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Old 09-06-2019, 04:49 PM   #1
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Draw half the power by balancing loads

Great article in the MTOA Turtle Times engineering corner this month. Talks about 125v loads. If you have one 20amp load on one leg to nuetral and then add a second load of 20amps to the other leg to nuetral you still only draw 20 amps. But in contrary if you were to add the second load to the same first leg you would draw 40 amps.
Well known in the electrical industry but probably not in the boating and trawling industries.
So to put it in laymans terms. On a boat a/c panel you have two rows of switches side by side. Each row is a different leg (phase). so if you have one switch on on one side you can put a second switch on the row beside it of equal load (watts) and you will not be drawing any more amps. "Balanced loads"
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Old 09-06-2019, 05:07 PM   #2
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That's true in terms of current flow, but it's somewhat of an incomplete story. In particular, balanced vs not balanced doesn't change you power consumption (watts). A laymen reading the "take away" might conclude that it does. Also, it's only applicable to boats with split phase power systems, e.g. a 50A/240V power cord. Many boats have 30A 120V power cords and this wouldn't be applicable to them. Same for 50A/120V shore power, though that's becoming pretty rare.



All that said, balanced loads are good. Just don't expect any reduction in your power bill or power meter.
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Old 09-06-2019, 06:06 PM   #3
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That's true in terms of current flow, but it's somewhat of an incomplete story. In particular, balanced vs not balanced doesn't change you power consumption (watts). A laymen reading the "take away" might conclude that it does. Also, it's only applicable to boats with split phase power systems, e.g. a 50A/240V power cord. Many boats have 30A 120V power cords and this wouldn't be applicable to them. Same for 50A/120V shore power, though that's becoming pretty rare.



All that said, balanced loads are good. Just don't expect any reduction in your power bill or power meter.
Well usually the limitations in boat power is in amps. If you are connected to a 20 amp 2 pole breaker and your drawing 19 amps at 125v through one leg(L1) and nuetral then you cannot add anymore devices on that leg. but if you add it to the opposing leg (L2) you can add up to the 19 amps an then your nuetral current goes to zero. This the point I would like to get across. So if your tripping the breaker at the dock it may be because your loads are not balanced you may be ok if you rebalance the loads.
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Old 09-06-2019, 06:13 PM   #4
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That being said, I would say balanced loads are a little more than just good. I would say they are pretty close to necessary.
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Old 09-06-2019, 06:48 PM   #5
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That being said, I would say balanced loads are a little more than just good. I would say they are pretty close to necessary.
Why? On my 50 amp 220 setup I have unbalanced loads normally as requirements dictate. With an amp meter on each leg I monitor both to ensure 50 amps on that leg are not exceeded. Easy enough to do but only by luck are they balanced.
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Old 09-06-2019, 07:10 PM   #6
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Maybe there not unbalanced. Maybe whoever wired the panel put appropriate loads on opposite power legs. AN example would be if you had two air conditioners you would wire those on opposing legs because chances are they both be on at the same time.
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Old 09-06-2019, 07:29 PM   #7
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I'm very interested in this, as our boat is set up for 50 amp 240 volt. My problem is when running the generator, I am limited as to the number of breakers I can have turned on without exceeding capacity on leg one. Only the air conditioners, rarely used in the PNW, are on leg two. If I could swap a few loads to leg two then I could have more things running at the same time and also load the generator more. Does anyone see a problem with this? When on shore power we are generally on 30 amp 120 volt with an adapter that ties both legs together, so two phase operation is not possible.
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Old 09-06-2019, 07:38 PM   #8
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Yes you are correct you should change some of your loads that would be on at the same time on to different legs.
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Old 09-06-2019, 07:44 PM   #9
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Well usually the limitations in boat power is in amps. If you are connected to a 20 amp 2 pole breaker and your drawing 19 amps at 125v through one leg(L1) and nuetral then you cannot add anymore devices on that leg. but if you add it to the opposing leg (L2) you can add up to the 19 amps an then your nuetral current goes to zero. This the point I would like to get across. So if your tripping the breaker at the dock it may be because your loads are not balanced you may be ok if you rebalance the loads.

But in reality, what 20A/240V outlet are you plugging into?


And if you are talking about two separate cords to two separate 120V dock outlets, you have no way to know if they are the same leg or opposite leg, short of taking measurements that are beyond the interest of most boaters.
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Old 09-06-2019, 07:49 PM   #10
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And counter to the thread's title, you won't draw less power. Current will be either concentrated on one leg, or distributed across two. But the power will be the same in both cases.
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Old 09-06-2019, 07:52 PM   #11
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But in reality, what 20A/240V outlet are you plugging into?


And if you are talking about two separate cords to two separate 120V dock outlets, you have no way to know if they are the same leg or opposite leg, short of taking measurements that are beyond the interest of most boaters.

