Jump to content
Barms

Generator “load shedding”

Recommended Posts

Man.  It’s been a long time since I’ve been on here. Time flies during lockdown.  
So I’m told because of small diameter gas lines that I can’t get a generator that can power the whole house.   But alas he says you can get a smaller generator that load sheds.   It was an extremely confusing conversation.  We boiled it down that one of my 3 ACs would be on the load shed.   But there was also some talk about like load A. And then load B.   I’m totally confused.   Is this all determined at the panel?  Or at the generator?   What I think is this:   The generator goes on.  I run my house normal.  If too many ACs turn on then one “sheds”?   Means it turns itself off?

does it turn itself off or does it just not turn on?  I’m totally confused.  Then I have to pick which AC.   Do they “shed” it at the panel or at the cindensor itself?   What if later I want to switch what device is “shed”?  Is that hard?  Arrgh was like talking Latin to someone. 

Share this post


Link to post
Share on other sites

I’ve not seen a residential transfer switch that manages loads.  I suspect they may exist but they might be expensive.

A couple of other options you have are....

- a large propane tank. Not ideal in every situation, but an option.

- a manual transfer switch that has 10 breakers. Reliance Controls make a few you can install yourself or have installed if you prefer.  For these you pick the loads you want to run off the generator.  They have 30A and 50A models.  You can gang Up to two breakers for two double pole loads. Like for a well pump.  Even on the 30A model, one of the two pole loads can be 30A.  All other breaker can be 15A or 20A. These xfer switches are usually intended to run off of portable gens with a 30A or 50A out line.  Outdoor connection boxes are used to make the connection. Reliance has good videos that explain install and operation.   So not as easy to use when needed when compared with a whole house gen and automatic transfer switch, but it will keep the important stuff running.

Motor Snorkel makes Tri-Fuel conversion kits for a lot of generators models.

Good luck.

Share this post


Link to post
Share on other sites

Here's an example of a load shed module that can be put on a generator.  https://www.kohlerpower.com/home/home-generators/products?prodNum=GM88281-KP1-QS

 It monitors the generators production and compares it to the demand (what is asking for power).  If the demand is greater than the supply, it will start shutting off non-essential loads to free up power for other stuff.  You and your installer would sit down ahead of time and plan out what circuits are essential and what ones are ok to get shut off whenever the power demand is greater than the supply.  So if you have your 3rd AC running and the well pump kicks on, the load management module would turn off the 3rd AC so there is enough power for the well pump.  When the well pump goes off, power will again be available for the 3rd AC.

Typically, the highest priority circuits are any of the following:

circuits that provide power for medical equipment (think eldery people or people with specific medical conditions)

furnaces (by law in a lot of states, heat is essential while air conditioning is a luxury)

Well pump, sewer ejector pump and/or sump pump 

fire suppression system (if applicable)

refrigerators/freezers

Microwave/stove/cooking device

minimal lighting

Any of those would go into group A and always get power.  Once a load calculation is done for what ever combination of those systems and appliances you have in your house, the remaining power can be allocated to group B. Group B is any additional appliances, rooms, circuits, etc that you would like to use but deem ok to suddenly lose power when something in group A needs to come on.  Most of the items in Group A don't run continuously and when they do run, it's usually for a short period of time and it is rare that they all run at the same time.  With that said, a lot of variables go into how often group B gets dumped to keep group A powered.  Number of people in the house putting a load on the systems, the time of year, type and efficiency of systems and appliances, location and orientation of the house, and quality of building materials all contribute to energy consumption.  

Air conditioners suck up a lot of power along with any sort of resistance heating (electric stoves, electric water heaters, electric furnaces).  While air conditioners are considered a luxury item, I know there are circumstances where there are older people or those with medical conditions being cared for in the home and you would need to have AC as a high priority circuit.  you mentioned 3 AC systems, which is a big electrical load.  I don't know your living situation and I'm not asking you to share it, but if you can't get a generator that will allow you to run the whole house like normal, you may want to consider altering the living arrangements just while on back up power and perhaps run AC in just a part of the house.  This could allow for a smaller generator to provide enough power to other circuits without a lot of load shedding and still keep everyone comfortable and entertained during an extended power outage.

Share this post


Link to post
Share on other sites

i have a transfer switch (APC UTS 10BI) that can do dynamic load shedding, among other fancy tricks.  It's not rated to handle things like AC condensers though (hence my other thread.)  My old/current methodology is to use window A/C units (which aren't as taxing) in case of a long term outage, and either condense activities to a couple rooms, or "flee" to the basement if needed.

As @Regular Guy mentions, I have my loads broken into 2 zones basically: those on the UTS (which eventually will control the generator itself), and the rest that are still exclusively in the panel.  The goal is to have the UTS kick on the generator and supply power to critical loads, until I can manually throw the backfeed breaker into the panel to restore service to the rest of the house.

Share this post


Link to post
Share on other sites

Load shedding is all automatic. Its designed really to manage startup loads. Once a central A/C is up and running it will allow another to start.  it will also dropout  a load if your generator is close to max output.  Another option you can do is a propane tank. I put in a 1000 gallon tank at my house in Florida.  It feeds a Kohler 30RCL. generator.  

Share this post


Link to post
Share on other sites

These were great explanations.  I have a very technical question:  is a CIRCUIT shed or is just the appliance shed?   So I had to pick an AC to shed and yes like you said we would need to alter living conditions for the short term.   That’s easy.  But what if I wanted to “switch” which AC is the shed.   Is it easy to switch?   Is that switch done in the panel?  Or is it a wire that runs to the appliance?

 

Share this post


Link to post
Share on other sites
2 hours ago, Barms said:

These were great explanations.  I have a very technical question:  is a CIRCUIT shed or is just the appliance shed?   So I had to pick an AC to shed and yes like you said we would need to alter living conditions for the short term.   That’s easy.  But what if I wanted to “switch” which AC is the shed.   Is it easy to switch?   Is that switch done in the panel?  Or is it a wire that runs to the appliance?

 

So power comes in the house to the breaker panel.  From there, each circuit begins at its individual breaker.  The breaker protects that circuit.  The entire circuit is shed, not just one appliance.  This is because the generators load shed device is installed by having it connected at the beginning of the circuit.  Larger items like AC units have their own circuit, where as bedrooms usually have room lights, closet light and multiple outlets all on the same circuit.  Depending on when and where the house was built, code may require the microwave and refrigerators to have their own circuits, meaning those appliances are the only thing getting power from their respective breakers.  Other outlets in the kitchen (not electric stove outlet) for things like toaster, blender, etc can all be on one circuit.  So shedding a bedroom would kill power to all the lights and outlets. You can't have it interrupt power to part of the circuit so it cuts off certain appliances or certain outlets.  The device can't be wired to the middle of a circuit.  Those outlets would have to be individually wired to the breaker panel as their own circuit to get them to shut off and leave the rest of the room with power. 

A more expensive load shedding device might have an interface that would allow you to program which circuits have priority over others, but the one I posted a link to is more typical I think for residential.  It has 6 circuits hard wired to it.  #1 has priority over all others.  #6 has the least priority so its the first to get cut off, then 5 then 4 if necessary.  You can't change it without rewiring the circuits to different terminals.  

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

  • Recently Browsing   0 members

    No registered users viewing this page.



×
×
  • Create New...