Transfer Switch Wiring Question: Hot 1? Hot 2?

RussOnTheRoadRussOnTheRoad Registered Users Posts: 14 ✭✭
edited November 29 in Solar Beginners Corner #1
The transfer switch in my 5th wheel has inputs for shore power and generator. Each has connectors marked Hot 1, Hot 2 and Neutral. What is the difference between Hot 1 and Hot 2? 

I want to run the output from my inverter to the transfer switch but apart from the ground I don't know which wire to hook to Hot 1 and whcih to hook to Hot 2. I assume it matters. How do I tell which goes whwere?

Comments

  • BB.BB. Super Moderators Posts: 26,870 admin
    It does depend on how your 5th wheel is wired... Do you have 120/240 VAC (split phase 60 Hz) or do you have 120 VAC 60 Hz only?

    Assuming you have 120/240 VAC power in the RV, think of the power source as a transformer with three wires on the output. L1 and L2 are the outer most connections to the transformer, and Neutral is the "center tap". (technically, L1 and L2 are 180 degrees out of phase with each other--120 VAC L1 to N or L2 to N. 240 L1 to L2).

    FileTransformer Centre-tap Iron Coresvg

    If you connect L1 (or L2) to the Neutral, you get 120 VAC. If you connect to L1 and L2 with your load (say an air conditioner or large battery charger/inverter), you get 240 VAC.

    Then there are your power sources... Is your genset a 120/240 VAC output or 120 VAC only? Is your inverter a 120/240 or 120 only output?

    Lastly, there is the grounding... Or specifically the "bonding" of the neutral wire to the green wire/safety ground. In North America, we typically connect the Neutral wire (in one location) to the chassis+green wire ground (and cold water pipe/ground rod if fixed home installation).

    With RV's, that gets very complicated very quickly. When connected to shore power, the Neutral+Ground bonding is done at the camp ground's main panel (or similar). With a genset, typically smaller generators (less than 3,500 watts or so) do not bond Neutral+greenwire genset chassis ground together. Similar for AC inverters (pure/true sine wave only)--Larger inverters connect the green+neutral wire internally in the inverter and smaller inverter tend to "float" the neutral.

    To add more complexity, if you have a MSW (modified sine/square wave) AC inverter--You never bond the "Neutral"+Ground together... If the battery bank is also ground referenced, this creates a short through the MSW Inverter which can destroy the inverter and cause smoke/fire.

    Note the above TSW/MSW inverter rules are typical--But there are exceptions, you need to read through the instruction manual(s) to see what your unit requires for grounding.

    For smaller systems--Floating the TSW Inverter and genset AC output is typical.

    So--I guess the question is what brand/model of AC inverter do you have?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RussOnTheRoadRussOnTheRoad Registered Users Posts: 14 ✭✭
    BB. said:
    It does depend on how your 5th wheel is wired... Do you have 120/240 VAC (split phase 60 Hz) or do you have 120 VAC 60 Hz only?

    Assuming you have 120/240 VAC power in the RV, think of the power source as a transformer with three wires on the output. L1 and L2 are the outer most connections to the transformer, and Neutral is the "center tap". (technically, L1 and L2 are 180 degrees out of phase with each other--120 VAC L1 to N or L2 to N. 240 L1 to L2).

    FileTransformer Centre-tap Iron Coresvg

    If you connect L1 (or L2) to the Neutral, you get 120 VAC. If you connect to L1 and L2 with your load (say an air conditioner or large battery charger/inverter), you get 240 VAC.

    Then there are your power sources... Is your genset a 120/240 VAC output or 120 VAC only? Is your inverter a 120/240 or 120 only output?

    Lastly, there is the grounding... Or specifically the "bonding" of the neutral wire to the green wire/safety ground. In North America, we typically connect the Neutral wire (in one location) to the chassis+green wire ground (and cold water pipe/ground rod if fixed home installation).

    With RV's, that gets very complicated very quickly. When connected to shore power, the Neutral+Ground bonding is done at the camp ground's main panel (or similar). With a genset, typically smaller generators (less than 3,500 watts or so) do not bond Neutral+greenwire genset chassis ground together. Similar for AC inverters (pure/true sine wave only)--Larger inverters connect the green+neutral wire internally in the inverter and smaller inverter tend to "float" the neutral.

    To add more complexity, if you have a MSW (modified sine/square wave) AC inverter--You never bond the "Neutral"+Ground together... If the battery bank is also ground referenced, this creates a short through the MSW Inverter which can destroy the inverter and cause smoke/fire.

    Note the above TSW/MSW inverter rules are typical--But there are exceptions, you need to read through the instruction manual(s) to see what your unit requires for grounding.

    For smaller systems--Floating the TSW Inverter and genset AC output is typical.

    So--I guess the question is what brand/model of AC inverter do you have?

