Load Shedding and Load Calculations

EXECON

Member
Location
MARYLAND
After reading thoroughly the discussions here and in the 2008 NEC regarding the use of Load Shed Modules for Generators I have come up with this conclusion: Huh?

Can I get an answer that is simple and concise please?

How do load shed modules affect a load calculation for a residential system? My customer wants a 20kw unit with a 200a service, and ATS and the entire house is electric. Can I use load shedding to reduce the load calculation total? At present the total load calculation calls for 116.7a. Obviously this is a problem.

Any help would be appreciated
 

GoldDigger

Moderator
Staff member
The only thing the load shed modules do is allow you to size the generator smaller than the calculated load and still use an ATS. If the calculated (or measured?) load is greater than the rated output of the generator, closing the ATS onto that load after starting the generator would cause it to fail or shut down.
You can reduce the load the generator has to supply by installing load shedding modules (controlled disconnects) on specific loads or sub panels downstream of the ATS to allow the generator controller to selectively shed major loads until the actual running load is within the generator rating.
If the background load (lighting, appliances, etc.) is low enough, those large loads like AC can be reconnected and used.
As far as the NEC goes, you just have to calculate the reduction in load that each module can give.

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EXECON

Member
Location
MARYLAND
Thank you GoldDigger.

I understand how the load shedding works and I know what is required to help the generator on startup. I may not have asked the questions properly. Forgive me. When submitting the load calc to the AHJ, what/how will the load shedding modules ratings affect the load calc total? Based on the NEC 702.5 I'm trying to figure out whether the load calc total with load shedding figures included will reduce the total amps required to an amount acceptable to the AHJ. ie...if the current total load is 116.7a, will adding load shedding modules to the cooktop, water heater, and wall oven (which would reduce the total load needed to 84.8) be acceptable. I know each AHJ has it's own thoughts on what might be acceptable and what might not, but as a general guideline per the NEC, will load shedding modules give me what I need to get the load calc down to what should be acceptable?

As I am not always good at expressing my thoughts and questions into words (which my wife reminds of repeatedly) I may still not be explaining my question properly. I apologize again (which I do to the Mrs. alot too).

Thanks for the help!
 
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