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Thread: another relay question

  1. #1

    another relay question

    going to install 3 relays, fuel, fan and pump. what gauge wire is safe to use to supply all 3 from batt.? also is it better to put relays close to the pumps and fan or the switches. thanks.

  2. #2
    Senior Member RACING JUNKIE TheYellaBrick's Avatar
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    "going to install 3 relays, fuel, fan and pump. what gauge wire is safe to use to supply all 3 from batt.? also is it better to put relays close to the pumps and fan or the switches. thanks."


    - I'm assuming that is fuel 'pump' ?
    - What is the 'pump' you list last ?
    Any pump is going to be a high draw item.
    - Are you saying you are going to feed all 3 items off of ONE single wire, or each on separate wires ?
    You need to run a SEPARATE ground wire from EACH power draw to a gang post next to the battery using the SAME size as the power wire.
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  3. #3

    another relay question

    yes water pump rad fan and fuel pump. I want to run one wire that will feed main power and will run same size to ground from all 3.

  4. #4
    The wire size depends on the amperage maximum draw of each of the components, the temperature rating of the wire itself and the distance it will be running. there are many charts available online, here is a simple one that is kind of "corrected" for 12 volts DC. Please note that I am not the author of this chart, there are actual NEC and Automotive approved charts - and this is NOT one of them !

    Gauge 110V 12V
    22 5A 5A
    20 7.5A 8A
    18 10A 10A
    16 13A 20A
    14 17A 40A
    12 23A 60A
    10 33A 100A
    8 46A 150A

    This is assuming common (cheap) automotive "hook up" wire which is typically rated at only 75 degrees C or at best 90 degrees C (we produce wire that is rated at 200 deg and even 250 deg C, it makes a huge difference)

    If you do not know the max amp draw of your pump or fan, there are 2 solutions, put a common automotive amp meter in line with the device and power it up, watch it when it starts (it is when the amps are max) and this will give you the amp draw. Add a little resistance if you like to see the amps go up - "don't get caught up in the fan !!!" (I know you have an old amp meter banging around in your toolbox). Add all the amp draws together, and there you go.

    another method is if you know the power of the device (for example; 750 watts) Current (I) in AMPS is equal to Power (P) in WATTS divided by Voltage (V) applied in VOLTS - or more simply put in "Ohm's Law" I=P/V

    Always "round up" to the next size wire, especially if it is a long run or if the temperature rating of the wire is unknown (or you know it is cheap wire, lol)

    Hope this helps.
    JD


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