residential line load q and a

Another question guys. I have been inspected and according to my NEC, solid copper in EMT is good. He said from the panels to the inverter inside 3/4 EMT has to be #8 stranded? I am dreading pulling that all the way through the conduit and pulling out my #8 solid, but he also said, which is confusing to me after doing a search here, came up with nothing as well, but outside, my AC disconnect and additional meter socket for the utilities and my house main I wired line and load in each with the load being the main service breaker and the line being the PV systems inverted DC to AC power (5000 watts 22 amps). I believe that like the utility power coming into the main service panel, and being distributed to the loads, another source of AC power supplying the loads with AC would be the line and even feeding excess into the grid, is a load and would be considered a load albeit one large one. The inspector said the main service panel is always the line and in my case, the PV system is the load. He wants me to swap wires to conform to the latter view. I'm confused and if anyone had a reference to a page in the NEC that clears this up I would be grateful. Any suggestions on how to ground my panels and rails without stuffing stranded into the conduit. NEC says if that is the scenario then all connections along the conduit have to be bonded to the conduit and boxes bonded to the conduit I guess so the conduit would be grounded, but why is that not so by just running stranded wire inside it? More confused. Thanks ahead of time for any expert input. I spent an hour and a half with the inspector and did learn quite a bit of interesting stuff and questioned his knowledge of the 2014 NEC, brought him the book. He said he teaches the NEC at night to apprentices so I closed the book and my mouth so hole digging would cease. Mike

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: residential line load q and a

    You have a problem: the inspector is an idiot.

    Grid-tie PV is NEVER a load. Not ever under any circumstances. It is a power source just as the grid is, but with a GT system the grid is sometimes a load.

    You do not need to exchange the #8 solid in conduit for #8 stranded either. Stranded is used where the possibility of flexing may occur, and conduit rules that out.

    He teaches NEC? Pity he doesn't know what he's doing; lots of people will be learning wrong.

    I do not know any way of defeating such pig-headed ignorance short of getting a different inspector. Good luck with that too, as they tend to stick together.
  • michaelc
    michaelc Solar Expert Posts: 36
    Re: residential line load q and a
    You have a problem: the inspector is an idiot.

    Grid-tie PV is NEVER a load. Not ever under any circumstances. It is a power source just as the grid is, but with a GT system the grid is sometimes a load.

    You do not need to exchange the #8 solid in conduit for #8 stranded either. Stranded is used where the possibility of flexing may occur, and conduit rules that out.

    He teaches NEC? Pity he doesn't know what he's doing; lots of people will be learning wrong.

    I do not know any way of defeating such pig-headed ignorance short of getting a different inspector. Good luck with that too, as they tend to stick together.

    I am with you....his comments make no sense at all - trying a diff inspector
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: residential line load q and a

    FWIW, if the grid tie system is going into your panel (or directly to the service wires) through a backfed breaker, the NEC makes it very easy to determine which way to connect up the breaker:

    If the breaker has actual line and load markings on it, you cannot use it in either direction. The breaker must be designed to safely interrupt energy going in either direction.
    In the case of a short in the wiring, the power may well be flowing from the grid through the breaker to the short.
    Under other circumstances (not at all likely) the GTI might develop more than the rated current and trip the breaker from a power flow toward the grid. The interrupting mechanism of the breaker MUST be symmetrical for both situations to work.

    The inspector is at fault for not properly explaining this and directing you to the applicable NEC section. But his conclusion is not wrong.
    Look at 690.10(E) in the 2011 NEC, for example. This is a section headed "Standalone inverters" but has been interpreted to apply to GTI backfeed also.
    705.12(D)(5) is more directly applicable to GTI and says much the same thing but does not directly prohibit use of a breaker marked with line and load, nor does it indicate which way such a breaker should face if it is used.
    (5) Suitable for Backfeed. Circuit breakers, if backfed, shall be suitable for such operation.
    Informational Note: Circuit breakers that are marked “Line” and “Load” have been evaluated only in the direction marked. Circuit breakers without “Line” and “Load” have been evaluated in both directions.
    SMA SB 3000, old BP panels.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: residential line load q and a
    You do not need to exchange the #8 solid in conduit for #8 stranded either. Stranded is used where the possibility of flexing may occur, and conduit rules that out.

    I think you're quite right... since the conduit is EMT. What if it was flexible conduit?

    Customary practice is to use stranded because it's so much easier to pull through conduit. Some inspectors don't think... they just want everything to look the way they're used to seeing it.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: residential line load q and a

    Even directional breakers will work either way. They 'work best' as labeled. A disconnect (not a breaker) may be labeled as 'line' and 'load' for safety reasons: the portion which remains 'hot' when turned off will present the least amount of exposure (think 'knife switch' where the moving bars are connected to the load and the fixed contacts are connected to power).

    If there is a short on the output of a GTI it will shut down by itself because there would be no qualifying power to keep it running. The inspector is probably thinking "what happens if the GTI shorts? Then it is a load." This is not necessarily the right way to think.

    vtMaps comment about flex conduit is correct: running solid wire through it is a dichotomy. But this is solid, the wire is already there, and electrically there's no difference between the two. Be glad he didn't demand 6 AWG; a lot of people do not understand the ESG wiring need only take current momentarily and as such does not need to be sized to meet full current of the circuit.

