# Wire sizing.



## major (Apr 4, 2008)

McRat said:


> It appears that everyone with EV's is running smaller dia wire than is normal in construction.
> 
> Is there a chart somewhere that tells you what amps = what wire size for EV use?
> 
> IIRC, 3/0 wire is good for 200amps for buildings, and #10 is only good for 30amps, but I've seen a LOT smaller wire being used.


How many times have we been through this  I'll see if I can find some of those threads. http://www.diyelectriccar.com/forums/showpost.php?p=245897&postcount=6


----------



## McRat (Jul 10, 2012)

Thanks!

I think I will be using the alum frame as ground, and run as short of copper positive multifilament leads (allowing for flex) as possible. Perhaps even an isolated copper tube a main positive buss? It's very easy to work with and protect, and easy to make junctions. And have good cooling.

PS - Thanks for your reply, it was very helpful.


----------



## Roy Von Rogers (Mar 21, 2009)

McRat said:


> Thanks!
> 
> *I think I will be using the alum frame as ground*, and run as short of copper positive multifilament leads (allowing for flex) as possible. Perhaps even an isolated copper tube a main positive buss? It's very easy to work with and protect, and easy to make junctions. And have good cooling.
> 
> ...


I hope your not talking about pack ground. ????


Roy


----------



## McRat (Jul 10, 2012)

Why not use an alum frame for grounding? Better conductor than steel. Cross sectional area of alum frame is 1.900 sq inches. Huge conductor.


----------



## Ziggythewiz (May 16, 2010)

The issue isn't the material, it's the circuit. Are you wanting to use the frame to ground your AUX circuit (~12v) or your traction (high voltage) circuit?


----------



## McRat (Jul 10, 2012)

Ziggythewiz said:


> The issue isn't the material, it's the circuit. Are you wanting to use the frame to ground your AUX circuit (~12v) or your traction (high voltage) circuit?


Ah... Gotcha. Not sure I'm running any 12v.


----------



## palmer_md (Jul 22, 2011)

McRat said:


> Why not use an alum frame for grounding? Better conductor than steel. Cross sectional area of alum frame is 1.900 sq inches. Huge conductor.



Well you definitely do not want to be working on the pack connecting battery interconnects while leaning on a fender if you have the negative end of the pack connected to the frame. Could be quite an adrenaline rush.


----------



## McRat (Jul 10, 2012)

palmer_md said:


> Well you definitely do not want to be working on the pack connecting battery interconnects while leaning on a fender if you have the negative end of the pack connected to the frame. Could be quite an adrenaline rush.


There is a reason I never wear any jewelry or watches (and my belt buckle fastens on my hip) when working on vehicles. Melt one metal wristband watch on your arm, and you'll join the club. Tools go on a tool cart.

Our building is 460/277v. All the metal conduit is ground. I work on it live sometimes.

AND, I spent a week in the UCI Critical Burn center. I've stayed at much nicer hotels, but at $175,000 for a week stay, I've never stayed at anything that was so upscale. 

Electricity and I are bitter enemies. For my EV experiments, we decided to call a truce. But it's like a North Korea / South Korea truce. I did not enjoy filling out my last-will-and-testament on a hospital gurney. 

The goal of using the alum subframe structure is both economic, and current capacity. While paint won't stop high voltage, it will be painted. The body won't be ground.


----------



## palmer_md (Jul 22, 2011)

it does not matter if you wear any jewelry or watches. If the chassis is the return path and you have any contact with the chassis and at the same time touch any other point in the pack, you've completed the loop and YOU become part of the circuit. This is a VERY dangerous situation and it is why the main pack should always be "floating" with respect to the chassis. Please do not use the frame as the return path!


----------



## McRat (Jul 10, 2012)

palmer_md said:


> it does not matter if you wear any jewelry or watches. If the chassis is the return path and you have any contact with the chassis and at the same time touch any other point in the pack, you've completed the loop and YOU become part of the circuit. This is a VERY dangerous situation and it is why the main pack should always be "floating" with respect to the chassis. Please do not use the frame as the return path!


This is true for all motorcycles, cars, and trucks I've owned or worked on. All were frame grounds. Watch out for the brits though, positive ground wasn't the smartest move in history.

12v will only give you 3rd degree burns and possible shower you with sulphuric acid, and perhaps even a mild explosion, but the risk is still there.

If you are working on ANYTHING, ideally there is no power connected to it. If there is, you must take extra precautions. Ground don't kill you. Completing a circuit does. I'm not planning on working on 190vdc with the power connected, but then again, I normally disconnect 12v vehicles anyhow.


----------



## Ziggythewiz (May 16, 2010)

The purpose of using the frame as 12V ground is because there are dozens of things that connect to it, so you're saving hundreds of feet of wire by doing so.

How many high voltage components do you have in addition to the controller? It's not tough to run a pair of cables to two or three separate things.


----------



## McRat (Jul 10, 2012)

Ziggythewiz said:


> The purpose of using the frame as 12V ground is because there are dozens of things that connect to it, so you're saving hundreds of feet of wire by doing so.
> 
> How many high voltage components do you have in addition to the controller? It's not tough to run a pair of cables to two or three separate things.


Guess I should have said this is a science fair project, and weight is important. 

In this case, the vehicle is 25' long and has two motors, one forward, one aft. Things become less confusing using the frame as a conductor, since I have to ground all the panels anyhow. 

It might end up being over 100' long. We will see what 25' long does.


----------



## Ziggythewiz (May 16, 2010)

Won't you be using the panels in series? That means you would only ground ~1 of them.

While you're at it, the driver could wear an anklet for the pack positive connection, and then a necklace for another, and save a few feet of wire on the positive side as well!


----------



## PStechPaul (May 1, 2012)

Although it may be somewhat safer to have the main battery pack floating, there will always be some leakage and there is no guarantee that you will not get a dangerous shock if you touch any high power conductor while also touching the frame. You should always avoid touching anything that is in the power circuit. Even the 12 VDC auxiliary circuit, which probably is grounded, can cause a dangerous shock if your skin is very sweaty and/or if you have wounds that allow the current to enter the bloodstream. 

We deal with grounded electrical systems in our homes every day. 120 VAC to ground, which is 170 volts peak, and at 60 Hz which is especially dangerous because of the risk of VF (ventricular fibrillation). A GFCI can reduce the chance of shock, but will not eliminate it. There may be a way to do the same thing on the battery circuit of an EV, but it is difficult to resolve 50mA or so out of a 1000 amp circuit. GFCIs are typically 20mA out of 20 amps.


----------