    -Bill
    Bill,

    Thanks for your very thoughtful and thorough reply! It is going to take awhile for me to digest it... if I even can. I would have to learn more than what now know to understand. I'm in over my head. I poked around online looking for an explantion of these things I could understand but found none.

    I don't know if my RV has "120/240 VAC (split phase 60 Hz) or 120 VAC 60 Hz only" nor do I know how to tell or what these things mean. I know my RV has a 50 amp system. There is a red, white, black and green wire coming into the transfer switch from the shore power cord and the generator prewiring also has red, white, black and green wires coming into the transfer switch. (There is no generator hooked to the transfer switch, just the prewiring. I have two portable Honda 2000 generators I can connect in parallel that I do not plan to wire into the generator prewiring but rather plug the shore power cord into them directly when I use them. Thus, the generator prewiring is free to be used for something else such as this temporary inverter I am hoping to hook up.)

    I have two inverters, actually, neither of which is installed. I have a Magnum MS2812 which I plan to have professionally installed later on but right now I am looking to hook up something temporary until the 2812 is installed. That temp inverter is a Sunforce 11240 1000w pure sine wave inverter. Hooking up the battery (12v input) side seems straight forward enough. On the output side I have to plug a standard 3 prong extension cord into one of two 110-120v outlets built into the inverter. (Unfortunately, with this inverter the 1000w is divided between two 500w receptacles so I may replace this inverter with one where I can get all 1000w out of one receptacle so I can run all the watts through the transfer switch, not just half of them.) The specs seem to indicate the Sunforce unit's output is 110v, 60 Hz. 

    The generator prewiring in my RV is wired into the transfer switch on one end and the other terminates at what I think is called a double gang box, the kind that would hold two duplex 110v or 120v receptacles. The wires aren't hooked up to anything on this end. This terminus is in the forward storage compartment under the overhang of my 5th wheel and is very close to my two AGM batteries is an adjoining compartment. The Sunforce (or similar) inverter could be hooked up to the generator prewiring in the double gang box, thereby substituing its output for the output a generator would typically proivide.

    So, I would have three wires coming out of the inverter in the form of an extension cord where I cut off the female end, the male end being plugged into the inverter. The generator prewiring has 4 wires. So there are 4 connections that would normally be made but I will only have three wires. This is where I am stumped.

    I just remembered that in speaking with a tech from the transfer switch company he said something about using a jumper inside the transfer switch. That said, my current best guess would be to hook the ground from the inverter's 120v receptacle (the rounded hole in the outlet) to the green wire of the generator prewiring. This green wire is connected to the metal double gang box with bare coper wire as part of the generator prewiring, so it would seem to be the ground. The wire from the larger of the two flat blade holes in the outlet of the inverter should be neutral and hooked to the white wire of the generator prewiring, I suppose. The hot lead of the inverter output (small flat blade) would be hooked to the black wire of the generator prewiring. Then inside the transfer switch I would place a jumper between Hot 1 and Hot 2 at the connections for the generator input. Does that sound right? The red wire would be unattached to anything at either end, I'm guessing. The case of the Sunforce inverter also has a hookup labeled ground. So, I guess that should be wired up too, but I don't understand why it would be necessary to have the case grounded as well as the receptacles.

    (Separately, the tech at the transfer switch company suggested I swap the positions of the generator input and shore power input inside the switch because the transfer switch relay demands current to energize it in the generator postion which would place an additional, unnecessary load on the RV battery bank if powered by the inverter. 

    I'm not sure, but I think the transfer switch would normally connect to the load via the generator input if it detected both shore power and generator power. This would be another reason to swap the generator and shore power inputs at the switch: it would then default to shore power in the vent both shore power and inverter power were available.

    Does my wiring plan sound correct (two paragraphs up)?

    Thanks again.
  • EstragonEstragon Registered Users Posts: 1,616 ✭✭✭✭
    edited December 2 #4
    I assume you have no 240v loads (eg air conditioning), and no plans to add any?

    Jumpering the black and red ("live", sometimes called hots) wires at the transfer switch is *probably* right, but I would want to be sure of the branch wiring. Most likely, each of the live wires feeds one side of a branch circuit distibution panel. Jumpering at the switch should put them at 120v with respect to neutral (white), and 0v with respect to each other.

    Grounding is a bit more complex. With outlets, the inverter is designed to provide a ground for loads on the green wire, and itself be grounded with the bare copper wire to its grounding lug.

    The inverter claims to be PSW, most of which are okay with a neutral/ground bond. At 10lbs for a 1000w inverter, and not being designed for hardwiring, I'm not so sure about this one.

