a good way of keeping the amount of cabling down to a reasonable level.
 
Re: Is battery negative and \'ground\' the same thing?

Many thanks for all the replies. And going back to my original post the consensus seems to be (I think?) that I can connect the 'earth' wires from my electronics as well as the 12 V negative return to the negative bus bar rather than leading the earth wire to some separate earthing point.
Dave
 
Re: Is battery negative and \'ground\' the same thing?

If the earth wire is a shield, it's purpose is to shield the internal wires from electric fields of other wiring. In that case it is better to connect the shield to earth at only one end, because connecting it at both ends can set up a ground loop which can partially defeat it's purpose.
 
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