Neutral connection wiring for off grid inverter with sub panel

Fabian
Fabian Registered Users Posts: 134 ✭✭
edited December 2024 in Off Grid Solar & Battery Systems #1
My setup is a 220v high frequency hybrid inverter with input and output connections. But I don't use the input port which takes in L1, L2 and grounds. Instead I feed the output to a step down transformer to produce 120v. Then I feed the transformer 120v output to the inverter side on the transfer switch and then I connect the L1 and neutral coming from the main panel disconnect to the grid side of the transfer switch and then I connect the sub panel L1 and neutral to the load side of the transfer switch. My sub have all my load breakers.

My main panel disconnect with just the breaker for the grid alone is located close to my solar setup .Therefore can I use the neutral from it to connect to the load neutral slot on the transfer switch???
Instead of running a 30feet neutral wire from the sub seeing that the neutral in the main panel disconnect is the same like in the sub.

​​​​​​​I am only using 1 phase 120v that's why i am only working with the L1 & N from the grid and the L1 and N coming from the step down transformer.
Please note that the neutral and grounds are tied only in the main panel disconnect. Which setup is the correct one and will the switching of the transfer switch to either solar or grid goes smoothly without any issues?
Please note the transfer switches only 2 legs at a time. Either L1 and L2 or L1 or N
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Comments

  • SumPower
    SumPower Registered Users Posts: 81 ✭✭
    #2
    If I came across this as an inspector. With the information you have given. I would write a correction notice stating that you must hire a licensed electrical contractor to correct and complete your work. Some states allow an electrical inspector to make this determination.
    I have written that notice a couple times.
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  • Fabian
    Fabian Registered Users Posts: 134 ✭✭
    #3
    Please tell me the correct way to do it then please with the equipments that i have.
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  • SumPower
    SumPower Registered Users Posts: 81 ✭✭
    edited December 2024 #4
    The problem as I understand it, and I may be wrong as it is hard to get the actual setup described in text. Is you are switching line 1 and neutral from a service panel through the transfer switch one way to serve the subpanel. Then you are switching the line 1 and neutral from your inverter (via an Xformer) through the same transfer switch to serve the sub panel. 

     Is this correct?


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  • Fabian
    Fabian Registered Users Posts: 134 ✭✭
    #5
    yes that is indeed correct.
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  • SumPower
    SumPower Registered Users Posts: 81 ✭✭
    #6
    The code requires that you have only one location were the neutral is bonded to ground. This is done at the main panel were the utility service conductors enter the home. It is usually done with a green screw that comes with the panel. This green screw physically connects all metal parts of the panel together making them all at the same electrical potential.

    Next you have a sub panel that can be fed from the main service panel. So this panel is required by code to isolate the ground from the neutral. The required neutral and the required ground conductor can't be bonded together in a sub panel.

    Now add in the solar inverter and the question is where do we bond the neutral to ground and drive the ground rods for this system? This is best done at the first panel and this panel is now not a sub panel but is the main service panel supplied by your inverter (through a transfer switch). So to comply with code this panel (now a service panel) needs to have the neutral and ground bonded together.

    So the dillema here is this second panel we are discussing must be a sub panel when connected to the grid, then it must be a service panel when connected to the solar inverter. Can't have it both ways.

    The solution is to grid tie your inverter if it is UL listed for the purpose.

    Maybe someone else will chime in here with other information and I will learn something, I am hoping that is the case.


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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,935 ✭✭✭✭✭✭
    #7
    Hurts my brain this close to Christmas !   Draw it out !
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • ray188
    ray188 Registered Users, Users Awaiting Email Confirmation Posts: 1 ✭
    edited January 18 #8
    You should get a split phase off grid inverter. If you have many induction loads (eg, fridge, aircon, pumps, anything with a motor), you should get a LF (low frequency) instead of HF (high freq) inverter. LF are heavier, costlier, but last 3-5x longer than HF. Also LF has 3x surge power vs typical 2x for HF. Most industrial grade inverters are LF. LF use real iron transformer instead of semiconductors found in HF inverters. With Split Phase, you don't need to mess with a separate transformer. i bought a 3KW LF split phase from solartorrents website and its been running spotless for 6 years. They have both HF and LF inverters of different wattages to meet most  needs and their support is v helpful even if you are not a customer yet.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,011 ✭✭✭✭✭
    #9
    Not sure what the situation is?

    If you are off grid, Not sure why you need a transfer switch other than for a genny or other alternative power source.

    If you are connecting to the grid, you need to be posting in a different section!

    When I took my home off grid. My E-Panel became my main(s) and I disconnected the neutral ground bond in my home breaker box. 

    FWIW - I'm 120 only and jumped the input at the breaker box and later added a mini busbar to make it to code so I didn't have 2 wires under the same clamp.

    Midnite Solar MNPV3-BUSBAR 3 Finger 093 for Midnite Solar PV3 Combiner Box - Picture 1 of 1
    If it's a hybrid system with a grid connection I'd post with the Grid tied Systems and perhaps you'll find folks who will deal with your situation.

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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