# grounding the chasis



## Zak650 (Sep 20, 2008)

YOU DIE! Your car becomes a white hot ball of plasma if a short ever happens. DO NOT DO THIS!!!! If you have one hand touching the car frame and happen to touch one of the high end connections YOU are the dead short with your heart in the middle!


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## crackerjackz (Jun 26, 2009)

Zak650 said:


> YOU DIE! Your car becomes a white hot ball of plasma if a short ever happens. DO NOT DO THIS!!!! If you have one hand touching the car frame and happen to touch one of the high end connections YOU are the dead short with your heart in the middle!





Lol i second that . Very bad idea !! 12 volt negative to chasis ... Nothing else !!


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## Roy Von Rogers (Mar 21, 2009)

You confusing the word "Ground", with the word "Common". The chassis on a vehicle is not Ground, its a Common.

Ground is something connected to the earth, like the ground in your household electrical system.

Negative battery voltage is never earth ground.

Believe it or not, in the old days we had vehicles that had the chassis positive, showing that the vehicle doesn't care which is positive or negative, its all relative.

Roy


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## Tesseract (Sep 27, 2008)

Roy Von Rogers said:


> You confusing the word "Ground", with the word "Common". The chassis on a vehicle is not Ground, its a Common.
> 
> Ground is something connected to the earth, like the ground in your household electrical system....


Actually... a ground is a type of common (or bus) to which all other potentials in a circuit are referenced. Thus it is entirely correct to refer to a vehicle's chassis as "ground".

Furthermore, a chassis ground can also be connected to the Earth (by stakes literally driven into the dirt), at which point the chassis is considered "earthed" and can then be called an Earth ground. 

All that nitpicking aside, I concur that the traction battery circuit should always be totally isolated from the 12V system in an EV. The only times an exception is acceptable is during ground fault check (which should only be performed intermittently) or if the traction battery is 48V or less. Even in the latter case I would still keep the two circuits separate to reduce the coupling of noise into the 12V side.


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## Roy Von Rogers (Mar 21, 2009)

Well you got it right, nitpicking. Geez Tess you just cant resist writing yourself smart..grin

I never said that one cant earth anything, it was an attempt to convey that there is a difference between what is common in a circuit, and what is a true ground (earth), to a newcomer to the craft.

Such misconceptions are very common in my business, and lead to many misdiagnoses of equipment failures, measuring from ground to hot, being too lazy to look for a neutral (common), to make sure they have what they should have.

I know it has been common through the years to also refer common to ground, but I have always believe is was a misapplication of the term.



Roy


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## dragonsgate (May 19, 2012)

Earth, common, ground or what ever you call it, if you connect your traction battery pack to the frame in any way you will be just as dead. When I was a kid living in Kansas I remember seeing trucks with a piece of heavy chain dragging on the ground. I asked my dad what the chain was for and he said it was grounding the body of the truck to the earth so static electricity wouldn't build up and attract lightning. When my parents moved me to SoCal I did not see the chains. Now that I am living back in the Midwest I don't see chains on trucks any more.


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## nikita (Aug 24, 2013)

Tesseract said:


> Actually... a ground is a type of common (or bus) to which all other potentials in a circuit are referenced. Thus it is entirely correct to refer to a vehicle's chassis as "ground".
> 
> Furthermore, a chassis ground can also be connected to the Earth (by stakes literally driven into the dirt), at which point the chassis is considered "earthed" and can then be called an Earth ground.
> 
> All that nitpicking aside, I concur that the traction battery circuit should always be totally isolated from the 12V system in an EV. The only times an exception is acceptable is during ground fault check (which should only be performed intermittently) or if the traction battery is 48V or less. Even in the latter case I would still keep the two circuits separate to reduce the coupling of noise into the 12V side.


thanks for your reply.
to separate 12v and 144v we can use galvanic isolation. but again question remain if we can't ground them to chasis,what should we do to ground high voltage and low system voltage of the car.


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## Tesseract (Sep 27, 2008)

nikita said:


> ...
> to separate 12v and 144v we can use galvanic isolation. but again question remain if we can't ground them to chasis,what should we do to ground high voltage and low system voltage of the car.


I'm not following your logic... probably because what you are asking makes no sense.

