Wire Nuts, Parallel Batteries and other thoughts

[Arne]

One thing not mentioned enough, is mounting of the wire. I used romex in the ceiling because it was sandwiched into foam insulation. It can't move, so I'm not concerned about vibration.

If you look at page 10, second picture of my link, that is the longest stretch of wire not clipped and screwed. Notice that all wires have been taped together for strength.

How you mount/restrain the wire is just as important as the type of wire you use.

[Alphacarina]

The stranded is easier to work with and unless you are using the more expensive stab in receptacles, stranded is so much easier to wrap around screws. I think that is the only real reason to use it over something else.

You're obviously a better electrician than me - I hate working with stranded wire when it comes to screw connections - I have so little luck getting all the strands to stay under the screw heads that I usually solder some crimp-on spade lugs (I solder all crimped connections) to the ends so I can get a nice job of terminating it under the screws. I find the solid wire is a piece of cake to put under screw terminals

I think by code you must use either ring or spade lugs under screws for marine or aircraft electrical connections made with stranded wire - The connections have a way of working themselves loose if you don't

The only real reason to use it is because it's a better wire, handles more current (due to the 'skin effect' and the fact that stranded wire has lots more 'skin') is flexible and doesn't break and because it's required by code for most vehicular work

Don

[Alphacarina]

Miriam's 'proof' that stranded wire carries more current that solid wire:

Stranded vs. Solid Wire

"This one is a bit of a mind-boggler, but it's important. When electricity flows through a wire, it mostly flows on the surface of the wire, not through the middle. This effect is more pronounced on high frequency AC than it is on DC or low frequency AC. This means that a "wire" of a given size that made up of many smaller strands can carry more power than a solid wire - simply because the stranded wire has more surface area. This is one reason why battery cables in your car and welding cables are made up of many very fine strands of smaller wire - it allows them to safely carry more power with less of that power being dissipated as heat. However, this "skin" effect is not as pronounced in a typical 12V DC automotive application, and the wire and cable used there is stranded for flexibility reasons.

When looking at a chart or description of wire capacity, take note of whether it is referring to stranded or solid wire - some charts may not specify but instead assume a default based on the typical wiring used in a given application. For example, almost all automotive wiring is stranded while almost all home wiring is solid."

Don

[Alphacarina]

Well, by code you don't have to use a crimp terminal - But if you don't, the strands of the wire must all be soldered together

from UL508a standard

29.3.3 A connection to a wire-binding screw shall be made as follows such that no loose strands protrude from the connection:
a) Solid wire formed into a loop at least three quarters (270 degrees) around the terminal; or
b) Stranded wire that is:
1) Soldered;
2) Connected to a terminal provided with upturned ends;
3) Connected to a terminal provided with a cup washer; or
4) Connected to a crimped pressure terminal connector or eyelet;

I know from personal experience running a million miles of stranded wire installing systems for the Air Force for more than 35 years that they required a terminal on all stranded connections - Soldering the ends would not get past any of our inspectors

Don

[brian_bp]

Miriam's 'proof' that stranded wire carries more current that solid wire:

Stranded vs. Solid Wire

"This one is a bit of a mind-boggler, but it's important. When electricity flows through a wire, it mostly flows on the surface of the wire, not through the middle. This effect is more pronounced on high frequency AC than it is on DC or low frequency AC...

It appears to me that since 60 Hz is low frequency (in this context) and conductors for a few tens of amps are only a few millimetres thick, skin effect is irrelevant to household (or trailer) AC power wiring. I suggest the Wikipedia article on Skin Effect as a starting point if anyone wants to investigate the science more deeply.

I do agree that stranded wire makes sense for mobile applications at any frequency, but for flexibility rather than conductivity.



Also, like Don, I find stranded wire around screw terminals to be much more difficult to work with; it is also inherently less secure, as the individual strands shifting can allow the connection to loosen more than a solid conductor. The end of a stranded wire can be "tinned" (soldered) to address some of the concerns with terminations, but I realize that opens up a whole new can of worms. The crimped-on terminal still seems like the best solution to me.

[wlooper89]

I am very curious about the objection to tinning the ends of stranded wire. It seems to me this would help keep the strands together and prevent corrosion of the copper wire. I would also use a connector when possible. With ring connectors I crimp and then solder them. Whenever I have used crimping alone, the connections too often pull loose. Perhaps my technique is not the best, but it still seems solder makes the connection more secure.

With my Hubbell power inlet there were instructions not to tin the wires before inserting in the holes for them in the inlet housing. My wire was stranded and I used solder to tin them anyway. I am curious about the reason for this objection to using solder. Why is it a can of worms?

