# load shedding



## rookie sparky (Nov 6, 2014)

You don't need a transformer to do this. You use the 120 volts available at the t1 terminals to power one side of the dry contacts and use 120 volt coil in your contractor. However, humming is a given.


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## Black Dog (Oct 16, 2011)

dogleg said:


> I need to drop out dryer,h20 heater and a 40amp load for a generac 17000 kw generator.Using a smart switch with load shedding capabilities I wanted to use the contacts of contactor 1 thru 4 (priority contacts) I would supply my own 24 volt xfmer and use appropriate rated contactors with 24 volt coils in an adjacent j-box.When the load increased It would drop out the contactors in sequence.Will this work without buying the pmm kit provided by generac? I assume so if those priority contacts are dry.If not I could drop out the contactors at once using an AC contact.
> The only other problem I see is using contacts to hold in (close) the loads at normal operation ,constant humming,.Maybe someone could suggest a quieter contactor to use.


Can you locate the contactor so the noise is less of a problem?


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## piette (Feb 7, 2008)

Load shedding a dryer is an enormous waste of money. When the power goes out, if the dryer was running it will not turn itself back on unless the home owner goes and pushes the button. Dryers load shed themselves basically. 

Also, the way you are thinking Generac load shedding works is incorrect. Generac load shedding is simple. When the generator starts it sends a 12 volt signal to the transfer switch to tell it to transfer. When the switch transfers it starts a 5 minute timer. A/C 1 or priority 1 will stay off for 5 minutes. A/C 2 or priority 2 will stay off for 5 1/2 minutes. Priority 3 will stay off for 6 minutes and priority 4 will stay off for 6 1/2 minutes. Generac does this to allow everything else to get past the inrush currents and let the generator settle down, then it allows the big items to come back in one at a time. Generac does not however monitor load and shed accordingly.

If thats what you want, you need to do a briggs and stratton or GE generator system. They monitor actual load and shed accordingly.


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## dogleg (Dec 22, 2008)

Okay , yes I am trying to load shed because , of a code rule which states that for an automatic transfer of power the generator shall be sized for the load.This generator was already adquired by the homeowner before he called us.So to be code compliant is why I would consider dropping the dryer load.I agree with you that it seems kind of useless but it does take off the needed wattage of my load calc to get the 17000 watt generator sized to the load.I don't have the code reference memorized but have read it earlier.From your information the generac will not do what I am looking for,but still ac load 1 and 2 open automatically when the genny starts or are they also part of the priority sequence?


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## nrp3 (Jan 24, 2009)

AC1 and 2 and the first two set of terminals to the contactors operate at the same time.


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## dogleg (Dec 22, 2008)

I just read your post again and realize that ac 1 and 2 still will come on in priority sequence.I need to figure out how to shed the load at start up of the generator maybe voltage sensing relay on the genny feed side to open up the chosen circiuts??


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## nrp3 (Jan 24, 2009)

The loads are off at start up to allow for AC condensers and not starting until pressure has been bled off.


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## dogleg (Dec 22, 2008)

Maybe use some type of isolator(piece of rubber or bakelite between the the metal parts) to reduce noise.Can't really move the location but it in the utility room maybe it won't be an issue?


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## nrp3 (Jan 24, 2009)

What about mechanically held contactors? You don't need to use the 12v pmm kits. You can jumper t1 and neutral to the terminals on the load shed controller instead of the 12v.


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## nrp3 (Jan 24, 2009)

These guys have all sorts of aftermarket load shed stuff. Haven't tried any of it yet, but worth a look:

http://www.pspproducts.net/GeneratorCatalog.pdf


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## samgregger (Jan 23, 2013)

Could you use the 12v signal from the generator to open a contactor?


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## Sparky J (May 17, 2011)

nrp3 said:


> These guys have all sorts of aftermarket load shed stuff. Haven't tried any of it yet, but worth a look:
> 
> http://www.pspproducts.net/GeneratorCatalog.pdf


It's funny these guys are (or were in early 2000) a small family business that started selling surge protectors and other electrical equipment as a side business. The wife (co-owner) is a realtor and sold me my first townhouse in 2001. I'm sorry but I have not used any of their products though.


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## Sparky J (May 17, 2011)

Sorry to steal the thread. Carry on.


