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Old 09-09-2016, 06:13 AM   #1
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15 amp vs 20 amp circuits?

I am installing a new WFCO WF8735 Power Centre/Charger in our 76 Trillium 1300 and replacing all the wiring. I will install a 30 Amp breaker for the Shore Power, but the manual indicates 20 Amp breakers for the remaining circuits. Is there a reason why they say 20 Amp instead of 15 like most house circuits? I will only be running a couple of circuits going to plugs and one for a small bar fridge.

I have a whole spool of 14/2 left over from house reno's so was hoping I could use it with 15 amp breakers.

Thanks!
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Old 09-09-2016, 06:28 AM   #2
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You should be able to use 15 amp breakers, obviously assuming you can find them. A 15 amp breaker is identical to a 20 amp breaker other than it will trip at a lower threshold.


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Old 09-09-2016, 06:53 AM   #3
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Originally Posted by CPW View Post
You should be able to use 15 amp breakers, obviously assuming you can find them. A 15 amp breaker is identical to a 20 amp breaker other than it will trip at a lower threshold.


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Thanks CPW, our local Lowes carries the double 15 single pole breakers for about $15 so that is the way I will go.
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Old 09-09-2016, 07:00 AM   #4
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The manual for the WFCO WF8735 says that 20 amp breakers is the maximum for the branch circuits.. see this excerpt form page two (highlighting added).

Use the appropriate rated breaker for the wiring, outlets, etc.

My Scamp (for example) has the 30 amp main breaker, one 20 amp for the A/C which uses larger gauge wire, and two 15 amp branch breakers for the five AC outlets.
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Old 09-09-2016, 07:35 AM   #5
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Thinner 14 gauge wire is much easier to work with and lighter in weight to boot. It has plenty of ampacity for the loads you describe and I find the breakers quite common in Wisconsin at least. Larger conductors have an advantage in reducing voltage drop in long runs, but that means full load runs of 75 or 100 feet, which are uncommon in a fiberglass trailer. I think the longest run in my scamp is about 7 feet. I do carry a 12 gauge extension cord for my detachable shore power; just some added protection since its subject to constant handling, rocks, footfalls, etc.

The only possible place I see the need for #12 wire is to run a huge air conditioner, larger than that from the factory. I have yet to see a common electric heater, coffee pot or microwave demanding more than 15 amps/1800 watts. Breakers are designed to handle the starting current overload of compressors, motors, etc.

Larger than necessary breakers trip at higher loads allowing more risk of fire.

I recommend 15 amp wires and breakers.

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Old 09-09-2016, 07:39 AM   #6
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Thinner 14 gauge wire is much easier to work with and lighter in weight to boot. It has plenty of ampacity for the loads you describe and I find 15 amp breakers quite common in Wisconsin at least. Larger conductors have an advantage in reducing voltage drop in long runs, but that means full load runs of 75 or 100 feet, which are uncommon in a fiberglass trailer. I think the longest run in my scamp is about 7 feet. I do carry a 12 gauge extension cord for my detachable shore power. The extra size provides some added protection since its subject to constant handling, rocks, footfalls, etc.

The only possible place I see the need for #12 wire is to run a huge air conditioner, larger than stock from the factory. I have yet to see a common electric heater, coffee pot or microwave demanding more than 15 amps/1800 watts. Breakers are designed to handle the starting current overload of compressors, motors, etc.

Larger than necessary breakers trip at higher loads allowing more risk of fire in the advent of shorts / arcs.

I recommend 15 amp wires and breakers.

Cheers, john
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Old 09-09-2016, 08:05 AM   #7
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Thanks gordon2!
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Old 09-09-2016, 08:06 AM   #8
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Thanks John, great info
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Old 09-09-2016, 09:19 AM   #9
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I always use 12 Gauge wiring and then I can use the 15 Amp breaker or even a 20 if I want. We built our own house and wired with 12 Gauge and even larger wire in certain kitchen receptacles. It Costs more Yes but I have never had a problem.

Here is a test: The next time you use your vacuum cleaner, feel how hot the cord when you are done. That is because of the thin wiring on that device.
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Old 09-09-2016, 01:02 PM   #10
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I would most definitely go with 20 amp circuits. A properly done 20 amp circuit matched with #12 wire poses no additional fire risk. You may at some point want to put additional loads on that circuit and then you will have the capacity to do so. ......Also if by leftover house wiring you mean solid wire, do not use that in a trailer. It will not hold up to vibrations like stranded wire does. And never use wire nuts for the same reason.
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Old 09-09-2016, 02:01 PM   #11
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gee Dave....

you better call Bigfoot and let them know.....

my 97 is wired with hard wire on the AC side of things...

FWIW BF used 15 breakers except for the AC (20)....ALL plugs were run on one 15A circuit....one plug intented for Microwave on it's own circuit also 15

I use wire nuts sometimes if I think I might change/improve things later....well taped up to mitigate the vibration issue

YMMV
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Old 09-09-2016, 02:21 PM   #12
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15 amp vs 20 amp circuits?

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Originally Posted by Dave W. View Post
I would most definitely go with 20 amp circuits. A properly done 20 amp circuit matched with #12 wire poses no additional fire risk. You may at some point want to put additional loads on that circuit and then you will have the capacity to do so. ......Also if by leftover house wiring you mean solid wire, do not use that in a trailer. It will not hold up to vibrations like stranded wire does. And never use wire nuts for the same reason.

