Fusing question for main power cord - Fiberglass RV


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Old 03-14-2009, 09:20 AM   #1
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I'm thinking pretty seriously about removing the factory 50 amp cable from our (non-air conditioned) 13' Scamp and replacing it with a shorted pig tail sized for 20 amps. Some of us kicked this around here a few month ago in terms of installing a male connector where the cord door is now, and more recently I saw someone showed a pig tail with a twist lock sized for 20 amp service. I like that idea in terms of simplicity. So here is my question. On the odd occasion when I need to plug into a 50 amp receptacle with the appropriate adapter, there does not seem to be any circuit protection for my 20 amp feeder. When everything is sized for 50 amps, like the original setup, the circuit breaker in the pedestal provides protection. If I can plug into the (often worn out) 20 amp receptacle in the pedestal, then everything should be okay. However, plugged into the 50 amp receptacle, I may melt a power cord well before the breaker opens. This leads me to question the simplicity of this arrangement if I need to provide some secondary circuit protection. Any thoughts on this?

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Parker
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Old 03-14-2009, 10:52 AM   #2
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Parker, to my knowledge the power system on most travel trailers including the Scamp is a 30 amp not 50 amp unless someone has replaced it. Not sure what replacing the power cord with a 20 amp cobbled together design is going to accomplish except create a safety hazard. Why not just buy a couple of conversion plugs at and rv store or Wally World and you can plug the present system into 50, 30, or 20 amp. Maybe I am missing something.

Martin
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Old 03-14-2009, 11:36 AM   #3
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Parker, to my knowledge the power system on most travel trailers including the Scamp is a 30 amp not 50 amp unless someone has replaced it. Not sure what replacing the power cord with a 20 amp cobbled together design is going to accomplish except create a safety hazard. Why not just buy a couple of conversion plugs at and rv store or Wally World and you can plug the present system into 50, 30, or 20 amp. Maybe I am missing something.

Martin
Martin,

You're right. I just looked, and it's a 30 amp cord. What started all this is a desire to get rid of the heavy built in cable to free up the bench area for storage. Several have mounted receptacles on the side of the trailer to hook in an external cord, which is stored along with the hoses, etc. So the question is whether to stay with the monstor cable size that I don't really need since we don't have an air conditioner, or switch to a lighter 12 or 14 gage extension cord with appropriate connectors. Normally I would plug that into the 15 amp receptacle (or whatever it is) in the pedestal. Sometimes, however, that one doesn't work so I have to use the 30 amp one. Now that you've recalibrated me in terms of amperage, maybe this isn't the problem I thought it was. I just didn't want to be in a situation where the cord became the circuit breaker.

Parker
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Old 03-14-2009, 11:51 AM   #4
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What started all this is a desire to get rid of the heavy [b]built in cable to free up the bench area for storage. Several have mounted receptacles on the side of the trailer to hook in an external cord, which is stored along with the hoses, etc.
I think you'd gain a lot by making the cord removable using a mounted connector on the trailer's shell, but I would keep the 30 amp cord size. They do make twist-lock 30 amp connectors for this application.
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Old 03-14-2009, 12:10 PM   #5
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You have the electrical system protection backwards -- The circuit breaker is there to protect the CG wiring between the pedestal outlet and the pedestal buss bars, not the load. The wiring feeding the pedestal is likewise protected by a circuit breaker located elsewhere in a distribution panel in the CG.

The design process goes like this:

1. Figure the expected load.
2. Size the outlet to handle the load by meeting or *exceeding* it.
3. Size the wires to handle the outlet and distance from circuit breaker.
4. Size the circuit breaker/fuse to protect the wiring.

It's called *circuit* protection, not load protection.

The point of the design is to move problems from inside the wall to outside the wall.

At home, you routinely plug in small loads to much larger breakers, i.e., a 40 Watt light into an 1,800 Watt outlet (120VAC x 15 A = 1,800W)... If there is a dead short of 10 Amps on the outlet, the short's wiring will burn and the breaker may not trip EVEN IF IT IS A GFCI!!!! (As long as the short is hot to neutral, withot any leakage to ground, another neutral, etc.).

Thing is, it's hard to create a dead short without a reasonably high momentary spike in the current that is greater than the breaker's rating, so the 15A breaker normally trips, but if you plug both ends of a small gauge wire into your home dryer's outlet, you can likely let the smoke out of the wire without tripping the breaker. In fact, if you put yourself across the hot and neutral of a 50A circuit of 120/240VAC, you will likely smoke without tripping the 50A breaker.
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Old 03-14-2009, 12:11 PM   #6
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Fredrick is correct that their are disconnect connections available for the 30 amp cord at the Scamp cord input area. They can be purchased at Camping World or most boat and marine supply stores. About $80 for all the parts but they are a simple install and you are only going to buy them once. Probably twice the cost of the extension cord mod you are considering but much safer and will last the life of your egg. Got it on my Casita and one of the best conversions I have installed. When you can remove the cord and coil, storage problems are eliminated. Martin
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Old 03-14-2009, 12:14 PM   #7
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You may want to consider installing a marine 30Amp twist-lock male shore power inlet. Then you can store your power cord wherever you like and not have to lose space under your bench, or have to reinsert the cord into that stupid little compartment hatch which is always a pain in the ___!

