Dangers of Backfeeding

I know there is much discussion about the dangers to utility workers from backfeeding the grid during a power outage. If I remember correctly though, it seems that nobody had ever heard of it actually happening.

Well, here in Bartow Florida it did happen, but thankfully the lineman is OK. It wasn't a PV system, it was a generator that was improperly hooked up and started during a power outage. Also, the line crew that was working on the downed lines did not take the required safety precautions. So it was a combination of factors.

Quoting the article "Watson yelled to the crew to get him off the line, and Scott Harrison, a groundman helper, tackled Watson, Radford said. Watson fell, dropping the lines, but the live line fell across his chest. 'Scott got him out from under it,' Radford said. 'He's really to be commended for all that he did.” The entire story is at http://www.theledger.com/article/20090901/NEWS/909019984/1134?Title=Bartow-Lineman-Shocked-When-Power-Comes-On

So it really is imperitave to follow all those safety precautions.

Comments

  • mikeomikeo Solar Expert Posts: 386 ✭✭✭
    Re: Dangers of Backfeeding

    The linemen around these parts treat all high lines as hot whether the power is up or not. They are required to ground the lines with flagged grounds on both sides of the work areas. This has probably saved many lives as people plug in generators with out having proper bypass switches around here is quite commonly.
  • mike95490mike95490 Solar Expert Posts: 8,285 ✭✭✭✭✭
    Re: Dangers of Backfeeding

    It's really amazing a 7hp 5KW genset can attempt to power an entire neighborhood, not trip it;s own breakers, and still zap a lineman. I better buy one of those - what brand was it ?
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • AntronXAntronX Solar Expert Posts: 462 ✭✭
    Re: Dangers of Backfeeding

    There were no amps going through the line because the electricity wasn't feeding anything at the time, like an appliance or air conditioner. The amps, which measure the volume of electricity flowing through a line, are the most deadly element in the power cyle.

    “That's probably what saved him,” Radford said.


    :cry:
  • boBboB Solar Expert Posts: 962 ✭✭✭✭
    Re: Dangers of Backfeeding

    Most smaller inverters won't even power the pole pig transformer. They'll just
    crap out.

    boB
  • BB.BB. Super Moderators, Administrators Posts: 29,207 admin
    Re: Dangers of Backfeeding

    But... The whole idea is to not find out. :roll:

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Dangers of Backfeeding
    BB. wrote: »
    But... The whole idea is to not find out. :roll:

    -Bill

    Yup.

    It's not as simple as "the generator/inverter can't power the whole neighborhood" - it only has to energize the wire the unfortunate lineman touches. Although I've always seen them work under such well-insulated conditions it would allow them to work with live wires.

    But there is always that chance that the planets are mis-aligned and then ... ZAP!

    Better to be sure all potential power sources are off/disconnected first.
  • sub3marathonmansub3marathonman Solar Expert Posts: 300 ✭✭✭
    Re: Dangers of Backfeeding
    Yup.

    Although I've always seen them work under such well-insulated conditions it would allow them to work with live wires.



    Quoting from the article: "Eddie Watson, who was shocked twice during the incident, was wearing leather gloves instead of rubber ones and the crew failed to lay a ground wire before beginning the repair."
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Dangers of Backfeeding

    When I was in training as an electrician, one of the journeymen I worked with came to work one day with a nice new set of lineman's pliers. First thing he did was whip out a knife and cut off the insulation on the handles.

    I asked him why and he said,

    "Because you can't trust it. Most of the time it will have a pinhole nick in it somewhere that you won't know about until you get bit. So I just toss that crap out and just do the work assuming that everything is hot.

    If I have to work on something where I need those handles for sure insulated, then I'll tape them *for that one use* and then take off the tape and toss it, since if I leave it I might screw up and trust it tomorrow...when it might have a hole that I didn't notice."
  • mike95490mike95490 Solar Expert Posts: 8,285 ✭✭✭✭✭
    Re: Dangers of Backfeeding
    dwh wrote: »
    When I was in training as an electrician, one of the journeymen I worked with came to work one day with a nice new set of lineman's pliers. First thing he did was whip out a knife and cut off the insulation on the handles.

    I asked him why and he said,

    "Because you can't trust it. Most of the time it will have a pinhole nick in it somewhere that you won't know about until you get bit. So I just toss that crap out and just do the work assuming that everything is hot.

    If I have to work on something where I need those handles for sure insulated, then I'll tape them *for that one use* and then take off the tape and toss it, since if I leave it I might screw up and trust it tomorrow...when it might have a hole that I didn't notice."

    Reading that , was worth trudging through all the "can I push 30A through speaker wire" posts.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • tallgirltallgirl Solar Expert Posts: 413 ✭✭
    Re: Dangers of Backfeeding
    mike90045 wrote: »
    Reading that , was worth trudging through all the "can I push 30A through speaker wire" posts.

    Depends on the speaker wires. I've got #8 fine strand to my speakers. Never know when I'm going to want to listen to music REALLY REALLY LOUD.

    When I was doing Katrina relief, I'd hear about people backfeeding transmission lines, many of which were down on the ground. For the 4 days I was up north of New Orleans, I'd hear the mayor of the town I was by begging people to keep their generators disconnected from the grid.
  • System2System2 Posts: 6,290 admin
    Re: Dangers of Backfeeding

    Just to clarify - In a commercial site that has a complete generator backup the grid-tie connection is upstream of the transfer switch? This is to ensure that the grid-tied PV will not back-feed the generator output during an outage.
  • strawbalestrawbale Solar Expert Posts: 29 ✭✭✭
    Re: Dangers of Backfeeding

    Newbie here. We have a 7kw system, net-metered, on order for early next year. Somewhere I read about a break-out switch(?) or something like that which would allow us to power our house in the event of an outage. Can anyone point me in the direction of more information on this or tell me whether it is worth considering?

