# Load shedding vs ... ?



## lasitter (Oct 1, 2016)

Contemplating a generator and trying to figure out the smartest way to combine generator + transfer switch + load center. Siemens has a generator ready load center, where you install the transfer switch module directly inside the load center. It has protected and utility only setup, but I may be looking for something more. 

I understand the idea behind load shedding, de-prioritizing selected circuits if the generator falls behind. My other consideration is this: If you had a big enough generator for your whole house (13-20kw), why wouldn't you just power everything?

My major area of ignorance has to do with how generator power is connected at the time of grid failure. If you turned on everything at once, the surge could easily be more than the generator could sustain. I'm sure there's a solution out there starts up loads in sequence, so that this outcome is avoided.

Ideas and links to good reading appreciated!


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## aandpdan (Oct 8, 2012)

Not sure where you live, and I'm assuming this is a residence so it won't meet the definition of "life safety." 
Here's what the NEC says:

_NEC ARTICLE 702.5
Optional Standby Systems

(2) Automatic Transfer Equipment. Where automatic transfer equipment is used, an optional standby system shall comply with (2)(a) or (2)(b).

(a)Full Load. The standby source shall be capable of supplying the full load that is transferred by the automatic transfer equipment.

(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_.

So if your generator is large enough to supply the whole house (including start up loads) then you don't need load management. 

Any competent generator installer should be able to do a load calculation for you and determine what you need for the automatic transfer switch/generator size.


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## lasitter (Oct 1, 2016)

*Load shedding, priority circuits ...*



aandpdan said:


> So if your generator is large enough to supply the whole house (including start up loads) then you don't need load management. Any competent generator installer should be able to do a load calculation for you and determine what you need for the automatic transfer switch/generator size.


 This would be a residential whole house unit. The other wrinkle is that I have solar available, but it's not set to operate without the grid. How many kWh do you need to cover a typical 200 amp panel? The only thing I'm really worried about is the initial startup load where everything tries to kick in at once. That's why I was considering a load shedding arrangement. Something that could make sure that the well pump was always covered and could then in turn dump and restart one of the two cooling compressor / air handler loads as needed. 

The idea of intelligent management is appealing to me, especially since prices have dropped since first introduction for commercial users and hospitals long ago.

Maybe some Siemens/Generac genset ready load center plus some of the Powermaster load shedding devices would be an obvious choice. I really like the idea of combining components that are designed to work together ...


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## aandpdan (Oct 8, 2012)

lasitter said:


> How many kWh do you need to cover a typical 200 amp panel?


It depends.

Unless you are electric everything you likely aren't even getting close to 24kw. A load calculation would be a good starting point - to properly size the generator. Bigger generators = more fuel. Not a big problem if you have natural gas piped to the house but you may still need the service line upgraded.

Check out those intelligent transfer switches. A dealer can help you in your decisions. 

You are correct. Your grid tie solar will not function when not connected to POCO.


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## lasitter (Oct 1, 2016)

aandpdan said:


> Bigger generators = more fuel. Not a big problem if you have natural gas piped to the house but you may still need the service line upgraded.


We had natural gas run in from the street in 2015 and have since had as many appliances switched over as possible. Electric stove to natural gas was the first. Electric dryer to natural gas soon followed. Propane fireplace to natural gas was next. Just switched our boiler over from a Buderus oil to a condensing natural gas. That also covers the indirect fired hot water.

All that's all-electric is the usual remaining list of loads and appliances. The biggest draws are well pump and two cooling zones / air handlers. We're planning to upgrade there as well because the current First air handlers pull two kWh just to stir the air -- before any heating or cooling.

So somehow it should be possible to have a generator that just carries everything, and what would be the best strategy to deal with make / break on restart to generator power?


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## lasitter (Oct 1, 2016)

Forgot: We presently have a 400 (something) natural gas meter, which could be upgraded to the 800 (something) largest meter if needed. Gas company said this wouldn't be a problem, since I indicated plans for a whole house generator and multiple on-demand water heaters. I declined to insist on the biggest meter they had right from the start because it would kind of generate some kind of moral obligation to use a matching quantity of natural gas. And as it turns out, our winter rate for gas more than doubled from less than a buck a therm to over $2.25 per therm. 

Ouch!

We just removed an Buderus oil boiler, of course, and in the past year oil has dropped in price by almost half. And now it's headed back up again.

**** near impossible to make the best decisions when different fuel costs are fluctuating so wildly.


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## aandpdan (Oct 8, 2012)

lasitter said:


> So somehow it should be possible to have a generator that just carries everything, and what would be the best strategy to deal with make / break on restart to generator power?


The ATS will handle the transfer. There are delay start kits for your HVAC that will delay the startup so that the generator doesn't get hit all at once. It will also help the compressor in that it won't try to immediately restart it after a power failure.


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## Dan N. (Jul 23, 2015)

On my system I have 22KW Generac sand by, propane fueled, to get the max 22kw, if natural gas fueled; you only get 19.5kw out of the 22kw unit. I have 200 amp service, all electric home. My furnace on emergency heat is 14KW alone. I have load management modules on 3 of the biggest items. Standalone stove, dryer, and hot water tank. When power failure occurs, the load management modules lock out the 3 appliances as soon as the power goes off, because it takes power to keep them unlocked. The Generator starts in 5 seconds, transfer power to the generator by the transfer switch, at 10 seconds. Then my heat pump has a 3 minute lock built into it. The Emergency heat does not have a lock out, it will immediately slam the generator the 14kw about 2 seconds after the generator restores power. It would never overload, because the other 3 major items are locked out until the generator can handle the load. With that said here is the sequence they come back on line.

Power goes out. 5 seconds the generator starts. 5 more seconds the transfer switch transfers from utility to generator. 3 minutes the heat pump would re-engage, either air conditioning or heat, 2 minutes later the 1st lock out module would turn on, which is my hot water tank, 15 seconds later, the 2nd lock out would turn on, which is my range(stove), then 15 seconds after that, the dryer would come on. Now the dryer would have to be restarted by going to it and setting a selection and pushing start, so the actual dryer would not come back on by itself, but power to would be restored. My oven is digital so it would have to be turned back on as well, but the range top is knob controlled and would start heating back up as soon as the lock out module was reenergized. The lock out modules will go on and off line to maintain not having an overload happen. 

When the inspector was here I ask him why I need a lock out on the dryer when I would have to go manually go restart it, seemed like a waste of $100 for the lock out module. He said if the emergency heat was running at 14kw, and I started the dryer with another 5kw, I’m now at 19kw and I could surly have over 3kw from tv’s, lights, and all the other items that are plugged in throughout the house. It would overload the generator, where with a lock out module on the dryer it would cut the dryer and allow the furnace to keep running and support the additional lights or whatever that would be turned on. Which, with the monitor I have I see how easily I can pull 3kw to 4kw from, the kids turning stuff on, wife with the curling iron, microwave, coffee pot, freezers kicking on, operating the garage door, etc. No major heavy load items, but with the lock outs, I don’t think I would ever have an overload.
Check out my YouTube page, I got 3 videos that cover the lock out modules, generator, and a pretty nifty, voltage monitor from current cost that you can use to monitor your load of electricity on and off generator. It’s a little box that connects to the hot legs in your breaker panel and sends a remote signal to a display screen box that shows the amount of the power you’re currently using. The most I’ve seen mine at is 21kw.

https://www.youtube.com/channel/UCdalg07wBEpFaRcp4CAyClA?view_as=public


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