View Full Version : Breaker questions

08-10-2007, 04:58 PM
Hello all.

I am working on a vintage Shasta travel trailer and I am slightly concerned about the electrical situation with it. It uses a normal 15 amp electrical hookup vs the large 30 amp that RVs now use.

I suspect the last owner put in this standard circuit breaker as a replacement for some other original fuse box or something. In any case, they put in two breakers, a 20 amp and a 15 amp. That would total over 35 amps being allowed to go through the wires before it would kick off. That seems excessive and a fire hazard.

I don't need to consume much power at a time so replacing the breakers to total 15 amps would be fine. The RV fridge is 1.5 amps on AC power according to a tech doc I found online and the 5000k BTU window AC I installed says 5.0 amps (I guess it may have a higher starting requirement? Anyone know?). I only have a small propane heater for it right now so I'll need to run an electric one as well. I have a way to safely run in an extra extension cord into the trailer to run an electric heater on seperately from the trailer's circuit if need be. A 1500w heater would use about 13-14 amps. Wouldn't be able to have much else going at the same time if I run an 1500w heater on the trailer's breakers if I change it to total 15 amps.

Now my question is this: Which way is better to do the breakers? Put in two single pole 7.5 amp breakers or put in a 15 amp double pole breaker, assuming a double pole provides 7.5 to each pole (or does it provide 15 to each totaling 30?). I just don't think it could handle 30 amps without being a fire hazard for the extension cord, and the electrical hookup between the plug-in and the breaker box where it splits off to 2 circuits. Or would 2 15 amp breakers be safe running off of a normal heavy duty household extension cord assuming I get a heavy duty extension cord?

I'm thinking, however, that RV parks should only allow 15 amp service on those normal household plugs. If thats the case I can leave in the 20 and 15 amp breakers since the breaker switch where they plug in would never allow them to get beyond 15 amps. However I'm thinking I should probably redo the breakers anyway since you never know when someplace might have screwy electrical hookups allowing 30amp service to go through 15 amp cords, though I should hope that wouldn't happen.

Any advice will be most appreciated.

Bob NH
08-10-2007, 05:35 PM
It doesn't matter if the total Amps of the breakers exceeds the Amps of the breaker on the supply. The following rules are important.

1. The breaker protecting the wires should not be larger than the ampacity of the wires.

2. The actual load in use at one time should not exceed the capacity of the wire and breaker supplying the load.

Don't mess with trying to find 7.5 Amp breakers. If you find them they will be expensive.

If you follow Rule 1 you will be safe.

If you follow Rule 2 you will not suffer the inconvenience of tripping breakers.

08-10-2007, 06:41 PM
I'll have to see if I can fine the wire gauge on the insulation. I guess I'll just put the old breakers back and just try to count my amps and hope the electrical hookup I use isn't over 15 or 20 amps which tends to be the lowest at an RV park or campground.

08-10-2007, 07:17 PM
The important thing, as Bob said, is that you don't feed a breaker with a wire that can't handle the load. Ensure that is okay, and you should be okay.

So, if the wiring going to the plug, for example is 14g, the CB should not be bigger than 15A on that leg.

08-10-2007, 07:48 PM
That is one factor I overlooked, I look into that also.

The factor I was considering is the wire between the socket that the extension cord plugs into and the breakers since that has to bear the entire load until it gets to the circuit breakers to be sent off on two separate circuits (2 breakers). That section of wiring is what I'm concerned about the most, more so than the wiring for the outlets/lights since it may not be any heavier gauge than the wire running to the lights and outlets.

I haven't verified the gauge of the wires yet so this is just speculation. If thats the case though, I wonder if I need to just redo the wiring in that small section or just count my amps and be careful about the load I put on it. I think I'd rather count the amps if I had to choose between the two.

From what I've been told, the GFCI outlets used at RV parks are 20 amp (but some may be 15 I think) so I'd end up kicking off that breaker before I'd get up too high anyway.

But what I mainly would like to know I guess for now, is if the wire gauge is fine as it is for a 15 and 20 gauge breaker, would that allow 35 amps max draw total from the power source its plugged into since its two circuits? Seems to me it would. One circuit would allow 20 amps and one would allow 15 amps, totaling 35 amps.

Of course the 15-20 amp breaker outside would kick off over 20 amps preventing that. Another factor is if I have to, at some point, use a 30 amp cheater adapter (which would allow me to plug into 30amp if there is nothing else available). It would then allow 30 amps max to be used in the trailer.

Looks like I just need to keep track of the amps I'm using so I don't overload the wires. Heating devices seem to be the largest constant drain I will be using at about 12-13 amps for a 1500w heater.