    Putting the inverter on the shore power input makes sense. Presumably, that's the normally closed side of a non-latching relay. If there is power to the normally open side, the coil is energized and the relay changes state (opening the NC shore power side, and closing the NO generator side).
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • RussOnTheRoadRussOnTheRoad Registered Users Posts: 14 ✭✭
    Estragon said:
    I assume you have no 240v loads (eg air conditioning), and no plans to add any?

    Jumpering the black and red ("live", sometimes called hots) wires at the transfer switch is *probably* right, but I would want to be sure of the branch wiring. Most likely, each of the live wires feeds one side of a branch circuit distibution panel. Jumpering at the switch should put them at 120v with respect to neutral (white), and 0v with respect to each other.

    Grounding is a bit more complex. With outlets, the inverter is designed to provide a ground for loads on the green wire, and itself be grounded with the bare copper wire to its grounding lug.

    The inverter claims to be PSW, most of which are okay with a neutral/ground bond. At 10lbs for a 1000w inverter, and not being designed for hardwiring, I'm not so sure about this one.

    Putting the inverter on the shore power input makes sense. Presumably, that's the normally closed side of a non-latching relay. If there is power to the normally open side, the coil is energized and the relay changes state (opening the NC shore power side, and closing the NO generator side).

    Thanks for chiming in!

    It seems with each helpful reply I'm faced with unfamiliar terminology and something new to learn or consider. Don't get me wrong... I like the learning.

    My fifth wheel does in fact have air-conditioning. It has one such unit. I know enough that I would never expect to power an air-conditioner off an inverter in the RV as the electrical demands of the air-conditioner would be far too great. Something else has come up too: in other reading it was mentioned that one has to be careful to make sure that an RV's converter is not powered by the inverter which would result in a wasteful use of power running endlessly in a loop that looses power due to inefficiencies of the equipment and wires. My RV has a converter. I'm not sure what circuit it is on and I would have to make sure that any inverter installation avoids the potential problem I just described.

    My original plan was to self-install the Magnum MS2812 in such a way as to power the 110v AC outlets in the RV but not the air-conditioning. I assume the 110 volt receptacles in the RV are on a different circuit or branch than the air-conditioning. I hope I'm right. (I have to confess that I am not 100% certain of the meaning of "branch" as used here. I can only guess that it means a discrete, separate circuit.) I am also hoping that powering those receptacles would allow use of the microwave (for brief spurts) since it plugs into one of the 110v receptacles. I guess that may not be knowable until the power supply panel(s) are examined. 

    I decided that lacking the both general knowledge needed to do a proper installation of the MS2812 as well as the specific knowledge as to how the RV is wired, I would have the 2812 professionally installed. In purchasing the Sunforce 1000w inverter I was hoping for an easier wiring job that I could handle myself until the 2812 is installed at some future point. Now I'm seeing that while it might be easier it still comes with some complexities I hadn't anticipated. It might be simpler to bypass the transfer switch, placing the inverter inside the RV, but it might not because besides having to find a suitable place inside the RV it might involve drilling holes and running extension cords getting to power to where it is wanted.

    As of the moment it seems to me what I need to do is either install the Sunforce on a discrete circuit bypassing the existing wiring in the RV or roll up my sleeves and get a solid grip on the RV's electrical system making certain to exclude both the air-conditioner and converter from being powered by the Sunforce should I wire it into the transfer switch. Progress on either path is being impeded, momentarily, by a sore shoulder I've been wrestling with.

    Thanks again!
  • EstragonEstragon Registered Users Posts: 1,616 ✭✭✭✭
    The 2812 should be able to handle a microwave, but the smaller one probably not. Even if the microwave is rated under 1000w, that's normally output power. Input power can be much higher. They're generally wired to a dedicated 15a breaker.

    Operationally, the simplest way to deal with air and battery charger (and any other big loads, like electric heaters), would be to put them on a small panel of their own fed by shore power only.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • RussOnTheRoadRussOnTheRoad Registered Users Posts: 14 ✭✭
    Estragon said:
    The 2812 should be able to handle a microwave, but the smaller one probably not. Even if the microwave is rated under 1000w, that's normally output power. Input power can be much higher. They're generally wired to a dedicated 15a breaker.

    Operationally, the simplest way to deal with air and battery charger (and any other big loads, like electric heaters), would be to put them on a small panel of their own fed by shore power only.
    I never intended to attempt running the microwave on the 1000w temporary Sunforce inverter, especially considering the Suforce has only 500w per receptacle, (they are discrete), and I could only use one of them whether wired into the RV's system or stand-alone. The microwave would draw much more than 500w and maybe more than 1000w.

    I do wish to isolate the air-conditioning from the inverter and run it only off shore power (or when my shore power cord is plugged into my portable Honda generators).

    Except for our water heater which runs on either or both gas and electricity I don't think there are any other appliances built into the rig we would want relegated to shore power only apart from the converter/charger and this will be disconnected when the Magnum MS2812 is hooked up.

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