# [EVDL] wire gauge and max amps



## EVDL List (Jul 27, 2007)

Hi Brian,
As an electrician, I would recommend looking at table 316-10 in the NEC code
book to size your wire to the known load that you intend to support. I would
suggest doing a search for that table if you do not own an electrical code
book. The table will ask for wire information such as the type of wire (THHN
is the most common for automotive use, and #10 at a peak rating of 40 amps
momentary, 30 amps continuous or #12 at a peak rating of 30 amps momentary,
20 amps continuous is a good rule of thumb for most applications).
Good luck with your project.
Regards,
Tom True



> Brian Pikkula <[email protected]> wrote:
> 
> > Evers:
> >
> ...


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## EVDL List (Jul 27, 2007)

And there is the distance factor in determining the size of conductor. It 
is recommended by NEC to have no more than 1 to 3 percent voltage drop in a 
conductor. Normally in a EV the length of conductor is a short run, so you 
could use the continuous rating as Tom stated.

In longer runs, I have deride a formula that can calculated the length of 
conductor at a certain amperage that will maintain a voltage drop between 1 
to 3 percent. 1 percent for lighting and 3 percent for power.

The formula using copper wire.

The continuous amp rating square divided by the actual ampere =
the circuit length. Example for a No. 12 AWG copper wire the
calculation is:

20 amp x 20 amp = 400

400 / 10 actual ampere = 40 feet for 1-3% VD.


No. 12 AWG - 20 Ampere - 20 feet or
10 Ampere - 40 feet or
5 Ampere - 80 feet

No. 10 AWG - 30 Ampere - 30 feet or
15 Ampere - 60 feet or
7.5 Ampere - 120 feet and so on.

In my EV, I have a 12 volt ignition separate wire circuit that starts from 
the DC-DC converters that are located in the very rear of the vehicle that 
has a run of 25 feet to the front of the vehicle, back to the control 
console which selects either the DC-DC converters or onboard 12 volt 
charging system or a onboard 12 volt charging system power by commercial 
power.

This ignition run is over a 75 feet circuit depending how I select the 
different modes, and is fuse for 20 amps, so I choose a No. 8 AWG copper 
wire by using the calculation as:

No. 8 AWG = 40 ampere - 40 feet at 1 to 3% VD or
20 ampere - 80 feet

These wire tables and calculations can be downloading some pages by typing 
in your search engine: Handbook for Electrical Engineers or try Electrical 
Engineers Handbooks.

Roland


----- Original Message ----- 
From: "Thos True" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Sunday, May 01, 2011 8:37 AM
Subject: Re: [EVDL] wire gauge and max amps


> Hi Brian,
> As an electrician, I would recommend looking at table 316-10 in the NEC 
> code
> book to size your wire to the known load that you intend to support. I 
> would
> suggest doing a search for that table if you do not own an electrical code
> book. The table will ask for wire information such as the type of wire 
> (THHN
> is the most common for automotive use, and #10 at a peak rating of 40 amps
> momentary, 30 amps continuous or #12 at a peak rating of 30 amps 
> momentary,
> 20 amps continuous is a good rule of thumb for most applications).
> Good luck with your project.
> Regards,
> Tom True
>
> On Sun, May 1, 2011 at 7:02 AM, Brian Pikkula <[email protected]> 


> > wrote:
> >
> > > Evers:
> > >
> ...


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## EVDL List (Jul 27, 2007)

> Brian Pikkula wrote:
> > I am trying to appropriately size my 12V wiring for various systems:
> > DC/DC, heater, vacuum pump, signal to relays, etc. I have found
> > tables like the one in the link:
> ...


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