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Author Topic: Need opinions on wire size for 110 volt to inverter  (Read 4009 times)
belfert
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« on: September 16, 2009, 08:59:30 AM »

If I get a new inverter it will require 30 feet of wire to get to my 110 volt electrical panels.

The input and output circuits will be 30 amp.  Is there any reason I need wire larger than 10 AWG for this?  The guy I will buy the new inverter from is recommending 8AWG due to the length, but that seems overkill and doubles the expense for the wire.  I can understand going larger if it was DC and not AC.
« Last Edit: September 16, 2009, 09:01:41 AM by belfert » Logged

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« Reply #1 on: September 16, 2009, 09:07:30 AM »

Hi Brian,

I ran 6 AWG from my inverter to the panel.   50A service/3000w inverter and about 9 ft. in length.

I would use the 8 AWG for your 30a service. Length= amps usage..

Good Luck
Nick-
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« Reply #2 on: September 16, 2009, 09:13:14 AM »

A better Idea...

Try and get the distance between your inverter and panel closer... You may have to rethink your layout.

Usually, most of your electrical equipment is located centrally in one or two bays and an interior panel not too far away from that.

Then your branch runs after the breakers can run the long distance runs.

Nick-
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« Reply #3 on: September 16, 2009, 09:21:35 AM »

I agree with Nick, move it closer if you can.  However, the distance from the inverter to the batteries is much more critical than the distance to your electrical panel.  Unless you can move the batteries as well, it's not a good idea.

8 gauge is the way to go, both in and out.  Consider that if your inverter is 30 feet away from the panel that is 60 feet when in pass through mode.

There are lots of tables on the net that will confirm that, or, you can just trust those who have the experience.
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« Reply #4 on: September 16, 2009, 10:28:56 AM »

Brian,

#10 is allowable.  However, as previously noted, bigger is better.  If the issue is raceway space, you could do #8 on the input side and #10 on the output side, since there will almost always be more current carried on the input lines if it is a charger-equipped model.

Also, remember that you can go one trade size smaller for the grounds.  So #8 hot and neutral with a #10 ground, or #10 hot and neutral with #12 ground.

If it were my installation, I would go with four #8 for the current-carrying wires, and two #10 for the grounds.  Anything you run from this circuit will thank you for the lower voltage drop, especially important if that includes a motor, such as an air conditioner.

JMO and FWIW.

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« Reply #5 on: September 16, 2009, 10:45:33 AM »

My currently broken inverter is mounted next to the electrical panels, but it is also some 25 feet from the batteries.  Yes, everything really should be together, but that doesn't always work out.  The battery cables are 4/0.  My batteries are all the way in the back of the bus.  I guess nothing says I couldn't move the current inverter if I fixed it.

If I get a new inverter it will be mounted next to the batteries in the back of the bus, but it means the AC cables will be longer.

I suppose I could move the electrical panels, but man would that be a lot of work to finish in a week by the time I ordered wire.  I also run into the issue of having to run the 50 amp service an extra 10 or 15 feet whcih might mean going to 4 AWG cable.  I suppose the cost of wire wouldn't be much different between the two options, but the amount of labor would be huge.  I also have the delimma of where to run all the cable and wire to the rear with minimal cabinetry and woodwork to hide it all.

It sounds like I really need to go with 8 AWG for the 110 volt for the new inverter unless I move the electrical panels all together.
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« Reply #6 on: September 16, 2009, 11:24:12 AM »

One of the issues was extra cost (double) for the 8 AWG cable and the second issue was do I really need 8 AWG.  They run 10 AWG for 30 amp circuits pretty far in houses all the time.

I have room for the larger cable.  I am planning to use flat marine cable with three 8 AWG conductors for this.
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« Reply #7 on: September 16, 2009, 11:32:14 AM »

I would probably rethink putting the invertor right next to the batteries. The out gassing of charging batteries is not very healthy for electronics. I am installing a 3500 heart. Manual says as close as possible, but op to 20' is acceptable. I am going to use welder wire for the connection between the two. Higher amp. carring cap. due to the braid, more flexible, and usually better insulated than battery cable. The connectors on the ends are also critical. Soldered ends make a better connection than the clamp on ones. Just my $.015 cents worth!! Cheesy Cheesy
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« Reply #8 on: September 16, 2009, 11:59:25 AM »

I have room for the larger cable.  I am planning to use flat marine cable with three 8 AWG conductors for this.


At the risk of opening the "boat cable" can of worms here, I strongly recommend you stick to NEC-approved and rated wiring materials for the 120-volt side.  That would not include marine cable.

