Back-feed Through Circuit Breaker Okay Temporarily?

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  #1  
Old 10-06-07, 12:39 PM
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Back-feed Through Circuit Breaker Okay Temporarily?

Okay, I know how a circuit breaker works and so I think I know the answer to my own question, but thought I'd run it past you folks for your input. Can you think of any reason it might be a bad idea to temporarily feed a service panel from power coming INTO what is normally the output of a circuit breaker? In my mind, circuit breakers are not directional devices and should theoretically work fine either way.

Two different scenarios I have here:
1) I'm replacing my frighteningly miswired 60 A service fusebox with a 200 A main panel. Didn't want to be without power during the rewiring & main feed switchover, so I've tied 240 V from the old fuse panel's 60 A range fuse back through what will be the 60 A range breaker when new service is connected. This supplies the new panel, to which I now have all the old house wiring connected through new breakers. Main (200 A) breaker is turned off and will stay off until new 200 Amp service is connected. This hookup works fine and I cannot see any potential gotchas here. Any thoughts? Oh, BTW, I just finished switching over the house to the new breaker panel and will hopefuly get a city inspector's blessings on Monday so the local power company can then switch over the service.

2) A friend has an emergency generator that he uses to power his home in the event of grid loss. His technique is very similar to mine -- he turns off the main breaker and back-feeds the panel through his water heater breaker. Works fine. I see where Johns Hopkins APL came up with an "anti-backfeed circuit breaker" designed for making sure an emergency generator does not accidentally get connected to the power grid. I'm guessing it's basically a 3-pole switch + breaker. I don't know if these are commercially available and didn't look too hard, but I bet they're expensive and unnecessary unless, of course, code requires it. Any thoughts about any of this?

Thank you for sharing your wisdom and experience,
Joel
 

Last edited by Joel777; 10-06-07 at 12:40 PM. Reason: enabled email notification
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  #2  
Old 10-06-07, 01:25 PM
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Your first question is concerning a practice that is common in my area but in other areas may have the electrical inspector having a fit.

Technically, when back-feeding a breaker you need to have the breaker "properly" (according to the NEC and the panel / breaker manufacturer) secured to the panel. A "plug-in" breaker is not acceptable without additional means of securing it in place. As I wrote, this may not be a problem for temporary use depending on your local inspector.

Concerning what your friend is doing with his standby generator...he is in violation of both the NEC and his local code. On-site generators MAY NOT be connected to a service that is also connected to a utility without the use of an APPROVED transfer switch, transfer panel or circuit breaker interlock. What your friend is doing can KILL someone.

I had not seen the circuit breaker that you linked to. Notice that it is a new design and that it is not currently in production. Also, before it can be used in the manner you described it will require approval by the NEC and any local jurisdiction.
 
  #3  
Old 10-06-07, 01:37 PM
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furd has addressed your questions nicely.

What you propose works for your system is fine for a temporary basis. The inspector might complain and might make you fix things, but that is a different issue. AFCI and GFCI breakers are not bi-directional, but regular ones are, for the most part.

What your friend is doing (when he makes the hookup) is dangerous, stupid, and illegal. Personally, I would like to see him caught and out in jail. If he ever hurt anyone by backfeeding the grid, he would likely go to jail. If he killed someone the charge would be manslaughter. Please do your best to convince him to give up this practice and make his hookup properly.
 
  #4  
Old 10-06-07, 01:57 PM
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Thank you for the thoughts about code and safety. I wasn't aware of the NEC rule about main feed breakers needing to be secured in place. Makes sense, though, since you wouldn't want a live breaker flopping around in the air like a wild hose just because someone tripped over the temporary cabling.

Now, for my 60A-to-200A service panel retrofit, I'm guessing that if the inspector doesn't like the backfeed, he may just tell me to disconnect it. No problem -- I switch off the backfeed breaker, pull the main fuse, and ask nicely, "Now will you sign off on this so the utility can bring in my new service?" Then I hope and pray that he's having a nice day.

Concerning my friend who may potentially backfeed the grid with his generator hookup and kill some poor pole climber who's trying to restore service, yes, I see your point. I will try to encourage him to a find a safer way of doing this. He's not evil, just innocent and perhaps naive. May I safely assume any electrical supply house (though maybe not Lowe's or Home Depot) sells this type of breaker? Any suggestions on a particular mfr. or product line?

Thanks,
Joel
 
  #5  
Old 10-06-07, 02:20 PM
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Windmills and Co-generators?

Okay, this discussion makes me wonder how folks with home windmills and other cogeneration sources can legally and safely feed their extra power back to the grid. Any idea? Or maybe it's an urban legend that people actually do that. Just curious.

Thanks,
Joel
 
  #6  
Old 10-06-07, 03:06 PM
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Feeding power back to the grid when it is active is a lot different than when the grid is inactive. In order to feed power to the grid when it is active requires that your power be in synch with their power. The sine waves must match. If this isn't the case, one side or the other will jump to be in synch with the other. That, or one side will become so damaged that it will cease to function. Which side do you think will change? The power company, with much larger equipment and much more power behind it, or the homeowner with his little wind mill or other source of power.

Simply put, the equipment that allows the power to back feed the system while it is active, ensures that the system (grid) is active. If the is inactive (ie a power outage), then no power is fed into the system.

I have no doubt that your friend does not fully understand what he is doing. I hope you will explain it to him. My concern is that he learned from someone else or somewhere else that he could back feed his panel in this manner. Someone or something is spreading this dangerous misinformation.

You can buy transfer panels from a variety of source on-line and in real stores, including the big box stores. You can buy circuit breaker interlok kits on-line and at electrical supply stores. I have not seen these at the big box stores.
 
  #7  
Old 10-06-07, 03:16 PM
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Racraft gave the answers.

As for the circuit breaker that you linked to...it is ONLY a patented idea and NOT in production. Many ideas get patented and never go into production for several different reasons. It appears that each load would need one of these proposed CBs if it were to be supplied with either utility or generator power.

Personally, I doubt that this circuit breaker will ever be placed into production as there are easier existing ways to handle the situation.
 
  #8  
Old 10-06-07, 05:44 PM
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Originally Posted by Joel777 View Post
Okay, this discussion makes me wonder how folks with home windmills and other cogeneration sources can legally and safely feed their extra power back to the grid.
Search the net for "grid connected inverter". Any alternative DC source (wind, solar) must be fed through an inverter. Inverters which are designed (and UL tested) for connection to line voltage have interlocks that will not allow backfeed in the event of a mains outage.
 
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