# Connect motor case to chassis ground?



## Tyn245GL (Oct 12, 2009)

Question: do I need to ground the MES-DEA motor case (or one of its mounting bolts) to the car's chassis?
Reason I ask: currently there is only rubber between the motor and the chassis.

Explanation:
My MES-DEA motor is connected to the existing Volvo clutch and transmission. At the motor side the motor is mounted to the original Volvo rubber engine mounts. At the transmission tail side the transmission is also supported by a rubber mounting.
So in short: the whole unit is only making contact to the rubber mounts; there is no (or limited) metal-to-metal connection with the car's chassis.

What could happen if the motor case is not grounded to the car's chassis?


----------



## Huub3 (Aug 16, 2009)

Dear Tyn,

I think there are at least two reasons for grounding I think (not an expert in this domain thought):
- to ensure that an isolation failure is noted/secured, either by a Ground Failure device (when on AC) or fuse (when on DC) all metal parts with electrical connection must be grounded to a common point

- To avoid stray currents leave the motor via the bearings and the drive shaft, potentially leading to bearing failures (and remember, that might even be as far away as in the diff!)

Hope this helps a bit, regards,


Huub 




Tyn245GL said:


> Question: do I need to ground the MES-DEA motor case (or one of its mounting bolts) to the car's chassis?
> Reason I ask: currently there is only rubber between the motor and the chassis.
> 
> Explanation:
> ...


----------



## ElectriCar (Jun 15, 2008)

I did. It's not connected to the pack anyway. The motor case is just a shell.


----------



## Woodsmith (Jun 5, 2008)

As stated above I would have said ground the case for electrical safety. 
This is on the basis that if there was a short circuit to the motor frame you would want it to blow a fuse and not leave the frame live at pack voltage. 

But would that work given the pack is isolated from the vehicle frame anyway?


----------



## ElectriCar (Jun 15, 2008)

Woodsmith said:


> As stated above I would have said ground the case for electrical safety.
> This is on the basis that if there was a short circuit to the motor frame you would want it to blow a fuse and not leave the frame live at pack voltage.
> 
> But would that work given the pack is isolated from the vehicle frame anyway?


Only if a 12V wire fell on it. 

I DID NOT TIE MY PACK TO THE 12V SYSTEM! And won't either. It won't cause any problems UNLESS you lean over and touch the frame of the car AND contact ANYWHERE along the pack of batteries. If it's the + terminal of the 1st battery you contact, the one tied to the chassis, you have the voltage of that battery between the two places you touch. If it's ANYWHERE else it's going to be more. And with DC, it's lethal at a lower voltage than AC and you will fell it much worse than AC when you touch it.

That's what scares me so much. People doing this DC wiring at much higher voltages than you would contact anywhere inside your home and are not knowledgeable of how electricity works, how to fuse things properly to prevent meltdowns & fires etc. Fires often start because things are not fused properly or at all and when there's a failure or short somewhere there's nothing to stop damaging currents, thus they see smoke, fire and whatever.


----------



## jehan12413 (Feb 4, 2010)

If you take a look at the transmission it should already have a ground strap to the chassis somewhere.


----------



## ElectriCar (Jun 15, 2008)

Mine didn't have a ground strap. I thought it was grounded via mounting brackets but when I installed a temp sensor on the motor which one wire was attached to for a ground, it didn't work. After grounding the motor housing it worked.


----------



## EVfun (Mar 14, 2010)

Huub3 gave the right answer and the right reasons. Most home built EVs don't have a pack ground fault detection system, but it is not a bad idea (a GFI system for DC systems.)

ElectriCar, you are exactly right when you assert the traction pack system is NOT tied into the 12 volt system. Isolation between these two system is important (over 36 volts nominal pack voltage.)


----------

