Selecting Transfer Switches for Home Generators?

RC 6 Circuit Transfer Switch

RC 6 Circuit Transfer Switch

Selecting transfer switches for my house or business generators, what you need to know to make an informed decision.

Should I Consider a Transfer Switch for my Home or Building?

Transfer switches are used to allow you to provide power to your home by hooking up your portable or standby generator output directly into your house wiring system. It can connect power from as little as one major circuit up to 10 or more.

Code considerations?

There are a number of code requirements to hooking up a transfer switch, and unless you are sure how to connect one you should use a qualified electrician to install the final wiring. It may also be a requirement of your Local County or municipality.

Extension Cord vs Transfer Switches

Extension cords are needed to hook up appliances from your generator unless you install a transfer switch directly into your dwelling. This wired option eliminates the need to store several cords and eliminates the time to run them to appliances and plug or hook them up.

It provides for easier power management and less effort on your part to accommodate your power requirements. With good power management it allows smaller and more efficient generators to be used.

There are several other types of electrical equipment that cannot use extension cords. Well pumps, some sump pumps, and furnaces are typical of those items requiring a transfer switch. These are often single or dual circuit switches specifically for these items.

How a Transfer Switch Works

Transfer Switch Make-Before BreakIn electrical talk for using alternate power sources, a transfer switch is a break before make switch. That simply means that it breaks the main power circuit from the utility before it makes a circuit from the other side for your personal generator.

They have a three position switch as “ON-OFF-ON” or may use “LINE-OFF-GEN” This prevents a back feed into the utilities power lines. When you go the opposite way it breaks the local feed before connecting the utility feed.

A transfer switch is installed as a hard-wired breaker panel next to your main breaker in your dwelling be it your home or business. It allows you to easily supply power to a partial number of circuits you decide that are necessary in an emergency or when the utility power is down.

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Guide to Choosing Transfer Switches

Transfer switches come in various options and sizes. These options and other considerations can be confusing to the uninformed, the objective of this article is to cover several considerations to help you make better choices and decisions for your own needs and wants.

The following considerations are discussed below and you should have a firm understanding as to function and needs when making these choices.

  • Manual vs Automatic
  • Single circuit to multi circuit and dual circuit
  • Indoor vs outdoor
  • Unwired and pre-wired
  • Direct plugin vs hard wired

The available household transfer switches are designed to supply power to a limited number of circuits in your house and is usually based on wattage that will be supplied. Typically you’ll see 6 circuits for 5000 watts or 8 or 10 for 7500W.

With very large units at 10kV to 20kV or more you can get panels that would nearly have as many as your main house panel. Of course some smaller homes only have 6 to 8 circuits.

The multiple circuits give you a capability for power management by switching on and off circuits you may or may not need to be able to utilize the power supplied to the house. That will allow you to base load some circuits and then alternate, say, the fridge and freezer circuits to manage the larger appliances.

Individual switches will have circuit breakers typically at 15 amp or 20 amp, although there may be options for 30 or 50 amps depending on the service needed. The number of switches and amp ratings vary depending on the model and number of circuits available.

Additionally the transfer switch can have what is called a dual pole circuit for running 240V appliances such as electric dryers. Tthis is commonly accomplished with a tie bar across two single switches which is added at the initial time of wiring.

Deciding on a Manual or Automatic Type of Transfer Switch

There are two main types when it comes to buying your transfer switch; either a manual switch or an automatic switch.

In the case of portable generators the manual option is used most often. The automatic transfer switch is used with portable generators that have an electric start (with remote capability) or more typically with standby generators that are at a fixed location.

Do you have a need for an automatic transfer switch?

Those considerations are:

  • Do you have an essential facility –
    • Must your home or office be available for emergency services or provide a necessary function to society?
    • It could be that you’re place would be a gathering point for neighbors or officials and having the automatic function would be highly beneficial. Although not everyone will agree, but I could see that the local tavern might be just such a requirement. After all, if we can’t watch TV then maybe we’d better have cold adult beverages.
  • Disabilities or restrictions
    • Do you have folks with disabilities that would limit your access or capability to do things manually in case of an power outage?
  • Peace of Mind
    • Does having an automated system give you comfort knowing that if you are not there your family would not know how to get the power up and plugged in?
  • Shear unadulterated convenience
    • Convenience is a personal thing and stickily up to you when it’s considered. If you have a larger home or more appliances to be used, or experience many outages, then an automatic transfer switch with standby generator may be a convenience you would desire.
  • Funds and Effort
    • Do you want to spend the extra money and effort to go automatic? Automatic switches require additional installation time and knowledge to install as well as can have a direct impact on the funds you may want to spend.

Here are a couple of examples of manual and automatic switches.

Manual Transfer Switch:

Automatic Transfer Switch:

In most cases, having immediate instantaneous power available will not apply to vast majority of us. We can surely survive a few minutes or even a couple of hours if need be. Therefore, a manual switch is the base line to select and going automatic will be purely a personal decision based on other considerations, such as installing a permanent standby genie.

