# Generators



## Salvatoreg02 (Feb 26, 2011)

I need to clarify a question that I have. 
Can a 20kw generator back a entire house panel that is 200amps 240volt. The generator has a 100 main breaker. I know the load of the house is 66 amps one leg second leg 53 amps. 
I wanna know if the install is nec complaint. Regardless of load!!


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## Dennis Alwon (May 9, 2009)

Salvatoreg02 said:


> I need to clarify a question that I have.
> Can a 20kw generator back a entire house panel that is 200amps 240volt. The generator has a 100 main breaker. I know the load of the house is 66 amps one leg second leg 53 amps.
> I wanna know if the install is nec complaint. Regardless of load!!


What do you mean regardless of the load. If the generator is rated 100 amps and the panel has a max load of 66 amps then it should be okay.


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## Salvatoreg02 (Feb 26, 2011)

Dennis Alwon said:


> What do you mean regardless of the load. If the generator is rated 100 amps and the panel has a max load of 66 amps then it should be okay.


Rumor is that there was an issue from ecmag or some other mag, that stated you can only back up a 200 amp house with and equal generator cable of handling 200 amps. Anyone here of this


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## MDShunk (Jan 7, 2007)

Salvatoreg02 said:


> Rumor is that there was an issue from ecmag or some other mag, that stated you can only back up a 200 amp house with and equal generator cable of handling 200 amps. Anyone here of this


If that was true (it is not), few generators would get installed. Owners like the ability to select different loads at different times.


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## Speedy Petey (Jan 10, 2007)

Salvatoreg02 said:


> I know the load of the house is 66 amps one leg second leg 53 amps.


How do you know this? I hope not by an amp clamp.


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## Dennis Alwon (May 9, 2009)

Salvatoreg02 said:


> Rumor is that there was an issue from ecmag or some other mag, that stated you can only back up a 200 amp house with and equal generator cable of handling 200 amps. Anyone here of this


I believe you cannot have a generator that is 100 amps feeding loads totalling more than 100 amps with an automatic transfer switch unless there is a system that will shed the loads.


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## tufts46argled (Dec 23, 2007)

We install 20KW generators on homes ranging 1500 to 3500 sq ft with no problem, depending on the set up. Using automatic transfer switches, with load shedding capacity. It's all about load management. New transfer switches dump loads to stay on line. Basically, it is what are you asking the generator to handle. If generators had to handle the entire load of a building or home, then they would never be practical.


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## Salvatoreg02 (Feb 26, 2011)

tufts46argled said:


> We install 20KW generators on homes ranging 1500 to 3500 sq ft with no problem, depending on the set up. Using automatic transfer switches, with load shedding capacity. It's all about load management. New transfer switches dump loads to stay on line. Basically, it is what are you asking the generator to handle. If generators had to handle the entire load of a building or home, then they would never be practical.


Let me rephrase the question. Is it code complaint to backup an entire house panel for a " residential application. " That has a 200 amp 120/240 service with a automatic transfer switch that is capable of shedding loads referred to as " load management. " as anyone done this type of installation and have AHJ pass the installation?


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## jefft110 (Jul 7, 2010)

Salvatoreg02 said:


> Let me rephrase the question. Is it code complaint to backup an entire house panel for a " residential application. " That has a 200 amp 120/240 service with a automatic transfer switch that is capable of shedding loads referred to as " load management. " as anyone done this type of installation and have AHJ pass the installation?


Never hurts to call your AHJ to verify, but as long as the T-switch is service rated @ 200amps and you utilize the load shedding controls, I don't see why it wouldn't be compliant.


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## jefft110 (Jul 7, 2010)

Another thing you may need to consider is if the existing panel is a 3-wire service. 

I believe that once you install the t-switch, it becomes a feeder, and the main panel a sub panel. 4-wire will be required.


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## tufts46argled (Dec 23, 2007)

Salvatoreg02 said:


> Let me rephrase the question. Is it code complaint to backup an entire house panel for a " residential application. " That has a 200 amp 120/240 service with a automatic transfer switch that is capable of shedding loads referred to as " load management. " as anyone done this type of installation and have AHJ pass the installation?


Let me just say, we have never had an issue with an AHJ and we work in multiple districts.


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## tufts46argled (Dec 23, 2007)

jefft110 said:


> Another thing you may need to consider is if the existing panel is a 3-wire service.
> 
> I believe that once you install the t-switch, it becomes a feeder, and the main panel a sub panel. 4-wire will be required.


We wire the ATS and the panel down stream from the ATS 4-wire.


