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Okay so this is my first shot at this question, but not my first time trying to research the subject. I am in the process of designing a tiny house and have started thinking electrical. NOTE : I will be hiring a professional electrician to carry out the work but for now I'm looking for a better understanding of how this will all work.

Pretty much what I'm looking for is a sub-panel that will have two feeds powering it. One 20 amp regular heavy duty extension and one 30amp RV extension. Is it possible to have two feeds into a sub-panel like this? and have two separate circuits inside? My reasoning is for future purposes, either a small solar setup and even a generator during blackouts on the smaller 20amp circuit while keeping the 30amp on grid for our larger draw uses.

What kind of panel would i be looking for here? Or which direction should i be starting? Everything is 120V.

Again this is solely for my understanding as the builder and owner of the home but an electrician will be hired to do the work.

So are split sub panels with dual feeds a thing? thats my question

Running solely off a 30 amp service would be really really tight given what we need to run. Mostly propane for the larger pulls but no need for a 50amp 240 nor do we have that set up like we already do with an existing 30amp rv hookup on site. So it got me thinking the 30 amp taking some of the load off of that and putting it on a separate 20 amp feed and having both the 20 and 30 in the house at the same time yet separately...? if this makes any sense.

  • Hello, and welcome to Home Improvement. This sounds like you need a transfer switch, which commits you to use one source or another; in general you can't have both. And, you should probably take our tour so you'll know how best to participate here. – Daniel Griscom Dec 21 '19 at 2:23
  • I guess thats what im trying to avoid. What about two separate panels altogether? – Jason Baumel Dec 21 '19 at 2:25
  • Will the 30A supply be 120V (TT30) or 240V (NEMA 14-30)? – Harper - Reinstate Monica Dec 21 '19 at 2:27
  • 120v everything will use 120 the larger items are all running on propane – Jason Baumel Dec 21 '19 at 2:28
  • Is this tiny house on wheels, or a full foundation? – ThreePhaseEel Dec 21 '19 at 2:39
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Abosolutely not. There is no way to combine two feeders in one panel.

Look, I do this myself -- providing multiple services to a vehicle. In one case I have 23 x 120V@5A heaters, and I have a 50A/240V inlet driving 14 of them, six on a 240V/20A connection, and 3 on a 120V/20A connection. You can drive as many as you can plug in.

But they have to be completely firewalled. No connections.

Feeding a 240V split-phase panel, one leg with the 30A and the other leg with the 20A, is illegal and dangerous, not least, it will burn your house down. Not the tiny house, the big house. So that's right out.

Do it this way instead.

First, for the 20A circuit, you fit a 20A inlet on the underside of your building. Cable a single circuit from that inlet to red-colored receptacles in multiple locations around the tiny house. This system does not connect to the other system in any way, shape or form. Not at all. I would even get a red magic marker and red-stripe both side of the Romex involved so you know it's a different service. The yellow-red or gray-red Romex will be distinctive.

Second, have the normal service panel as you intend. This is powered by only the 30A/120V TT30 circuit. The various branch circuits come off it, etc. etc.

If the red socket situation doesn't appeal, you can have a red "second subpanel", but once again, they are effectively two services, and the hot and neutral wires cannot contact each other or interact in any way. I'm not a fan of this one because it's just asking for confusion.

Cool hack: Allow feeding the red circuit from the 30A

To do this, fit a common receptacle quite close to that 20A inlet. Power this recep from a dedicated 15A or 20A breaker in the service panel. Now, if 20A power is not available separately, simply install a 1' long extension cord from the outlet to the inlet. Voila!

Further cool hack: Be 120/240V ready

A main "breaker" is already mandatory. It is only there to be a disconnect, so its amperage doesn't matter. Go at least 50A (really, go 225A so you have enough breaker spaces, but I digress). Cable from a 50A/240V NEMA 14-50 inlet or short cable to the main breaker. To connect to a 30A/240V supply, use an adapter. To connect to a 30A/120V supply, use an adapter. These are readily available in the RV community. Any RV shop like RV World probably has them in stock. Or, you can build your own from a couple feet of proper cordage from the electrical supply house, and the appropriate plugs and sockets.

If you don't want to do that now, then buy the correct panel, and 6/3 cable if it'll be buried, and fit the TT30 as you planned. Then you can always upgrade later for just a few bucks, since you haven't painted yourself into a corner.

It is illegal to serve multiple circuits of the same voltage to a building.

You cannot, for instance, run two 120V lines out to a shed, of any amperage. You are expected to bring out one circuit of that voltage and split it with a subpanel. However, it's allowed if the second line is switched, on a solar/powerwall/generator and the other is not, or some other utilization issue like that.

To be clear, it's not allowed to a shed, barn, pumphouse, pool, spa, workshed, office, storage unit, gazebo, tennis court or garage. Fortunately, a tiny house on wheels is a vehicle.

  • That you very much that helped my brain out a lot here! Would two separate panels be acceptable? – Jason Baumel Dec 21 '19 at 6:38
  • @JasonBaumel Yeah, but don't spare the red magic marker! And I don't see a point to a second subpanel when the input is 20A. Actually no, I take that back, it seems to me like a PowerWall (or other onboard battery scheme) + a tiny house are a match made in heaven, so you might have the PowerWall-fed panel + the utility-fed panel that recharges the PowerWall. The PowerWall could smooth out your energy input, so when you surge, it borrows from the battery... – Harper - Reinstate Monica Dec 21 '19 at 6:41
  • Solar will eventually be the path for one of the circuits yes! And the second panel for the 20amp feed is just so i can control whats going on in the house when. it will only be running the fridge and some very small draw items like led lights and a constant fan inside the composting toilet and a few receptacles. – Jason Baumel Dec 21 '19 at 7:00
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No code doesn’t allow for 2 feeders. With mobile’s there are 50 amp 240v , 30 amp 120v or 15 / 20 amp 120v connections there is no other allowed services,

A detached building can have a multi wire branch circuit but this is a single feed, unless the 2020 code has a change that I doubt you can have 2 separate feeds and your best option would be to use a 240v 50 amp service that would be code compliant.

Now with that said could you feed the mini with a 120v at one location and 240 at another ? YES but not at the same time.

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Although not exactly designed with your intent a Reliance Controls Corporation 510C Pro/Tran2 https://amzn.to/2reouNE transfer switch might accomplish your intent. You can select at any time which loads are fed by generator, and which loads are fed by utility.

  • OP doesn't want to run either/or, wants to draw both sources at once. And those transfer switches are rubbish. You have to hook up like 40 wires, and the makers aren't very reputable. – Harper - Reinstate Monica Dec 21 '19 at 5:53
  • Those will operate both sources at once. I agree they are a pain to install, but you can run from both sources. After install as a test to display capacity of a generator you can connect and fire up the generator and switch individual loads to the generator while leaving the rest of the house on utility. – NoSparksPlease Dec 21 '19 at 6:15
  • Oh, now I remember what I hate the worst about those. They play fast-and-loose with the neutral. Seriously, their fat bundle (note how the whip is <2' long) only has one neutral wire in it WTH!!! It's supposed to have 40 wires. It only has 21. This is the core of what makes OP's plan dangerous! OP wants to parallel neutral back to the house! You might sell me if those boxes switched neutral; they do not, which is a whole 'nother bag o' trouble... – Harper - Reinstate Monica Dec 21 '19 at 6:22

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