Transfer Switch for a Portable Generator

Reliance Controls 6 circuit Transfer Switch with 4 prong 30Amp Receptacle

This article will give you a basic understanding of how a manual transfer switch is used with a portable generator. You’ll learn how a manual transfer switch differs from an automatic transfer switch. This explanation will be rather elementary for the more experienced. It is meant as education for someone with little or no knowledge of the process.

Let’s say you experience a power outage and you want to use your portable generator to give you some of the comforts in your home. A transfer switch allows you to connect your generator via a suitable power cord from your generator to your selected circuits on your home’s power panel. You can then switch the power source from the power utility, which is down, to the power generated by your generator.

A transfer switch like the Reliance Controls 6 circuit model pictured above, is an electrical switch that switches a load (electrical supply) between two sources. It’s for those who choose not to run generator cords throughout their home.  but you must first decide where the power will be allocated within your home by selecting the appropriate circuits.

Your home requires more power than can be supplied by a portable generator. The size of the generator you have will determine how much power you can use in your home. For example the mid-size popular 5000W models would no way be able to provide the 20,000W or so, supplied by many standby generators. So we must determine how best to use our available power.

When you look at your home’s electrical panel, you see many circuit breakers labeled, for example, refrigerator, oven, kitchen outlets, bedrooms, living room, washroom, air conditioner, etc. Your transfer switch will tie into some of these and provide power to the circuits that you choose. For example, maybe you want your outlets of your kitchen, bedroom and living room to be supplied power, while leaving your AC or garage or guest rooms without power. The circuits in your transfer switch would then be connected to the circuits that you want to use.  This is referred to as mapping.

This mapping of your needs up front will be time well spent before you do any hard-wiring. You’ll want to balance your proposed draw as equally as possible to the two sides of your transfer switch.

Reliance Controls 10 circuit transfer switch with 4 prong 30Amp receptacle

Typically you would choose between a 6-circuit model, suitable for up to a 5,000 Watt generator, or a 10-circuit switch (Reliance Controls model pictured above) for the larger 8kW portable generators. These are able to support 30Amp or 20Amp output from your generator and the 120volt or 240volt capability.  There are all sorts of variations (8 or 12 circuits), or with higher capacity to accommodate 50Amp generators with 12kW outputs or more. Much larger than that and you’re approaching standby generator abilities which loses the versatility of the portable generator.

Note: if you are the least bit confused by electrical terminology and wiring, have an electrician perform the installation. It will be a few hundred dollars well spent if even for the peace of mind knowing it was done right. The installation is, of course, governed by the NEC.

The Best Deal is a Kit

When shopping for a transfer switch (Amazon), you can find the main brands Reliance and Generac and some others. You can get the individual pieces that you need, or you may choose to get a kit that includes the switch, inlet box for your generator cord, a 30Amp cord to connect your generator, and even a 20Amp replacement plug if your generator only has a 20Amp outlet. Again, unless you already have the smaller capacity 20Amp generator, I recommend getting one with the 30Amp L14-30 outlet if a transfer switch is in the cards for you.  You will be glad that you have the extra available power and versatility at just a bit more cost.

Although you can purchase a transfer switch for a 20Amp supply, I recommend that unless you have very little power needs, that you not consider using a generator that only supplies 20Amps. For a smaller generator like this, you may be better off just running cords to selective appliances.

If you don’t have a generator yet, and you are considering hooking into your home panel from time to time, get yourself at least a 5000W model with 120/240 capability with a 30Amp locking receptacle (type L14-30). Remember, the more power available, the more things you can run at the same time, or not have to worry about shutting things off to give you enough power to run something else.

What Power Cord Should I Get?

30Amp 40 foot cord by Reliance Controls for connecting generator to transfer switch

If it doesn’t come in the transfer switch kit, you’ll need a cord (30Amp) that you plug into your generator with the other end capable of plugging into your transfer switch receptacle box. This cord can be pricey. The one included with a kit is usually only 10 feet long. If your generator must be further away from the switch, you’ll need to get a longer cord anyway.

When the power goes out, you simply crank up the generator and run this power cord from it to a transfer switch.

Once the generator is running, you can choose which circuits to energize by simply flipping the switches on the transfer switch.  A kit is a good way to go since a cord and the outlet box can cost approximately $50 each separately.  Remember that the cord may be a bit short though.

Check out the article on this site to understand the relationship between cord length and gauge.  How Amp rating is affected by gauge.  You want to choose the correct generator cord for you use whether you are using it to hook into your home’s power panel or running cords through your home.

Are They Hard to Set Up?

