solid vs stranded wire for 12 volt

[Michael W]

You definately want to use stranded wire in mobile applications. Mark Nemeth's 12 Volt Side of Life website offers lots of tips on 12 volt system design and contains a handy chart to determine the approprite wire gage for the anticipated circuit maximum current draw. As an added safety factor, I always upgage one wire size and then protect the circuit with a fuse rated just above the maximum anticipated current when all loads on that circuit are energized at the same time.

http://www.ccis.com/home/mnemeth/12volt/12volta.htm

[bdosborn]

In my house the lights and most of the oulets are 14 gauge wire except in the kitchen, and the pool circuits which are 12 gauge.


So even if its free using very large wires bigger will cause problems. Use 12 gauge for an A/C or heater larger than 1800 watts. Voltage drop in a 12 to 15 foot trail is minor.

Dan

Remember that the wire has to be protected by a circuit breaker. In most commercial applications, 20Amps is the minimum circuit breaker size. Residential use is about the only place where you find a 15A circuit breaker. So, unless you install a 15A circuit breaker in your trailer (always a good idea), chances are that the circuit breaker at a camp ground will not protect a #14 wire from an overload. This is especially true since the NEC requires a 20A receptacle for RV power. I'd use a #12awg minimum for 120V shore power. Also, a #14 wire is rated for 15 amps but small molded case circuit breakers are only rated for 80% of the nameplate ampacity, meaning you should use a #12 for a load larger than 1440 watts and a #10 for a load larger than 1920 watts, etc. Fuses are 100% rated so you can size the wire at the same rating as the fuse.
Persnickity Bruce

[Cutterpup]

I can not say this enough! We do not need to build our trailers so heavy, so overloaded with with extra's that we going to need a Kennelworth tractor to move them! Our trailers are not commercial applications they are place to sleep and cook. Further do not rely on the campground circuit breaker to prevent an overload on your trailer, it's to protect the campground. I.E. when your trailer burns to the ground from an overloaded circuit, bad wiring or anything else, they can say well our wiring was installed correctly! As for circiut breakers less than 20 amps just look into RV supply companies such as this one:

http://www.dyersonline.com/p-16601-10-amp-circuit-breaker-wi.aspx

Persnickity Bruce, Your point about breaker are rated at only 80% is new to me

From: L. W. Brittian, Mechanical-Electrical Instructor

CIRCUIT BREAKER AMPERE RATINGS

Circuit breakers have an ampere rating (typically marked on the end of the operating handle). This is the maximum continuous current that the breaker can carry without exceeding its rating. As a general rule the circuit breaker’s ampere rating should be the same as the conductor’s ampacity. In other words we would not want to put a 60 amp breaker on a 10 amp wire. Breakers are tested in open air, with a temperature of some 40 or 50 degrees C.

So again I say build it to what is needed not so over the top.

Dan[/url]

[GeorgeTelford]

Hi Dan

I have heard this 80% expressed before, its true after a fashion an MCB depending on type needs up to 5 times its current rating to trip (thats a Type B)

so a 10 Amp Breaker needs 80% more to blow.

The following is a link to a UK electricians guide, but MCB's operate the same the world over.


http://www.tlc-direct.co.uk/Technical/Distribution/Mcb.htm

[Cutterpup]

George, I went to that site and the way I read it it takes 3 to 5 times the current to pop the breaker and some take even more. So when you overload a circuit for a short period of time such as when an A/C starts up the breaker has a lag time before poping. This is not the same as a slow increase of load where as the breaker starts to over heat and then pops to keep from damaging the circuit. So again, lets not put larger than necessary equipment into our trailer!

From the web page:

The level of this magnetic trip gives the MCB its type characteristic as follows: - ·

Type B - trips between 3 and 5 time full load current

Type C - trips between 5 and 10 times full load current

Type D - trips between 10 and 20 times full load current

Apart from compliance with the Wiring Regulations, which is the subject of another sheet, the importance of the "types" is to ensure that the MCB does not give unwanted tripping when a device it is protection is started up.

