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Author Topic: Need opinions on wire size for 110 volt to inverter  (Read 3412 times)
junkman42
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« Reply #15 on: September 16, 2009, 12:32:08 PM »

The optimal terminal connection for low voltage cables is a proper crimp and proper soldering.  Wicking solder up the wire is not the proper way to solder terminal ends.  There is big difference between wire types and there suitability for crimp connectors.  One cannot paint a lot of the wiring options with one brush.  Tinned and stranded wire will out last and be safer than residential wire in a vibrating and flexing vehicle provided it is properly supported and terminated.  My take from many years of industrial wiring and NASA high reliability soldering.  YMMV.  Regards, John
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Sean
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« Reply #16 on: September 16, 2009, 12:32:47 PM »

So, I should use solid copper cable that will break with the flexing and potentially cause a fire when the conductor is only partially broken and it heats up?  Yes, the RVIA allows solid copper (romex), but is that really the best option for an RV?  Remember the RVIA  is a group of manufacturers who want to spend the least amount when building a product.


First off, I did not say to use solid wire.  To begin with, even NM (sometimes called by the trademark Romex) is stranded in #10 and #8, not solid.  Secondly, I said nothing about the RVIA, which is a trade group and has nothing whatever to do with 120-volt wiring standards, which are developed by the National Fire Protection Association (NFPA).

I recommend THHN, which is an approved material, is flexible and stranded, is smaller than any other approved wire, and has the best insulation characteristics.  This wire must be installed in a raceway; if you need flexibility there, ENT (often referred to as "smurf tube" because Carlon, the largest manufacturer, produces it in a bright blue color) is easy to run, flexible, and approved.  THHN in ENT is comparable in price to boat cable.  An additional advantage of THHN in ENT is that adding or modifying wires later on is a snap.

Lastly, I hear this "solid wire breaks" argument all the time, and yet, in spite of asking here many times over the last seven years or so, not a single person on this forum has ever seen it happen in a properly secured installation.  FWIW, the code requires stranded wire where vibration or movement will be an issue, for example, the generator must be connected to the first J-box with stranded.  No where in the code does it say solid is required or even recommended.  But you can't have it both ways -- if you want the convenience of using NM, you have to deal with the fact that no one today makes it in stranded below #12.  Note that there is no prohibition on doing so -- there just isn't enough of a market for anyone to make it.

As I said, "at the risk of opening ... [a] can of worms"...

-Sean
http://OurOdyssey.BlogSpot.com
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Full-timing in a 1985 Neoplan Spaceliner since 2004.
Our blog: http://OurOdyssey.BlogSpot.com
junkman42
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« Reply #17 on: September 16, 2009, 12:35:16 PM »

Sorry John Ed, I was typing while You were posting!  Spatial disorientation that comes with old age!  John
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kyle4501
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« Reply #18 on: September 16, 2009, 12:57:06 PM »

Wire size is determined by voltage drop & temperature rise.

Voltage drop isn't so big an issue when the power is cheap.

Temperature rise of the wires is wasted power in the form of heat. The larger the wire, the less power from the batteries goes to heat the wire.
Something else to consider is the insulation on the wire - you wouldn't want to have to replace the wire due to failed insulation . . . .

Power from batteries is one of the most expensive sources of electric power you will use. Doesn't it make sense to minimize wasted power?

Of course 'proper installation' is crucial to the success of anything.

Boat cable isn't UL listed (for use in an RV) because there is such a limited market to make getting the UL listing profitable to the wire manufacturer.
Especially when there are plenty of acceptable alternatives.

If one was to use boat cable, the wire terminations must be done according to the boat cable requirements. If memory serves, there are special requirements/ terminals for boat cable that makes connecting it to a standard outlet or switch difficult/ expensive . . .



If one has to ask basic questions concerning electrical wiring, it is best if they stick with code approved materials rather than try to make non approved materials work.
You shouldn't argue against the code unless you understand the basis behind it.

