Generator Transfer Switch Current Rating

Question

I have a 30 amp generator (5R-30 connectors) and expect to buy either a 310C Pro/Tran2 30-Amp 10-Circuit 2 Manual Transfer Switch or a A510C Pro/Tran2 50-Amp 10-Circuit 2 Manual Transfer Switch. Would the A510C Pro provide any "future proofing" by allowing me eventually to put in a 50 amp, 240 volt generator or should I stay in the 30 amp, 120 volt world?

Answer 1

DO. NOT. BUY. A. TRANSFER. SWITCH.

In many (arguably most) situations, a generator interlock is a far better investment than a "transfer switch". That is for a bunch of reasons, including:

• Absolute future-proofing because you could potentially upgrade to a generator as large as your entire service - 30A, 50A, 60A, 100A, even 200A!
• No restriction, even at 30A, on which breakers to power. Getting really hot and you want to run your air conditioning that needs 25A? No problem! Just turn off most of your other stuff except lights and internet and then turn on the air conditioning breaker. Want to bake cookies? Sure, provided your oven is on a 30A or smaller circuit. Etc.
• No restriction on the number of circuits. Have a whole bunch of 15A or 20A 120V circuits that each only power a few things? You don't have to worry about limiting to a specific set of 10 (or whatever) circuits that the transfer switch can handle.
• No problems with GFCI or AFCI breakers. If you already have the breakers in place then with an interlock they will work just as well on generator power as on utility power. With a transfer switch there are likely to be problems.

The basic concept is:

• Figure out how to arrange your breaker panel so that you can have an interlock. This prevents using utility power and generator at the same time for safety (both your safety and the utility repair crews safety).
• Install a breaker in the correct location next to your main breaker. Connect it to an appropriate inlet. You can size the wires for the current 30A generator (10 AWG) or upsize so that if you upgrade later you just have to replace the inlet and the breaker.

And that's pretty much it. No need to rewire a whole bunch of circuits.

The catch is that if your existing panel is really full or very old it could get complicated. But then you may have other problems (as I did) and be due for a panel replacement anyway.

An interlock is usually a couple of pieces of metal and some screws. Totally passive. Wildly overpriced for a couple of pieces of metal. I would guess that including an interlock with every single panel would add perhaps $1 to the cost of the panel, perhaps $2 at retail, because they would be mass-produced on a really large scale instead of small batches as they are produced now. But since most people don't need an interlock, no manufacturer is going to include it because that puts them at a competitive disadvantage. (I see similar things in many other industries.)

However, an interlock is still a whole lot cheaper than a transfer switch, 100% reliable, easy to use, a lot easier to install than a transfer switch and just plain makes more sense.

A whole-house automatic transfer switch is, of course, something entirely different. But that only works if you have a whole-house generator to go with it.

Answer 2

Unless I'm missing something obvious it appears either option is limited to 10 circuits. If there's any "future proofing" then it is in allowing a 20 or 30 amp air conditioner circuit to be upgraded to a 40 amp heat pump circuit, or something similar. But then you are starting with a 30 amp 120 VAC input so I'd guess that's more like having a couple 120 VAC window air conditioner units now and then later moving up to a 240 VAC central air conditioner in their place on the circuit panel.

I'm with manassehkatz-Moving 2 Codidact on this and would suggest a generator interlock, that's what I have on my house. It means not needing to plan out carefully which circuits in the house have power, the whole house will be connected. And if there's a desire for a larger generator than 50 amps then it's just a switch of the breaker, wire, and inlet than a whole new transfer panel.

A couple anecdotes that might help prove the point.

One of my brothers put in a generator inlet like I did that's rated for 30 amp 240 VAC. In the first big power outage he had I helped him hook up his portable generator and he had lights in every room of the house and could run the air conditioner. He had to take care on not having too many lights on since that could trip the breaker if the AC kicked in. If the refrigerator ran at the same time as the AC then it's a coin flip on if the current spike was enough to trip a breaker.

Later on he did some home improvements and that included a new more powerful air conditioner. When the power went out after that I again helped him hook up his generator and all was well. Until the AC kicked in. The new AC had a 40 amp breaker on it which told me the start up current was just too much for the 30 amp inlet breaker.

I have a 30 amp 240 VAC inlet on my house and then bought a 2000 watt 120 VAC generator to plug into it. This works by using an adapter that shorts the two 240 volt poles into a single 120 volt pole. This means no 240 VAC load will run but I can run some LED lights, refrigerator, a fan or the furnace (depending on the weather), and a few other small loads.

Later on I got a deal on a 6000 watt 240 VAC generator. With the larger generator I can run the air conditioner and still have plenty left over for other loads.

With a 50 amp 240VAC inlet you can connect a 30 amp 120 VAC generator with an adapter, only no 240 VAC loads will run. If a larger generator enters your life then use the same generator cord and inlet but with no adapter (assuming a 50 amp outlet on the generator) or suitable adapter.