12v DC - 100amps Wire Gauge

rampantbunny

Hi folks. Need to buy some capable of carrying 100 Amps a distance of approx. 5-7 feet in a 12v DC circuit.

I've googled this but depending on the site I seem to get different results, and to be honest the use of "AWG" versus "#gauge" confuses me.

If answering can you if possible provide the wire diameter and mm2 too.

Cheers.

Bruthal

rampantbunny wrote: »

Hi folks. Need to buy some capable of carrying 100 Amps a distance of approx. 5-7 feet in a 12v DC circuit.

I've googled this but depending on the site I seem to get different results, and to be honest the use of "AWG" versus "#gauge" confuses me.

If answering can you if possible provide the wire diameter and mm2 too.

Cheers.

25 square will carry that. Thats 3 AWG, and diameter around 5.8mm

If its going to continously carry 100 amps for long periods though, 35 square might be recommended, AWG 2, and diameter of 6.5 mm.

What is it going to be running?

M cebee

id say 25 will be fine

unless theres a high ambient temperature

rampantbunny

rampantbunny wrote: »

Hi folks. Need to buy some capable of carrying 100 Amps a distance of approx. 5-7 feet in a 12v DC circuit.

I've googled this but depending on the site I seem to get different results, and to be honest the use of "AWG" versus "#gauge" confuses me.

If answering can you if possible provide the wire diameter and mm2 too.

Cheers.

Hi Robbie7730 - the question is a continuation of an earlier post to this forum that you provided answers to (automotive cabling):(http://www.boards.ie/vbulletin/showthread.php? p=78139303).

I think it's possible that 80-85 AMPs of current can be drawn from a 12v car battery, if a certain combination of electrical items are turned on at the same time (all lights, hazards, horn and more). Is this continuous? Not really (for example the horn is only momentary) but a fair percentage of the rest is.

The problem is, if using wire of that size is necessary, the distribution is going to be a headache once it enters the cab.

Bruthal

rampantbunny wrote: »

Hi Robbie7730 - the question is a continuation of an earlier post to this forum that you provided answers to (automotive cabling):(http://www.boards.ie/vbulletin/showthread.php? p=78139303).

I think it's possible that 80-85 AMPs of current can be drawn from a 12v car battery, if a certain combination of electrical items are turned on at the same time (all lights, hazards, horn and more). Is this continuous? Not really (for example the horn is only momentary) but a fair percentage of the rest is.

The problem is, if using wire of that size is necessary, the distribution is going to be a headache once it enters the cab.

10 square flexible cable would be more than enough to do that. A seperate supply circuit will be connected directly from the battery to the starter motor. The 10 square only has to supply the fusebox really. Distribution is then with smaller wiring according to the fuse size of each of the final circuits coming from the fuses.

Hazards, horn etc use very little. The headlights of cars use 10 amps for both main beams combined as an example, and the indicators are far lower than this, using less than an amp each. I would say more than 20 or 30 amps continuous would be unlikely.

Wipers are not that heavy a load either.

Multi strand cable should be used to allow for vibration on the main supply cables to the fusebox and the starter motor. The starter motor on its own would probably want the 25 square flex single cores to it for a tractor starter. Positive direct to it, negative to ground/frame which should do everything.

All the circuit negatives can be connected to the tractor frame then.

rampantbunny

robbie7730 wrote: »

10 square flexible cable would be more than enough to do that. A seperate supply circuit will be connected directly from the battery to the starter motor. The 10 square only has to supply the fusebox really. Distribution is then with smaller wiring according to the fuse size of each of the final circuits coming from the fuses.

Hazards, horn etc use very little. The headlights of cars use 10 amps for both main beams combined as an example, and the indicators are far lower than this, using less than an amp each. I would say more than 20 or 30 amps continuous would be unlikely.

Wipers are not that heavy a load either.

Multi strand cable should be used to allow for vibration on the main supply cables to the fusebox and the starter motor. The starter motor on its own would probably want the 25 square flex single cores to it for a tractor starter. Positive direct to it, negative to ground/frame which should do everything.

All the circuit negatives can be connected to the tractor frame then.

20-30A...Hmm, can you take a look at my calculations below and be critical where necessary?

2 Head-lights: (2 x 55W)/12 = 9.16A
4 Work-lights: (4 x 55W)/12 = 18.32A
6 Parking lights (4 x 21W + 2 x 10W)/12 = 8.66A (inc. trailer board)
6 Indicators: (4 x 21W +2 x10W)/12 = 8.66A (hazards inc. trailer board)
1 Horn: 20A (only because 20A used in car it was taken from)
2 Cab-lights: 2A
1 Radio: 7.5A
1 Flashing Beacon: 2A

Total is about 77A...notice that the starter is not included in the above as it is indeed wired separately.
Add in some overhead (for expansion) and that comes to maybe 85Amps. Use a cable size with some leg-room and I figured 100A would be comfortable.

Your suggestion of 10 squared is 7AWG (3.66 Dia\10.5mm squared) - correct?
The links below indicate that 10AWG (2.58 Dia\5.26mm squared) wire can carry 100A for up to 20 feet.
http://www.offroaders.com/tech/12-volt-wire-gauge-amps.htm
http://www.rbeelectronics.com/wtable.htm

There are other tables dotted around suggesting a much heavier cable is required - more in line with your 7AWG estimate, but because of the above links it makes it seem like 7AWG would carry between 150-200A 10 feet. It confuses me greatly.

Bruthal

rampantbunny wrote: »

20-30A...Hmm, can you take a look at my calculations below and be critical where necessary?