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Single to Multi Circuits and Dual Circuit

Picking which circuits and how will I run them.

main panel wiring

Main Panel Wiring

The next consideration is in coming to grips with what appliances or electrical equipment you will want to power and when you will want to run them. Do you need a 4, 6, 8, or 10 circuit transfer switch? See below about translating that for the normal user.

You’ll need to consider amount of total power needed as well as how big a generator you have or will need. In your home you’ll be adding up appliance power needs and which circuits they are on. These will become your important circuits.

Next you need to determine which circuits will be used on at least a nearly continuous basis and which will be used on an alternating basis allowing you to manage the power available from your generator.

You may well have 20 circuits or more in your home and if you get a ten circuit transfer box you’ll have to decide which of the main circuits you want to power and which can be left without power. (I suppose you can elect to use two transfer boxes and an additional generator to power the second set of 10, but let’s not get carried away yet.)

In the basic 10 circuits you will be able to power up to your generator maximum rated supply. Keep in mind however, that you’re also limited by the individual circuit breaker maximum amperage which is likely 15 or 20 amps, but can be as larger depending on the specific switch specification.

On a twist lock L14 you will have two supply circuits and they will likely be in the 20 to 30 amp range for each circuit from the generator. That provides up to 3600 watts in each circuit for around 7200 watts. (Assumes a 7500 watt rated output).

For the individual house circuits that might average about 5 amps (600W) per house circuit if all 10 are in service (5 per circuit). Alternatively, if you use 4 circuits as primary (2 each supply) you will have 12.5 amps (1500W) on average for those circuits.

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Power Need Evaluation

How Many Watts do I need?

How Many Watts?

How does this circuit supply translate for a normal user?

First let’s say you have a house with 15 circuits, but you need to power different rooms at different power requirements. And you have determined that a 4000W generator is enough to meet your needs. The recommended transfer switch configuration would be a 6 circuit for up to 5000 watts, which is configured for 4 single (15A) circuits and two 20 amp circuits which can be tied as a dual pole (2-20A breakers).

We could set up simple table like this:

Continuous need

Circuit watts to power amps needed
Kitchen 1800 15
Living room w TV 600 5
bedroom 360 3
bathroom 240 2
Intermittent need    
Fridge 750 6.25
Dryer* 4000 33.33
furnace fan 700 5.8

* Right off the bat we see that the dryer is likely to be a problem unless we turn everything else off.

Likely we would wire 6 circuits without the dryer and use an L14 extension cord for running it; if it was really needed. In this case we’d wire the kitchen to a 20 amp circuit and maybe the living room with everything else to the 15 amp circuits. We’d be able to run 4 circuits without worry and then alternate the fridge and furnace to keep it under our generator max load.

However, should you have purchased a 5000W generator you’d likely be able to run everything as needed except your big dryer load.

Power Management requires rotating load

When considering a power management plan you need to consider the circuits you are most likely to use continuously and what you’ll be powering on a rotating basis. Therefore, you can manage to use fewer items and alternate your power needs to effectively use a generator with less power output and more fuel economy.

One way to manage your power needs is to wire up base loads and move them to one or two circuits to maximize consumption to few circuits. Then utilize the other circuits to provide intermittent loads. It might be good to consider two circuits in a kitchen one for small appliance and hot plate and one for the fridge. With planning ahead on wiring you could do this on the separate power supply circuits from the generator in the L14 plug. See load balancing below.

One thought about power usage is replacing high wattage bulbs with the CFLs or LEDs to reduce the needed power consumption, this may provide useful

Manual transfer switches are not difficult to learn.

Nearly anyone in the family can quickly learn how to use them once they have been installed properly for power management. Of course having a larger generator with enough to power for all your needs is another approach, but you’ll use more fuel and have less available power over the long run.  

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Load Balancing with Transfer Switch

Load Balancing comes into play once you’ve decided your power management needs. In multi-breaker transfer switches each of the two circuits supplied by a L14 plug is tied to side 1 or side 2. To load balance you create a chart that accounts for the circuit (toggle switch), the item to be hooked up, running watts, and starting watts if needed. An example chart is here could be based on using a 6500W* generator with 7500W surge capability.

Also see our article: Watts Needed for Your Generator? on determining your needs.

Load Balancing Table

Side 1 Supply   Side 2 Supply
Switch Item Run Watts Starting Watts   Switch Item Run Watts Starting Watts
1 Refrigerator 750 500   5 Freezer 1000 1250
2 Kitchen 1250     6 Family TV Room 800  
3 Bedroom 500     7 Bathroom 400  
4 Basement 350     8 Furnace 750 1500
Total 2850     Total 2950  
Max Surge   500         1500
               

Calculating the load balance and max usage:

  • Total Running Watts = 2850W + 2950W = 5800W
  • Max Surge Watts = 1500W
  • Generator Max Running > Total Running = 6500W > 5800W* therefore OK
  • Generator Max Starting > Total running + Starting = 7500W > 7200W* therefore OK

* Output should be adjusted for elevation losses and other factors.