From Reliance Controls, you can purchase just the switch, or the switch and outlet box, or you can purchase a kit which also comes with a cord as well.  The kit is a much better deal than purchasing the components separately.  The sales of the kits over the individual pieces would indicate that consumers agree.

Lets take for example a 6 circuit switch like the Reliance Control Pro/Tran. This is the best seller for a 6 circuit transfer switch with several great reviews.  There are four 15Amp circuits and two 20Amp circuits. The two 20Amp circuits can be combined into a 40Amp circuit to allow you to use your 240 Volt ability of your generator.

Reliance Controls 6 circuit Kit including 10ft 30Amp cord, outlet box and extra plug for 20Amp generator.

Reliance Controls 10 circuit Kit including 10ft 30Amp cord, outlet box and extra plug for 20Amp generator

In the 10 circuit switch (Reliance Controls 31410B), there are six 15Amp and four 20Amp circuits. Here you can combine two sets of 20Amp circuits. This type would be suited to generators up to 8000 watts.

Most transfer switches come pre-wired with the circuit breakers already selected. If you have a unique installation, you should purchase a transfer switch with interchangeable breakers, so you can modify it exactly to your needs.

Keep in mind that your loads should be balanced, so that you are not pulling too much from one side over the other. Transfer switches come with wattage meters so that you can keep an eye on the wattage draw. Without them, you can overload the system, damaging your generator and appliances.  Again the importance of mapping out your needs before wiring comes into play.

You have two options when installing a manual transfer switch. The easiest and least expensive way is to install it on the wall like you would mount a picture frame. This option works well in garages where looks is not a priority.

Mounting kit for recessed 6 circuit transfer switch

If style matters, you can buy a mounting kit to recess the manual transfer switch into the wall. You simply inset it into the drywall between two studs.

The electrician that performs the initial installation (or you) does not have to cut incoming power and perform heavy service entrance conductor work during the install. All you have to supply is a 60A double-pole breaker to match the service entrance panel make and model.  If this sounds foreign to you like it does to me, hire a professional.

By design, when properly installed it is a physical impossibility for both power sources (power grid and generator) to supply the load simultaneously. It’s impossible for the two sources to mix — or for one source to backfeed into the other. Otherwise a lineman working on what he thinks is a dead power line could be seriously injured by the wattage supplied by your generator.

What About Grounding?

Be sure to ground your generator as described in the owner’s manual. You can connect the generator’s chassis ground to your home’s grounding rod, or buy an 8-foot grounding rod and ground according to your generator manual instruction.

There is a difference between Gounded Neutral vs. Floating Neutral. You can have an issue if you’re double grounded (at the generator and at the transfer panel). You only want one path to ground. Again, the particulars are beyond my understanding.  If confused, get that electrician!

Most portable generators are bonded neutral. The reason being is the unit then is grounded to the frame so there is no shock hazard.  Manufacturers know that most consumers use them as without grounding them properly due to their portability. They should be changed to floating neutral when you are installing to the transfer switch. You (or your electrician) can convert to a floating neutral configuration by breaking the neutral-ground bond.

How Does an Automatic Transfer Switch Work?

Automatic Transfer Switches are usually used with Standby Generators, the non-portable built-in generators used exclusively for power outages.

An automatic transfer switch (ATS) continuously monitors electric utility power. Fluctuations or serious power  issues, which might indicate an upcoming outage, trigger a start command to the generator. After backup voltage and frequency stabilize in the generator, the transfer switch brings the generator online. Once electric utility power is restored, with no fluctuations for a predetermined amount of time, the switch goes back to its normal position. After a cooling down interval, the generator is automatically shut down. All of these actions take place with no human intervention.

Yes automatic is more convenient, but standby generators are much more expensive.

Summary

To cord or not to cord, that is the question.  Would you like to run generator cords throughout your home in a power outage, powering appliances by sharing plugs?  Or would you like the convenience of plugging in your appliances into your normal wall outlets?

With just a bit of preparation you can have the latter convenience.  Keep in mind the the convenience comes at a cost.  A one time fee for the manual switch (and installation) can’t be avoided.  In some cases, the cost will approach the cost of the generator itself.

If you choose to use power cords instead, these can be quite pricey as well.  Remember you must keep your generator well away from your home when in operation.  Then the distance can make your extension cords expensive.  A good 30Amp cord with multiple standard three prong receptacles at the business end can run over $100 .

The choice is yours.  I hope that this simple explanation gives you enough information to make an good decision.  When you’re ready, whether you plan to install it yourself or by a professional, Amazon tends to have the best selection and lowest prices.

Filed under: Accessories • Transfer Switch