G

g zero

Well Known Member
Did some searching on the forums ,looks like 6awg wire is the prefered wire from the alternator , looks awful big ! Is a 6 wire overkill ?
 
40 amp or less alternator and 8 gauge is sufficient IMHO,
50 amps or higher alternator, use the larger wire for the B-lead.

This is for 12v systems. Nobody builds RVs with 24v electrical systems, else you could use smaller gauge wire
 
The way I read the chart is:

A 6ga wire can handle 70 amps continuous at 15 ft.

A 8ga wire can handle 70 amps continuous for 10'

A 10ga wire can handle 70 amps for 5.5'

Being that a more realistic length for the the 'B' lead in an RV is 3-4 ft and it generally will be less than 40 amps, you could really use 12 ga wire which is good for 50 amps continuous at 5' according to the bible (43-13, Chp 11, fig 11-2)
 
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Voltage drops

Walt said:
The way I read the chart is:

A 6ga wire can handle 70 amps continuous at 15 ft.

A 8ga wire can handle 70 amps continuous for 10'

A 10ga wire can handle 70 amps for 5.5'

Being that a more realistic length for the the 'B' lead in an RV is 3-4 ft and it generally will be less than 40 amps, you could really use 12 ga wire which is good for 50 amps continuous at 5' according to the bible (43-13, Chp 11, fig 11-2)
Click to expand...

Those are current handling numbers for a 1/2 volt voltage drop.

Depending on the way your Voltage Regulator is set up and where it's sensing location is, this 1/2 volt drop may not be good since this wire is a direct part of the charging system
 
az_gila said:
Those are current handling numbers for a 1/2 volt voltage drop.

Depending on the way your Voltage Regulator is set up and where it's sensing location is, this 1/2 volt drop may not be good since this wire is a direct part of the charging system
Click to expand...

Which happens to be one of the reasons I prefer the externally regulated B&C unit to the PP as it actually senses bus voltage as compared to voltage at the alt like the PP unit.

My point was mainly that a 6ga wire is overkill for most RV's with a short 'B' lead and current draws that likely average under 25 amps with a fully charged battery.
 
The voltage drop is only one consideration. A safety consideration is the temperature of the wire at continuous load. Wires in a bundle need to be larger because they can not dissipate the heat as easily.
AC 43.13-1B TABLE 11-9 gives the ampacity of different wire sizes. 12 AWG is rated between 13 and 25 amps, depending on the temperature rating of the insulation. A #12 AWG wire carrying 40 amps will be too hot to hang onto.
Joe Gores
 
Voltage drop is power lost even if an the regulator can compensate for it. I always vote for lower voltage drop if it can be accomplished without too much of a weight sacrifice. In this case the currents are high so the power loss is high (Power = Current * Current * Resistance) so I would go with the more conservative wire size.
 
May I suggest that you up-size to the next larger wire, just in case you end up changing the alternator in the future??

These planes are becoming more and more loaded with electronic dodads, and it never hurts to plan ahead.

The weight gains is almost nil..............
 
Walt said:
The way I read the chart is:

A 6ga wire can handle 70 amps continuous at 15 ft.

A 8ga wire can handle 70 amps continuous for 10'

A 10ga wire can handle 70 amps for 5.5'

Being that a more realistic length for the the 'B' lead in an RV is 3-4 ft and it generally will be less than 40 amps, you could really use 12 ga wire which is good for 50 amps continuous at 5' according to the bible (43-13, Chp 11, fig 11-2)
Click to expand...

On all of e planes I have wired, I use 8 gauge wire run to the panel for the bus. This is less than or equal to 10' and never was a problem. 10 would be too small and 6 is not needed. If you have a longer run, then 6 should be used.
 
Alt wire

Ran the big wires today , used 6 Awg for the Alternator.

Left the hangar thinking "I'm getting close ........"
 
Me too!

As has been said above. We new we had a 60 Amp. Alt. to start with and 6 gage would do the job even in a bundle. But most of the replacement Alt. that are out now, even to replace the new one we put on will be 70 Amps. or more. So We when with some wire we had to beg for, It specs in at 5 gage and is made for very though hot places. Doing that and putting a 60 Amp. breaker in the panel before the "B" lead go's the Buss, makes us feel about as safe as we are likely to get. Hope this helps. Yours as always R.E.A. III #80888
 
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