I would agree with the other poster above that you should keep the 30 Amp cord, even if your power usage doesn't require it. It will help to reduce voltage drop caused by excessive resistance which is inherent to small gauge conductors. A lot of RV site power grids are marginal at best. Reduction of your current carrying capacity will only hasten the demise of your electrical appliances. Give them the full voltage/amperage they call for and they will be much happier.

Here's a couple of pics on my shore power inlet modification.

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Old 03-14-2009, 12:16 PM   #8
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I just disconnected my heavy 30A/120VAC shore cable from my breaker box (newer arrangements may go to converter box first) and replaced it with a short, heavy 15A/120VAC pigtail salvaged from a washing machine. I then use a heavy-duty extension cord to reach the power source, using adapters as required.

I gave my former shore power cable to a friend with a/c in his trailer and he put a female end on it to make a 30A/120VAC extension cable.
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Old 03-14-2009, 02:33 PM   #9
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You have the electrical system protection backwards -- The circuit breaker is there to protect the CG wiring between the pedestal outlet and the pedestal buss bars, not the load. The wiring feeding the pedestal is likewise protected by a circuit breaker located elsewhere in a distribution panel in the CG.
Pete,

I guess if I had thought it through, I would have come to a similar understanding, but certainly not so eloquently stated! I was thinking that the original heavy Scamp feeder was sized to match the current rating and circuit breaker on the pedestal, and that my plugging in a lower capability cord would be risky since it would let the smoke out before the breaker opened. I guess there are many examples of that, even plugging in a 120V lamp fed with zip cord at home. The only 120V items in our Scamp are the converter to charge the battery, the 3-way fridge, and occasionally a small cube heater, so 30 amp service is surely overkill for us. For that reason, I was thinking of doing the pigtail connector like you described in a later posting. I'm just not convinced I need a heavy male jack installation on the trailer for the small amount of power we use. Thanks for your comments!

Parker
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Old 03-14-2009, 02:39 PM   #10
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Here's a couple of pics on my shore power inlet modification.
Greg,

That's certainly a nice setup, and if we were in a 16 or 17 ft RV, I would probably do exactly the same thing. Since our power requirements are so modest, I'm not quite ready to make that leap. Ours is not so painful to use, but it wastes a huge amount of storage space. I plan to "fence off" the backside of the converter area in a manner that allows it to continue to cool properly, then will probably be able store much of our bedding under the bench. Thanks for posting. I'm sure it is helpful to anyone considering changing out the permanent cord setup.

Parker
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Old 03-14-2009, 03:48 PM   #11
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[quote]I would agree with the other poster above that you should keep the 30 Amp cord, even if your power usage doesn't require it. It will help to reduce voltage drop caused by excessive resistance which is inherent to small gauge conductors. A lot of RV site power grids are marginal at best. Reduction of your current carrying capacity will only hasten the demise of your electrical appliances. Give them the full voltage/amperage they call for and they will be much happier.

Here's a couple of pics on my shore power inlet modification.

Attachment 18444


I did a very similar modification on our Scamp 5er, but I have two shore-line power cords. One is the original 30-amp cord that used to feed through the camper wall with a 30-Amp twist-lock connector at the trailer end, the other is a construction-grade extension cord with the same type of connector.

We keep the 30-amp cord neatly zip-tied and stowed in one of the least accessible and hard to get to corners under the dinette bench, so w have it if we really need it.

Thus far we've never needed it.


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Old 03-14-2009, 06:31 PM   #12
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I have seen this at Bass Pro Shops for under $20.00 and it is one way to do what you are asking cheaply.

I agree though that I would use the 30 amp twist-lock set myself and I have on each trailer I have had.

There is nothing though about this one I picture that you would have to worry about given your stated needs.

https://www.berrylandcampers.com/rv-parts/p...?productid=4419

This is also made by the same company that makes the twist-lock models so it seems to be very high quality,just for simpler loads.
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Old 03-14-2009, 08:35 PM   #13
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The 30A[at]120VAC shore power cable is likely there to accommodate a/c, but I don't have one, and wanted to lighten my load, so there was just no point. All I have is lights, battery charger, cube heater and some small stuf like laptop, etc. I don't even have a fridge or a converter.
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Old 03-14-2009, 10:14 PM   #14
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Parker,

You can replace the stock 30A shore power cable with a 20A cable as you described, just make sure the 120V circuit breaker(s) in your camper are sized accordingly. You probably have two or three 15A breakers in your camper's breaker box. One option you might want to think about is to run all the 120V circuits through just one of the 15A breakers; that would provide protection to a 20A shore power cable.

Pat
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