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Balance the generator output through a sub-panel



A power failure can be a daunting event. After a disaster has subsided, the injuries are listed and concerns about family, food and shelter are put to rest, you may want to consider the possibility of setting up a backup generator to build in some stability and comfort for your next close call.

But the cost of such equipment varies widely – from a few hundred to several thousand dollars, so it is easy to be overwhelmed by the idea and let it disappear in the coming weeks. But it is a real opportunity. Here are some considerations that you can take into consideration when making your decision.

Planning For a Generator

Getting a good deal is usually at the top of the priority list, and the first thing you need to determine before you shop is the specific power needs of your family, which can differ greatly between households. Buildings use different methods for heating, ovens, cooking, cooling and cleaning appliances.

Performs a review of heavy energy consuming appliances, such as refrigerators, fans, air conditioners, televisions, computers and video game consoles. Then prioritize which of these is the most important to keep going during a crisis.

 Fig 1- Appliance operating periods

Calculating the power load for these units allows you to define the size of the generator you need. Figure 1 lists some electrical appliances that can be classified as priority items, although of course I am up to each household to determine what belongs to the list.

A 30 amp generator (8000 watts) could provide enough power for most people to run the necessary appliances around the house. If you decide to keep a 5000 watt hot water heater online, 22 out of 30 amps will be required just for that, so a bigger generator would probably be better.

 Fig 2- Balancing Distribution

Transmission switch detailed

A transfer switch is designed to isolate the generator from the main panel and supply power to specific circuits in the home. As shown in Figure 3a, it has two bus rails, each connected to a 120V line from the main panel during normal operation, or from the generator during a power failure. In the diagram below, the heavy dotted black contour represents the busbar connected to the black thread entering, and the heavy dotted red contour represents the busbar from the red wire coming in. 230V would be measured across the two. Each switch opposite each other connects to the same busbar and the next pair, up or down, to the other busbar.

Significance of the Switches and Load Assigned Each

A total load of 1800 watts on a switch will require 15 amps while 2400 watts will draw 20 amps and require 12 gauge wires. So if you decide that a 20 amp plug should be available in the kitchen but the current ones are only connected to 14 gauge cables, one must be switched on, or a new plug should be installed.

It is a good idea to treat appliances such as refrigerators, freezers and water pumps (in rural areas) and whatever systems heat the house, separately from the appliances usually needed for just a few hours a day, such as light, kitchen appliances to process food , alternative heat source, hair dryer, clothes wash, etc.

  Fig 3a Actual view of the transfer switch

Split load

Cooking and using a hair dryer or portable heater can add an additional 3000 to 4000 extra watts during peak times, but this can be coordinated effectively with some planning – they do not all need to be run simultaneously. Furthermore, the kitchen counters should be housed with two ampere plugs from different switches and busbars to improve the situation.

 switch bus rod wiring diagram

Calculate the wattage of your priority units on each switch so that you do not exceed its capacity. With a little structuring, the generator's performance can be greatly optimized, which can potentially reduce the size required.

Wiring repair projects should be completed by a licensed electrician, but it is always a good idea to know what you are looking for as a homeowner, as you understand the specific needs of your household.


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