Grid tie could you kill a man by accident

Please have a proper disconnect in place

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Grid tie could you kill a man by accident

    Nick,

    Just out of curiosity, given that there is no difference between a listed grid tie inverter being connected to the utility line with or without utility notification (assuming both meet code)--does a lineman receive notification from dispatch/computer when a grid tied install is on a local distribution circuit?

    When my local utility (PG&E) "inspected" my installation and changed the meter--all that he did was look for the building inspector tag and change the meter... No testing was done (listed as required by my "small generator" contract) and he did not verify the inverter model number/listing mark either (I don't think my building inspector did either). It was just another meter swap for him.

    Are you seeing issues where the anti-islanding function of a listed inverter is not functioning correctly and energizing the local distribution grid from back driving?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Grid tie could you kill a man by accident

    "Back-feeding" the grid from a utility-interactive (U-I) inverter is a legitimate issue and and a valid safety concern. However, I would submit that the matter has been adequately addressed via built-in "anti-islanding" technology, features, and processes.

    Specifically, UL spec 1741 requires that a UL-listed U-I inverter drop its grid connection within 0.1 second (6 cycles) of the (single phase) line voltage falling below 60 VAC. All UL-listed U-I inverters are individually tested by their manufacturers to meet this spec as well as the other conditions of 1741. A related requirement is that the U-I inverter must wait for five minutes of continuous grid restoration before it can reconnect to the grid and again start "selling".

    Regards,
    Jim / crewzer
  • Telco
    Telco Solar Expert Posts: 201 ✭✭✭✭✭
    Re: Grid tie could you kill a man by accident

    I'd like to add another question. Do linemen regularly grab transformer poles on dead lines without verifying first with a meter that the line is dead? I'm no field pro, but the last thing I'd ever do is grab a potentially live line lead regardless of what some remote tech might be telling me about the line being dead. If I'm out there working on the line, it's because there is a problem, and that problem might actually be the monitor/control system, not the power lines.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Grid tie could you kill a man by accident

    And in any case, grounding the utility feed should not damage the grid tie inverter...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nigtomdaw
    nigtomdaw Solar Expert Posts: 705 ✭✭
    Re: Grid tie could you kill a man by accident

    A very interesting thread, does selling grid tied inverters require a registration system where by Gorilla installations can be traced, one death is one to many :grr

    Regardless of system design and protection the Cowboy always manages to screw up or by pass the best laid plans of the creator, my example is Microsoft :cry:
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Grid tie could you kill a man by accident

    The normal U/I Inverter (Grid Tie) is designed to not backdrive any lines that are out of spec. (voltage, frequency). And they cannot be operated without a source to sync/follow.

    In the US (and I am sure Canada), it is considered very bad form to connect a generator that can backdrive the utility lines (unless you are registered as a generating site)... We have to use transfer switches to ensure that the line is never energized, only the loads...

    But, of course, there is always that one person in a neighborhood that will connect something backwards.

    The general discussions about meters was because there have been serveral of here that have had RE systems installed and in one case, OK'ed for connection to the grid by the building department (and paperwork filed with the utility) and his meter billed (debited the account) no matter if he used or generated power. And another person where this must have been the first install of Grid Tie--and the utility did not realize that their meter did not "run/log" backwards correctly either...

    And in my case, my meter ran backwards enough that my meter showed a surplus of power (allowed for 1 year net metering contracts), but thought that they read the meter wrong and billed me for several hundred dollars of power use, instead of a few dollars of credit (when we are allowed to turn on our systems is not clear--paper work filed, building inspector OK's, but it takes two weeks for the utility to come out and change the meter).

    So--there are reasons to discuss how the meters operate--where everything is still legal...

    Problem is, for example in California, they practically stopped all home solar RE installs for quite a few months because the forced people onto very expensive (for peak) tiered pricing (my pricing gets up to $0.50 per kWhr in summer peak and over 1,000 kWh per month usage). And if the homeowner installed a small solar system (for whatever reason), they could end up with higher bills than if they never installed the solar system in the first place. It took the better part of 1/2 a year before the state PUC/law makers (law givers?) fixed the worst of the problems.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • sawmill
    sawmill Solar Expert Posts: 93 ✭✭✭
    Re: Grid tie could you kill a man by accident

    I don't know what the utility standards are for linemen in Canada. I understand that standard operating practice here in the states requires grounding on BOTH sides of a transformer.

    Not only is backfeeding always a present danger from unapproved generator connections, several miles of UNenergized utility wire under certain conditions can become energized from induction with lethal results if proper safety is not followed.

    Since all utility poles have a ground and most repair is done from an insulated bucket there is no excuse for a lineman to be injured if he follows proper safety standards.

    Since all of us on this forum know that backfeeding with grid-tie inverters is impossible these safety concerns sound like utility propaganda.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Grid tie could you kill a man by accident

    I don't want to label anyone as supplying propaganda here... I think that Nick was very concerned about what illegal grid tie system installs and was truly trying to prevent injury/death of his fellow linemen.

    Nick already said that he was unaware of the details regarding the functioning of U/I inverters and safety requirements built into the device. He apparently thought that this was just the equivalent of plugging in a portable generator to the line and firing it up (which is illegal and can energize the utility network).

    Anyone asking about how to run a meter backwards that is not familiar with Net Metering and U/I RE systems (which Nick said has not yet been installed in his utility's service area) would certainly raise concerns.

    Now that this has been clarified--I hope that if Nick has any further questions or information that he will feel free to discuss them here.

    Sincerely,
    -Bill

    PS: Nick, has changed his first post to ask that a proper disconnect be in place...

    Nick, there was a requirement that there be a separate Solar RE disconnect installed near the meter and it be placarded with warnings about generator installed on premise and energize circuits may be present even if the main power is out...

    IIRC correctly (Jim can correct me if I am wrong), the external disconnect requirement near the meter has now been removed as a requirement for new installs (in some states?). In any case, it was originally required to allow the utility to disconnect the U/I inverter AC output without the need for turning off the main breaker (or pulling the meter) as a favor for the customer so that they get their power back on as soon as possible without having to be manually reconnected...

    At this point, since the power has to be stable for at least 5 minutes before the inverter will attempt to reconnect to the utility network--I believe--it has been found that the external disconnect is no longer needed for safety.

    And the inverters (are supposed to be) behind a normal branch breaker (pair of 20 amp / 240 VAC in my case) on a properly sized breaker panel and utility feed. The U/I inverters are not tied directly behind the meter bypassing all protective devices/disconnects...

    -BB
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • newenergy
    newenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: Grid tie could you kill a man by accident

    I guess there could be cases where everything goes wrong, but here in California you will first apply for the rebate and you'll be specifying the inverter and they'll only take those with anti-islanding (as mentioned already - they shut down automatically when power goes out). The utility and the building department should be inspecting the system. They won't really test this, but the utility inspector should see that it is a proper type of inverter at least.

    15 years down the line someone could replace the inverter with something that won't doesn't have anti-islanding.