2 Head-lights: (2 x 55W)/12 = 9.16A
4 Work-lights: (4 x 55W)/12 = 18.32A
6 Parking lights (4 x 21W + 2 x 10W)/12 = 8.66A (inc. trailer board)
6 Indicators: (4 x 21W +2 x10W)/12 = 8.66A (hazards inc. trailer board)
1 Horn: 20A (only because 20A used in car it was taken from)
2 Cab-lights: 2A
1 Radio: 7.5A
1 Flashing Beacon: 2A

Total is about 77A...notice that the starter is not included in the above as it is indeed wired separately.
Add in some overhead (for expansion) and that comes to maybe 85Amps. Use a cable size with some leg-room and I figured 100A would be comfortable.

Your suggestion of 10 squared is 7AWG (3.66 Dia\10.5mm squared) - correct?
The links below indicate that 10AWG (2.58 Dia\5.26mm squared) wire can carry 100A for up to 20 feet.
http://www.offroaders.com/tech/12-volt-wire-gauge-amps.htm
http://www.rbeelectronics.com/wtable.htm

There are other tables dotted around suggesting a much heavier cable is required - more in line with your 7AWG estimate, but because of the above links it makes it seem like 7AWG would carry between 150-200A 10 feet. It confuses me greatly.

For the loads you have above, its unlikely you will have everything on together. But if you do want 100 amp capable, then use 25 square from battery to fuse box. From there its all final circuits according to loads.

The radio wont take near 7.5 amps. The horn you can disregard. If it was a 20 amp fuse, that doesnt mean it was taking 20 amps. Its use would be so infrequent anyway, i wouldnt count it in loading.

So 50 amps would cover everything in my opinion. And 10 square to fusebox would do that and more.

rampantbunny

robbie7730 wrote: »

For the loads you have above, its unlikely you will have everything on together. But if you do want 100 amp capable, then use 25 square from battery to fuse box. From there its all final circuits according to loads.

The radio wont take near 7.5 amps. The horn you can disregard. If it was a 20 amp fuse, that doesnt mean it was taking 20 amps. Its use would be so infrequent anyway, i wouldnt count it in loading.

So 50 amps would cover everything in my opinion. And 10 square to fusebox would do that and more.

That's great...will order some 10 square so. I've an in-line fuse holder that I plan to insert near the battery before running to fuse box. What size fuse would you use?

Bruthal

rampantbunny wrote: »

That's great...will order some 10 square so. I've an in-line fuse holder that I plan to insert near the battery before running to fuse box. What size fuse would you use?

You could try a 50 amp and see how that goes, and have a spare or 2:)

Make sure you get the flexible multi stranded cable. You need good connections onto it such as lugs as well. 12v connections carrying a decent bit of current need very good connections.

rampantbunny

robbie7730 wrote: »

You could try a 50 amp and see how that goes, and have a spare or 2:)

Make sure you get the flexible multi stranded cable. You need good connections onto it such as lugs as well. 12v connections carrying a decent bit of current need very good connections.

Excellent, I've been waiting your call
True, could try 50Amp but was hoping for a one stop sort of effort here. What is the cable actually rated for?

And ignoring my complete ignorance, what constitutes good connections? Googling "lugs" I see this http://www.asklug.com/terminal-lugs-2.html (I've no commercial interest in the company) - these the lugs you speak of?

Bruthal

rampantbunny wrote: »

Excellent, I've been waiting your call
True, could try 50Amp but was hoping for a one stop sort of effort here. What is the cable actually rated for?

And ignoring my complete ignorance, what constitutes good connections? Googling "lugs" I see this http://www.asklug.com/terminal-lugs-2.html (I've no commercial interest in the company) - these the lugs you speak of?

10 square would be good for about 60 amps in an automotive application. If you think you might expand or want extra headroom, you could use 16 square flexible, which might be better as it wont be much dearer for such a short run. And still use a 50 amp fuse. But you can use bigger if that goes.

Yes they are lugs you linked. They allow you to bolt on the cable to whatever your connecting to. They are sized by the cable size and bolt hole.

You will need small ones for the negative connection of circuits to connect to the tractor chasis (ground) probably by drilling and tapping. So a lighting circuit for example would go from the fuse, to switch/relay, then bulb, and out of the bulb to the frame beside it via a suitable lug.

So various lugs, a crimper, bolts, and (taps if required) will be needed.

Good connections means good solid and tight terminations.

rampantbunny

robbie7730 wrote: »

10 square would be good for about 60 amps in an automotive application. If you think you might expand or want extra headroom, you could use 16 square flexible, which might be better as it wont be much dearer for such a short run. And still use a 50 amp fuse. But you can use bigger if that goes.

Yes they are lugs you linked. They allow you to bolt on the cable to whatever your connecting to. They are sized by the cable size and bolt hole.

You will need small ones for the negative connection of circuits to connect to the tractor chasis (ground) probably by drilling and tapping. So a lighting circuit for example would go from the fuse, to switch/relay, then bulb, and out of the bulb to the frame beside it via a suitable lug.

So various lugs, a crimper, bolts, and (taps if required) will be needed.

Good connections means good solid and tight terminations.

I've got spades and ring connectors for the smaller gauge wires already so off to get some lugs.
Thanks for the excellent pointers once again Robbie7730.

Bruthal

rampantbunny wrote: »

I've got spades and ring connectors for the smaller gauge wires already so off to get some lugs.
Thanks for the excellent pointers once again Robbie7730.

No bother. Just dont forget to get the very flexible cable for automotive usage. Stiffer cables would fatigue and break from vibration.