... The connectors on the ends are also critical. Soldered ends make a better connection than the clamp on ones. Just my $.015 cents worth!! Cheesy Cheesy


With all due respect, soldered ends on battery cables are extremely dangerous.  Best practices call for mechanically secured ends.

The reasons are simple:  Ohmic heating of the cable (possibly exacerbated by other heat sources such as the engine, inverter, charger, etc.) can easily and quickly approach the melting temperature of the solder.  As the solder softens the conductors can move inside the fitting; in the case where there is any mechanical tension on the cable at all (not uncommon in battery installations), this can even go as far as the conductors pulling partially or fully out of the fitting.  That, in turn, can cause higher resistance in the connection, leading to even more ohmic heating in a vicious cycle.  A fire, electrical short circuit, or battery explosion could result.

The other reason is that the solder impregnates well into the stranding of the conductors, making the end of the cable unacceptably stiff and brittle.  In a moving vehicle, vibration and other flexing induced in the cable can actually cause the conductors or even the entire joint to fracture and break, again possibly leading to the above conditions.

Crimp your cables; do not solder.

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« Reply #9 on: September 16, 2009, 12:05:17 PM »

Brian,

What Eric and Len said.

Getting the inverter closest to the bats is the real issue and the wire costs between 4-0 stranded and #8 should prove that out at a glance.

House wire size is specified with temp rise as the issue....not voltage drop.  I have been told.  So saying that a given size "will do the job or meet the spec" is missing the mark.  Me thinks.  I have always been one to upgrade if possible.  I note that my house voltage goes down dramatically as the current draw approaches 30 amps.  Sooo, to avoid the normal deterioration that we associate with age, go bigger.

What I have done in the past is to NOT remove the original wire but rather run an additional wire of equal size in parallel.  By doubling the wire size you increase the wire "gauge" by three points.  So if you run the second wire the effective gauge would be #7 and that should tickle the pants off everyone.  And, it will definitely be cheaper and the added benefit is that you will be carrying a "hot spare".  Electronics tech joke, that.  That wire doesn't have to be in the same chase.  Also, make sure that when you take Sean's advice you make the NEUTRAL the same size as the hot lead and the unshielded GROUND is the one that can be downsized.  Probably knew that and that is not to say he wasn't clear....sorta like up sizing the wire....overkill on my part. Huh Grin Grin Grin

# 12?  #14?  total capacity for each config?

Good luck with your project.

HTH,

John

« Last Edit: September 16, 2009, 12:23:20 PM by JohnEd » Logged

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« Reply #10 on: September 16, 2009, 12:11:05 PM »

#10 is minumum for 30 amp.  Run #8 in case you add some more appliances. 
Listen to Sean.  He knows what he is talking about.

David
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« Reply #11 on: September 16, 2009, 12:11:16 PM »

I have room for the larger cable.  I am planning to use flat marine cable with three 8 AWG conductors for this.

At the risk of opening the "boat cable" can of worms here, I strongly recommend you stick to NEC-approved and rated wiring materials for the 120-volt side.  That would not include marine cable.

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.

The biggest complaint I have seen over the years on the bus boards is lack of UL listing for marine wire and cable.  ALL of the marine wire and cable I have used is UL listed.
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« Reply #12 on: September 16, 2009, 12:15:57 PM »

Getting the inverter closest to the bats is the real issue and the wire costs between 4-0 stranded and #8 should prove that out at a glance.

I already have the 4/0 cable installed and paid for.  I got the 4/0 cable for scrap price or less from a guy I know.  It is welding cable. 

I don't have any 10 AWG or 8 AWG cable.  The 4/0 cable needs to stay in place as I have DC distribution next to the current inverter.  I plan to relocate the inverter, but not the DC panel for now.  I will need to get a small amount of additional 4/0 cable to connect the inverter to the batteries at the new location.
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« Reply #13 on: September 16, 2009, 12:22:13 PM »

Sean makes very good points.  In practice, the soldered joint does not become more resistive with age and is the preferred method and is "old school" as well..  It does have a down side , as Sean mentioned, in that if not done properly, the stranded cable is stiffened.  But, the crimp/clamp joint will also have the stiffened point at the connector junction point.  Assembly technique is important.  You can't simply fry the connector and then apply a glob of solder(my method Grin Embarrassed).  Do that and the solder will get wicked into the wire an inch.  Heat it, apply the solder and make sure it filled the connector all the way around.  Applying the solder will lower the temp and slightly prevent excessive molten time and heat transfer to the cable.

The spec for all joints is "mechanically secure and electrically complete"...old school.  I would not use one of those clamping type terminals....too much corrosion over time.  Get the copper crimp type and crimp it before you solder it. You can enjoy the benefit of the soldered joint and not worry if the bat terminal connection deteriorates in the future and generates heat.  Make sure you put a wrap of vulcanizing tape on the seam/ joint of wire and connector and then wrap it with electrical tape for a vapor proof joint and NEVER any corrosion.