** Technically, some would argue that the running watts are not in effect for the initial surge so a lower total run + surge is all that is needed. This simple calculation just makes sure you have adequate margin.

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Inside or Outside Transfer Switch Box

Most transfer switches come in two models either for indoor or outdoor service.

Outdoor service is usually labeled with a NEMA 3R designation, sometimes referred to as rain tight, and indicating that the enclosure is suited to outdoor environmental conditions.

The choice as to whether to use an outdoor or indoor service may depend on the following considerations:

  • Available space – do you have space internal to the building to mount and connect to your panel box? You do have a potential to bring the switch inside and wire out to the main panel.
  • Access – your panel box may be a defining issue as to where it can and should be located. If your panel is already on the outside of the house that may be the only point you have to mount it.
  • Security concerns. External access also allows would be vandals or other interests to access your unit without your authorization. This can really depend on your community or property access. This is an area you definitely need to decide the level of risk associated for your specific circumstances.  

If you decide to have your box on the inside it will likely be hardwired with a Power Inlet Box to the outside wall. You could use an outside box on the inside which would allow you to plug an extension cord into it, but seems to defeat the purpose of using an indoor box.

Where your generator is located and the distance to the transfer switch or inlet box will determine where and how you may want to set up the switch.

You’ll be locating your generator away from windows and doors and typically like to use a 6 or 10 foot connection cord to make the shortest connection possible to reduce voltage and line losses. Thus locating the inlet box and transfer switch becomes relatively straight forward.

Configurations – Wired or Not

Transfer switches can come without wiring and are wired by you or an electrician. Many come fully pre-wired. Prewired switches are more expense, but worth it for installation ease. Frankly we believe that having wires already in place is a time saver and is alleviates part of the labor grief in getting your switch installed.

Possible the only drawback may be if your installation of the switch is further away from your panel than the wires are long.  Be sure to check out the length of wire supplied before getting a prewire box or you’ll be adding junction box and adding more wire. In that case you should have just got an unwired one.

Direct plugin vs hard wired

As touched on above you have the hard wired and plugin options to consider.

First the outdoor are typically plug in, but can be hardwired in many cases to standby generators which are permanently fixed locations.  Indoor or typically hardwired to an exterior inlet box.

There may be cases where you have an easy opening in your garage or shed and being able to pull a plug into the inside unit would work. An exterior switch can just as easily be mounted inside. It would be protected from the kids water pistols that way!

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Installing a transfer switch

In many cases with the right knowledge you can install your own transfer switch however, some code enforcement agencies will require a licensed electrician to install if not at least wire the switch. You should always check with the local county or city on requirements before installing one yourself. Typically your utility is only responsible for the incoming power up to the house meter, but may provide optional services for hooking up a transfer switch.

For a more step by step approach to actually installing a transfer switch you can refer to this article at wikihow: Step by Step to Install-a-Transfer-Switch

Other installation considerations

transfer switch panel locationInstalling the switch has a few other considerations that you may want to explore before purchasing your unit.

  • Location of main panel
  • If pre-wired the length of the Transfer switch pigtail for connection to main panel.
  • Location of where inlet box will be located for internal switch.
  • Safe location of generator to protect against exhaust inlet
  • Need for extension cord for inlet box or exterior box hook up.
  • Surface mount vs flush mount switches. An additional flush mount kit may be needed.

Additional information

Reliance controls is a leader in home protection and has many configurations for transfer switches. If you want to learn more specifics we encourage you to take a look at their frequently asked questions page: Reliance Controls Transfer Switch FAQs

Maintenance and testing

This should, and dare we say “must”, be done regularly to ensure proper operation. Of course the manufacture will provide recommendations for testing and maintenance and we suggest you schedule this on a yearly calendar. Especially if you have seasons where it is likely you may lose power. Better be prepared than spending time trying to fix!

For manual switching you can safely perform generator/switch testing while the house is still on utility power as the switches are break before make as discussed previously. There is no risk of line power getting to the generator or generator power feeding the line, if everything has been wired correctly. Individual circuits can be flipped to make sure things are working before a power outage occurs.

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Summary

Many folks don’t give a lot of consideration for buying a transfer switch. As I’ve demonstrated here there one should be aware of the various considerations to make informed decisions. Each individual transfer switch will also have its own unique quarks.

Be sure to check out our posts about specific transfer switches and various types we have looked into.

View various switches:

The following links will take you to Amazon to view a selection of switches available from various manufacturers and suppliers.

Reliance Controls Transfer Switches Generac Transfer Switches Go Power Transfer Switches Progressive Dynamics Transfer Switches

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