Dan

[bdosborn]

Persnickity Bruce, Your point about breaker are rated at only 80% is new to me

Dan

Dan,

Let me rephrase the last part of my post:

Also, a #14 wire is rated for 15 amps but small molded case circuit breakers are only rated for 80% of the nameplate ampacity, meaning you should use a 20 amp CB for a load larger than 1440 watts and a 30 amp CB for a load larger than 1920 watts, etc. Fuses are 100% rated so you can load the wire at the same rating as the fuse.

Sorry for confusing everyone.

Now to muddy the water even further, will an 80% rated CB trip at 80% load? Probably not. The 80% rating is used because circuit breakers are tested at 100% ampacity in free air, meaning there's lots of air to cool the CB. The 80% rating is an NEC restriction designed to prevent over-heating and nuisance tripping of enclosed breakers and breakers in panelboards and switchboards, which may experience a heat build-up due to air-flow restrictions and the thermal contributions of other breakers.

So get to the point, right?

The reason I used #12 with a 20 amp CB is because all the receptacles in campgrounds are required to be 20 amp. Why not rate everything for 20 amps and then you don't have to worry about it? The difference between a #12 and a #14 is pretty minimal and I don't have any difficulty terminating until I get into the #10 and larger sizes.


Bruce

[Cutterpup]

Bruce, don't get hot under the collar. Just show me a specification or a regulation fron NEC or CEC or anything else that proves that circuit breakers are only rated at 80% of stated ampacity. As for the campgrounds are rated at 20 amps does that mean that they are only giving you 16 amps of power before they trip?

Dan

[bdosborn]

Bruce, don't get hot under the collar. Just show me a specification or a regulation fron NEC or CEC ...
<snip>
Dan

Me hot? No way. And don't expect a straight answer. Here's as straight as it gets:

Here's the NEC sections:
II. Branch-Circuit Ratings
210.19 Conductors — Minimum Ampacity and Size.
1) General. The ampacity of branch-circuit conductors shall not be less than 125 percent of the designed potential load of utilization equipment that will be operated simultaneously.

210.20 Overcurrent Protection.
Branch-circuit conductors and equipment shall be protected by overcurrent protective devices that have a rating or setting that complies with 210.20(A) through (D).
(A) Continuous and Noncontinuous Loads. Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load.

Exception: Where the assembly, including the overcurrent devices protecting the branch circuit(s), is listed for operation at 100 percent of its rating, the ampere rating of the overcurrent device shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.

Here's an interpretation:

Branch and Feeder Circuits
For branch circuits, NEC 210.19 states the rules for sizing conductors. The general rule is that conductors are sized to have an ampacity of not less than the noncontinuous load plus 125 percent of the continuous load. The corresponding rule for overcurrent protection is given in NEC 210.20(A). It states that the OCPD rating is to be not less than the noncontinuous load plus 125 percent of the continuous load. According to the definition in Article 100, continuous load means that it continues for 3 hours or more. Similar rules for feeders appear in NEC 215.2 and 215.3. Two points are clear:

• Ampacity of the conductors is matched to OCPD rating by the same rule.

• OCPDs are sized for 125 percent of continuous current, which means that they are expected to carry continuously 80 percent of rated current.

Those points don't seem that clear to me but there you have it.
Bruce

[Cutterpup]

Bruce, your right the rules are as clear to me as the missisippi mud


But I still say we don't have to overbuild over engineer everything, and yes I do have 12 gauge wire for my Refrigerator and water heater (500 watts) the rest of the trailer is 14 gauge for 120 volts and 16/18 gauge for 12 volts.

HOWEVER:

Everyone of these posts have a problem and therefor the trailer:

Make sure that you use only 12guage for outlets!!! All regular house wiring to outlets is 12guage!

