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Old 01-25-2010, 10:43 PM   #1
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portable generator questions--long post


Hi all. I have a few generator questions. My house was built in 2004 and has a 200 amp breaker box in the garage with a main disconnect in the box. The biggest draw is my central air unit (LRA is 104--RLA is 18.3----3 ton unit) that I am not sure if I am going to hook up to a generator. Right now I have a smaller generator (5k)--obviously not big enough for the a/c. I might get a bigger one in the future. I want to hook up a transfer switch. I have assembled some parts that did not cost me anything (no not stolen). Here's what I have so far--

I have an almost new 100 amp D square breaker panel. It does not have a "main" breaker switch, but it has a spot for it. It has a 100 amp utility double breaker ( was used to get the 240 into it) along with a 30 amp double breaker that was used as a generator input--they are interlocked so they cannot both be on at the same time. I also have some regular breakers--10a, 15a, 20a.....can I use this as a transfer switch? or do I need to get a main/generator disconnect and install it where the main switch would go in the panel.

also can I get a larger generator and hook up a 50 amp (15kw) generator to this breaker box?

also what size generator do I need to run my a/c? I saw an old post where someone ran a 4 ton a/c from a 8k/13.5k briggs generator.

thanks in advance

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Old 01-26-2010, 01:19 AM   #2
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portable generator questions--long post


I can't answer the electrical question, but just curious why the a/c is a priority on a generator question?
If I needed an emergency generator, chances are the a/c would be the least of my concerns.

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Old 01-26-2010, 06:24 AM   #3
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portable generator questions--long post


It is the least of my concerns, but down the road I might get a bigger generator and add it in. I see your location is the Canadian Rockies. Try going a week in late July or August here in North Carolina without A/C. It's not fun. We have had over 21 days straight where the heat index is over 100. I live in the central/southern part of the state and I work outside year round. I can deal with it but it's nice to get a break when i get off work.
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Old 01-26-2010, 12:01 PM   #4
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portable generator questions--long post


Try this, www.interlockkit.com. Keep this simple.
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Old 01-26-2010, 01:04 PM   #5
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Generator sizing chart here

http://www.yamaha-motor.com/outdoor/...or/sizing.aspx

You can use the 100 amp panel as a generator panel by moving the circuits you want to operate to that panel.. You will install a breaker in the main panel big enough to support the loads in the generator panel when utility is on. This breaker will back feed the 100 amp breaker in the generator panel. It can be smaller than the 100 amp breaker and should be sized to the hot conductors you run as the feeder to back feed the 100 amp main breaker in the generator panel. You will only need a breaker in the main panel that will be sufficient for the loads you move to the generator panel when the utility is on.

You then backfeed the 30 amp generator breaker with a 30 amp outlet generator by using a generator power inlet like below.

Equipment ground and neutral must be separated in the generator panel and a 4 wire feeder between the two panels (H-H)-N-GRD)

The link John posted is also a good way to go and you will not need the 100 amp generator panel. The only drawback is if they have a kit that fits your main panel it is around 175.00 dollars with shipping. If they don't it is 275 dollars to have one custom made. You must provide all the measurements and if your wrong on them you don't get to return it.



Your configuration will look like this
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Old 01-26-2010, 08:53 PM   #6
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portable generator questions--long post


Thanks stubbie. I understand it now. I am going to try to upload some photo's. The photo's of the 100 amp panel and the 30 amp plug that I need to get an enclosure for.
I am planning to use a 100 amp double pole in the 100 amp box. What size breaker should I feed it with from the original 200 amp main panel?

one other question---do I need a seperate ground rod for my generator, or does it get it's ground from the panel when it's plugged in to it. It's a portable 5kw.

thanks all
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Last edited by daddyrabbit; 01-26-2010 at 08:57 PM. Reason: add more info
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Old 01-26-2010, 09:22 PM   #7
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portable generator questions--long post


No you do not need a ground rod for the portable generator. The breaker in the service equipment (main panel) needs to be sized to adequately supply the generator panel. If your going to move several circuits to the generator panel that you will not use (turn off) when the generator is on then probably just install a 100 amp breaker in the 200 amp panel this will give the generator panel its full rating. If you are going to be using a 30 amp generator and all the circuits in the generator panel will be generator powered then all that you would need in the 200 amp panel is a 30 amp breaker or maybe a 40 amp breaker at most. If you upgrade to a 50 amp portable generator someday you will need to change the generator breaker in the panel and the power inlet to 50 amps.

You are confusing me by saying your going to use a 100 amp breaker in the generator panel. It all ready has that breaker in it. You must back feed the 100 amp breaker that has the interlock on it from the breaker in the 200 amp panel. This is so you do not backfeed the 200 amp panel and the utility when the generator is running.
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Old 01-26-2010, 09:27 PM   #8
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understood. Thanks for your help. I will post picks when I get the job done.
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Old 01-26-2010, 09:31 PM   #9
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portable generator questions--long post


I edited the last post in the bottom paragraph do you understand what I'm saying...?
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Old 01-26-2010, 09:54 PM   #10
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I think I understand. I have the 100 amp breaker in the gen panel as shown in the pic. I am going to get another 100 amp 2 pole and put it in the main (200amp) panel to feed the gen panel 100 amp breaker thus supplying the gen panel with 240 from the main service. the 30 amp for the generator has the bar interconnected on it so you can't throw the generator on without cutting off the supply line from the main panel
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Old 01-26-2010, 10:06 PM   #11
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portable generator questions--long post


Quote:
Originally Posted by daddyrabbit View Post
I think I understand. I have the 100 amp breaker in the gen panel as shown in the pic. I am going to get another 100 amp 2 pole and put it in the main (200amp) panel to feed the gen panel 100 amp breaker thus supplying the gen panel with 240 from the main service. the 30 amp for the generator has the bar interconnected on it so you can't throw the generator on without cutting off the supply line from the main panel
Yep you got it .. just wanted to make sure ... I thought you were going to add a 100 amp breaker to the panel that wasn't interlocked and back feed it.
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Old 01-26-2010, 10:54 PM   #12
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portable generator questions--long post


Where can you get the 100amp/30amp Square D breakers with the nifty little interlock? Looks inexpensive but effective.
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Old 01-27-2010, 03:51 AM   #13
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Hi KC

The interlocks are kits and the breakers you just buy across the counter anywhere. Lowes has them for 150 amp and up square d panels but they can be ordered by any electrical supply. Not sure about Menards and HD.
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Old 01-27-2010, 06:33 AM   #14
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I would add when using the QO2DTI interlock kit, to purchase the breaker hold down kit to comply with 408.36(F)' 05 or 408.36(D) '08

The kit PK4DTIM4LA (breakers on the right) or PK4DTIM4LAL (breakers on the left) has the hold downs and the QO2DTI.
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Old 01-27-2010, 07:25 AM   #15
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portable generator questions--long post


KC--the interlock pictured just snaps in to the breaker.

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