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Old 02-14-2014, 01:53 PM   #71
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I wonder if we are misunderstanding each other...

Myron, the concern we have is on the flow of power between your battery and your inverter when you have a large load on the inverter. Is any of it passing through the 8AWG wire?

What I think you are saying is that the electrical connection from battery to inverter is a mix of 8AWG and 4AWG wire -- 8AWG at the battery, and 4AWG from the midpoint to the inverter.

If that is true, you do have a serious problem. 8AWG wire is only rated for 24A power transmission. If you have a 600W draw on your inverter, it's going to need over twice that. The 8AWG wire will get hot. I don't know how hot, but it wouldn't surprise me if it was wire-melting hot. It will almost certainly be "burn the insulation and any other nearby plastic" hot.

Or do you have 4AWG wire all the way from the inverter to the battery and the 8AWG wire, originally installed all the way to the battery, now only goes between the pre-existing electronics (converter) and a midpoint on the new 4AWG run you've put in? If that's the case, then I think you're safe.

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Old 02-14-2014, 02:02 PM   #72
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Originally Posted by MyronL View Post
Yes I read the manual (see my post #forty-seven and fifty-eight).
So you know that at full load (which you might never use) the inverter will draw 60 amps and blow the 50 amp fuse in the wiring you've added, right? The AGU fuse holder looks like a good design - it's just not enough capacity for the peak current that might flow in normal operation of the inverter.

I'm guessing the fuse holder is this one: Lightning Audio 4ga or 8ga AGU In-Line Fuse Holder The web page does not specify a current capacity, but if it allows more than 50 amps, why not put in at least a 60 amp fuse (which happens to be the highest in the Littelfuse AGU line)? Of course, if you never use more than about 500 watts, the 50 amp fuse will never blow so maybe it's not a problem.
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Old 02-14-2014, 02:22 PM   #73
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All this is making me appreciate the simplicity of only running AC devices when plugged into shore power....
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Old 02-14-2014, 02:40 PM   #74
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I've done a bit more reading, and now I'm less sure of whether or not it's a problem running 50A through 8AWG wire. The sources (I've seen it repeated in many places) that indicate the maximum capaity of 8AWG wire as 24A all note that it's a very conservative number. The same charts show the maximum capacity for 14AWG wire as 6A. I know house wiring allows 15A on 14 gauge wire. Is house wiring on the AWG scale? I think so... Is AC vs DC relevant for amperage rating? I don't think so...

And, I'm seeing lots of different numbers for current capacity from lots of different places.

And, Brian indicated that Escape used 8AWG wire for the converter, with a 50A fuse. So they seem to think that 49A won't overheat the 8AWG wire.

So, I'm no longer sure whether 8AWG is sufficient for 50A or not. Were it me, I'd play it safe. Either have somebody that I trust knows what they're doing install the inverter (or at least give me advice), or go with the worst case and use 4AWG where I might need 50A.
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Old 02-14-2014, 02:42 PM   #75
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My 4AWG wire runs from the inverter to that machine screw where the red wires converge in my picture. No farther. If that is a bad idea I will change it and continue the inverter line out to the battery. I really do not want to do that. Dbailey, might an option be to reduce its inline fuse (AGU fuse holder) to say, 30 amps?

On Page 2 of my users manual, "Comprehensive Protection" states the inverter automatically shuts down if the battery voltage drops below 10.5 V. or if the input voltage rises to more than 15.5 V. , or, if AC output overloads attached to the inverter exceeds its operating limits. Converter installed fuses max out to 50 and my in-line inverter fuse is a 50. How could I not conclude no wiring changes are needed?

It is the AGU 4ga input fuseholder and yes I deliberately chose the 50 over the 60 amp fuse. I cannot imagine using the inverter simultaneously for anything fuller than my laptop and a camera battery charger and (this is a real stretch)my 19 inch tv.

Corrales Dave loves his Cappuccino machine but me, I'll be sticking to my propane-fired Melita.
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Old 02-14-2014, 02:56 PM   #76
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Myron,

It is incorrect to state that the fuse is protecting the inverter; the fuse and circuit breakers protect the wire. Furthermore, the water pipe analogy does not work here.

The 8 gauge wire will happily provide as much current as you need, however it will heat up like the element on a stove. The current rating of a wire is intended, more than anything else, to limit the temperature so that it will not exceed the rating of the insulation. That is evident in the excerpt from the National Electrical Code table (attached) which shows current varies with insulation temperature rating.

This is a good site with ampacity ratings more appropriate to the PVC insulation that is likely in the trailer, and taking into consideration resistance for long runs: Amps and Wire Gauge - 12V Circuit

So when the inverter is drawing its maximum current (50A as limited by the fuse) the power distribution panel may draw up to say 40A (as limited by the circuit breaker). The 8 gauge wire will supply 90 amps. The wire will get hot, because the total protection (fuse and CB) are too high to prevent the wire from getting hot.

Hot wires are bad... unless it is a stove element.
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Old 02-14-2014, 02:56 PM   #77
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Originally Posted by MyronL View Post
Converter installed fuses max out to 50 and my in-line inverter fuse is a 50. How could I not conclude no wiring changes are needed?
This is really what's making me think those conservative capacity charts I was looking at are *way* too conservative...

So, I'm thinking you may be right. But, I lack confidence.

If anybody can educate me, I'd appreciate it...

The chart where I got the 24A number for 8AWG wire (reproduced in many places) can be seen here: American Wire Gauge (AWG) Cable Conductor Size Chart / Table -- that site notes that "The current ratings shown in the table are for power transmission and have been determined using the rule of 1 amp per 700 circular mils, which is a very conservative rating" (emphasis theirs). Now, I have no idea where that rule comes from. But judging from the fact that it rates 14 gauge wire at 6A, when we know housing code allows 15A in 14 gauge wire, suggests that their "very conservative" is far too conservative to be useful in this instance.

Now here Ampacity Charts is a chart that says if your wire is rated to 75 degrees C you can put 50A over an 8AWG wire. I don't know if I'd want to let the wire get that hot. If you restrict it to 60 degrees C you're limited to 40A. This seems to be in the standard that Escape has designed towards. Still, I find it a little concerning.
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Old 02-14-2014, 03:08 PM   #78
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Myron
Just trying to figure this out for myself, can you tell me the distance from the converter the batteries?

Doug
I may be missing it but I don't see where the distance of the run is used on either of the 2 charts you mention.
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Old 02-14-2014, 03:09 PM   #79
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Quote:
Originally Posted by thoer View Post
All this is making me appreciate the simplicity of only running AC devices when plugged into shore power....
...or not having any at all.
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Old 02-14-2014, 03:12 PM   #80
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Doug,

The ratings on the "ampacity charts" link are out of the NEC.

NEC treats 14 through 10 gauge as special cases, and they are quite conservative. Also, the expected wire length in a building is considerably more than a trailer, and I expect the NEC ratings consider voltage drop as well.

However, the quality/temperature of the insulation will vary. I would not be supprised if the (probably) PVC wire insulation in a trailer is on the low end of that scale. Conservative is prbably a good thing.

But even if you would go with the 50, or even 55 amps on 8AWG, Myrons installation is still a concern.

John
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