Draw half the power by balancing loads

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Bud

Bud

Senior Member
Joined
Aug 11, 2017
Messages
374
Location
United States
Vessel Name
Izzy Rose
Vessel Make
Grand Banks 49
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"
 
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.
 
twistedtree said:
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.
Click to expand...

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.
 
That being said, I would say balanced loads are a little more than just good. I would say they are pretty close to necessary.
 
Bud said:
That being said, I would say balanced loads are a little more than just good. I would say they are pretty close to necessary.
Click to expand...

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.
 
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.
 
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.
 
Yes you are correct you should change some of your loads that would be on at the same time on to different legs.
 
Bud said:
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.
Click to expand...


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.
 
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.
 
twistedtree said:
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.
Click to expand...


Sound like he jumpered the two hot legs of his adapter so when pluged into 120v both sides of his panel are live.
 
twistedtree said:
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.
Click to expand...

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.
 
twistedtree said:
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.
Click to expand...


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.
 
porman said:
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.
Click to expand...

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.
4339-albums438-picture4290.jpg
 
CaptTom said:
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.
4339-albums438-picture4290.jpg
Click to expand...

Good Idea
 
Bud said:
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.
Click to expand...

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.
 
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.
 
"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!
 
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.
 
rslifkin said:
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.
Click to expand...

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.
Others
 
Bud said:
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.
Others
Click to expand...

My panel is wired as 2 single phase legs. When plugged into a 250V outlet it does run as split phase, however. The adapter sends 1 phase down the line connected to output 1 and the other phase down the line connected to output 2.

The way it's wired is basically a more flexible version of a 125/250V split phase inlet for a boat that has no 250V loads (leaving the 2 legs totally independent). Because it's connected as 2 separate 125V inlets, it's easy to adapt to whatever outlets are available. Anything from a single 30A or 50A 125V (with the selector set to feed the whole panel from 1 input) to 2x 30A or 2x 50A (or a 50A 125/250 with the Y splitter).

To handle those options, I use 2 separate 50A 125V power lines from the boat and then carry a pair of 30A pigtail adapters as well as the 50A 125/250V to 50A 125V splitter. Outside of the rare case of finding a pair of 50A 125V outlets, it's just a matter of attaching the correct adapter to the dock end of the lines and plugging in.

In my mind, this setup carries a few advantages over the more common 2x 30A setups. The 2x 30A will plug in most places, but if all that's available is a 50A 125/250V outlet, it's not really safe to use unless you build a custom adapter box with a breaker in it. The off the shelf adapters for that situation don't have overcurrent protection, so you end up with 30A shore lines and boat inlets protected by a 50A breaker (so everything upstream of the boat's inlet breakers isn't protected).
 
Bud said:
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.
Click to expand...

You used the term "Power" in your thread title, so are the one guilty of misleading here.

Load balancing should be done by setting up the panels correctly in the first place.

Twisted Tree definitely has the high ground on this thread.
 
rslifkin said:
My panel is wired as 2 single phase legs. When plugged into a 250V outlet it does run as split phase, however. The adapter sends 1 phase down the line connected to output 1 and the other phase down the line connected to output 2.

The way it's wired is basically a more flexible version of a 125/250V split phase inlet for a boat that has no 250V loads (leaving the 2 legs totally independent). Because it's connected as 2 separate 125V inlets, it's easy to adapt to whatever outlets are available. Anything from a single 30A or 50A 125V (with the selector set to feed the whole panel from 1 input) to 2x 30A or 2x 50A (or a 50A 125/250 with the Y splitter).

To handle those options, I use 2 separate 50A 125V power lines from the boat and then carry a pair of 30A pigtail adapters as well as the 50A 125/250V to 50A 125V splitter. Outside of the rare case of finding a pair of 50A 125V outlets, it's just a matter of attaching the correct adapter to the dock end of the lines and plugging in.

In my mind, this setup carries a few advantages over the more common 2x 30A setups. The 2x 30A will plug in most places, but if all that's available is a 50A 125/250V outlet, it's not really safe to use unless you build a custom adapter box with a breaker in it. The off the shelf adapters for that situation don't have overcurrent protection, so you end up with 30A shore lines and boat inlets protected by a 50A breaker (so everything upstream of the boat's inlet breakers isn't protected).
Click to expand...

If it is the "250v adapter" that ties the two legs together then why is your generator wired for single phase?
 
caltexflanc said:
You used the term "Power" in your thread title, so are the one guilty of misleading here.

