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Old 05-28-2016, 02:48 PM   #1
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1971 27' Overlander
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Can I change the wiring in the breaker box?

The photo shows the box wiring in my '71. Is there a reason for the black shore power wire to connect to the 30a breaker? Can I rewire to match the set up shown in the diagram?

This looks straightforward, but electrical is not my area of expertise, and I would not do this without someone looking over my shoulder.

Any help is greatly appreciated!

Alan
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Old 05-28-2016, 03:51 PM   #2
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You need to have a main overcurrent protection device (30a main circuit breaker) when there are more than two cricuits. In the picture at left that is the 30a breaker.

If you rewire as shown in the right hand diagram you will have no main circuit breaker.
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Old 05-28-2016, 04:40 PM   #3
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Quote:
Originally Posted by TennTex View Post
The photo shows the box wiring in my '71. Is there a reason for the black shore power wire to connect to the 30a breaker? Can I rewire to match the set up shown in the diagram?

This looks straightforward, but electrical is not my area of expertise, and I would not do this without someone looking over my shoulder.

Any help is greatly appreciated!

Alan
To elaborate on Mark Doane's response, your trailer is rated for 30 amps maximum current. As Mark says, the 30 amp breaker is between your external power and the buss bar which feeds the 20 amp circuit breakers.

The way you are currently wired, the 30 amp breaker protects your electrical from too much combined draw on all three 20 amp circuits. Your trailer's wiring between inlet and breaker box is sized for 30A max draw. Ditto the shore power cord that came with the trailer.

If you bypass the 30 A breaker as suggested by the diagram, you could exceed the amperage rating of either or both your trailers' main wiring and shore cord, with possible unpleasantness following.

The wiring schematic you provide is for a sub panel, which would normally be protected by a breaker in the main panel supplying the current. This main panel breaker would serve the same function as the 30A breaker in your Airstream.
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Old 05-28-2016, 05:46 PM   #4
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There wiring diagram is for the Canadian market.
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Old 05-28-2016, 06:05 PM   #5
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Many thanks to both of you -

The service manual I have makes no mention of a main panel 30a breaker or any 30a protection upstream from the panel shown, either for the "Canada" version or for the "U.S." Your explanation of the need for such a breaker is clear, however.

What are the options for the 30a protection - is a "pre-" or "main" panel install the best way? I am trying to gain the additional circuit for the microwave. The circuits now are for rear outlets/outside/converter, front outlets, and ac.

Thanks again,
Alan
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Old 05-28-2016, 06:16 PM   #6
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It's fine the way it is, the 30amp is being used as the main breaker for the trailer. If you changed it to like the diagram your 30A rated power cord would have to rely on whatever rated breaker you were plugged into.
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Old 05-28-2016, 06:24 PM   #7
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If you want more circuit capacity. Install a larger electrical panel. You must use the 30 amp breaker in the new panel in the same fashion as the old panel in order to have the protection needed. Especially since you are adding a circuit for a microwave.
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Old 05-28-2016, 06:41 PM   #8
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If you want another circuit for the microwave:
Microwaves are 110 volts - you will need a inverter to go from 12 volts to 110.
If you come off directly off your batteries (through a inline circuit breaker) to the inverter - you will have 110 volts to the microwave.
Your converter will charge the batteries, and the batteries will supply the inverter, which will supply the microwave.
Mime is set up that way and works fine, hooked up to the shore or not!
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Old 05-28-2016, 07:59 PM   #9
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Quote:
Originally Posted by TennTex View Post
I am trying to gain the additional circuit for the microwave. The circuits now are for rear outlets/outside/converter, front outlets, and ac.

Thanks again,
Alan
Thanks for giving some detail on your objective--microwave circuit.

I am not familiar with the layout of your Airstream, although I had a 31' Sovereign from the '73 vintage, which almost certainly had the same components as yours. The breakers and converter were under the galley counter, making it relatively easy to add an outlet for a microwave.