That is at least 3.5 cents,

John
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« Reply #14 on: September 16, 2009, 12:30:41 PM »

Brian,

I agree with you about the stranded but I don't have a tech/spec reason.  Just what I know is the reason for installing stranded in any location.  I think stranded is superior for any environment that has vibration.

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.

Having all the 4-0 you need gives you great flex. in siting.  Good for you.

John
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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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« 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
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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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« 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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« 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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« 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.
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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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« 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.
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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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« 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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« 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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« 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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« 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

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« Reply #30 on: September 16, 2009, 05:26:18 PM »

I would like to bring attention back to one point that got touched on and left behind and yet could become a very expensive mistake.  Putting the inverter next to the batteries if done in the same air space.

As was noted, the gases from the batteries will eat up the inverter's sensitive circuits.  The installation manual for several inverters warn against putting them in the same air space as the batteries and citing that reason.
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« Reply #31 on: September 16, 2009, 05:51:15 PM »

Had to send this one in. I am a lic. res. builder in SC. I hear the phrase built to code, it must be good all the time. Code is a basic requirement that covers minimal safety, and structure requirements. A good builder, electrician, plumber, etc. will exceed code almost every time. Experience has taught them that a little extra won't hurt, but a weak foundation, plumbing, or wiring is a costly fix every time. I say follow the code. If you feel that a heavier wire will suit your need better, then by all means go for it. After all, its you who is going to be sleeping in the thing!!!! I'll take my chances going over code requirements every time. !!!
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« Reply #32 on: September 16, 2009, 06:46:47 PM »

I would like to bring attention back to one point that got touched on and left behind and yet could become a very expensive mistake.  Putting the inverter next to the batteries if done in the same air space.

As was noted, the gases from the batteries will eat up the inverter's sensitive circuits.  The installation manual for several inverters warn against putting them in the same air space as the batteries and citing that reason.

The inverter will be very close to the batteries, but not exposed to the gases.
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« Reply #33 on: September 16, 2009, 06:59:31 PM »

Had to send this one in. I am a lic. res. builder in SC. I hear the phrase built to code, it must be good all the time. Code is a basic requirement that covers minimal safety, and structure requirements. A good builder, electrician, plumber, etc. will exceed code almost every time. Experience has taught them that a little extra won't hurt, but a weak foundation, plumbing, or wiring is a costly fix every time. I say follow the code. If you feel that a heavier wire will suit your need better, then by all means go for it. After all, its you who is going to be sleeping in the thing!!!! I'll take my chances going over code requirements every time. !!!

Bravo..... at least someone else thinks like I do!
Nick-
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« Reply #34 on: September 16, 2009, 08:15:44 PM »

Had to send this one in. I am a lic. res. builder in SC. I hear the phrase built to code, it must be good all the time. Code is a basic requirement that covers minimal safety, and structure requirements. A good builder, electrician, plumber, etc. will exceed code almost

The NEC covers so many things that I don't know how you can improve all that much.  You can add more (and better) receptacles, switches, and fixtures that code calls for.  I suppose you could anchor cable more often than required. 

When I wired my house I added more receptacles than code requires, but after I moved in I was wondering why I hadn't added a few more in some locations.
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« Reply #35 on: September 16, 2009, 09:09:11 PM »

You can only improve on the code if you have done the homework to understand why the code is there to start with, & that will take more than 2 weeks.

Just like improving your car's engine to make more power - If you don't understand how it works - you're just guessing.

Simply adding more outlets may cause other problems - like not enough breakers in the panel or having to increase the service entrance due to having too many circuts . . .

everything is connected. . .

If it were me, I'd leave what is installed alone - provided it was properly installed & protected by a correctly sized fuse or circut breaker.

Don't skimp on the base as it is so expensive to upgrade later.



BTW, DC is usually lower volts than AC, since power = volts * amps, the current at lower voltages will be higher than at higher voltages to provide the same amount of power.
AC voltage can easily be changed in a transformer - where DC doesn't work that way.

Wire tables are based on voltage drop & temp rise with an eye towards economy of materials.

What is best for YOUR needs can only be determined once your needs are fully understood.

Opinions are mostly useless if they don't take your intended needs.
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« Reply #36 on: September 16, 2009, 09:17:05 PM »

Brian,

Me too!  You would have to be pretty savvy to go beyond code for a good reason.  I am not.  That said, I have always installed wire one size larger than required.  Well, almost always.  I use more staples and I use positive clamps at the box penetrations.  I have only used those plastic boxes once in all the years that they have been available and not because the plastic isn't safe.  I also use silicone grease in my wire nuts because they support a better and longer lasting connection.  I always use my linemans to twist up the joined wires in a wire nut instead of letting the nut do it alone.  I guess I do go beyond in a lot of things, after all.  You got me thinking about that.

