AC Circuit Breaker Panel

With the installation of the Electric Hot Water Heater there was the addition of a circuit breaker and as the panel was full I replaced a single with a tandem. (A double circuit breaker that takes up the same space as a single). Turns out the panel accepted tandems, not all do, and that was a lucky break. But, as I dove in to it, it turned out this needed a little more thought.

First I’ll explain the circuit breaker panel. Even though I had a working knowledge of residential service panels, the inverter threw me for a loop and it took me some asking questions and eventually taking it apart to get my head around it. So here goes.

Interestingly enough, if you have an RV with 30A service, you have 30A. Three pins on the plug: hot, neutral and ground. If you have 50A service, you have 100A. Yes, four pins: 2 hot, 1 neutral and 1 ground. The two hots are EACH 50A, lets call them 1 and 2. So some users are on 1, some are on 2. What immediately becomes apparent is that it is important to spread the load between them. If you run 2 AC’s, a microwave and a hot water heater and a coffee maker on 1, and only a phone charger on 2…… 1 is going to exceed it’s 50A and POP goes the breaker, while 2 is totally not doing a thing.

So, how is the panel put together? When you open the lid you see a whole bunch of breakers in a row. But, they are not all connected to the same source… Here’s a diagram, depicting the situation as it came out of the factory


The two “HOT” leads from the pedestal OR generator come in on the left and go to a 50A breaker each, in the BACK side…. Yes, circuit breakers work in both directions, so it’s protecting the feed coming INTO the panel. They each power one of two steel bars that the other circuit breakers clip on to. As you can see in the diagram, they alternate. So, from left to right, the first user is the Front AC, on the bar powered by MAIN1, then the rear AC on the bar powered by MAIN2, the fireplace on 1, the inverter on 2, the washer and dryer on a tandem together on 1 and finally the block heater on 2.

Let’s talk about the INVERTER/CHARGER. If there is no shore/generator power it is fed by 12V DC and it makes 120V AC out of the DC and feeds it downline to a number of circuits. If there is shore/generator power, 120V AC passes through the I/C to those circuits, AND it takes 120V AC and makes 12V DC to charge the batteries. As you can see in the diagram above the AC 120V (if available) going in to the I/C is protected by a 30A breaker. To the right in the diagram you see a third bar which are the circuits powered by the I/C either by passing through 120VAC if on shore power/generator, or by making it from 12V DC. These circuits are the kitchen GFI outlets, the general outlets around the coach, the refrigerator, the bathroom GFI outlets (which on my 38A also power the outlets in the cockpit) and finally the microwave. (This also answers the question: “What is powered if I only have inverter power?”)

So let’s talk about load distribution again…… On shore power, wintertime = cold. MAIN1 supplies the front AC in heat pump mode, the fireplace and maybe the washer dryer….. MAIN2 is supplying the inverter  and the block heater. The AC passes through the inverter (with a max of 30A) and feeds all the outlets, the fridge and the microwave. It also charges the batteries. Summer = hot. MAIN1 = Front AC, Washer/Dryer, MAIN 2 = Rear AC and all the circuits on the inverter bus plus battery charging.

So now I want to add a water heater….. Originally I replaced the rear AC 20A breaker with a tandem. Then I took another look at that….. Summer: MAIN1 = Front AC, Washer Dryer. MAIN2 = Rear AC, Water Heater and all the circuits on the inverter bus…… Charge batteries, make coffee, fire up the Microwave…that’s a lot. In fact, rough math that’s 8A for the AC (running, starting is more) 12 for the Water Heater, 8 for the coffee maker, and another 15 for the microwave…. we’re at 43A and the battery charger, TV’s phone chargers etc etc aren’t counted yet…… So here’s what I did:


I put the tandem breaker on the MAIN1 bar and put both AC’s on there, and I took the single 20A and used it for the water heater on main 2. Summer: MAIN1 =AC-1 and 2, washer dryer. I MAY have to turn off one of the AC’s to run the dryer, but that’s only for a few minutes. MAIN2 carries the water heater and all the inverter circuits.  Winter: MAIN1 is front AC in heat pump mode and fireplace, which you may need to turn off if you want to run the dryer. MAIN2 the same as above plus block heater, keep an eye on the miscellaneous loads when using it. Nicely balanced.

ADD ON….. 11/17

Just to see what’s happening on the various legs I put some volt/ammeters in. Yes, this information is available outside on the SurgeGuard, but it’s a pain to run outside every time you want to check the load. I used two of these:

Screen Shot 2017-11-06 at 7.00.54 PM

They are easy to install other than having to modify the plastic box a little bit…… I could have put them in the bed itself, but they recommend keeping the lines as short as possible. Here’s the result. Top one is Main 1, bottom one is Main 2. NOTE: I installed, and recommend anyone else do the same, two in-line automotive fuses in the power feed for the gauges. 15A….. yes the fuses are DC,  and the gauges are AC but they WILL blow if the gauge starts frying for some reason.

Screen Shot 2017-11-06 at 7.31.46 PM

EDIT….. 11/17

Some VERY interesting developments. More in the “fixin” than “modifying” arena, but it concerns the panel, so I’ll just put it here.

Fellow Berk owner had the TANDEM BREAKER for the “general outlets” and “fridge” pop and fry on him. It happens. The space heater probably didn’t help. (See diagram above). No big deal, go to Home Depot and get  another one right? Not so fast. As I mentioned in the description of the addition of the breaker for the electric water heater SOME panels restrict the use of tandems by having a certain shape tab on the bus bar which does not accept a tandem with a rejector tab. Most of what you find at Home Depot et al has rejector tabs on the tandem breakers. The INVERTER SIDE of our panels does not accept CTL breakers……..Sooooo what Forest River uses here is known as a NON-CTL breaker…… Read about CTL HERE

Now you know.