As long as you are a safe distance from anyone else, I don't care how you choose to 'do it your way'. However, I'd rather not be parked near someone when the 'superior' materials they used in their conversion start smoking due to improper installation.  Roll Eyes
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belfert
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« Reply #19 on: September 16, 2009, 01:06:31 PM »

So, I should use solid copper cable that will break with the flexing and potentially cause a fire when the conductor is only partially broken and it heats up?  Yes, the RVIA allows solid copper (romex), but is that really the best option for an RV?  Remember the RVIA  is a group of manufacturers who want to spend the least amount when building a product.

First off, I did not say to use solid wire.  To begin with, even NM (sometimes called by the trademark Romex) is stranded in #10 and #8, not solid.  Secondly, I said nothing about the RVIA, which is a trade group and has nothing whatever to do with 120-volt wiring standards, which are developed by the National Fire Protection Association (NFPA).

I recommend THHN, which is an approved material, is flexible and stranded, is smaller than any other approved wire, and has the best insulation characteristics.  This wire must be installed in a raceway; if you need flexibility there, ENT (often referred to as "smurf tube" because Carlon, the largest manufacturer, produces it in a bright blue color) is easy to run, flexible, and approved.  THHN in ENT is comparable in price to boat cable.  An additional advantage of THHN in ENT is that adding or modifying wires later on is a snap.

Can anyone explain why boat cable or wire is not approved.? How is a boat so much different from an RV?  My personal belief is that a stranded tinned wire like boat cable is superior to regular old stranded wire.  I have seen plain non-tinned stranded wire in my bus with lots of corrosion at the end.

For one thing, I simply have ZERO room for ENT conduit in my bus.  The boat cable runs in a space that would not accomodate conduit of any size.  It would cost me probably $1000 or more to rewire plus days of labor to rewire the whole bus.  I would have to rethink how the entire bus is wired and rebuild a bunch of stuff to make space for conduit.
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Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
Len Silva
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« Reply #20 on: September 16, 2009, 01:10:08 PM »

I agree with Sean (as usual) on all points.  However, I would strongly recommend that you have the battery cable ends crimped on by someone with the proper equipment.  The crimping tool must match the connector, (T&B, Amp, Burndy, etc.)  The tool with the proper die must be matched to the connector.

These tools cost hundreds, even thousands of dollars and will not be available at your local Home Depot.  When properly crimped the cable and lug will be fused into one solid mass.  There would not be any room for solder to flow in such a connection.

If you are using a hammer crimp or some other make do connection, then by all means, solder it. It will fail eventually but will last a lot longer than a poor mechanical crimp.
« Last Edit: September 16, 2009, 01:11:45 PM by Len Silva » Logged


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« Reply #21 on: September 16, 2009, 01:21:31 PM »

If one has to ask basic questions concerning electrical wiring, it is best if they stick with code approved materials rather than try to make non approved materials work.
You shouldn't argue against the code unless you understand the basis behind it.

The all started as a question about wire sizing for 110 volt AC.  I talked to two electricians who both agreed that 10 AWG should be plenty for 30 amps.  All of the ampacity tables say to use 10 AWG for 30 amps.  I wanted to get some opinions here.  I didn't want to spend twice as much for wire if I don't need to.  Now, if this was DC I would have no issue increasing the wire size.  I used the largest cables I could reasonably get (4/0) for the power feed to my inverter.

I wired my own house and it passed inspection.  I didn't cut any corners and I added more outlets and such than required by code.  The inspector said I did a really good job.

I spared no expense in wiring my bus where it made sense.  Everything on the DC side has heat shrink terminals where terminals are required.  I used Weather Pack connectors on all of the LED lights in case I ever need to replace one.

I'll rewire my whole bus if necessary.  I still fail to see how THHN with plain stranded copper is so superior to nice tinned stranded wire.
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Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
Len Silva
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« Reply #22 on: September 16, 2009, 01:25:26 PM »

Brian
 Boat wire is not approved simply because it is not approved.  Chances are 100% (IMHO) that it would be approved if tested.  The cost of approving it for the small amount sold is the only reason it is not approved.

That said, you can buy type NM in 8-2 or 8-3 stranded at any electrical house and it will cost quite a bit less than boat wire.  You might even find 8-4 with a single ground that I think would serve your purposes with a single run.  I don't think there would be any prohibition against running the in and out of the inverter in the same cable.  Sean?

