Is a Neutral Required Here?

I have recently started to work for a solar company as their electrician. I have run into an issue that I was wondering if anyone could help me out with. Here is my situation.

I have a 200 amp meter with a 200 amp breaker at the meter. The array that is being installed is a 11.8kw the panels are each equiped with micro inverters. The breaker required to handle the array is 70amp. This is what we plan to do step by step.

1. Change out the main breaker of the house panel from 200amp to a 150amp.
2. Line tap out of the meter main breaker to a 100a disconnect fused at 70amp.
3. come out of the disconnect to the solar disconnect.
4. come out of the solar disconnect to a sub panel (combiner) that will hold (3) 2 pole 20a breakers to handle the 3 strings
5. From the sub panel to the roof.

My question is: Do I need to carry a seperate neutral to the sub panel (combiner). I plan to bring a neatral from the house meter to the 100amp disconnect. The neutral will be bonded there. I am just not sure if I need to bring it all the way to the sub panel. I would like to run a 2-2-3 SEU cable out of our solar disconnect to the sub panel. Is this the proper way to do this or do I need to run a neutral all the way through.

Any help would be much appreciated, I am having trouble finding this in the code book and would really like to get this figuared out before installing the wrong wire! Thanks in advance!

Comments

  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: Is a Neutral Required Here?

    Not quite sure why you would change out the 200 amp breaker - that is the main house breaker and all power to the house should go through that. What happens at night when the solar is producing no power is that you have effectively reduced it to a 150 amp service.

    You did not say which inverters you are using, but the only UL listed ones I know of are the Enphase, and they require a neutral all the way from source to end.
  • SolaRevolutionSolaRevolution Solar Expert Posts: 407 ✭✭✭✭✭✭
    Re: Is a Neutral Required Here?

    You need an isolated neutral buss for you AC combiner/sub panel.

    You did not say which micro inverter you were going to use but it probably has a 4 wire (L1,L2,N,G) AC output. If the AC output cable only has 3 pins they will probably be L1,L2,N. (Any exceptions?)

    Because each inverter is a "seperately derived" DC system and requires a DC neutral bond the grounding is often handled seperately with a grounding electrode conductor bonded to the case of each inverter.

    Some Enphase micro inverters have 4 pin connectors with 3 conductor cables (L1,L2,N) with no equipment grounding conductor in the AC output cable.

    Some micro inverters also use the AC neutral for data transmission.
  • SolaRevolutionSolaRevolution Solar Expert Posts: 407 ✭✭✭✭✭✭
    Re: Is a Neutral Required Here?

    Also, if you can do a line-side tap you don't need to replace your main breaker to reduce the ampacity available to your 200 amp busbar.
  • FroniusFronius Registered Users Posts: 3
    Re: Is a Neutral Required Here?
    Windsun wrote: »
    Not quite sure why you would change out the 200 amp breaker - that is the main house breaker and all power to the house should go through that. What happens at night when the solar is producing no power is that you have effectively reduced it to a 150 amp service.

    You did not say which inverters you are using, but the only UL listed ones I know of are the Enphase, and they require a neutral all the way from source to end.

    Reason is that the bus is able to handle the extra 70 amps. (due to 125%) By downsizing the breaker size I am able to use a 70a fused disconnect and be with in 125% of the bus rating. The 200 amp service is overkill for the residential house that it is powering. Total amperage on the house panel is not pulling anything close to the 200 amps.
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: Is a Neutral Required Here?

    That may be true, but some local codes require that houses over a certain sq-ft have a 200 amp service. You might want to check that before you go too far. Without knowing what brand, model or voltage (240 volt - 120-0-120 or ??) of inverter you are using it is hard to say what is wrong, but something does not seem right with your description.

    All the systems we have done, we have never had any occasion to change the main breaker - in fact I never heard of it being done. In every household grid tie system I have seen (not only ours), the inverter output ties directly to the main L1 and L2 in the main power panel for the house. Between the actual inverter and power panel you may have disconnects, combiners, and breakers but the connection is basically the same.
  • solar_davesolar_dave Solar Expert Posts: 2,382 ✭✭✭✭
    Re: Is a Neutral Required Here?
    Windsun wrote: »
    That may be true, but some local codes require that houses over a certain sq-ft have a 200 amp service. You might want to check that before you go too far. Without knowing what brand, model or voltage (240 volt - 120-0-120 or ??) of inverter you are using it is hard to say what is wrong, but something does not seem right with your description.

    All the systems we have done, we have never had any occasion to change the main breaker - in fact I never heard of it being done. In every household grid tie system I have seen (not only ours), the inverter output ties directly to the main L1 and L2 in the main power panel for the house. Between the actual inverter and power panel you may have disconnects, combiners, and breakers but the connection is basically the same.

    Actually many of the Valley municipalities disallow line side taps and require a panel down sizing to get the 120% NEC code rating. Then there is always the 200 amp requirement for residential especially if multiple AC units and electric kitchens, dryers or hot water heaters are involved (i.e. lots of high load devices). They disallowed derating the main panel on mine so service entrance upgrade to 400 amps with the included transformer to service entrance upgrade in wire size was required. Then a pair of 200 amp panels were installed, one for the main house rated @ 200 amp and one derated to 175 amps for the add in of a 60amp breaker for the solar. I thought it was way overkill but the code guys would not do it any other way.

    Since then I have added an 125 amp sub panel for my office/workshop building and a 60 sub panel for the 2 Chevy Volt chargers off the derated panel. What will be interesting is the 3920 watt Enphase powered solar addition happening in the next 90 days and how those guys will have to upgrade that solar breaker to 80 amps from the solar AC combiner panel. The current dual PVPowered 5200 inverters are rated to only output 46 amps max combined, but the Enphase install needs a 20 amp breaker for there 16.5 amp rated output in the combiner. That will mean the AC combiner will have two 30 amp breakers and a 20 amp breaker. I think a further derating of the panel will be required to 150 amp main breaker and an upgrade of all the wiring between the AC combiner and the main panel to the next size wire will be needed, although the total amperage will only be slightly over the 60 amp panel breaker (62.5 amps, 46 + 16.5) rating from the combiner and the next size breaker is 80 amps. Fortunately all the devices (AC combiner, AC disconnect and Solar output meter) in that line are rated high enough so none of them will need replacing and the wiring runs are fairly short at less than 20 feet total.

    I am starting to worry about the loads I have placed on the derated panel because they total 185 amps at least in breaker sizing.
Sign In or Register to comment.