The simplest solution, if you don't have a lot of alternating current draws, would be to plug the microwave into one of the two existing circuits. (The AC is on a dedicated circuit, and you probably don't want to put the micro on the circuit serving the converter) A smaller micro would be rated around 900-1000 watts, or approx 9 amps at 110 Volts AC. A 1500 watt unit, which might be rather large for your galley, would pull 13.5 amps at 110 volts.

If you have to have a dedicated AC circuit for the micro, you could look into a double circuit breaker of the same brand. These incorporate two circuits into the same die size. Most manufacturers make these as the necessity of adding a circuit in a full panel is a common one. You could start at Lowe's or Home Depot and, if they don't have the right breaker, then Platt Electric.

To add a circuit will require access to the wall cavity to run the wiring from your panel to the point of use. That could be the most work of the whole project as the wall cavities in Airstreams are full of insulation and there are cross members, detectable by those without x-ray vision by rows of horizontal rivits in the trailer interior.

Going the inverter route, as Silver Hawk suggests, is a possibility but you still need to run wires. If your Airstream is like my '73, it has one battery, so inverter option is limited by your battery unless you plan a serious systems upgrade. Many threads here discuss the intricacies of these major upgrades--which are really useful if you want to microwave while off grid. Very cool but expensive stuff, that.

If you aren't using the trailer off grid, the inverter option is probably too expensive to justify when compared to the cost of adding an AC circuit at the panel.

Note that adding an AC outlet in an area that has water service, like the galley, usually requires use of a GFIC outlet.

Good luck!!
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Old 05-28-2016, 09:12 PM   #10
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Quote:
Originally Posted by TennTex View Post
The photo shows the box wiring in my '71. Is there a reason for the black shore power wire to connect to the 30a breaker? Can I rewire to match the set up shown in the diagram?

This looks straightforward, but electrical is not my area of expertise, and I would not do this without someone looking over my shoulder.

Any help is greatly appreciated!

Alan
Looks like you have several good answers. If it were me, I would leave the 30 amp main breaker like it is. If you need one more circuit you could change out one of the existing 20 amp breakers to a tandem twin breaker (single pole 120v, NOT double pole 240v). Make sure to get one that is made specifically for your type of panel. There should be a label somewhere. Or, if the label is missing get the same brand and type as the existing breakers. (in your photo it looks to me like a Square-D type QO)

A breaker like the one shown here:
http://www.homedepot.com/p/Square-D-...20CP/100021761
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Old 05-28-2016, 10:05 PM   #11
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I'm grateful for all the responses and knowledgeable advice. You Forums folks are invaluable.

I guess I'll grit my teeth and put in a new panel, if the protective breaker has to be as it is. (If they make true twin breakers of this skinny little THQP type, I would try that route.) The box is in the bathroom cabinet, and my knees and back hurt just thinking about it. Rebuilding this trailer has surfaced my genetically-inevitable arthritis about 10 years early, I think.

A metal shielded run through the cabinets forward will be easy. GFCI receptacles have been installed.

I am still curious about the original setup. Where was the "overcurrent protection" then?
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Old 05-28-2016, 10:51 PM   #12
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Overcurrent protection device is just a general term that means a circuit breaker or fuse. In the picture you posted earlier, the 30a breaker is your main breaker, the same as the main breaker in your house.

In this installation, the power feeds in from the 30a power cord, flows "backward" through the 30a main breaker, and then flows to the main buss at the top of the breaker box and flows into the three other breakers and out to the A/C and other branch circuits. There is a jumper between the two main lugs at the top which feeds current to both side os the breaker box.

This is the conventional wiring method for most travel trailers.

In the diagrams you show in your later post, the first diagram (#11) does not have a main breaker beacuse, as I stated in post number 2, if you only have 2 circuits you do not need a main breaker. More than 2 circuits needs a main breaker.

Your second diagram is apparently for Canadian wiring standards. They are different than NEC (National Electrical Code) which applies in the US. By your member name and location I assumed you were interested in US wiring standards.
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Old 05-29-2016, 12:28 AM   #13
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You could add a small fuse box (like an air conditioner service box) below the breaker box to act as the main line protection and then use all four positions for trailer circuits.

(That is how I fused my inputs)


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