How to Install a Generator Manual Transfer Switch
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How to Select the Right Generator Transfer Switch: How to Save Money on a Generator Transfer Switch – These two items actually work hand in hand, and the end result will actually be how large the generator will be and there are a few more options that may be much easier to install and much less costly that a large transfer switch. |
Home Generator Transfer Switch
Electrical Question: We want to install a manual transfer switch for a 6500 watt 30 amp portable generator 30amp.
- While an electrician will do work to be safe, we would like to know what is required.
- Issue is the house has two (2) electrical panels > main enters into a 125 amp panel, then feeds across house to another 40amp panel.
- Can we use a 100 amp or require a 200 amp transfer switch?
This Home Generator Electrical Question came from: Ted, from Kensington, Connecticut.
Dave’s Reply:
Thanks for your Electrical Wiring Question Ted.
Installing a Generator Transfer Switch
Application: Generator Transfer Switch.
Skill Level: Advanced – Best installed by a Licensed Electrical Contractor.
Tools Required: Electricians pouch of hand tools and the various power tools necessary for installing the generator and transfer switch.
Estimated Time: Depends on the type and size of the generator and transfer switch and the available access to the project area.
Precaution: Any existing electrical wiring within the immediate area that may interfere with the installation of the transfer switch may need to be relocated if necessary. The selection of the transfer switch or generator connection or generator circuit panel will affect the over all project.
Important: Installing a generator, transfer switch or generator panel must be well thought out and performed with a permit with all work being inspected.
Electrical Code Compliance: Generators and transfer switches should only be installed with a permit and inspected. A generator project is best installed by a Licensed Electrical Contractor.
How to Select the Right Generator Transfer Switch
The process of choosing the type and size generator transfer switch depends on two things:
- What size the generator will be, specifically the volts and amperage rating and capability.
- The actual load that will be placed on the generator.
These two items actually work hand in hand, and the end result will actually be how large the generator will be. Once the size of the generator is known then the type of transfer switch may be selected, and if the size of the generator is not that large then there are a few more options that may be much easier to install and much less costly that a large transfer switch.
Factoring in the Size of the Electrical Service or Panel
If a manual transfer switch will be installed then the size of the transfer switch must be rated as the same size as the electrical service that will be brought into and switched by the transfer switch, regardless of the size of the generator. So, if the generator power will be providing power for a 240 volt 125 amp panel then the transfer switch must be rated for at least 240 volts 125 amps.
Generator Transfer Switch Options
How to Save Money on a Generator Transfer Switch
- When a generator is rated at 240 volts and 60 amps or less then a UL Approved Circuit Breaker Interlock Kit may be installed if one is available and compatible with the electrical panel.
- The point is this, there is no reason to install a large transfer switch if the generator will not produce a large amount of power and there are options for installing one of these other interlock systems or a smaller generator circuit panel.
- However, if you are planning to have the whole house on full power and a larger generator will be installed then yes, you will need a large transfer switch that is rated the same as the home electrical service panel.
More about Generators and Transfer Switches
Home Electric Generators
This series covers a wide variety of topics all about home generators including sizing, selecting, connecting and safely operating this all important addition to your home.
Generator Section
The Importance of a Generator Transfer Switch
Generator Articles
Generator Questions and Answers
House Wiring Circuits and Circuit Breakers
This article looks at common 120 volt and 240 volt house wiring circuits and the circuit breakers that are installed identifying the types and amperage sizes used in most homes.
Electrical Panel Circuit Listing
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Manual Transfer for a Generator
I want to connect at portable 17.5kW generator into my house. Problem: typical manual transfer panel connection will not work, since I have two panels from my service meter; 200A and 150A. they do not feed each other. (350A service to house). how can I best use all the available power from the 17.5kW generator? without rewiring the panels to ensure all the circuits I want to power are in one panel, can I install two manual transfer switches (50A and 30A) and two plugs from the generator? heard this might pose a problem with no power meter to balance the load between the two outputs on the generator, but why is this a problem to begin with? the generator has the two outputs, don’t they expect people to use them in tandem anyway?
Thank you for your help!
Hi Steve,
Commercial and industrial facilities face this type of situation as well. I worked with this first hand while I was the electrician at a hospital where we had three generators and several different electrical service entrance locations, panels and transfer switches which provided emergency backup power for normal, fire and safety and critical life support systems.
With your application I would feel confident that when configured and installed correctly, two power feeds may be extended from the generator to the different locations where transfer switches are installed to provide the necessary separation between the normal utility company power source and the generator power source. There should not be an issue about the watt hour meters because the transfer switch is typically installed after the meter.
If for some reason you are limited to connecting the generator to only one panel then the panel which provides power for the most desired circuits should be the panel that the generator is connected to.
I hope this helps,
Dave
I have an AC and Furnace combo unit outside. Its power ratings are Voltage phase (60 Hz)208/230-1 Volts
Total unit amps 21.2 Min. circuit Ampacity 25.4 Max.Overcurrent Protection 40 amps.
This unit is connected to a subfeed with double 60 amp circuit breaker(overkill?)
Can a Reliance CSR302(30amp) transfer switch be installed at the subfeed?
My generator is a PowerHorse 7000max 5500continuous watts.
Hi Larry,
The 60 amp circuit for the HVAC unit could have been 40 amps, however the 60 amp circuit may be used, but as the label states, the unit should have a maximum of 40 amp overcurrent protection, therefore the service disconnect should either be a 40 amp fuse disconnect, or a non fused disconnect with a 2-pole circuit breaker at the panel.
In my estimation, the generator is undersized when considering that the generator capacity should be rated at least 125% of the total load, especially when considering that the HVAC unit has three motor type loads, the AC compressor, the condensing unit fan motor, and the blower motor. Other factors would be how far away the HVAC unit is from the generator, or how long the circuit cable is for the HVAC circuit.
Dave