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## dogleg (Dec 22, 2008)

The load shedding module will monitor the generator while it is operating to ensure it is not overloaded. If the generator becomes overloaded, (if the engine frequency drops) the load shed module will shed all of the connected loads, reducing the demand on the generator. The load shed module will then begin a five minute timer, after which, each load will be brought on in priority order, typically via 30 second stagger start. Each time the generator becomes overloaded, the load shed module will intervene to prevent the unit from shutting down.
Thanks for the info people , basically the generac nexus is a form of load shedding which I'm sure will meet code as it will continue to shed load and keep chosen loads off if the current rises enough to slow the RPM down.So in fact it is a load shedding transfer switch.
Thanks to nrp3 I did buy some relays and modules from that website you suggested.I could have built my own relay box but they offered everything I wanted in a box.Just have to pass it on to the customer.:thumbsup:


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## dronai (Apr 11, 2011)

piette said:


> ally.
> 
> Also, the way you are thinking Generac load shedding works is incorrect. Generac load shedding is simple. When the generator starts it sends a 12 volt signal to the transfer switch to tell it to transfer. When the switch transfers it starts a 5 minute timer. A/C 1 or priority 1 will stay off for 5 minutes. A/C 2 or priority 2 will stay off for 5 1/2 minutes. Priority 3 will stay off for 6 minutes and priority 4 will stay off for 6 1/2 minutes. Generac does this to allow everything else to get past the inrush currents and let the generator settle down, then it allows the big items to come back in one at a time. *Generac does not however monitor load and shed accordingly.
> 
> *If thats what you want, you need to do a briggs and stratton or GE generator system. They monitor actual load and shed accordingly.





dogleg said:


> *The load shedding module will monitor the generator while it is operating to ensure it is not overloaded. If the generator becomes overloaded, (if the engine frequency drops) the load shed module will shed all of the connected loads*, reducing the demand on the generator. The load shed module will then begin a five minute timer, after which, each load will be brought on in priority order, typically via 30 second stagger start. Each time the generator becomes overloaded, the load shed module will intervene to prevent the unit from shutting down.
> Thanks for the info people , basically the generac nexus is a form of load shedding which I'm sure will meet code as it will continue to shed load and keep chosen loads off if the current rises enough to slow the RPM down.So in fact it is a load shedding transfer switch.
> Thanks to nrp3 I did buy some relays and modules from that website you suggested.I could have built my own relay box but they offered everything I wanted in a box.Just have to pass it on to the customer.:thumbsup:


I don't know why Piette said that, he is wrong. Yes you are right, that's what the modules are designed to do.


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## nrp3 (Jan 24, 2009)

The GE system monitors amperage opposed to frequency and has more intelligence built in . Whether using frequency or amperage is better, I haven't had enough experience to tell. I sell both brands and will be trying some GE product with management modules soon. I like the idea that I can juggle 8 loads instead of 4 with two shared. I can also drop as many as I like.


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## dogleg (Dec 22, 2008)

I Like the generac features as compared to Milbank.Our supply house furnishes Milbank and I have installed 3 10kw units(Milbank).Out of the 3 two have given me problems with overspeed .One to the point where I purchased a manometer to check the gas pressure ,frequency meter and tiny tach.All looks good (within the parameters by the tech dept.)but on it's own it drops out intermittenly and twice during power outages.To say the least the homeowner has been patient.I just changed the board out as a last resort before we pulkl the whole unit out, all under warranty and they have been good to work with , but I don't need the headaches or time to deal with the reliablity issue.


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## nrp3 (Jan 24, 2009)

I have always liked the generac controller for its ability to allow you to set the exercise time instead of those stupid push the button and hold at the exact day and time the customer wanted it to exercise. The history function is nice too. The downside to the nexus was that you couldn't update the software without replacement. The evolution is more complicated, but at least you can update software. Now Briggs has these features on many of their models. I don't work enough Briggs to judge the reliability yet. Most installers I have talked to have had good luck. Driving three hours out to the middle of nowhere tomorrow for a annual service and transfer switch fault.


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## dogleg (Dec 22, 2008)

So an advantage to getting into these installs are the once a year change the oil, air cleaner and load test? More revenue.:thumbup:


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## nrp3 (Jan 24, 2009)

More revenue yes, but don't be one of those oil changers. Sell some value. Clean up the debris, look for damage, gap the plugs, check the voltage and frequency, open up the transfer switch and watch it transfer. Price accordingly, but catch the problems if you can before they become problems. Can't always but try. Change the batteries regularly. Clean the terminals and use a battery tester.


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## McClary’s Electrical (Feb 21, 2009)

nrp3 said:


> More revenue yes, but don't be one of those oil changers. Sell some value. Clean up the debris, look for damage, gap the plugs, check the voltage and frequency, open up the transfer switch and watch it transfer. Price accordingly, but catch the problems if you can before they become problems. Can't always but try. Change the batteries regularly. Clean the terminals and use a battery tester.


Don't forget the second servicing on 14,17,20 kw requires valve adjustment also


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