Code is a min and I think most meet it,

John
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« Reply #37 on: September 16, 2009, 09:23:57 PM »

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.


That's not quite how it works.  UL is a for-profit testing laboratory (and not unique; there are other labs, and the code recognizes many of them as legitimate listing sources).  Products are not tested as a category, IOTW, just because Rome Cable submits a sample of its Romex brand NM for testing, and UL finds it acceptable and assigns a listing number, does not mean that, say, Southwire can just market its brand of NM cable as being UL listed.  Even if Southwire's product is virtually identical to Rome's, it still must submit its own sample to a lab, the lab must do the mandatory tests to all applicable standards, and, if the wire meets the standards, it will be listed and be assigned its own, separate, unique listing number.

So in order for boat cable made by, say, Ancor, to be listed as Type NM (which would make it acceptable under the NEC), Ancor would need to send it to UL (or whomever) and pay, if you will pardon the pun, a boatload of money to have it certified to that standard.

Now, note that Ancor does, in fact, already pay UL a boatload of money to have the wire tested and certified to an entirely different standard, which is the one required for the marine industry.  That expense makes sense, because without that listing, they'll never sell any wire.  However, it makes no sense to spend the money on listing to the NM standard because no one will buy boat cable to wire a house, or a business -- you just can't justify the extra expense.  Even the commercial RV industry will generally not pay the premium for boat cable, because existing NM, at roughly 1/5 the price, works fine and is approved under the code.  So that leaves a handful of DIY busnuts who might be interested in buying this product if it had the proper listing -- not enough to justify the hundreds of thousands of dollars UL charges for the testing.

I wrote an entire article for Bus Conversions on this topic a few years ago, which I would be happy to repost here if anyone would like to see it.

Quote
Is there a listing of what the UL listing number means the product has been approved for.


UL listing numbers, as I wrote above, are unique to each item tested.  You can get the manufacturer, product, and standard for every UL number from UL.  However, wire is also required to be marked with its type approval, which is probably more useful information.  Boat cable, for example, is listed type "BDFX" and if you look that up, you will find the relevant standards and approved uses.  "Romex" and other brands of similar cables are listed Type NM, which is a specific standard within the NEC.  There are literally hundreds of listed "types" of wire; your shore cable is probably type SO or SJ (hard service or junior hard service cord), large battery cables are often type DLO (diesel locomotive cable), and most commercial wiring for branch circuits is done with type THHN, THWN, or THNN.  Note that many wires carry multiple type listings; it is not uncommon to see THHN and THNN together.  It is entirely permissible for a single cable to be listed Type NM and Type BDFX at the same time, but, to my knowledge, no manufacturer submits any wire to be listed to both of these types.

You might find this UL guide to wire and cable markings useful:
http://www.ul.com/global/eng/documents/offerings/perspectives/regulators/electrical/newsletters/W&CMG_April2007_Final.pdf

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.


Well, #10 is actually a dividing line of sorts.  Typically, NM up to #12 is solid, and many manufacturers start stranding at #10.  AFAIK, there is no solid #8 NM, it's always stranded.  Mind you, this is very coarse stranding, compared to the rather fine stranding of boat cable.  If you need the flexibility, either for installation reasons or due to flexing under way, then something like THHN with finer stranding is called for.

... 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?


Len, this is an excellent question, and I will have to research the code and get back to you.  Off the cuff, though, I will say it is not acceptable, if for no other reason than color coding.  The code requires the neutral for each circuit to run with the hot (so a neutral needs to run each way, to and from the inverter) and it also requires the neutral to be white (hot wires can be any color except white or green).  Since 8-4/wg would only have a single white wire, there's no way to meet the neutral color requirement.  In very large gauges (where wire is typically only made in black), the neutral and even the ground is permitted to be marked with colored tape at the ends, but this is not a legal option in the smaller gauges.

Your point that 8-3 NM is certain to be stranded and will be less expensive even than 10-3 boat cable is a good one.

BTW, FWIW, every wire that has failed in my coach has been a stranded wire that was, against my recommendation, soldered into the crimp, and the wires later broke off at the joint.  None of the solid wire in my coach has ever had any problem.

-Sean
http://OurOdyssey.BlogSpot.com

(Edited to add link to UL Wire and Cable Marking Guide)
« Last Edit: September 16, 2009, 09:32:19 PM by Sean » Logged

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