Kerry

If you put in a water heater and a A/C you better have a 10 gauge wire or split the loads into two circuits each one dedicated to one appliance.

I ran #10 house wire under my tear, exposed, held on with clips/screws. The wire in quite stiff, the clips or a frame member are every 10 inches.... I'm not concerened..... if inside a wall,surrounded with insulation, I see no problem..

And all above are right on, it's the flexing that will kill it....

House wire (solid conductor) will vibrate just how long it takes, who knows. When (not if) it breaks hopefully it breaks on the hot side at the first connector not off one of the outlets shorting out the box (if grounded) or cause the box to be hot (120 volts).

I went to buy some wire for the AC side but the Depot was closed. I ended up just going to Wally World and buying an extension cord. I'll just cut it up and use that for the wiring.

Extension cords depending on thier construction can be used but most are 16 gauge or less! Which is only 10 amps!

You definately want to use stranded wire in mobile applications. Mark Nemeth's 12 Volt Side of Life website offers lots of tips on 12 volt system design and contains a handy chart to determine the approprite wire gage for the anticipated circuit maximum current draw. As an added safety factor, I always upgage one wire size and then protect the circuit with a fuse rated just above the maximum anticipated current when all loads on that circuit are energized at the same time.

Using larger wires and circuit breakers can result in a devise over heating and burn up possibly causing a fire before the electric loads trip the breaker.

And now for the one everybody should do:

I read that stranded is prefered because of the ability of the wire to flex and not break. Also the stranded wire tends to make more durable DC crimp connections. I think the most secure DC connection is strand wire, crimp and also solder.

DEE BEE

BUT NOT FOR 120V the solder can melt when the circuit gets hot!

Dan

[JunkMan]

I read that stranded is prefered because of the ability of the wire to flex and not break. Also the stranded wire tends to make more durable DC crimp connections. I think the most secure DC connection is strand wire, crimp and also solder.

DEE BEE

BUT NOT FOR 120V the solder can melt when the circuit gets hot!

Dan

I read a thread on a bus converters page a couple of years back concerning solid versus stranded wire. The general consensus there was to use stranded wire and not to solder it, because that makes it rigid, and therefore subject to the same problems solid wire has. One bus converter said that he never had a problem with stranded wire breaking, unless it had the end soldered, then it broke where the solder began. He never mentioned the solder melting. A good crimp connection was all that was needed.

[asianflava]

The general consensus there was to use stranded wire and not to solder it, because that makes it rigid, and therefore subject to the same problems solid wire has.

Kinda defeats the reason behind going with stranded wires huh?

[asianflava]

I went to buy some wire for the AC side but the Depot was closed. I ended up just going to Wally World and buying an extension cord. I'll just cut it up and use that for the wiring.

Extension cords depending on thier construction can be used but most are 16 gauge or less! Which is only 10 amps!

[quote]

I checked, the one I'm using is 14ga.

[Cutterpup]

asianflava I saw some in HD that was 10 gauge wire and 100 ft long.

The one you bought should be fine.

Dan

Be safe and keep a fire extingusher nearby. Its satifying to put out the other guys mistake.

[An Ol Timer]

Just what is the difference between a soldered wire termination and a crimped wire termination? They both make a transistion from flexible to solid and both will break at the same point which is where they become solid. The lacing and strapping of a wire to make it as solid as the connections and by not allowing it to flex is how you keep from breaking.

[bdosborn]

Using larger wires and circuit breakers can result in a devise over heating and burn up possibly causing a fire before the electric loads trip the breaker.
Dan

Dan,
I agree with the rest of your advise but I'm not sure about this.
The *only* thing a Thermal Magnetic CB is designed to protect is the wire, not an end device. As long as you use the right size wire with the right size CB, you should be okay. On the other hand, I agree that you don't want to throw a huge circuit in your trailer. I don't like spending my money on things I'll never use. Either way, thanks for the thread. I like this electrical stuff and my wife's just not into it. Go figure.
Bruce