Help with generator wiring

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  #1  
Old 08-01-05, 01:38 PM
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Help with generator wiring

First off, I consider myself compentent in load management and would have no problem in managing load (to prevent overload) on a small generator.

With that said, I recently purchased on small 5000 Watt generator. I have contacted 2 electricians about installing a receptacle to connect it to our current breaker panel.

Electrian 1 tells me I need a new panel for the generator (I have seen them at various chain stores). I know installation of the panel will prevent powering a load from both generator and line.

Electrician 2 tells me the 1 is out to lunch, I can run the generator into the main panel as long as I have an interlocked breaker that prevents the generator breaker and main breaker from being closed at the same time.

I want to believe 2, but I also want it done correctly. I would like to know which one is correct.

Second, I have been told that it is possible to backfeed the grid (or turn a generator into a motor once the power returns) even if the main is open through the neutral. Is this possible? And if so, how do either of the methods described the the 2 electricians prevent this from happening (both methods use the same neutral/ground)?

Thanks,
Dave
 
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  #2  
Old 08-01-05, 01:48 PM
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Either method is acceptable by code. However, most people consider it to be a safer option to use a generator subpanel (like the chain store models) or to use a full transfer switch. The interlock system may very well cost as much as a generator subpanel.

Ultimately, it's up to your local inspector and local/state ammendments to the National Electric Code. Sometimes rules vary by utility company also; you generator connection may have to be approved by the power company in addition to the local inspector.
 
  #3  
Old 08-02-05, 10:15 AM
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My decision and another question

Thanks for the input.

My second question in the initial post was regarding a backfeed to the grid via the neutral (white) wire. I do not see how this is possible (with proper wiring), but there are those who warn against it but cannot explain it. Nor can they explain how code wired systems could prevent it (since the neutrals do not pass through a breaker).

I have decided to use a pre-wired transfer box kit that I can get at a local supplier. To verify it met code, I contacted the county and was told such a device meets all codes (makes sense, the box has several breakers/switches that select the supply for selected loads, of course this means I will have access to a limited number of loads on the generator so I have to plan better).

I am going this route because I can do it myself without cutting large holes in the wall to mount a new panel (at least that is what I was told at the store, and looking at the box, it is made for a wall mount with conduit encased wiring to go into the main box).

Here is the big question, the generator is 5000 W, 20 amp rated output on the 220 V outlet. I will be installing the transfer box approximately 50 feet away from the transfer box. As an engineer, I tend to "overdesign things", but I was told at the store, 12 gauge wire to the generator hookup should be fine, but I would feel more comfortable with 10 (actually, I initially thought 8, but based on recommendation, that may be too conservative). The largest load on the system will be a water pump (only on when other circuits are off due to the size of the generator) that draws a little more than a 1000 watts when running, 3000 (+/-) when starting. Is my hunch (10 gauge) correct, or is 12 sufficient?

Thanks
 
  #4  
Old 08-02-05, 10:32 AM
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12 gage wire is probably sufficient.

A transfer switch does switch the nrutral wire as well.

You probably can't run your pump with this generator.
 
  #5  
Old 08-02-05, 10:40 AM
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I'm presuming you meant that the generator inlet would be 50 ft from the transfer panel... 12 ga is sufficient, but I'd go with 10 ga. You may find that the generator won't start your pump and step up a size to a 30A model. I ran a 2.5 hp pump from a 5600 W (continuous) generator and it strained on start up, but nothing was damaged. Your mileage may vary.
 
  #6  
Old 08-02-05, 01:31 PM
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Pump starting?

You don't think a 5000 W generator will handle a 3000 W surge from a no load condition? The pump is a 3/4 horse submersible.
 
  #7  
Old 08-02-05, 01:46 PM
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No. I don't think your generator can handle this. My 5000 (6250 peak) watt generator would not be able to.
 
  #8  
Old 08-02-05, 05:43 PM
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I was just relating my personal experience.... Motor loads are funny though - especially pumps - on small generator power. What happens when the pump motor kicks on is that it will instantaneously require a large amount of current compared to the run current. The current demand would look like a huge spike followed by a declining hump on a graph as there is basically a short circuit for an instant and then declining demand over a second or so as the motor reaches speed. Unfortunately, this demand spike will severely drop the voltage at the generator before the governor can maintain the engine speed, (and may even kill the generator engine). This will, in turn, cause the pump motor to draw even more current as it's start up capacitor has been exhausted. The event doesn't last long - only until the generator gets back up to speed and the pump motor starts turning, or the generator or pump motor just gives up.