You totally separate the 12V and 144V systems. You do not ground any part of the 144V system, only the 12V side (in which the car chassis is typically the negative common, or ground, depending on how you roll).

When you charge the 144V battery pack, it is recommended to connect the chassis of the car to earth ground via the grounding conductor in the AC mains cord. This is true whether the charger is isolated (highly recommended) or non-isolated.

Again, at no point do you connect any part of the 144V wiring to the chassis.


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## crackerjackz (Jun 26, 2009)

Tesseract said:


> I'm not following your logic... probably because what you are asking makes no sense.
> 
> You totally separate the 12V and 144V systems. You do not ground any part of the 144V system, only the 12V side (in which the car chassis is typically the negative common, or ground, depending on how you roll).
> 
> ...



I concure lol ... Although technically if he was to buy very expensive high voltage wiring it comes with a interference collector around the wiring referred to as a shield or eccentric ground .This could be "grounded" .... but yes to be clear not ever should any high voltage wiring either negative or positive touch the car chassis in any way ...


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## aeroscott (Jan 5, 2008)

non grounded like the EU code calls for house and industrial use. In the U.S. we loose 10% of the power to earth grounding. It's for safety of the utility's money .


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## Tesseract (Sep 27, 2008)

aeroscott said:


> non grounded like the EU code calls for house and industrial use. In the U.S. we loose 10% of the power to earth grounding. It's for safety of the utility's money .


I can't quite tell for sure - mainly as a result of poor grammar - but it sure sounds like you are advocating not grounding the vehicle chassis when it is plugged in to the AC mains for charging. And your reasoning is that 10% of the energy (not power... ahem) in the US is lost to grounding.

As your "advice" is dangerous and contrary to established practice, you either need to supply a credible reference to back this up or edit/delete your post.


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## aeroscott (Jan 5, 2008)

I was told this by a SMUD EE during a master electrician class. We all agree that you float a cars vfd , but you ground the vfd battery charger?
This conflict came up using code grounding on boats , the Delta King(steam boat) was grounded per code and had a great deal of de plating damage to her hull.
This instructor said that in the E.U. they think having a uninsulated current carrying conductor bonded to everything is nuts. And the 10% was my instructors comment and not my reasoning .


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## Tesseract (Sep 27, 2008)

aeroscott said:


> I was told this by a SMUD EE during a master electrician class. We all agree that you float a cars vfd , but you ground the vfd battery charger?


I don't know what a SMUD EE is, nor do I know what a "cars vfd" and a "vfd battery charger" are.

You do float the traction circuit - that is, the HV battery, controller and motor - in an EV, but you do ground the chassis of the car - which is synonymous with 12V negative common - to the AC mains whenever the _charger_ is plugged in. That protects against getting shocked from a single point insulation failure in the charger, which is kind of the whole point to running a grounding conductor in the first place...

Again, you should always bond the chassis of the car to earth ground when it is being charged, and you should never "ground" any part of the traction circuit at any time. These are two separate things, and easily seen as such, I would think.



aeroscott said:


> This conflict came up using code grounding on boats , the Delta King(steam boat) was grounded per code and had a great deal of de plating damage to her hull.


[Metal hull] boats are already grounded through the water, so if their internal chassis ground is also bonded to the AC mains ground then an electrochemical cell is formed between the boat hull and the grounding rod that will be driven into the earth somewhere nearby. The potential of this cell is usually in the range of 0.4-0.6V so it can be blocked by one or two silicon diodes in series with the grounding conductor. In fact, there are (overpriced) devices available at boating stores which do just that.

In other words, boats are still grounded when connected to shore power.



aeroscott said:


> This instructor said that in the E.U. they think having a uninsulated current carrying conductor bonded to everything is nuts. And the 10% was my instructors comment and not my reasoning .


I suspect you (or the instructor) were not clearly distinguishing between the grounding conductor - which does not carry significant current under normal circumstances, only during faults - and the neutral conductor, which is *sometimes* left bare in the US, but routinely carries significant current. I could see electricians in the EU thinking our bare neutral is nuts, but not the grounding conductor (which I believe is called the "protective earth" conductor in the EU and, incidentally, is almost always bare like it is here).


