Exceeding standby generator capacity??

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Old 03-24-10, 06:49 AM
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Exceeding standby generator capacity??

Hello,

We are considering purchasing a home standby generator. When the house was built, we had them rough in a generator transfer switch so we could install the actual generator in the future. At the time, we did not know there were different options for transfer switches. Ours is a automatic whole house transfer switch (full service), meaning it is wired into the main circuit breaker box with a single switch. All circuits that are on in the main circuit breaker box will be carried by the generator.

Well now we want to buy a generator, but do not want or need one that will power the entire house. My thoughts are to get one that will power only the circuits we absolutely need and to control that by flipping off circuits on the main circuit breaker box after the generator comes on.

Here's the potential problem. Since most of the standby generators are auto-on, when there is a power failure the generator will come on automatically. I then have to run downstairs and flip the circuits I do not want. I'm thinking it might take me 5-10 minutes to get down there to shut everything off, or longer (ie. never) if for instance no one is home.

What if there is a lot running at the time and these circuits are more than the generator can handle (for instance the central AC)? What will happen to the generator? Will it shut off to protect itself? Will it be harmed? Will it hurt the AC or other circuits in the house?

Thanks,
B

PS. We are looking at the Eaton generators. Has anyone had experience with these? Thoughts?
 
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Old 03-24-10, 07:30 AM
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An "Intelligent Load Center" would handle that situation...

http://www.squared.com/us/products/load_centers.nsf/unid/B004E5665ED5D82B862570D2005BC3CF/$file/intelligentloadcenterFrameset.htm
 
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Old 03-24-10, 07:36 AM
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Originally Posted by Bill190 View Post
An "Intelligent Load Center" would handle that situation...

http://www.squared.com/us/products/load_centers.nsf/unid/B004E5665ED5D82B862570D2005BC3CF/$file/intelligentloadcenterFrameset.htm
I already have an automatic transfer switch installed (and paid $$$ for). This seems like an alternative to that, rather than an add on to the transfer switch I already have. Is that correct?

If so, what can I do with what I already have? And will it hurt anything if I occasionally exceed the generator rating?
 
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Old 03-24-10, 08:41 AM
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With regular transfer switches, you need to manually switch things on or off.

With the new intelligent load centers (which would replace your breaker panel and transfer switch), these would automatically adjust the load. Per this flyer...
http://ecatalog.squared.com/pubs/Ele...1100HO0601.pdf

And with electronic things - electronically controlled things, you can typically adjust how you want things to be automatically controlled. Best to call Kohler generators and ask about this as they are partnering with Squared.

Here is more information from Kohler...
Kohler Power Entrance&prodnum=209961

http://www.kohlerpower.com/onlinecatalog/pdf/g11101.pdf

http://www.kohlerpower.com/common/pd...SellRevise.pdf
 
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Old 03-24-10, 08:58 AM
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Originally Posted by Bill190 View Post
With regular transfer switches, you need to manually switch things on or off.

With the new intelligent load centers (which would replace your breaker panel and transfer switch), these would automatically adjust the load. Per this flyer...
http://ecatalog.squared.com/pubs/Ele...1100HO0601.pdf

And with electronic things - electronically controlled things, you can typically adjust how you want things to be automatically controlled. Best to call Kohler generators and ask about this as they are partnering with Squared.
It looks like the cost of installing this and removing the existing switch and breaker box would be the same or more than just upgrading to a standby generator that would run the whole house (without turning off circuits). The only way I can see that switching everything out makes sense is I could get a smaller gen. and use less fuel. It would take a lot less fuel to to make the return on investment worthwhile.
 
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Old 03-24-10, 09:03 AM
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Hi Bart, just a thought for you and I'm not a pro in this field, but there are probably only a few circuits that would cause a problem, ac, elect stove, or whatever you have that are big loads. If those are the ones you would want OFF when the generator kicked in, could they be run through a control (contactor) where they would drop out before the generator kicked on?

I know power companies sometimes have the capability to shut down large loads during high demand periods, thus they must have a box through which to turn them off.

Just a thought.

Bud
 
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Old 03-24-10, 09:55 AM
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Unfortunately since the ATS is already installed on the main, there's no way to reconfigure it without a decent change to the service and a fair amount of labor.

What I would probably do to re-use as much of the stuff as you can is to add a new main panel upstream of your current panel (maybe with a meter/main combo). Convert your current main to a subpanel, and move the large loads that you do not want on the genny from the existing panel to the new panel. Put the ATS in between the new main panel and the old main panel (now a subpanel). This will allow you to still have the auto transfer capability for the majority of your general-purpose circuits, but have the large loads powered only from the line. How you would actually implement this with as little disruption as possible depends a lot on how it's laid out now.

