Manual Transfer switch or Generator interlock?


Old 09-17-09, 07:43 PM
Thread Starter
Join Date: Feb 2009
Location: New Hampshire
Posts: 10
Manual Transfer switch or Generator interlock?

Manual Switches are expensive. Some cost more than the generator does! I have another post about the sizing of generators and read about the interlock kit.

Generator InterLock Kit

at $149 vs the $300 I'm about to pay...

Pros and Cons anyone?

Or should I do both? If I read correctly a transfer switch prevents backfeed?
Sponsored Links
Old 09-18-09, 06:59 AM
Join Date: Jun 2009
Location: Virginia, USA
Posts: 45
as it appears the board tolerates links to other forums

on this subject, which is basically safety related, i'd suggest you review the thread on this very subject at: generator to home panel connection -

i didn't realize what a hell storm i would start with the posting - interestingly, for the most part, those opposed to the concept of an interlock kit were rather emotional in their logic - there were some intelligent postings negative to the concept but, so you can decide for yourself - it's a six page thread, i bailed out of the arguments when the main adversaries and myself reached a sort of truce - but the pros and cons of it get hammered out pretty thoroughly
Old 12-11-09, 04:32 PM
Join Date: Dec 2009
Location: Washington
Posts: 1
Transfer switches versus interlocks

The truth about a "transfer switch" subpanel and a "generator interlock" on your existing panel is pretty simple. If you have space in your existing panel to install another 240V breaker that will be the "generator main" and add the interlock, that does the same thing as "transfer switch" subpanels of "preventing back-feeding power to the street". The big reasons for not sending power to the street include not zapping workers with their hands on the lines as well as not overloading your generator by trying to power the whole neighborhood. If you go to gen-tran website, their newer "powerstay" transfer switch panels literally have 2 "main" breakers with an interlock, while they also have their "vintage" panels with switches that go from "line" to "gen" for individual circuits. Since over 1/2 of their panels are just a small panel with an "interlock" anyway, I don't see why just getting such for you existing panel isn't as good.

The benefits of "transfer switch" subpanels are they have a generator plug on them already, they usually come with meters (to show you power draw) and may be quicker to get being a "one size fits all" approach for stores to stock. I do agree that seeing some priced at $400+ and knowing I could buy a new panel, breakers, and interlock for that much makes me wonder why anyone buys some of them? Some may say they like subpanels because "you won't turn on too much to overload the generator as easily with a very limited number of things connected" which may be true, but anyone could still plug in too many things off of those few circuits you have connected, so you need to think about how many things you're turning on at once no matter what system you get.

The benefits of having your main panel with the interlock includes these: it allows you to send generator power to anything in your house as you choose (by just turning on the breaker in the box), everything's in the 1 box, and you only add 1 cable (4 wires) into the panel for the generator power coming in (not 12-24 wires going to each house circuit). The only reason I'd not go this way is if your existing panel doesn't have a "main" controlling everything from the street (which some older panels may not have), then you can't do this. With this, you'll also need to get a "power inlet box" for the generator to plug into (if the generator isn't a permanently mounted one with wires going directly to it).

I can picture myself using some common sense in an outage saying "I'll turn on the stove to heat up a pizza first (with only a few lights on with it going), then I'll turn that off and turn on the water heater to have water for clean-up, then turn that off & go back to space heaters in the bedroom & living room, etc" thinking about what I'm turning on to not go too much. If you have a generator rated between 6000-7000 watts, you will be able to run anything in your house 1-at-a-time like that except for the central heating "heat pump" or AC. I like that size since it's not into the $2000+ generator cost, yet can still run nearly anything if needed.

The only other thing to note is with generators under 10,000 watts you probably want to try to balance the load on each of the generators hot wires. Generators (and the street power) have 2 "hot wires" with 120V each and when one has a + charge, the other has a - charge. If you need 240V power, you use both of those hot wires at the same time, but 120V items use just 1. If you're generator has 4800 watt capasity total, it really has 2400 watts available from each hot wire (1/2 the generator capasity). FYI 2400 watt/120V=20 amp capasity each as another way to look at it. If I wanted to run 2 space heaters (1500 watts each) on that, it can do it, but each one must be on different hot wires (otherwise 24 amps or 3000 watts on the same one is too much). So when planning out things you'll want to try and pair off 120V things to split up that you may want to run at the same time, like say "I want the fridge in the kitchen on hot wire 1 with the freezer in the garage on hot wire 2, then the living room outlets for a heater on 1 with the bedrooms on 2, etc". The way things are wired in your panel will determine that and may require you to shuffle some breakers around to change things. Adding the "generator main" that must go at the top of the panel also requires shuffling things, so get a plan together to do it all at once.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Display Modes