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## Roy Von Rogers (Mar 21, 2009)

Maybe I'm misunderstanding something, but there are no bare neutral wires that I know of. The only bare connector allowed is a ground connector. Some 240v house circuits have a bare wire as in havac equipment, but is for grounding. If any 120v is used in such equipment, a 4 wire circuit must be used, two hot's, one neutral and the bare ground, such has in electric clothes dryers.

There are some older wiring where three insulated wires are used on appliances, where neutral is used to power up a 120v circuit, but the install manual states that an external ground wire needs to be attached to the chassis.

Roy


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## Tesseract (Sep 27, 2008)

Roy Von Rogers said:


> Maybe I'm misunderstanding something, but there are no bare neutral wires that I know of....


No, it was more that I was not specific enough with my wording. The neutral conductor on the service drop from a pole mount transformer is usually bare aluminum. Once inside a building the neutral is always insulated (AFAIK - I'm not an electrician, okay).


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## Roy Von Rogers (Mar 21, 2009)

Wasnt aware you were talking about the drop, I thought the conversation was about grounding vehicles etc.

Roy


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## Tesseract (Sep 27, 2008)

Roy Von Rogers said:


> Wasnt aware you were talking about the drop, I thought the conversation was about grounding vehicles etc.
> 
> Roy


Yeah, I thought so too, but then aeroscott derailed the topic. At least I think he derailed it... I'm not quite sure what he wrote, actually.


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## crackerjackz (Jun 26, 2009)

Tesseract said:


> No, it was more that I was not specific enough with my wording. The neutral conductor on the service drop from a pole mount transformer is usually bare aluminum. Once inside a building the neutral is always insulated (AFAIK - I'm not an electrician, okay).




Up here in quebec ( canada) the only bare neutral is from the top of the power pole for example a house to the first panel inside that house . Only legal bare if its copper not aluminium or else it must be insulated ...

As for the air exposed wiring from the hydro electric pole to the house the aluminium can be bare because it has steel in it ...


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## dcb (Dec 5, 2009)

Question, at what point is a battery pack considered high voltage? Should one feel it necessary to float a 48 volt pack for instance? (except as good practice)?

Edit, I assume floating the control circuitry along with it is kosher, and nothing else is tied to ground assuming your lights have separate ground leads and etc?


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## Russco (Dec 23, 2008)

dcb said:


> Question, at what point is a battery pack considered high voltage? Should one feel it necessary to float a 48 volt pack for instance? (except as good practice)?
> 
> Edit, I assume floating the control circuitry along with it is kosher, and nothing else is tied to ground assuming your lights have separate ground leads and etc?


The auto manufacturers were thinking of going with a 42 volt system to replace the 12 volt system. They felt 42 volts was the upper "safe" voltage.

So, if you believe the auto manufacturers, your 48 volt system should not be grounded to chassis.

Or, if you believe me, I wouldn't ground the propulsion system to chassis no matter what the voltage. 

See: 

http://en.wikipedia.org/wiki/42-volt_electrical_system


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## major (Apr 4, 2008)

Russco said:


> .....I wouldn't ground the propulsion system to chassis no matter what the voltage.


I'll second that.


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## Jan (Oct 5, 2009)

I notice often that the term Grounding is used for three totally different applications.

You have the automotive application where the negative wire is omitted and the chassis is used instead. Which makes the wiring a lot simpler. 

Then there is the safety grounding combined with a earth leakage switch. That’s probably not the right term. Anyway this is done for high voltage touching parts of the construction it’s not supposed to touch. Faults. If the construction is isolated from earth (not grounded) the construction becomes a high voltage source that could be lethal for anyone touching it. Making the earth connection with his body. An earth leak switch detects a difference in the in- and out going current and switches it off. Better have a ground wire causing this than a human being.

And last but not least there is shielding. This is to eliminate interference. 

They all look similar because they are often connected to the earth or in case of automotive to the chassis.

So, if your charger wants to be grounded. Don’t connect it to the chassis, but to the ground wire of the outlet. That’s safety grounding.

And if your inverter wants to be grounded. It’s probably for shielding. And the chassis might be the best object in the vicinity. But it will never suggest that the negative wirte should be 'grounded'.


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## crackerjackz (Jun 26, 2009)

dcb said:


> Question, at what point is a battery pack considered high voltage? Should one feel it necessary to float a 48 volt pack for instance? (except as good practice)?
> 
> Edit, I assume floating the control circuitry along with it is kosher, and nothing else is tied to ground assuming your lights have separate ground leads and etc?