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## Smoke (Feb 25, 2011)

Salvatoreg02 said:


> I need to clarify a question that I have.
> Can a 20kw generator back a entire house panel that is 200amps 240volt. The generator has a 100 main breaker. I know the load of the house is 66 amps one leg second leg 53 amps.
> I wanna know if the install is nec complaint. Regardless of load!!


yes, i did it year before last.
presuming this is a standard house generator:
if the gen.. is nat. gas its only 18kw, lp its 20kw (usually)
also, if you read into the gen manual a bit, its not supposed to be continuously loaded over a certain amount (i think its 50%).
if you look the 100a breaker is only fed with #6 or #8.

i would tell them if they have to serve that load continuously during an outage, the gen needs to be bigger, just to cover your arse when they kill it lol


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## BBQ (Nov 16, 2010)

This was added to the 2008 NEC




> *702.5 Capacity and Rating.
> 
> (A) Available Short-Circuit Current.* Optional standby
> system equipment shall be suitable for the maximum available
> ...


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## Southeast Power (Jan 18, 2009)

Our jurisdiction required us to do a full load calculation on the dwelling and size the generator according to the final calculations.
Most people here ended up with a 40kw. Way over kill due to the fact that the typical 2000 sf house really can only draw 60amps with everything running.
20kw seems to be practical for the average full electric house. 
Maybe the load shed equipment is the way to go. I have only installed one of those and it was a Briggs and Stratton that the owner supplied. 

Did I just jack this thread??


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## hardworkingstiff (Jan 22, 2007)

BBQ said:


> (b) Load Management. Where a system is employed
> that will automatically manage the connected load, the
> standby source shall have a capacity sufficient to supply the
> maximum load that will be connected by the load management
> system.



What are we talking about here with "automatic load management"?

A PLC with inputs that turns contactors on/off? or.... ?


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## Roger (Jul 7, 2007)

hardworkingstiff said:


> What are we talking about here with "automatic load management"?
> 
> A PLC with inputs that turns contactors on/off? or.... ?


That's a little over the top but it could be done. A more common way is to have the desired loads on a seperate panel fed from the ATS.

There are also smart panels that basically performs the same function in a single load center.

Roger


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## BBQ (Nov 16, 2010)

hardworkingstiff said:


> What are we talking about here with "automatic load management"?
> 
> A PLC with inputs that turns contactors on/off? or.... ?


In my opinion anything you can up with.

It might be as simple as using auxiliary contacts on the ATS to break the air conditioning control circuit(s).

I am guessing that for most homes it would be more economical to set a separate panel for the standby loads instead of getting too elaborate with PLCs or other controls.

(Looks like Roger beat me to it while I was typing)


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## BBQ (Nov 16, 2010)

Roger said:


> That's a little over the top


I once used a PLC to control an regular overhead door ...... OK I had spare time, I had the PLC and I was trying to learn programing ......... god help the people that had to figure it out after I was gone.


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## hardworkingstiff (Jan 22, 2007)

If I had a generator tied to my electrical system, I would want to be able to heat water, dry clothes, run my A/C, turn on my heater, or cook, but I'd hate to pay extra to be able to do them all at once as I'm capable of manual load control. Putting selective loads on a separate panel would not allow this.


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## BBQ (Nov 16, 2010)

hardworkingstiff said:


> If I had a generator tied to my electrical system, I would want to be able to heat water, dry clothes, run my A/C, turn on my heater, or cook, but I'd hate to pay extra to be able to do them all at once as I'm capable of manual load control. Putting selective loads on a separate panel would not allow this.


I agree and thought this code change should not have gone in. To me it is a design decision.


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## walter stewart (Aug 10, 2013)

Salvatoreg02 said:


> Rumor is that there was an issue from ecmag or some other mag, that stated you can only back up a 200 amp house with and equal generator cable of handling 200 amps. Anyone here of this


You mean hear of this?! I’ve installed many generators as a matter of fact I’m doing one right now and the service is 200 amp we are putting in a 20 kw generator with a 100 amp main breaker just like you are. Nothing wrong with that at all. They might just not be able to run their HVAC systems, electric hot water, electric, stove with all four burners and oven on, and electric, dryer at the same time! I can’t tell you how many times I have put an amprobe on a 200 amp service and had a reading of no more than 11 amps! The chances of everything running at the same time are slim and you might just have to tell them in the event of a power failure that they will have to refrain from using their HVAC or use those modules that regulate everything from running at the same time! Generac and Kolher both have the modules now.


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## Kevin (Feb 14, 2017)

walter stewart said:


> You mean hear of this?! I’ve installed many generators as a matter of fact I’m doing one right now and the service is 200 amp we are putting in a 20 kw generator with a 100 amp main breaker just like you are. Nothing wrong with that at all. They might just not be able to run their HVAC systems, electric hot water, electric, stove with all four burners and oven on, and electric, dryer at the same time! I can’t tell you how many times I have put an amprobe on a 200 amp service and had a reading of no more than 11 amps! The chances of everything running at the same time are slim and you might just have to tell them in the event of a power failure that they will have to refrain from using their HVAC or use those modules that regulate everything from running at the same time! Generac and Kolher both have the modules now.


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