Yes, the generator has internal breakers or fuses to protect itself in the event of an accidental overload. It will not harm the machine, but you will lose your backup power if it trips.

What kind of circuits do you not want on the genny? It will help to know the scope of the problem if you give us an idea of what you do and do not want powered.
 
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Old 03-24-10, 10:14 AM
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Originally Posted by ibpooks View Post
Yes, the generator has internal breakers or fuses to protect itself in the event of an accidental overload. It will not harm the machine, but you will lose your backup power if it trips.

What kind of circuits do you not want on the genny? It will help to know the scope of the problem if you give us an idea of what you do and do not want powered.
Want/need:
well pump (1hp)
freezer
refrigerator
some lights (CFLs)and ceiling fans
receptacles for box fans
circulating pumps for radiant heat (300 watts max)

optional:
TV (46 lcd)
Microwave (1200 watt)
toaster

No need:
Heat pump
Oven
washer
dryer
dishwasher
dehumidifier

I am looking at an 8kW gen.
 
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Old 03-24-10, 10:25 AM
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That sounds pretty good actually. I think you'll be okay leaving the ATS as-is. Should be no problem with the want + optionals on an 8kW unit. Also no problem with the don't want loads:

Heat pump
This one can be interrupted with an inexpensive relay off the ATS control signal, although I bet the generator will run it if it's less than about 3 ton.

dehumidifier
If it's a portable, not a big deal -- ideal if it didn't run, but won't kill an 8kW genny. If it's built-in it can also be interrupted with the heat pump relay.

Oven
washer
dryer
dishwasher
None of these should be on when you're not home anyway so it would be easy to switch them off if the generator kicks on.
 
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Old 03-24-10, 12:39 PM
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Originally Posted by ibpooks View Post
That sounds pretty good actually. I think you'll be okay leaving the ATS as-is. Should be no problem with the want + optionals on an 8kW unit. Also no problem with the don't want loads:



This one can be interrupted with an inexpensive relay off the ATS control signal, although I bet the generator will run it if it's less than about 3 ton.



If it's a portable, not a big deal -- ideal if it didn't run, but won't kill an 8kW genny. If it's built-in it can also be interrupted with the heat pump relay.



None of these should be on when you're not home anyway so it would be easy to switch them off if the generator kicks on.
4 ton heat pump. Portable dehumidifier. Tell me more about a relay off the ATS control signal? What exactly should I ask an electrician for?

Thanks for your help.
 
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Old 03-24-10, 12:46 PM
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Many ATS generate a control signal when the switch activates. The electrician can install a relay (contactor) which switches off when the transfer switch activates. Relays are a common item for electricians to install, so he should probably be familiar with what you're explaining. How you get the control signal from the ATS depends on the model of the switch.

If your ATS does not generate a control signal, you can still switch the relay using power from the generator inlet. I can't really give you any more specific details without seeing the exact equipment, but I don't think it would be a big deal to set this up.
 
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Old 03-24-10, 05:17 PM
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Just curious, why would you want the circulating pump for radiant heat to run if the heat pump won't be running?
 
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Old 03-24-10, 06:01 PM
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Originally Posted by CasualJoe View Post
Just curious, why would you want the circulating pump for radiant heat to run if the heat pump won't be running?
I can run my backup heat source, a propane fired water heater, if the HP is out.
 
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Old 03-29-10, 09:58 PM
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The Eaton generators sure look a lot like Generac generators. You may want to look into that.

One thing that no one has mentioned...generators can be set to "off", which means they won't start up even if there is a power outage. If you really don't want the auto-start, you can always leave the generator off. Then if there is a power outage, first make sure the stuff you don't want powered by the genset is off, then start the genset manually. You may have to also throw the switch in the ATS once the genset is started. I guess what I'm saying is that a standby (auto-start) genset with an ATS doesn't have to be auto-start.
 
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Old 03-30-10, 08:29 PM
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You may have to also throw the switch in the ATS once the genset is started. I guess what I'm saying is that a standby (auto-start) genset with an ATS doesn't have to be auto-start.
I think most automatic transfer switches will transfer the load to the generator circuit regardless if the generator starts or not. If the generator is set to off, you'll also have to remember to do a regular manual exercising of the generator if you want to be assured that it will start and run when you ask it to. I think I'd just go ahead and spend a few extra $$ and get a generator big enough to handle those loads.

By the way, I think the Eaton and Cutler Hammer labelled generators are made by Generac.
 
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Old 03-30-10, 10:47 PM
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you could leave the genset on for cycling but throw its breaker on the unit off
 
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