Sound like he jumpered the two hot legs of his adapter so when pluged into 120v both sides of his panel are live.
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Old 09-06-2019, 07:55 PM   #12
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And counter to the thread's title, you won't draw less power. Current will be either concentrated on one leg, or distributed across two. But the power will be the same in both cases.
Your misleading him when you use power (watts) as your reference when we are discussing amps. The breakers are not labeled in watts for a reason.
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Old 09-06-2019, 08:09 PM   #13
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And counter to the thread's title, you won't draw less power. Current will be either concentrated on one leg, or distributed across two. But the power will be the same in both cases.

I used power in the title as a general term, not as its technical meaning measured in watts. I did not want the title to sound to technical.
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Old 09-07-2019, 07:04 AM   #14
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I'm very interested in this, as our boat is set up for 50 amp 240 volt. My problem is when running the generator, I am limited as to the number of breakers I can have turned on without exceeding capacity on leg one. Only the air conditioners, rarely used in the PNW, are on leg two.
I addressed this exact problem by putting my water heater on a three-way rotary switch. I can power it from either leg, depending on what else I'm running, so neither leg exceeds 30A.

The switch is in the lower left of this photo.
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Old 09-07-2019, 07:08 AM   #15
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I addressed this exact problem by putting my water heater on a three-way rotary switch. I can power it from either leg, depending on what else I'm running, so neither leg exceeds 30A.

The switch is in the lower left of this photo.
Good Idea
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Old 09-07-2019, 07:38 AM   #16
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Maybe there not unbalanced. Maybe whoever wired the panel put appropriate loads on opposite power legs. AN example would be if you had two air conditioners you would wire those on opposing legs because chances are they both be on at the same time.
One leg has 3 AC reverse cycle units and the separate washer and dryer. The other leg has all the other stuff. Works fine for our needs. Came newly built that way.
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Old 09-07-2019, 07:56 AM   #17
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Sounds like you have room to spare on your electrical capacity. If you do run into a situation where you are tripping main breakers check your load balance.
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Old 09-07-2019, 07:57 AM   #18
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"When on shore power we are generally on 30 amp 120 volt with an adapter that ties both legs together, so two phase operation is not possible."

"Sound like he jumpered the two hot legs of his adapter so when pluged into 120v both sides of his panel are live."

Most of the 240 to 120 adapters are purchased. Since there may be any number in use on the wiring in a marina , they may all be powered by the same 120v leg.

If you wire up your own adapter to use the "other" leg you may find an extra 10v or more on the barely used leg.

Your air cond will love you!
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Old 09-07-2019, 08:20 AM   #19
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My setup is 2x 50A / 125V inlets on the boat, but typically used with the 2 cords running into a Y adapter to connect to a single 50A / 250V outlet on the dock (or with a pigtail on each cord to use 2x 30A / 125V outlets when traveling somewhere without 50A).

Because there's no 250V stuff in my setup and the 2 legs don't care if they're on one phase or separate, Chris Craft was nice enough to wire the generator for single phase 125V output instead of 125/250 split phase. So when on generator power, both legs are paralleled at the selector switch (before the panel breakers) meaning I can draw power however I need up to the 54A max for the generator (as long as it's under 50A per leg). There's also an option to tie both panel legs to the #1 inlet although that's a rarely-needed feature.

Balancing loads is still the ideal case when using the adapter on a split phase dock plug, but due to the nature of loads on a boat, it's rarely possible. My #2 leg runs the 3 A/Cs and the microwave, the #1 leg is everything else (water heater, battery charger, stove, outlets, etc.). So normally the #2 leg gets more load unless I'm using the stove or vacuuming while the water heater is heating. I can't think of any way to switch things around that wouldn't leave stuff unbalanced in a lot of cases. Plus, all 3 stove burners together is good for about 30 amps and that can't be split across the legs.
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Old 09-07-2019, 08:35 AM   #20
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My setup is 2x 50A / 125V inlets on the boat, but typically used with the 2 cords running into a Y adapter to connect to a single 50A / 250V outlet on the dock (or with a pigtail on each cord to use 2x 30A / 125V outlets when traveling somewhere without 50A).

Because there's no 250V stuff in my setup and the 2 legs don't care if they're on one phase or separate, Chris Craft was nice enough to wire the generator for single phase 125V output instead of 125/250 split phase. So when on generator power, both legs are paralleled at the selector switch (before the panel breakers) meaning I can draw power however I need up to the 54A max for the generator (as long as it's under 50A per leg). There's also an option to tie both panel legs to the #1 inlet although that's a rarely-needed feature.

Balancing loads is still the ideal case when using the adapter on a split phase dock plug, but due to the nature of loads on a boat, it's rarely possible. My #2 leg runs the 3 A/Cs and the microwave, the #1 leg is everything else (water heater, battery charger, stove, outlets, etc.). So normally the #2 leg gets more load unless I'm using the stove or vacuuming while the water heater is heating. I can't think of any way to switch things around that wouldn't leave stuff unbalanced in a lot of cases. Plus, all 3 stove burners together is good for about 30 amps and that can't be split across the legs.
In your case it would not help to balance loads because it sounds like your electrical panel is wired for single phase (125v). Even when your pluged into your Y 250v it sounds like your just using one leg of the 250v therefore getting 125v. Unless you can clarify with more specifics.
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