I'm sorry, but I cannot say I agree with this. First, in a trailer, it is unlikely that any circuit would need more than 15 amps, unless one were trying to run an electric skillet, a coffee maker, and a toaster at the SAME time. Second, every camping trailer I have ever owned that had 120v AC circuits has used romex wiring with solid conductors, the same as would be used in home construction. Finally, wire nuts, if used, should always be enclosed in a box. A properly sized wire nut correctly twisted onto the wires it joins, especially if the conductors are solid and not stranded, is not going to come loose as a result of vibration. However, that does not mean I would recommend using wire nuts in a trailer.


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Old 09-09-2016, 03:10 PM   #13
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All my new circuits/wiring in my Scamp have been run with 12 gauge wire, because that is what I had on hand. I would have not had a problem running 14, especially if I had to buy wire. I have no wire nuts as I have terminated at, or run everything through, a device. And not in the back stab holes either, old school wrapped (properly) around a screw. Cause old school is how I roll.
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Old 09-09-2016, 04:07 PM   #14
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I'm sorry, but I cannot say I agree with this. First, in a trailer, it is unlikely that any circuit would need more than 15 amps, unless one were trying to run an electric skillet, a coffee maker, and a toaster at the SAME time. Second, every camping trailer I have ever owned that had 120v AC circuits has used romex wiring with solid conductors, the same as would be used in home construction. Finally, wire nuts, if used, should always be enclosed in a box. A properly sized wire nut correctly twisted onto the wires it joins, especially if the conductors are solid and not stranded, is not going to come loose as a result of vibration. However, that does not mean I would recommend using wire nuts in a trailer.


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I'm just expressing my opinion based on many years as a union electrician and 34 years of owning and remodeling sailboats. I have no doubt that some manufactures use Romex but that does not mean it is a good practice. Manufactures do lots of things to cut corners. They often use undersized wires too. I'm sure it will be OK at least until the warranty is up. You can do what ever you like on your own trailer but I personally would never use solid wire or wire nuts on my own.
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Old 09-09-2016, 04:31 PM   #15
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The factory wiring in my Scamp is both solid and stranded. The 12 volt wiring is stranded copper. The 120 volt is all solid conductor Romex. That said I don't really consider Scamp designers electrical experts, not that I have had any problems. Their wiring techniques are pretty average RV quality, somewhat messy, but safe.

It seems to me that the boating industry is more careful with wiring than the RV industry. Is that your experience?

John
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Old 09-09-2016, 04:56 PM   #16
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In a small trailer like that, with the short runs you have, there is no need for more than 15A circuits, or use for anything larger than #14 wiring. Any more is a waste of time and money.

20A circuits in trailers are only used for the A/C if you plan on having that.

With the '76 Trillium 1300 I rebuilt, I just used one 15A circuit, just as the original did. Sure they can load up lots of devices at once, but there is little likelihood of that.

I just wired in a trickle charger to the the 120V circuit to charge the battery. Simple and effective.

I did run a 12V circuits from fused distribution panels I installed.

This trailer is for my daughter, and it would be very rare to have it plugged in, other than at home.
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Old 09-09-2016, 05:01 PM   #17
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Originally Posted by Dave W. View Post
I would most definitely go with 20 amp circuits. A properly done 20 amp circuit matched with #12 wire poses no additional fire risk. You may at some point want to put additional loads on that circuit and then you will have the capacity to do so. ......Also if by leftover house wiring you mean solid wire, do not use that in a trailer. It will not hold up to vibrations like stranded wire does. And never use wire nuts for the same reason.
I too disagree with doing the 20A circuits, it is just unnecessary overkill.

Stranded wire is better for running, but costs a lot more, and is harder to properly connect in devices.

If you plan your circuits well, that there is no more than the feed and a load cable, you can connect you wires to the plugs, eliminating the need for wire nuts.
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Old 09-09-2016, 05:09 PM   #18
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Here is a test: The next time you use your vacuum cleaner, feel how hot the cord when you are done. That is because of the thin wiring on that device.
This is very true with many appliances that should use heavier cords. Lamps are often the biggest culprit, often being #18 wire at the most. This is why here at least we now must use arc-fault breakers in bedrooms here in Alberta, and I am sure elsewhere too.

If the runs were possibly real long, like in many big homes, then using #12 wire could be beneficial, but the longest run in a Trillium is about 12'.

However, if you were to run a #14 circuit right at the full 15A capacity, you would feel next to no warming on the cable if you felt it.

I am all for everything being built strong enough, with a bit of a safety factor built in, but am not keen on over-building......well, just because. Having had to tear out 100's of home owner projects over the years, it is rare to find a job where they did not either underbuild or build improperly, or overbuild it to the nth degree just to be sure. Cutting the bottom half of a joist out to run plumbing is just wrong, but a 3" spike every 2" nailing one stud to another is not needed either.
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Old 09-09-2016, 06:25 PM   #19
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What would be the cost savings on a 12 foot run using 14 gauge vers 12 gauge?

Here i. The US we can purchase the wire by the foot at places like Lowes and Home Depot.

I really think the extra cost will not put someone in the poor house or on the street.
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Old 09-09-2016, 06:35 PM   #20
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I really think the extra cost will not put someone in the poor house or on the street.
Where do you stop? If #12 is better than #14 and only costs a few dollars more, why not #10, or #8 or #1?
You do what makes sense and no more.
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