Help with generator/wiring question

[Bartelby]

Can someone help me out with a generator/wiring question please?

I have a 7000 running watt (8750 surge) generator with an L14-30 (30 amp 240 twist lock) AND an L5-30 (30 amp 120 twist lock) receptacle. I'd like to connect the generator to a 60 amp double pole circuit breaker at the main panel. An interlock kit is installed on the panel. I'd also like to maximize the amount of amps the generator can bring in to the panel.

On the gen, if the voltage selector is set to 120/240 the 120V and 120/240V receptacles can be used simultaneously. I called the manufacturer, who said the L5 receptacle should be capable of full output because its wired through both windings. So If I run an inlet box for the L14 and a separate inlet box for the L5, is there some way to jump the 2 ends together at the main panel so both legs will be distributed evenly? Wouldn't this provide about 55 amps at 120V?

If this won't work would it be possible to run the 2 lines into 2 30 amp circuits in a sub-panel and then send them to the single 60 amp circuit in the main panel?

 

[Provincial]

20 amps at 240V = 7200 watts. Putting a load on the 120V side while the 240V side is maxed is going to exceed your generator's capacity. The "surge" rating is for momentary loads like starting a motor. The circuit breakers will allow a momentary load exceeding their rating by a moderate amount, which is where the "surge" rating comes from.

Wire your 240V circuit to the double pole breaker on the panel and don't try to add the 120V circuit. If you feel you must use the 120V circuit somewhere, run an extension cord directly to the 120v load, but don't expect the generator to handle a maximum 240V load and the 120V load as well.

Typo at the start of the post: I meant to type 30 amps at 240V = 7200 watts!

 

[Aceman]

7000 watts divided by 240 volts gives you 29 amps output. You don't need a 60 amp breaker, you need a 30.

Use the L14-30 recep only to feed the home.

 

[Bartelby]

I understand what you are saying Aceman, but if I'm only running 120v appliances it seems like I'm not maximizing the generators capacity... Couldn't I just selectively switch the breakers off if I decided to use something requiring 240?

 

[Provincial]

I understand what you are saying Aceman, but if I'm only running 120v appliances it seems like I'm not maximizing the generators capacity... Couldn't I just selectively switch the breakers off if I decided to use something requiring 240?

When you are running a 120V circuit, you are actually using one leg of the 240V system. Think of three garden hoses. Two are supply hoses and one is a return hose. If you want to use up to half of the water, use one of the hoses, and the drain water has to go back out the return hose. You can use the other supply hose at the same time, and all the water will fit in the return hose using both supply hoses even though it is the same size as the supply hoses (this is the magic of AC electrical systems). If you hook the two supply hoses together (as in the 240V system) you get the power of two 120V circuits and nothing goes out the return hose.

If you balance the loads on the two 120V circuits you can use all the power that the generator can supply continuously through the 30A 240V circuit, even if you don't use any 240V loads. Analyze your circuits and individual loads and swap your circuit breakers in your main panel to equalize the loads on each leg of the 240V. This requires a bit of thought and calculations, but it isn't necessary to be exact.

 

[nehog]

20 amps at 240V = 7200 watts. ...

Gotta work on yer math, there, it is 4800 watts!

Now 30 amps at 240 is 7200, which is what the OP can draw at one time. The L14-30 will deliver the generator's maximum power, and there is no need to use the other outlet.

 

[theoldwizard1]

If you balance the loads on the two 120V circuits you can use all the power that the generator can supply continuously through the 30A 240V circuit, even if you don't use any 240V loads. Analyze your circuits and individual loads and swap your circuit breakers in your main panel to equalize the loads on each leg of the 240V. This requires a bit of thought and calculations, but it isn't necessary to be exact.

This is EXTREMELY important !

When feeding a main panel directly with a generator (and an interlock to prevent back feeding the power lines) it is VERY EASY to get an unbalanced load. One leg could be running near 100% capacity and the other only 10% or less. Not a good situation !

When using a generator that feeds a main with interlock, something similar to the following procedure should be followed:

• Start the generator and attach the power cord to the building feed
• Turn off all breakers
• Turn off the main from the power company
• Move the interlock and turn on the generator feed
• Turn on the "required" breakers

The only way to check for a balanced load is connect your house to the running generator (with main power disconnected) and turn on the breakers that are "required". With and amp clamp, check each leg coming from the generator. While you are doing this make certain that high current loads are running (water pump, sump pump, furnace, refrigerator, freezer, medical equipment, etc.)

 

[Bartelby]

Thank you all. I get it now. Its 30 amps to each leg. The key is to distribute the loads evenly. I will go with a double pole 30 amp breaker at the main panel.

 

[Bartelby]

and just use the L14-30 recep only to feed the home.

 

[Jagmandave]

If you need more than 30 amps, maybe you should get a bigger genset?