25 or 30 amp main breaker on WF-8725-PB - Fiberglass RV


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Old 10-18-2017, 12:47 PM   #1
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25 or 30 amp main breaker on WF-8725-PB

My WFCO WF-8725-PB Black 25 Amp Power Center came in, so I ran over to Home Depot to get the breakers. I got a Square D 30 amp type HOM, and a Square D 15/15 amp type HOMT.

Then I checked the documentation again, and it says:

"One 30 Aac "Main circuit"........

and below it it says:

"UL-Listed Main Circuit Breakers, rated for 120 Vac, maximum 25 Aac"
"UL-Listed Branch Circuit Breakers, rated for 120 Vac, maximum 20 Aac"

So, does the main have to be 25 or 30amp?
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Old 10-18-2017, 01:08 PM   #2
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I have to admit the instructions have me scratching my head, but all the WFCO panels I've seen have 30 amp main breakers.
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Old 10-18-2017, 01:22 PM   #3
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After looking at the wiring some more I've decided to put a 20 and a 15 in. The 20 will feed the converter (4.4 amp) and 15 amp for several 120v outlets. The 15 amp will feed my AC.

I thought that the main breaker would be wired before all the branch breakers (and then 30 amp would make sense), but the way the thing is set up there is no difference between 'main' breaker and 'branch' breakers. They're all connected to the same bus.
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Old 10-18-2017, 05:16 PM   #4
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I received a private message on this and since I cannot post pictures there I've attached them here to explain.
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Old 10-18-2017, 07:11 PM   #5
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Here's a picture I just took. If I wanted the left breaker (main) to protect the other breakers (2 half ones on the right spot), wouldn't it make sense to get rid of the wire that is hooked up to the hot bar, hook up the 120V AC in to the main breaker on the left at the bottom, and hook up all 120V outputs at the 2 x 15 amp split breaker on the right?

That is assuming breakers work in both directions, because I would be feeding the shore 30amp into the 30amp breaker from the bottom instead of the top.
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Old 10-18-2017, 07:31 PM   #6
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Back wiring (the second schematic) the main breaker is standard practice.
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Old 10-18-2017, 10:49 PM   #7
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Ok. Go slow. This is high voltage.

If you use the main breaker separately in addition to the two smaller breakers, you will have a total potential amp load that exceeds the maximum for your distribution box.

The main breaker has to protect the entire distribution box from the loads being pulled by the two smaller breakers. The main breaker also protects the trailer-to-shore cord which is pulling all the amps from the shore power. The shore power should have its own breaker as well and the one you'll be plugging into will likely be 30 amps. But don't trust the shore power breaker that was wired by some campgrounds teenage helper that summer. So you definitely don't want a system that can pull more than 30 amps for that reason as well.

Each of the two smaller breakers protects the wires they are feeding.

The two smaller breakers should be no larger than 15 amps each.

If you put a 20 amp breaker in one of those small places you'll have to make sure that the wires leading from that into your camper is sufficient to handle a 20 amp load. That means a thicker wire than might be in there. Also, you will need to make sure that you have 20 amp switches and 20 amp outlets as well and those are different than the 15 amp switches and outlets that are standard.

The idea is that your breaker should never be bigger than the stuff it is protecting because you want the breaker to pop before one of those things pops. If your breaker is larger than the stuff downstream, then the stuff downstream is forced to act as a fuse so to speak and really ends up acting more like the filament in light bulb catching things on fire.

But don't take my word for this, I'm just some fool typing stuff on the internet. Research the h... e... double hockey sticks out of this stuff so that you're comfortable that you are your own expert it's not rocket science but it is science.
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Old 10-19-2017, 05:42 AM   #8
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I will go with the 30AMP main back wired, followed by a dual 15 amp breaker. However, look at this video: https://youtu.be/o_kEAvJWKiM?t=309. It's the same unit and it was wired in some RV factory the way the documentation describes: with the shore black directly on the main/hot bar, so the setup that we all agree is somewhat questionable.

I'm glad I questioned the documentation/instructions....
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Old 10-19-2017, 02:41 PM   #9
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Of coarse the main breaker and the other breakers are connected to the same buss. That is how you power the buss. Hook up the main breaker and turn it on and now the buss is energized so when you add breakers for branch circuits those breakers will have power and provide overload protection to the circuits they supply. You can turn off the main breaker and it will DE-energize the whole buss. It would be the same principle for your house. If you wanted to add a circuit or something to your house you would turn off the main breaker which would DE-energize the panel so it would be safe to work on. Of course if you don't feel comfortable working with electricity you might find somebody who is.
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Old 10-19-2017, 02:52 PM   #10
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Yes, that's what we all expect and how we all agree that it should be. But if you look at the diagram for the unit listed above (http://wfcoelectronics.com/wp-conten...ion-Manual.pdf) you see that shore power is fed onto the bus directly (see "BLACK WIRE (TO AC SHORE - HOT)"). That's what surprises everybody including me who has looked at this.

I will wire it correctly by feeding shore hot onto the 30 amp breaker instead, which in turn will feed it onto the bus, but that doesn't change what the manufacturer's wiring diagram shows.

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Originally Posted by Captleemo View Post
Of coarse the main breaker and the other breakers are connected to the same buss. That is how you power the buss. Hook up the main breaker and turn it on and now the buss is energized so when you add breakers for branch circuits those breakers will have power and provide overload protection to the circuits they supply. You can turn off the main breaker and it will DE-energize the whole buss. It would be the same principle for your house. If you wanted to add a circuit or something to your house you would turn off the main breaker which would DE-energize the panel so it would be safe to work on. Of course if you don't feel comfortable working with electricity you might find somebody who is.
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Old 10-19-2017, 03:44 PM   #11
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Your sure right about that wiring diagram being confusing. Kinda looks like the main breaker is half 30 amp and half 15 amp.
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Old 10-19-2017, 03:48 PM   #12
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It's a tandem breaker / 2 in one. It let's you jam twice as many breakers in that tight space...

Murray 30/15 Amp Single Pole Tandem Type MH-T Plug-In Circuit Breaker-MP3015 - The Home Depot

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Your sure right about that wiring diagram being confusing. Kinda looks like the main breaker is half 30 amp and half 15 amp.
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Old 10-19-2017, 03:59 PM   #13
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Never seen one like that. I have replaced some of the original ( fat ) breakers in my house panel with the slim line breakers but they were single breakers. Of course if hooking up the shore power right to the buss what good is the main breaker. It sounds like if you turned off the main breaker nothing would happen. Maybe somebody out there has actually worked on this brand of panel and can shed some light on it.
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Old 10-19-2017, 04:08 PM   #14
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If your trailer only has one or two 15 amp circuits then you are not required to have a main breaker. If your trailer service cord is 10/3 rated for 30 amps then you can have 2 -15 amp branch circuits (2x15=30) without a main breaker because the two circuits can not overload the 30 amp service cord. If you have 3 to 5 branch circuits in the trailer then you need a main breaker ( 30 amp ) in order to protect the 30 amp service cord.
Best practice is to install a main breaker.

I was a licensed electrician for over 40 years and if your looking for good electrical advice , I would listen to Jon Vermilye. He knows what he is talking about and is not a Wiki expert . He is a genuine , well educated and extremely smart electrician .
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