sean o'connell
New member
how do i size a generator to a new house.
thank's.
thank's.
help needed for calculations for generator sizing
- Thread starter sean o'connell
- Start date
- Status
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Determine if you want to run the entire house or selected loads.
Most loads are just adding up the KW. Motor loads get a little tricky.
See if the generator mgf has software you can use.
Most loads are just adding up the KW. Motor loads get a little tricky.
See if the generator mgf has software you can use.
goldstar
Senior Member
- Location
- New Jersey
- Occupation
- Electrical Contractor
From my experience I would say that you should calculate and transfer only those loads that absolutely have to run during a power failure (i.e refrigerator, sump pump, well pump, furnace, etc.) and size your generator accordingly. There's no need to run a double wall oven, 3 AC units, microwave, etc. However, if your customer wants every appliance, receptacle, and light to be available during a power outage the generator will end up being the size of a Buick, the transfer switch and related materials extremely expensive and you may end up needing a gas line whose size may not be available in a residence.
Most of the residential gen set installs that I've done have used between a 10K and a 16K genarator and have been more than ample. The auto-xfer switches have come pre-fab with 10-20 breaker spaces depending on the size of the generator. BTW, if you try to call Generac/Guardian (if that's who you're using) they won't give you any info unless you're a dealer. You can become a dealer by committing to buy 2 gen sets a year. You'll also have to go for their training in Wisconsin and you'll have to agree to service any Generac installations in your area.
Most of the residential gen set installs that I've done have used between a 10K and a 16K genarator and have been more than ample. The auto-xfer switches have come pre-fab with 10-20 breaker spaces depending on the size of the generator. BTW, if you try to call Generac/Guardian (if that's who you're using) they won't give you any info unless you're a dealer. You can become a dealer by committing to buy 2 gen sets a year. You'll also have to go for their training in Wisconsin and you'll have to agree to service any Generac installations in your area.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Generac did have a load calculator on their web site, I don't know if it is still there though, they didn't give us much support when we were a dealer, and we installed over a hundred a year until the big box store decided we were going to do them for half price. If you call their tech line, they will not help you unless you have a dealer number.
Sizing
Sizing
This is a great issue that needs to be addressed. With the changes in the 2008 code requiring us to size the generator based on the circuits being backed up (702.5 B) most contractors are over sizing the generator. What is most commonly missed is the remainder of the article ... "or by another approved method." What does this mean? Let?s start from the beginning, the first thing we need to determine is what code cycle are we in and if not 2008 when will it be adopted. What are the sizing requirements our inspector or utility going to accept and in most cases the contractor knows more then the inspector. If we are in the 2005 code the option are much more flexible then 2008, however with the introduction of load shedding devices we can use smaller generators for whole house back up. There are several different forms of sizing, load summation, billing history, power analyzer, Article 220 or clamp on measurement method.
The key when sizing is to understand the requirement of your customer and choosing a transfer switch and generator that best meet the needs. Educating the customer about back up power is a very important step to take.
Remember LRA of the largest motor, is or will the end user have a UPS, lighting control systems, flat screen TV's etc....
Sizing
This is a great issue that needs to be addressed. With the changes in the 2008 code requiring us to size the generator based on the circuits being backed up (702.5 B) most contractors are over sizing the generator. What is most commonly missed is the remainder of the article ... "or by another approved method." What does this mean? Let?s start from the beginning, the first thing we need to determine is what code cycle are we in and if not 2008 when will it be adopted. What are the sizing requirements our inspector or utility going to accept and in most cases the contractor knows more then the inspector. If we are in the 2005 code the option are much more flexible then 2008, however with the introduction of load shedding devices we can use smaller generators for whole house back up. There are several different forms of sizing, load summation, billing history, power analyzer, Article 220 or clamp on measurement method.
The key when sizing is to understand the requirement of your customer and choosing a transfer switch and generator that best meet the needs. Educating the customer about back up power is a very important step to take.
Remember LRA of the largest motor, is or will the end user have a UPS, lighting control systems, flat screen TV's etc....
- Status