The 10 ga will work and meet code.  Chances are that between the pass through current and battery charging, you will be right at 30 amps a lot of the time, it just seems good practice to go up one size.  Not a requirement, just a good idea.
« Last Edit: September 16, 2009, 01:30:04 PM by Len Silva » Logged


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belfert
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« Reply #23 on: September 16, 2009, 01:28:43 PM »

Sean, I used NM cable in 10 AWG to wire a circuit in my house.  Maybe I read your posting wrong, but you seem to be saying that it should have been stranded.  It most certainly was solid copper.
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Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
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« Reply #24 on: September 16, 2009, 01:31:48 PM »

Brian,

Right at the #10-#8 point is where most manufacturers go from solid to stranded.
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« Reply #25 on: September 16, 2009, 01:32:56 PM »

About that UL listing.  Lots of stuff has UL listing but it is not "approved" for a certain application.  I think the point is that stranded Marine isn't approved for RV applications.  I have not a clue as to why but I bet Sean does.

I guess the real question is has it been presented to the UL for listing and failed, or has it never been presented for UL listing for use in RVs?  My guess is nobody has asked the UL to list it for use in RVs since no RV manufacturer would go to the expense of using it.

Is there a listing of what the UL listing number means the product has been approved for.
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Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
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« Reply #26 on: September 16, 2009, 01:38:42 PM »

That said, you can buy type NM in 8-2 or 8-3 stranded at any electrical house and it will cost quite a bit less than boat wire.  You might even find 8-4 with a single ground that I think would serve your purposes with a single run.  I don't think there would be any prohibition against running the in and out of the inverter in the same cable.  Sean?

Would this be approved by NFPA 1192?  Do they make NM stranded in 12 AWG or 10 AWG?

The marine cable in 8 AWG is $185 for 70 feet.  Copper is just really expensive these days.
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Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
Len Silva
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« Reply #27 on: September 16, 2009, 01:51:34 PM »

Brian,

As I mentioned in a couple of other posts, 1192 has nothing to do with electrical.
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kyle4501
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« Reply #28 on: September 16, 2009, 02:20:41 PM »

The all started as a question about wire sizing for 110 volt AC.  I talked to two electricians who both agreed that 10 AWG should be plenty for 30 amps.  All of the ampacity tables say to use 10 AWG for 30 amps.  I wanted to get some opinions here.  I didn't want to spend twice as much for wire if I don't need to.  Now, if this was DC I would have no issue increasing the wire size.  I used the largest cables I could reasonably get (4/0) for the power feed to my inverter.

Did those electricians understand the finer points of using ac power from an inverter supplied by batteries?
What did the tables have to say about voltage drop?

That is why it is prudent to use larger wire.

BTW, 10 ga will get warm if you pull 30A, not hot, but warm.

The wire doesn't know the differance between AC & DC current.


I wired my own house and it passed inspection.  I didn't cut any corners and I added more outlets and such than required by code.  The inspector said I did a really good job.

A RV is a little different than a house . . . . If it was the same, why the questions?  Wink  Grin

I still fail to see how THHN with plain stranded copper is so superior to nice tinned stranded wire.

Depends on your definition of superior & the application;
If your concerns are -
- meeting codes for RV installation.
- a salt water environment.
- efficient use of financial resources is important.
- easily available resources.
- etc.


YMMV
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« Reply #29 on: September 16, 2009, 04:14:05 PM »

Okay, trying to quote Kyle was giving my PC fits.

I fail to comprehend how 30 amps of alternating current fed from a power plant is any different from 30 amps fed from an inverter.  I full well understand that direct current needs the largest possible wire and if this was DC I wouldn't hesitate to up the wire size.  I am planning to use 8 AWG now if I don't end up moving the electrical panels.

Yes, I wired my house, and if someone told me when wiring my house that I should ignore the ampacity tables and go a size bigger on the wire I would have asked questions too.

I am trying to get a copy of the National Electrical Code so I can read the section on RVs.  I'll probably be tearing out all of the electrical wiring in my bus before the weekend and redoing it.  I can pretty much assure you it is done to code other than the type of wire used.
« Last Edit: September 16, 2009, 04:39:13 PM by belfert » Logged

Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
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