I'm just trying to be safe and fire-free so please forgive me for my confusion and rambling on. ;)

08-11-2007, 01:12 PM
I went out today and checked the wires that come off of the breakers at the top and they are void of any insulation markings. One is just black insulation, no markings and the other has a white fabric-like cover over I think black insulation.

They look to be identical gauge wire but I have no clue what gauge since there is no markings on the one without the fabric stuff over it. I have a long section of it visible too and I just don't see any markings. It's in a dark place out of light too (inside the breaker box) so it couldn't have faded off or anything. I guess I may just have to get a sample of the wire and have someone tell me what gauge it is. The gauge looks pretty small but I don't know if its 12 or 14 or something else.

08-11-2007, 02:40 PM
Oh wonderful. I just found this page:


Those are the breakers in the trailer. Looks like I need to completely replace the breakers and the box according to that page.

It's the exceptions that cause fires. An FPE circuit breaker will appear to "work just fine" in passing along current to the circuit it feeds, until there is an overcurrent, short circuit, or similar condition. When those exceptional conditions occur, this equipment fails to protect the circuit and the building from overheating and fires, in some cases at a failure rate around 60% of the time. I estimate that the normal industry failure rate on circuit breakers is less than .01%.

08-11-2007, 03:16 PM
On second thought, maybe I won't need to since I will be plugging into 15 or 20 amp service, which is what they are rated to. The one is 15 amp and if plugged into 20 amp service it could possibley overload if I don't count my amps but it seems to be they may be safe enough to use since they will be plugged into breakered electrical service, unlike the breaker in a building that is wired directly to the utility service outside.

Any thoughts?

08-11-2007, 06:37 PM
Unless both breakers connected to the same wire, a 15 and 20 amp breaker would not add up to a 35 amp load.

08-11-2007, 11:23 PM
On the outter wiring they are be connected together for bringing in the power between the RV hookup (a standard 3 prong outlet) and the breaker, not on the inside where it powers the lights and outlets.

Of course, the plug they're getting the electricity from an outlet that has a breaker of 15 or 20 amps (the RV park/campground's outlet) so it would kick off at whichever the breaker is. If I were to use a cheater adapter on a 30 amp plug it would then allow 30 amps max in but I would only do so if I had no other choice. In which case I would have to be especially careful in the power I draw.

What I think I may do so I can have extra amperage without having to redo the entire system is wire in a second 20 amp RV electrical hookup completely independent from the original system and lead it to a single, standard double outlet. Then simply use power strips with 15/20 amp breakers built in. It would be like simply having an extension cord entering the trailer and plugging into a power strip. The power strip's breaker would substitute an actual breaker panel for that second plug in.

Here is another question. Pretty much all RV parks have 30 amp service plugs in addition to the 15/20 amp. Supposing I got a cheater adapter which converts the 30 amp outlet to a normal 3 prong outlet and plugged that into the new system I suggested above, not the original one where I'm unsure of the wire gauge, would it be bad for the wiring even if I only use a total of 15 amps? Would the fact that its 30 amp service require anything being plugged into it to allow for 30 amp capacity (#10 wire gauge and 30 amp extension cord) or would that only matter if the devices plugged into it are drawing up to 30 amps?

For example if I plugged a 15 amp extension cord into the 30 amp hookup with an adapter and ran a 1500w heater from it (roughly 12-14 amp draw) would it be feeding 30 amps through the cord and outlet or only the 12-14 amps that the heater requires to operate?

I guess what I'm asking is does an outlet constantly feed the amperage it's allowed to provide per the breaker or does it only provide what is needed by the device that is plugged in? I would guess that it only sends the amperage that is needed but, I'm certainly no expert on the subject of this amperage and such.

I'm wondering if I should instead of adding a second 15/20 amp hookup if I should just put in a new 30 amp hookup from the get go (separate from the current system) and hook that up to a standard double outlet and use two 15 amp power strips on that for extra amperage. Although, is 30 amps safe to feed into a standard 3 prong outlet? I might have to then add a breaker (although the 30 amp service I plug into will be breakered). Hmm.... so many options and things to consider. I'm thinking I'd end up kicking the breaker if I used two 15/20 amp hookups at once since the outlet would be set for only 15/20. If I add and make use of the 30 amp service in addition to the 15/20 amp service I'll have more than enough amperage than I'll ever need at once. I won't risk overloading my original electrical system plus I'll have an extra 30 amps to use off of two power strips. But all of that will depend on if its safe to feed 30 amps into a 3 prong outlet or not.