Canadian electric code applies to anything ac or dc over 30 volts . Anything under that is considered not dangerous and no laws apply ...


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## Tesseract (Sep 27, 2008)

dcb said:


> Question, at what point is a battery pack considered high voltage? Should one feel it necessary to float a 48 volt pack for instance? (except as good practice)?...


This is the topic that just won't die...

You should always keep the traction and 12V circuits totally separate for noise reasons if nothing else. Also, the traction battery will almost certainly be capable of delivering a higher fault current than the 12V "SLI" (starting-lighting-ignition) battery, so another good reason to float that system.

However, I have occasionally seen golf cart and utility vehicle motor controllers spec'ed for 48V or less that have connected the traction battery negative terminal to their chassis and/or in common with their 12V negative terminal (though, frequently such controllers don't have a 12V control side - everything is referenced to traction pack negative including the throttle pot [which is usually a variable resistor, and not a true 3-wire pot]).

Such controllers should not be used in an on-road vehicle for the aforementioned reasons of safety and noise.





Jan said:


> ...So, if your charger wants to be grounded. Don’t connect it to the chassis, but to the ground wire of the outlet. That’s safety grounding.
> 
> And if your inverter wants to be grounded. It’s probably for shielding. And the chassis might be the best object in the vicinity. But it will never suggest that the negative wirte should be 'grounded'.


This perfectly illustrates the confusion between generic "grounding" and the more specific "earth grounding" which should always be employed unless the entire device (ie - the vehicle!) is "double-insulated". 

Which is to say, if there is something in the car that plugs into the AC mains (e.g. - a charger) then the metal chassis of the vehicle should be earth grounded (via the grounding conductor in the line cord) whenever it is plugged in.

The positive and negative output terminals of the charger should always be floated from the chassis of the vehicle - whether the charger employs an isolation transformer or not.

Grounding of an EV motor controller (and/or the shielding that is used on the high power cables in OEM EVs) is mostly for noise reasons. Again, the controller's metal enclosure (and the cable shields, if used) will be isolated from the traction pack negative, and so when you bond the enclosure and/or shields to the vehicle's chassis you are not creating a ground fault.


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## Jan (Oct 5, 2009)

Tess, I have to rewire my entire vehicle. Is it wise to use wires for negative, instead of chassis for all components? And ground the entire chassis to the ‘outlet ground’ when plugged in. And has it any effect on shielding or vice versa? Or doesn’t it make any difference at all?


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## poprock (Apr 29, 2010)

In the state of NSW Australia, hazardous voltage is over 60v DC or 25vAC. All HAZV must be isolated from the chassis and also from ELV wiring circuits. Maximum leakage is 20mA


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## Tesseract (Sep 27, 2008)

Jan said:


> Tess, I have to rewire my entire vehicle. Is it wise to use wires for negative, instead of chassis for all components? And ground the entire chassis to the ‘outlet ground’ when plugged in. And has it any effect on shielding or vice versa? Or doesn’t it make any difference at all?


It's difficult to avoid using the vehicle chassis as 12V- common. Even ifyou totally rewire everything many devices intended for automotive use and with metal enclosures intentionally connect the enclosure to 12V-. Thus I would only run a separate wire for 12V- to those devices which are sensitive to noise and/or draw/supply a lot of current. Audio equipment and dc/dc converters and such. Take care to isolate the metal enclosure from the vehicle chassis if you run a separate ground wire, otherwise you will just make matters worse (by creating a ground loop).

Connecting the vehicle chassis to earth ground (when, e.g., the charger is plugged in to the AC mains) is mostly done for safety reasons; ie - to provide an alternate pathway for fault current should there be an insulation failure in mains-connected equipment. The stray inductance of the grounding conductor is usually too high to be of much help in draining away noise currents above a few kHz.


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## Frank (Dec 6, 2008)

FWIW, my first project was a 36V bike and I did not isolate the two systems. This let me get away with no dc/dc or aux. battery. Any practical vehicle would use higher voltage where the traction pack should definitely be isolated.


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## Jan (Oct 5, 2009)

Tesseract said:


> It's difficult to avoid using the vehicle chassis as 12V- common. Even ifyou totally rewire everything many devices intended for automotive use and with metal enclosures intentionally connect the enclosure to 12V-.


