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Old 11-02-2007, 09:42 PM   #1
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Question on generator wiring


Just purchased a generator, and my thoughts turn to a transfer switch, but I have a question.

Every transfer switch I've seen basically duplicates the existing breaker box and has no mechanism to ensure you kill the utility main (so you don't backfeed the utility w/ your generator).

My question is this: wouldn't it be much, much simpler to install a 3PDT switch directly upstream of the main breakers on your house?? This would ensure that you could either have the generator powering your house or the utility, but never both. It would also use the existing breakers in your breaker box. What am I missing here??

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Old 11-02-2007, 10:10 PM   #2
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Question on generator wiring


A transfer switch DOES by nature prevent backfeeding the utility feed. Otherwise it would not be a transfer switch.

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My question is this: wouldn't it be much, much simpler to install a 3PDT switch directly upstream of the main breakers on your house??
This would be a main transfer switch and would need to be service rated.

Can you tell us what switches you have been looking at?

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Old 11-03-2007, 12:07 AM   #3
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Question on generator wiring


Well, here:

http://www.green-trust.org/generator/genny_install.htm

...is a good example of what I'm seeing on the internet.

Can you recommend a good, simple transfer switch that doesn't cost more than the whole generator? Some of these that I'm seeing cost $300-400.
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Old 11-03-2007, 07:52 AM   #4
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Yes, Cutler Hammer makes a similar transfer switch to that Square D unit on that web site you linked. It's around $120, but that is for a 100A service. I'm not sure what the 200A panel costs.

Do you really want to transfer your whole panel?
How big is the service?
How big is the generator?
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Old 11-03-2007, 09:31 AM   #5
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Question on generator wiring


The generator is 5.2 kW/ 6.5 kW surge gasoline-powered.

Normal steady-state loads, which include normal lighting, computers on a UPS, I measured @ 8 amps, both legs total using a clamp-on ammeter at the main.

The house has natural gas heat and natural gas hot water, so the only potential big current draw would be a clothes dryer or television or microwave, which would still be well within the capacity of the generator.

So yes, I think I'd like to transfer the whole panel.

It just seems the simplest way to merely put a double-throw switch in at the main.
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Old 11-03-2007, 11:53 AM   #6
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You should be fine then. Only I would not consider running the dryer. With anything else running you'd be taxing the genny pretty hard.



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It just seems the simplest way to merely put a double-throw switch in at the main.
Like I said, a manual transfer switch IS simply a double-throw switch. You MUST be sure it is "service rated" though.
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Old 11-03-2007, 08:06 PM   #7
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Speedy (or any other electrical guru), if you might tell me what type/ model/ brand of switch you would recommend, I would be very much obliged.
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Old 11-03-2007, 10:04 PM   #8
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Here are the least expensive whole house manual transfer switches:

100A service:
Indoor switch - $125 - http://www.electricgeneratorsdirect....roducts_id=523
Outdoor switch - $149 - http://www.electricgeneratorsdirect....roducts_id=647


200A service:
Outdoor switch - $325 - http://www.electricgeneratorsdirect....roducts_id=524

I don't see an indoor 200A switch on this site but I know it is available.
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Old 11-04-2007, 01:00 PM   #9
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Why use a transfer switch? You can buy an inexpensive manual interlock kit. They are designed to lock the main breaker or the generator breaker when one or the other is in use. Cheap, effective and 3 or 4 screws and your finished. The one I have is UL approved.

You just need to know the panel manufacturer and model number and your good to go.
Your thinking is good thinking. And you are on to something.
www.interlockkit.com
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Old 11-04-2007, 01:30 PM   #10
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For what it is worth and you want things done correctly you need in many cases to contact the poco for approval of the type of switch for back up/emergency power you use. Unfortunately the interlock kit is one many poco's have on their can't use list. I personally don't see the problem with them but none the less approval is required by most poco's. Where I used to live I don't know of anyone who ever did contact the poco they just install whatever and think no further of it. Last time we had a power loss for more than half day was in a 1999 ice storm so the need for emergency power needs to be weighed before you install. Just thought I would throw this into the can of worms. The actual generators that the lineman worry about are the big boy's, if a small portable generator were wired into a panel and allowed to backfeed the grid it would likely trip out the circuit breaker on the generator rather quickly. Point is the poco doesn't have control of what Mr. Resourceful out there might come up with to power his house so they train to expect backfeed and take the necessary precautions.