Thanks, Bill

[Arne]

tinning basically turns a stranded wire into a solid wire. where the transition takes place can be a problem if not properly supported.

I don't think it is a 'big deal', but it is a 'deal' and has to be taken into account.

[Alphacarina]

With my Hubbell power inlet there were instructions not to tin the wires before inserting in the holes for them in the inlet housing

The Hubbel connections are of the clamp type - Two metal plates piulled together by a screw and they are 'legal' for stranded wire without tinning the conductors together

True, the skin effect is much less at low frequencies like the 60 Hertz we use, but it's still a factor with any frequency and is one of the advantages of using stranded wire - It's one reason why high tension cables used for transmssion lines are always composed of bundled wire and not a single conductor

Don

[wlooper89]

tinning basically turns a stranded wire into a solid wire. where the transition takes place can be a problem if not properly supported.

I don't think it is a 'big deal', but it is a 'deal' and has to be taken into account.

Thanks Arne, now I better understand the objection about solder. After reading your post and thinking about it long and hard, I will probably continue to use solder in part because I do not have to pass inspections. For me the advantages outweigh the down side you mentioned, and the extra work of adding solder to a connector is not a problem because I enjoy doing it.

I believe that solder gives a superior connection. It protects from corrosion of the copper wire and of the connection shaking loose from vibration or being pulled apart. When possible I crimp and then solder. This works very well with ring connectors.

In many cases without using solder the stranded wire would be attached to a fixed point such as a screw, and the wire would still be going from flexible to fixed. The effect would be about the same in my opinion. Most of the connectors I use support the wire pretty well. With ring connectors that I use most, there is no difference at all because the crimp is behind the point where I apply solder.

These comments are not meant to convince anyone a particular technique is better, and I would say "to each his own".

Bill

[starleen2]

If you think you will have a vibration issue then by all means use stranded. Only you know how and where you will be towing. I take mine down some pretty washboard roads and it even survived I-20 out of Shreveport LA Although I wasn't sure for a while there.

I thought i was the only one who had that problem on I-20?

[Miriam C.]

If you think you will have a vibration issue then by all means use stranded. Only you know how and where you will be towing. I take mine down some pretty washboard roads and it even survived I-20 out of Shreveport LA Although I wasn't sure for a while there.

I thought i was the only one who had that problem on I-20?

Oh child! My truck took up a rhythmic bounce. Truth is the TD did better because the suspension is too soft. But the truck just bounced all over the place. I will never go that way again. We took the back roads home and they were great.

Now back to the thread.

[starleen2]

I’ve always tried to run a single length of wire to the receptacle to the main distribution box to eliminate any splices in the wiring. I also run my wires in snap together conduit outside the walls so i can inspect them if necessary. It just makes me feel safer.

[brian_bp]

True, the skin effect is much less at low frequencies like the 60 Hertz we use, but it's still a factor with any frequency and is one of the advantages of using stranded wire - It's one reason why high tension cables used for transmssion lines are always composed of bundled wire and not a single conductor

Those large transmission lines are at the same frequency, but running much higher currents and therefore much thicker conductors. With conductors having a radius only one tenth of the skin depth, I still see no relevance to trailer wiring requirements. It's just a red herring... in my opinion.

Also, a bunch of conductors bundled directly together are not independent conductors, so the other strands in the bundle can't be ignored. I believe that transmission lines use cables (instead of solid single conductors) only for mechanical reasons, not to reduce skin effect; I note that the Wikipedia page for Electric power transmission treats the entire multi-strand cable (up to 750 mm2 cross sectional area, or over an inch in diameter) as a single conductor for skin effect purposes.

[Larwyn]

How would one uncoil, support, string, sag, or otherwise work with a single conductor of 750 mcm. That would be a round buss bar which does exist in flat form but not for transmission or distribution purposes.....

[Steve_Cox]

I am very curious about the objection to tinning the ends of stranded wire. Why is it a can of worms?

Thanks, Bill

Bill,

Not a can of worms really, just a contextual misunderstanding I would guess that comes from the marine environment, which has very little to do with the RV environment.

In marine grade stranded wire each individual strand in the conductor is tinned with solder, when it is heated with a soldering iron the small tinned strands heat very quickly and some of the solder is melted up the wire away from the connection being made exposing bare copper to a sometimes harsh, humid and salty environment. That tinning of the wire was to protect the ends of the wire stripped for crimped terminals. Therefore, on boats I don't use a soldering iron and crimp on wire terminals cold. This is my opinion and not necessarily the opinion of this station or its subsidiaries.