Half loading a Gen?

[westmarine]

I have a 9kw Northern Lights gen. 240V that splits off to two sides of 120V. I do not have any 240V items on the boat and no breakers for 240v. The shore power is the same. 240v 50a that splits into two 120V isolated breaker boards. As you can see, each 120V leg is switched independently. I have 3 air conditioner units on the right side and everything else on the left!

In the winter, I don’t use the air conditioners, but water heater, charger, all the house stuff, is all on the left phase! If I load up one phase or side and have 0 load on the other, is this harmful or sub optimal? What about just leaving one phase off?

Thanks!

 

[rslifkin]

Does the gen actually have a 120/240 output or is it wired for a single 120 output? I've got a split panel like that, but my gen is wired as a single 120 output, so it effectively puts both legs of the panel in parallel when on generator power.



Realistically, as long as you don't overload the capacity of 1 leg of the generator and overheat the windings, you shouldn't hurt it. So if it's wired as 120/240, you can only use 4.5kw on one leg regardless of what load the other leg does or doesn't have.

 

[westmarine]

Does the gen actually have a 120/240 output or is it wired for a single 120 output? I've got a split panel like that, but my gen is wired as a single 120 output, so it effectively puts both legs of the panel in parallel when on generator power.



Realistically, as long as you don't overload the capacity of 1 leg of the generator and overheat the windings, you shouldn't hurt it. So if it's wired as 120/240, you can only use 4.5kw on one leg regardless of what load the other leg does or doesn't have.

It is a 4 wire output. The two phases are independent of each other.

 

[rslifkin]

It is a 4 wire output. The two phases are independent of each other.

Ok. Then unless NL has documentation indicating otherwise, assume 4.5kw max per phase and you'll be safe. Uneven phase loading shouldn't hurt anything.

 

[Ski in NC]

It is a 4 wire output. The two phases are independent of each other.

Look in the control box, especially back of AC output breaker. Standard practice for this unit in 120v service is for the two outputs on the breaker to be tied together. Refer to the manual for details.

There is no need for split 120v panels to be fed by two separate gennie windings. Split panels do make sense with two 120v/30a shore cords, if only one outlet is available you can at least run one panel or the other. If you tried to run everything on one 30a cord, could overload it.

 

[westmarine]

Does the gen actually have a 120/240 output or is it wired for a single 120 output? I've got a split panel like that, but my gen is wired as a single 120 output, so it effectively puts both legs of the panel in parallel when on generator power.



Realistically, as long as you don't overload the capacity of 1 leg of the generator and overheat the windings, you shouldn't hurt it. So if it's wired as 120/240, you can only use 4.5kw on one leg regardless of what load the other leg does or doesn't have.

On second look, you are correct! Both legs are jumped together at the gen control output.

Thanks for the information!

 

[SailorGreg]

On second look, you are correct! Both legs are jumped together at the gen control output.



Thanks for the information!

Just a note on NL gensets. They are sensitive to unbalanced loads on the two legs. NL techs told me the max differential, but I can’t remember exactly, something like within 80% of each other on current.
Looking at your picture, You have a volt meter on each leg. I would think the V would be the same on both when on the genset if the legs are ganged. Or can you see current in each leg? Again, I think the current would be the same on both legs if the legs were combined.
Anyway, I agree that they are likely ganged since you have no 240 circuits.

 

[westmarine]

Just a note on NL gensets. They are sensitive to unbalanced loads on the two legs. NL techs told me the max differential, but I can’t remember exactly, something like within 80% of each other on current.
Looking at your picture, You have a volt meter on each leg. I would think the V would be the same on both when on the genset if the legs are ganged. Or can you see current in each leg? Again, I think the current would be the same on both legs if the legs were combined.
Anyway, I agree that they are likely ganged since you have no 240 circuits.

I agree, with the gen on, the voltage should be the same. The photo was taken on a 240V shore power. I suspect the voltage is not often exactly matched on each phase.

I’ll take a look when I’m on the gen next time!

 

[catalinajack]

I profess ignorance as well and am still trying to understand the 120/240 principles. Recently, I had to rewire my Westerbeke 7.7kw generator head. My boat is a 50-amp boat, no 240 volt appliances. The Westerbeke has four brushes. The wires from two are the neutral and safety and are ganged together at the generator as they should be. The other two are the hot wires. They are tied together on a bus bar with one wire going to the panel through a Square D 60-amp circuit breaker. Are those two hot wires from the generator brushes outputting different phases? And how is that single wire to the panel able to handle all of that current?

Just a note on NL gensets. They are sensitive to unbalanced loads on the two legs. NL techs told me the max differential, but I can’t remember exactly, something like within 80% of each other on current.
Looking at your picture, You have a volt meter on each leg. I would think the V would be the same on both when on the genset if the legs are ganged. Or can you see current in each leg? Again, I think the current would be the same on both legs if the legs were combined.
Anyway, I agree that they are likely ganged since you have no 240 circuits.

 

[rslifkin]

I profess ignorance as well and am still trying to understand the 120/240 principles. Recently, I had to rewire my Westerbeke 7.7kw generator head. My boat is a 50-amp boat, no 240 volt appliances. The Westerbeke has four brushes. The wires from two are the neutral and safety and are ganged together at the generator as they should be. The other two are the hot wires. They are tied together on a bus bar with one wire going to the panel through a Square D 60-amp circuit breaker. Are those two hot wires from the generator brushes outputting different phases? And how is that single wire to the panel able to handle all of that current?

A lot of generators (my old Onan included) can have the output wired in a few different ways. Depending on how everything is connected, you can either have the 2 outputs tied together (and in phase) like your setup, or you can have them out of phase to produce a 120/240 split phase output.


The image attached is a snip out of the manual for my generator, showing how the 4 output leads can be connected in different ways to produce either 120/240 or straight 120V output.

 

[bayview]

My genny had all the ACs, 40 Amps, on one side and house loads on another. The loads were never close to being balanced. When not using the AC it was half loaded. I often thought of moving some AC loads to the house side but never got around to it. It worked fine for 17 years.