Generator question

[mikester]

Ive been working on my basement for the past couple of months. Just doing a long needed cleanup. Its been a catch all for everything for the past 15 years so it was time.
One of the things in my plan is to finally have a transfer switch installed. I have a 7500 KW Generac portable with a 13500 surge. I keep it in my detached garage about 20' from the house. The only time I used it I pulled it outside and backfed the system through the outlet for my compressor after I shut the main breaker in the house. I know, not the safe way to do it. Thats why Im getting the transfer switch. I was looking at the 10 circuit Gentran panel. One of my friends was over the other day and I told him my plans. He told me that even though my generator is 7500 KW Im going to be limited on how many circuits I can run. The way he explained it, the full output of 7500 is only available if all the outlets on the generator are being used. If I use one of the 30 or 50 amp outlets to feed the transfer switch I'll only be getting the wattage that goes to that outlet. Like its divided up compared to a standby that gives the transfer switch the full KW that its rated for.
Is this really how it works ?

 

[offroadsteve]

Your friend is incorrect. Quick math shows that the 50 amp outlet on your generator (assuming 240V) is good for 12,000 watts (240*50=12,000), greater than the running capacity of your generator.

If you take the generator panel apart, I would suspect you will find the feed from the generator head goes first to the 50 amp breaker (which i'm assuming is present, give your statment that you have a 50 amp outlet), then from there gets split out to the smaller outlets.

 

[cglasgow]

Your friend is partially correct. The generator contains two sets of windings. Each puts out 120V and is capable of half the stated output. Think of it as two half-generators. If you "wired them together in series" you'd have 240V and the potential for full rated output. (internally, that's how they're wired.) But from each individually you can only get half. In addition, you don't want to load one set of windings fully and not load the other -- then you've got a big imbalance and that's not good. Better to divide the load (approximately) evenly between the two windings.

Some generators have a switch that puts the windings in parallel instead of in series. This lets you get your full output at 120V and automatically balances the loads because anything you plug in is across both sets of windings. However, the price you pay for this is that you no longer have 240V available.

 

[foolishpride]

Ive been working on my basement for the past couple of months. Just doing a long needed cleanup. Its been a catch all for everything for the past 15 years so it was time.
One of the things in my plan is to finally have a transfer switch installed. I have a 7500 KW Generac portable with a 13500 surge. I keep it in my detached garage about 20' from the house. The only time I used it I pulled it outside and backfed the system through the outlet for my compressor after I shut the main breaker in the house. I know, not the safe way to do it. Thats why Im getting the transfer switch. I was looking at the 10 circuit Gentran panel. One of my friends was over the other day and I told him my plans. He told me that even though my generator is 7500 KW Im going to be limited on how many circuits I can run. The way he explained it, the full output of 7500 is only available if all the outlets on the generator are being used. If I use one of the 30 or 50 amp outlets to feed the transfer switch I'll only be getting the wattage that goes to that outlet. Like its divided up compared to a standby that gives the transfer switch the full KW that its rated for.
Is this really how it works ?

You mentioned it was a 7500 KW Generator. You probably meant a 7500 Watt Generator. I didn't think you could get a generator with a 50 Amp plug unless you got the 10,000 Watt Generac. It comes with a 50 Amp and a 30 Amp plug. Usually the generators in the 5500 -8000 Watt range come with just a 30 Amp plug.

 

[mikester]

You mentioned it was a 7500 KW Generator. You probably meant a 7500 Watt Generator. I didn't think you could get a generator with a 50 Amp plug unless you got the 10,000 Watt Generac. It comes with a 50 Amp and a 30 Amp plug. Usually the generators in the 5500 -8000 Watt range come with just a 30 Amp plug.

Sorry, I should have written it as a 7.5 KW. A kilowatt is 1000 watts. And I stand corrected as far as the plugs. I didnt go out to my garage and actually look at the outlets, I looked online at some of the specs as I was writing the post and the site I was on had the wrong info. It has 4 outlets, 2 of them 30 Amp twist locks.

 

[nehog]

IIRC that Gentran transfer switch (the ten circuit version) is rated at 30 amps maximum.

 

[aandpdan]

Instead of the Gentran panel, have you considered an interlock?

Some panels will also accept interlock equipped breakers, Murray and Siemens for example.

Then you could choose any circuit to run.

 

[offroadsteve]

Well I stand corrected... 30 x 240 = 7,200 watts, so you'd be giving up approximatly 300 watts of output by only using the single outlet, assuming as cglasgow pointed out that your loads are divided equally between the two 120V phases. That seems like a poor design to me that you don't have an outlet on the generator rated to give you the full rated gen-head output...

I would also suggest looking into an interlocked connection directly into your main panel as aandpdan pointed out, then you aren't limited to 10 circuits, and your cost would be substantially less. I have seen websites that sell an interlock plate you can install in most any main-breaker panel (they make different ones for differnt panels) and then you feed your generator in with an appropriate breaker.

 

[gatchel]

I would also suggest looking into an interlocked connection directly into your main panel as aandpdan pointed out, then you aren't limited to 10 circuits, and your cost would be substantially less. I have seen websites that sell an interlock plate you can install in most any main-breaker panel (they make different ones for differnt panels) and then you feed your generator in with an appropriate breaker.

I agree with this also. A panel interlock is definitely the best way to go. If you really need to have wattmeters there are add on ones available.

There is a website that sells interlock kits but they are usually pretty high as far as price has been. I would suggest you get your model number of the main breaker panel and check your local electrical supplier for the appropiate kit. Pay attention to the style and location of the main breaker. That is usually what determines the interlock for that panel type.