    RULE #1: Just because the NEC says so doesn't mean it's right. Knowing the why behind the rules is more important than knowing the rules. Too many inspectors know neither and are too stubborn to listen to reason.

    Being stubborn should be left to old coots who have had the proper training and practice at it. ;)
  • michaelc
    michaelc Solar Expert Posts: 36
    Re: residential line load q and a

    The breaker is just a DPDT GE 30 amp. no marking. Line and load are marked on my AC disconnect box and the meter socket and he wants those reversed to the GI is the load and the main service box Line, not a big deal just doesn't make sense. Common sense makes sense so maybe he is using whatever experience he has to dicate what he thinks is safe he isn't very old so he doesn't appear to be a veteran. but yes the NEC at at least the 2014 doesn't say anything about the GTI being load or line
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: residential line load q and a

    The old discussion we have had here before...

    I like to look at what is the source of high current... A GT inverter will never be the source of 10,000 Amps in the case of something going wrong. The only source of high current is the utility mains. In the case of wiring/GT inverter failure--Then they will be the "load" that the breaker is protecting against.

    So--treating the AC side of a GT inverter just like any other branch circuit/load should be just fine and appropriate.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: residential line load q and a

    So ... breaker and disconnect?
    Yeah: regulations designed by the department of redundancy department.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: residential line load q and a

    When GT systems were first installed--The breaker plus disconnect was a requirement because the utilities wanted a way they could turn off the GT inverter if they were servicing/grid was down.

    If you did not have a disconnect installed on an outside wall, they reserved the right to pull your meter to "kill" the possibility of a GT inverter back feeding the grid during repairs (and put the meter back in--when they had the free time).

    But, at least in California 5+ years ago, GT inverters were accepted as being "safe" and the external disconnect was no longer required.

    Now--We are seeing the DC Array disconnects, versions of ground fault/arc fault breakers, and roof walkway access requirements by the fire department--Which can be more costly/limiting.

    Oh well...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: residential line load q and a

    Don't look at me. I use a generator for power, despite having solar panels.

    I wonder if it will ever stop raining? :p
  • michaelc
    michaelc Solar Expert Posts: 36
    Re: residential line load q and a
    BB. wrote: »
    When GT systems were first installed--The breaker plus disconnect was a requirement because the utilities wanted a way they could turn off the GT inverter if they were servicing/grid was down.

    If you did not have a disconnect installed on an outside wall, they reserved the right to pull your meter to "kill" the possibility of a GT inverter back feeding the grid during repairs (and put the meter back in--when they had the free time).

    Here the utility wants an AC disconnect and another meter which they supply and a back fed breaker at the main service located on the bottom. Bill, I think your way of seeing the issue in regard to line load makes sense to me so thank you! At least here we can plaster panels all over our roof to the edge and beyond and no one cares. I did prove though that those ferrmut sharraz (Cheap white fused circuit breaker things they put in combiner boxes) really do start on fire if you pull them while the sun is shining, luckily It blew out but showed me that even if no one is checking or looking, if it is your house and family you absolutely must do the safest option available>>>absolutely must, no shortcuts.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: residential line load q and a

    Yea--the "touch safe" fuse holder requirement to reduce the chance of electrical shock, also created a brand new fire hazard for people that want/need to disconnect a string for testing/servicing and creating a nice sustained arc in the process. Who could of thought of that happening. :roll:

    -Bill "with friends like that, who needs enemies" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: residential line load q and a
    michaelc wrote: »
    The breaker is just a DPDT GE 30 amp. no marking. Line and load are marked on my AC disconnect box and the meter socket and he wants those reversed to the GI is the load and the main service box Line, not a big deal just doesn't make sense. Common sense makes sense so maybe he is using whatever experience he has to dicate what he thinks is safe he isn't very old so he doesn't appear to be a veteran. but yes the NEC at at least the 2014 doesn't say anything about the GTI being load or line

    Maybe I am misinterpreting what you have written, but in the case of an AC disco between an inverter and the service, the service goes on the line side and the inverter goes on the load side. It's not a matter of direction of current flow under normal conditions, it's one of the direction of flow in the event of a fault. Also, if it's a fused disco, you don't want the fuses hot when the switch is open.
  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    Re: residential line load q and a

    This kind of stuff is why DIY is hard for solar. There is a lot of arcane B.S. to satisfying inspectors that only comes with experience.
    The AC disconnect issue varies widely with different AHJ's but around here it is required by the utility as a means of disconnecting you during an outage. They need it to meet OSHA rules for a lockout/tagout device with a visible disconnect. That is why they treat the utility side as "line" because the switch blades on the line side are touch safe. (and we all thought it had to do something with which way the power is flowing!)
    I don't know if there is a rule against using solid CU in EMT, but nobody does that and part of the purpose in the code is to standardize the industry so that the next poor slob that has to work on your wiring has some idea of what to expect.
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: residential line load q and a
    solarix wrote: »
    That is why they treat the utility side as "line" because the switch blades on the line side are touch safe. (and we all thought it had to do something with which way the power is flowing!)
    It does have to do with the way power is flowing, but only in a fault condition. The fuses in a fused AC disco between an inverter and a service are not there to protect the conductors from the inverter; in a correctly designed system there is no way that an inverter can endanger the conductors because the conductors are sized to be able to carry more current than the inverter can possibly produce. The fuses are there to protect the conductors in the event of a fault between the switch and the inverter from current flowing from the service, and in that case the service is the line and the fault is the load.