Yes, that's what I already noticed. So, I don't have to find a solution for those problems.



> ..dc/dc converters and such. Take care to isolate the metal enclosure from the vehicle chassis if you run a separate ground wire, otherwise you will just make matters worse (by creating a ground loop).


Read the wiki article about ground loops, but I don't really understand it. Anyway, I will isolate those components from the chassis.



> The stray inductance of the grounding conductor is usually too high to be of much help in draining away noise currents above a few kHz.


My DMOC has a ground connection. Is it then for safety reasons? But I don't understand the ground fault mechanisme for the battery pack. If there is a fault in the inverter, there will be a short, blowing the fuse. Or nothing will happen. Unless someone touches a battery at the other terminal and the inverter at the same time. And I still don't see how grounding would help then.


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## Roy Von Rogers (Mar 21, 2009)

You should never ground your pack to chassis ground. 

They are two separate system, and should be kept that way. And don't believe you cant get a nasty shock from 48v, think again, depending if the charger is on, it can get to over 60v at a very high amp potential.

Roy


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## Tesseract (Sep 27, 2008)

Jan said:


> Read the wiki article about ground loops, but I don't really understand it. Anyway, I will isolate those components from the chassis.


It's not complicated - but it seems every description I read makes it seem that way. Basically, a ground loop occurs whenever there is more than one pathway for return current to flow in a circuit. For example, say you run both 12V+ and 12V- cables from the battery directly to a car stereo amplifier but inside the amplifier the 12V- connection is also connected to the metal enclosure. If you bolt the amplifier to the vehicle chassis you will provide an alternate pathway for return current. The amount of magnetic noise then picked up will be proportional to the area enclosed by the alternate pathway and the dedicated 12V- cable. You either need to disconnect the 12V- cable or (better) isolate the amplifier's metal enclosure from the vehicle chassis (better because you can run the + & - cables next to each other, which minimizes their loop area).



Jan said:


> My DMOC has a ground connection. Is it then for safety reasons? But I don't understand the ground fault mechanisme for the battery pack. If there is a fault in the inverter, there will be a short, blowing the fuse. Or nothing will happen. Unless someone touches a battery at the other terminal and the inverter at the same time. And I still don't see how grounding would help then.


Re-read what I wrote: I was referring to the vehicle needing to be earth ground whenever the charger is connected to the AC mains. Earth grounding the vehicle won't protect you from a fault in the DMOC, and my other comment was that it won't reduce noise, either (but even if it did, how would that be practical? The inverter only runs when you are *driving*  ).


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## dcb (Dec 5, 2009)

Thanks for the responses. It seems a big factor too is how many non-isolated chargers there are out there. But even if it is isolated you re left with groundloops and whatnot (whole frame as antenna). Good info. Might be sticky worthy


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## Jan (Oct 5, 2009)

Tesseract said:


> It's not complicated...


OK, I think I uderstand.



> Re-read what I wrote...


I wasn't clear obviously. Because that's what I already thought you meant. So, why does my DMOC has a earth connection on its enclosure if it will not reduce noice, nor can help as a safety measure.


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## Tesseract (Sep 27, 2008)

Jan said:


> ....
> I wasn't clear obviously. Because that's what I already thought you meant. So, why does my DMOC has a earth connection on its enclosure if it will not reduce noice, nor can help as a safety measure.


I realize there is a language mismatch here, but I thought what I wrote was pretty clear:



Tesseract said:


> ....The stray inductance of the grounding conductor is usually too high to be of much help in draining away noise currents above a few kHz.


The "grounding conductor" is the wire in the AC mains cable that does nothing but carry fault current and low frequency noise current. Because of its length, it generally will have too high a stray inductance (~10nH/cm) to be of much use in draining away noise current above a few kHz. 

In contrast, bonding the metal enclosure of the DMOC to the vehicle chassis via, say, multiple metal screws, will generally result in a low impedance connection between the two and that turns the vehicle chassis into an extension of the DMOC's enclosure. This can improve radiated emissions and immunity for EMC compliance testing, especially when the idiot testing laboratory uses a standard "LISN" to supply power to the D.U.T.*.

* - Line Impedance Stabilization Network and Device Under Test, respectively.


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