My generator is about 15 yrs old and very very heavy and very very expensive compared to what is mass marketed today. As I said, your mileage may vary.

IMHO, the only way to accurately determine if your generator is capable of running your pump - is to power the pump from the generator now and see if it works... before you really need it to.
 
  #9  
Old 08-03-05, 10:16 AM
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This may be of interest; FPN#1, Art 250.20 (D)----

"An alternate A-C power source such as an on-site generator is not a Seperately Derived System if the Neutral is solidly inter-connected to the Service-supplied system Neutral"
 
  #10  
Old 08-05-05, 12:02 PM
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Quote;

This may be of interest; FPN#1, Art 250.20 (D)----


We're not recognizing the "FPN#1" reference. Where can we find this?
Also, do you have any explanation for a backfeed from the neutral alone with both legs open? I'm not understanding this.
 
  #11  
Old 08-05-05, 02:42 PM
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WFO, I don't understand your question. I think PATTBAA answered your question before you asked it. The FPN can be found at Art 250.20 (D) of the NEC. Who is the "we" in "We're not recognizing", and what does "recognizing" mean?
 
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Old 08-05-05, 05:45 PM
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Remember the phrase "It's better to remain silent and be thought a fool, than to speak and remove all doubt"? I feel pretty stupid right now.

I'm not a licensed electrician...I work in high voltage substations. So I did not "recognize" that "FNP" was referring to a footnote in the NEC. Chalk it up to ignorance.

On a disturbing note, none of the "licensed" electricians around here did either. (Now you know who the "we" was).

Our City Council passed a resolution requiring local electricians working in the city to be licensed. When none of them could pass the test, the Council decided to "grandfather" them all in.

You're lucky we figured out "NEC"
 
  #13  
Old 08-05-05, 08:39 PM
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FPN stands for "Fine Print Note". It's a unenforceable comment in the code, offered to add clarity.
 
  #14  
Old 08-12-07, 10:47 AM
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Help with wiring

Hi there,
Can anyone out there help me ? I'm looking for #12AWG wire to repair a generator. Is there a place on the net to get it?
Thanks for the help.

Dale Power
[email address removed]
 
  #15  
Old 08-12-07, 10:58 AM
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Wire is available at any home store, any electrical supplier, or on the Internet. Use any search engine to find it.

Email addresses are not allowed to be posted. It's against the rules, and its unwise.
 
  #16  
Old 08-13-07, 07:17 AM
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The real benefit of using the interlock kit is the time savings of not having to move all the emergency circuits to a new panel and the flexibility of choosing which circuits are powered from the generator.
 
  #17  
Old 08-13-07, 09:57 AM
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I am in the process of a main panel upgrade with a backfed breaker with an interlock kit installed. I read ibpooks' comment that, "Either method is acceptable by code. However, most people consider it to be a safer option to use a generator subpanel (like the chain store models) or to use a full transfer switch."

What are the downsides of a backfed breaker with a properly installed interlock kit? I know the interlock kit is ~$70 (which is expensive for a piece of metal and a screw, but ah well), and you have to be more careful as to which circuits are turned on as to not overload the generator. Are there other potential issues I should be aware of?

Thanks in advance,
Mike
 
  #18  
Old 08-13-07, 10:14 AM
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Originally Posted by Zorfdt View Post
What are the downsides of a backfed breaker with a properly installed interlock kit? I know the interlock kit is ~$70 (which is expensive for a piece of metal and a screw, but ah well), and you have to be more careful as to which circuits are turned on as to not overload the generator. Are there other potential issues I should be aware of?

Thanks in advance,
Mike
The only issue I can think of is you might have problems passing an electrical inspection. My city has a very strict code to where you need a permit to install a new circuit. Our city has put out word that interlocks are not allowed since both mains can be on with the cover off. I did it the "right" way, only because I want my house to pass no matter what. The interlock would be a much more convenient way, especially considering I now have lots of breakers that do nothing in my main as the circuits have moved to the subpanel.
 
  #19  
Old 08-16-07, 02:19 PM
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Fubar - good to know. I didn't really think of it being not accepted by the AHJ. Around here, I doubt they'd have a problem, but it'll be a question I'll ask before doing anything.

Thanks again
 
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