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Old 11-04-2007, 02:05 PM   #11
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Question on generator wiring


Stubbie,
Why involve POCO. All your asking for is trouble and a lighter wallet. Of course they are going to recommend or require a transfer switch. Then they
start telling you what you need. I have seen them in action.

Whats on my side of the meter is mine. Not theirs.

If the poster wants help he needs an electrician. Not the utility.
The interlock kit I mentioned in my post (did you look at it)? It's simple very safe and effective.
Of course their (POCO) safety is of utmost concern. DIY'ers do not realize what happens when you backfeed a dead POCO XFMR with 240 volts. You do. And should the power be restored while the generator is in operation, the generator is history.
Transfer switches are very useful, but in a residential setting the interlock is just as effective, and hundreds of dollars less.
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Old 11-04-2007, 03:01 PM   #12
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One of the reasons I don't usually recommend an interlock kit is because they are not nearly make for every panel out there. They are a relatively new invention and only fit newer panels.

I will say, a brand new service panel with a built-in interlock is a nice and easy thing, and there are many different ones out there.
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Old 11-04-2007, 03:48 PM   #13
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Because it is needed information. If you install a transfer switch or any transfer device in my area you need approval from local authority and an inspection. It is the local authority that involves the power companies list of dos' and don'ts. After all they work hand in hand on almost all issues with the distribution grid. The required inspection involves the poco requirements which are enforced by your inspector, not vice versa. In most cases your not going to have any issues other than you need room for the backfed breaker when using the interlock. You may own the service equipment but the city and poco own how it is used. It is a small issue IMO if they don't want an interlock transfer, then installation of one that is approved can save you a big head ache. Now my guess is that since some interlocks recieved the ul listing not too long ago it is likely they are being accepted by the power people and inspectors. Remember I said if you want to do this right or by the book it is likely you will have no choice but to involve the poco and local codes department.

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Old 11-05-2007, 09:11 AM   #14
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Gentlemen, excellent suggestions all around, and it's exactly why I come to this forum -- expert advice from guys who know what they're talking about.

But what's "POCO"? I assume that means the utility?

And those 100 & 200 amp transfer panels, Speedy? I assume the current rating refers to the max amount the generator can push through it, not the size of the panel? I have a 200-amp service panel, but there's no way on earth I will draw even 1/10 of that if the generator is supplying the power to the house.
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Old 11-05-2007, 10:34 AM   #15
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Question on generator wiring


Yes.... poco is the utility. For a whole house transfer , the transfer switch must equal the service disconnect rating in your case it must be a 200 amp service rated transfer switch . Remember to do what your wanting the service entrance wires will land on your transfer switch before going to your main panel. It essentially sits in between your meter and the main panel. Does that make sense to you? When in the utility position it must be able to carry the load of the service supplying the dwelling.

The interlock kit is a nice way to go if you can get one designed for your panel and you have room for the generator breaker. You need space for a double pole breaker that will be backfed from your generator and sized according to your needs and the output of the generator will be the outer parameter not the size of your service. You can only run so much on that generator of yours as you have mentioned and you will have to load manage very carefully using a 200 amp transfer switch. With a interlock kit you will probably need a 30 amp backfeed breaker for your generator size and load it accordingly. 200 amp transfer switches generally are meant for much larger generators than yours. They will work though for what you want. Running that dryer is going to tax your generator pretty good due to how long it will be pulling the load. I'm not saying it won't work but it is going to earn its keep if you understand what I'm saying.

There are more choices and I would use one that is accepted by the local code authority to avoid any down the road issues....they may have no restriction other that requiring it to be a listed transfer switch.

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Last edited by Stubbie; 11-05-2007 at 10:46 AM.
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