Load balancing should be done by setting up the panels correctly in the first place.

Twisted Tree definitely has the high ground on this thread.
Click to expand...

As I said earlier in the thread I was using power as a general term like a layman would use not as a technical term measured in watts. When you are on the dock or just hooking up power to the boat and you ask Do you have power? your not asking do you have watts its a broader use of the term.
Then as a question was asked about amps he answered it in watts which was misleading and i am sure confusing to the person asking. I realize technically the title should read Balance your loads and use half the amps.
 
caltexflanc said:
You used the term "Power" in your thread title, so are the one guilty of misleading here.

Load balancing should be done by setting up the panels correctly in the first place.

Twisted Tree definitely has the high ground on this thread.
Click to expand...


Load balancing can be done at any time thats why they attach the wires using screw terminals, so you remove them add or subtract, rebalance. It is not a one shot deal you can only do "the first time". Things change over time, items get added updated ect... Most new items draw less.
 
First of all, "power" is not a general term. Power is measured in watts. In most parts of the world, engines are measured in kilowatts, not horsepower. Electric bills are measured in Kilowatt hours. Generators are measured in watts, as are inverters, microwaves, lightbulbs and other appliances and so on and so on.

Secondly, balancing loads does not reduce your draw one ampere or one watt. They are just spread between two legs, which in turn additively draw from the originating power source. So even in your incorrect definition of power as amperes, belies the inaccuracy of your thread title. The reason you balance the potential loads is to be able to draw the maximum amount of power from your power souce, and thus the number of total loads you can use at one time.

By properly set up in the first place, that means the assignment of loads to panels accordingly via circuit breaker installation, and having room on each panel to add post-OEM add-ons.

I highly recommend reading Nigel Calder's "Boat Owners Mechanical and Electrical manual which discusses all this and more .in easy to read and understand terms.
 
Gettin' all passive-aggressive up in herr... :)
 
A consideration for using 230V gear. My 3 AC units, the seawater pump, watermaker are all 230V. Load balancing is inherent. No, I cannot use the A/C on a single 30A pedestal. Not a big deal. In 12 yrs of cruising, there has never been an instance of wanting A/C and not being able to power it from shore power. I use a smart wye when there's only 30A available, not too many times I can't find 230V, although I've had to run a 50ft cord to find a receptacle that would make it so.
 
Bud said:
If it is the "250v adapter" that ties the two legs together then why is your generator wired for single phase?
Click to expand...
The selector switch on the panel is wired with the following positions:

Inlet 1 Only: Shore Inlet #1 connected to both panel leg 1 and 2 (panel legs paralleled)
Both Inlets: Shore Inlet #1 -> Panel Leg #1, Shore Inlet #2 -> Panel Leg #2
Generator: Generator output connected to both panel leg 1 and 2 (panel legs paralleled)
 
caltexflanc said:
First of all, "power" is not a general term. Power is measured in watts. In most parts of the world, engines are measured in kilowatts, not horsepower. Electric bills are measured in Kilowatt hours. Generators are measured in watts, as are inverters, microwaves, lightbulbs and other appliances and so on and so on.

Secondly, balancing loads does not reduce your draw one ampere or one watt. They are just spread between two legs, which in turn additively draw from the originating power source. So even in your incorrect definition of power as amperes, belies the inaccuracy of your thread title. The reason you balance the potential loads is to be able to draw the maximum amount of power from your power souce, and thus the number of total loads you can use at one time.

By properly set up in the first place, that means the assignment of loads to panels accordingly via circuit breaker installation, and having room on each panel to add post-OEM add-ons.

I highly recommend reading Nigel Calder's "Boat Owners Mechanical and Electrical manual which discusses all this and more .in easy to read and understand terms.
Click to expand...

If you took the time and read the thread you would not be trying to give me a class in something I allready know. By the way you are wrong, you can draw more amps if you have a balanced load that is the whole point of this thread and a major point in the article I reference.
It was to try to help boaters who might have one leg of a panel overloaded. I will repeat this slowely so you can understand. If you are pluged into a 30 amp 250v 2 pole breaker and you have 250v panel. you can have a load of 125v 29 amps on one leg(L1) to nuetral if you put any additional loads on that leg you will trip the breaker. Allthough (now here it comes so pay attention) if you put the additional loads on the other leg (L2) you can add up to 29 amps. That is called a balance load. School is out.
But apparantly you do not want me to do that
 
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