    Strawbale
  • BB.BB. Super Moderators, Administrators Posts: 29,207 admin
    Re: Dangers of Backfeeding

    The switch is commonly known as a "Transfer Switch".... Mechanically, is just a switch that has the common end connected to your home's wiring (or emergency powered sub-panel). And the other two terminals -- one is connected to your utility power, and the other is connected to a generator (or inverter).

    When Utility power is OK--the switch is connected to utility power. When your power fails, you change the transfer switch over to the other contacts and the generator (or inverter) then powers your AC circuits...

    Of course, there are manual and automatic transfer switches. And many devices may have transfer switches built into them.

    Regarding your 7kW system... There are typically three types of Solar Systems...
    1. Grid Tied Inverter with Solar Power: The cheapest and most reliable type of solar AC power... Panels connect to a "GT" Inverter which then connects to your home's AC Wiring Panel--the power is then shared with your home and the utility meter (the utility grid basically behaves like a giant AC Battery system). Note, this system shuts down if there is no Utility Power and will not provide any power in an emergency.
    2. Off Gird Power: Basically, the solar panels charge a battery bank and an AC inverter takes the battery/solar power and provides AC Power to your home. Normally used where AC Lines are too far from the main utility distribution system or for emergency use during a storm (i.e., with a transfer switch). Most people will connect an AC Generator to power their home/cabin in cloudy weather/during winter and to recharge the batteries as needed. One of the more costly ways of generating AC power (if you have utility power) because batteries are costly, need replacement every 4-8 years or so, and you have additional losses due to battery and inverter inefficiencies. Typically, still better than using a genset only for your home power (if occupied more than 9 months of the year).
    3. Hybrid Inverter System: Basically combines the attributes of #2, with and inverter/transfer switch that allows the system to behave like #1 when AC Utility power is present. Basically becomes like a giant UPS (Uninterruptable Power Supply) for your home. Gives you many of the advantages of an off-grid system for when the power is down, and uses the utility (Grid Tied) as your "storage" when the grid is up and running.
    Normally, you have to choose #1, #2, or #3 up front... It is usually very costly to install #1 first--then decide you want #3 at a later time.

    Here is a simple drawing and explanation of what I typed out above.

    In general--make sure you understand what you will be doing before you spend your money--You certainly can install a transfer switch+genset with your grid tied system... But it does require your wiring to be done in a certain way so that you power your home with the genset in an emergency, but the Solar GT Inverter is not powered by the genset (gensets do not like being back feed by GT Inverters or other power sources).

    Also, make sure you have done all of your conservation measures up front (insulation, double pane windows, CFL lights, Energy Star Appliances/Air Conditioners/etc., use natural gas/propane for cooking, hot water, and heating, etc....).

    Normally, spending money on conservation is cheaper than spending money on generating AC power with solar.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • strawbalestrawbale Solar Expert Posts: 29 ✭✭✭
    Re: Dangers of Backfeeding

    Bill,

    Thanks for the info. Ours will be a grid-tied system. I was guessing it wouldn't be as simple as simply adding a switch to give us power during a rare outage, but thought I'd ask.

    I completely agree with conservation preceding a solar installation. I'm sure we could do better but we have made it to just under a megawatt/person/year for our family of four here in suburbia. Our pending system should produce about twice that, so we'll be able to feed back into the system and help offset our monthly $15. propane use. And possibly charge a PHEV sometime down the road.

    Strawbale
  • BB.BB. Super Moderators, Administrators Posts: 29,207 admin
    Re: Dangers of Backfeeding

    Since you have a propane tank (I assume)--if you get an 1,800 RPM propane genset that is sized to power your maximum load (say A/C in the summer)... You can have a very nice setup.

    Propane is clean and stores well--And with a tank for your property--you are not left handling the issues of diesel/gasoline storage/aging/etc.

    For random outages that don't last long--I am a believer that a genset (one just large enough to power your loads--over-sized gensets suck fuel at alarming rates--A 10+ kW unit can pull a $1.00 an hour or more with 50% or less loads) is usually the more cost effective solution.

    If you have ice storms/hurricanes/etc. that give you weeks or more of outages--a Hybrid Solar + Genset System is hard to beat.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • strawbalestrawbale Solar Expert Posts: 29 ✭✭✭
    Re: Dangers of Backfeeding

    Our outages are very rare. I just thought if it was simply adding a $50. switch, then it may be worth it. An hour or so without electricity each year adds a bit of spice to life.

    Strawbale
  • BB.BB. Super Moderators, Administrators Posts: 29,207 admin
    Re: Dangers of Backfeeding

    Nope--even with a transfer switch--you still need the alternate power source...

    Manual Transfer Switches usually start around $200 or so (6-10+ circuits). And you need a genset (or inverter, etc.) to plug into it to power your emergency circuits).

    There are meter socket transfer switches too... However, you may have an issue with your utility company (they don't like "strange hardware" around their billing meters).

    For my 2 cents--if you get a genset, get a nice quiet one (ether the small portable inverter/generators from Honda, Yamaha, etc. or the larger permanent installs). The "cheap" 5kW units are usually just too noisy (and fuel inefficient) to use around a home for any length of time.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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