Car Inverter earth connection.

ipbr21054 · 22 Jan 2021

Evening,
I’m currently fitting an Inverter into my jeep.
With regards the cable, I am using 4AWG & running a positive cable from the car battery under the bonnet & also under the interior trim panel along the sill to the boot where it will be connected to the Inverter.
My question is as opposed to running an earth wire along that same route can I not just connect it from the Inverter to the body of the vehicle in the boot ?

If YES must this wire also be 4AWG ?

Many Thanks.

Harry Bloomfield · 22 Jan 2021

Yes you can use the body as the earth/ negative and you can use a similar size as used for the positive supply. Usually you will be able to find an existing earth/negative terminal around the rear, already in use for lights. That will be fine.

AWG means nothing to me, so far as size is concerned.

ipbr21054 · 22 Jan 2021

4AWG is about 7mm diameter.

EFLImpudence · 22 Jan 2021

It is 21mm² or 25mm² depending which site you look at.

Rated at 70A if copper.

http://www.aic-controls.com/wire-size

EFLImpudence · 22 Jan 2021

What are you intending to run from the inverter?

ipbr21054 · 22 Jan 2021

I was measuring diameter where the mm2 is cross section etc.

I’m running a small key machine.
So can I earth the Inverter in the boot or must I run a full length back to the battery.
After all the battery is earthed straight to the cars body.

EFLImpudence · 22 Jan 2021

ipbr21054 said:
I was measuring diameter where the mm2 is cross section etc.

Yes, but we always use the cross sectional area.

I’m running a small key machine.

Ah, yes, didn't realise it was you.

So can I earth the Inverter in the boot or must I run a full length back to the battery.
After all the battery is earthed straight to the cars body.

You can ground it to the body (It's not actually earth)

The large battery cables are only for the starter motor. Much smaller would be adequate for other items.

Perhaps I should instead have asked what is the rating of the inverter? How many amps can it 'supply'?

EFLImpudence · 22 Jan 2021

I am confusing myself now.

You only need the battery cables to be large enough for charging it.
I would think 10mm² (AWG7) would suffice.

Do others agree?

ipbr21054 · 22 Jan 2021

As the other member didn’t understand AWG I thought it would be easier to say 7mm diameter so he then understood.

Inverter is 500w / 1200w but I think I’m using it for a motor of 300w

The cable size is due to the length or the run, the inverter wattage & motor of the machine wattage.

So I’ve feed though the red positive cable.
So just asking if I can connect the negative side of the Inverter to the chassis / bodywork.

winston1 · 22 Jan 2021

Harry Bloomfield said:
AWG means nothing to me, so far as size is concerned.

AWG stands for American wire gauge. It is not used here. SWG or standard wire gauge was used here and is different.

Astra99 · 22 Jan 2021

If the inverter is rated at 500W continuous (1200W peak) then that is just over 41A @ 12V continuous. 6mm² automobile flexible cable is rated at 50A, but, as you are installing the inverter at the rear of the vehicle, I would suggest going up to 8.5mm² (rated at 63A) to allow for voltage drop. The 12V negative connection at the inverter can be a short length of cable to the vehicle's bodywork. Do not be tempted to use solid domestic cable, the vibrations of the vehicle will cause it to fracture!

Harry Bloomfield · 22 Jan 2021

winston1 said:
AWG stands for American wire gauge. It is not used here. SWG or standard wire gauge was used here and is different.

Yes, I know and SWG means Standard Wire Gauge. I have never used either gauge.

EFLImpudence · 22 Jan 2021

I think I must be thinking of other threads.

Are you not installing another battery to run this inverter?

Harry Bloomfield · 22 Jan 2021

EFLImpudence said:
I think I must be thinking of other threads.

Are you not installing another battery to run this inverter?

I don't think so, but I did suggest it might be a good idea, to avoid flattening the vehicles own battery.

ipbr21054 · 22 Jan 2021

No
I am running the inverter from the car battery.
This is the same battery I use to drive the vehicle.
My homework tells me I can run this machine for 49 minutes before the battery is flat.
I will only run the machine at 4 minutes per use.

The cable in use is 7mm diameter.
So forget AWG / SWG you know the size of cable for the positive side.

So still my question is related to the negative side to the chassis etc and size of cable for this makes a difference or not ?

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Car Inverter earth connection.

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