Need opinions on wire size for 110 volt to inverter

[HighTechRedneck]

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.

[Ericbsc]

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. !!!

[belfert]

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.

[Nick Badame Refrig/ACC]

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-

[belfert]

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.

[kyle4501]

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.

[JohnEd]

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

[Sean]

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.

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)