Balancing Loads

[svetz]

WARNING!​

This thread deals with working inside your load center which can be deadly. It is not a place to "learn" about high voltages.
If you think you have a problem and have the slightest doubt as to what you're doing call an electrician to handle it for you.

Note: This is a split-phase topic and won't apply to countries with a single phase (e.g., EU, AU).

It might be anecdotal, but I've heard it's important with split phase to balance loads in a load center as "power" consumed isn't the sum of L1 + L2, it's the maximum. So, if it was always balanced all the time L1 would equal L2 which would minimize consumption thereby reducing costs if on-grid, or reducing demand if off-grid.

So, how do you check and then balance your loads?

Those with solar probably have CTs on L1 and L2 so we can inspect what's going on. For example, I have Enphase and this is mine for the last hour. It looks pretty good with L1 and L2 being close and is primarily the old F22 AC running. One leg being slightly higher than the other is probably my PC as it's a hog and on a single phase.

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I know some of the logic, for example, I have a small refrigerator and a small freezer that draw about the same amount of watts, so one is on L1 and the other is on L2 (circuits 3 & 5). Balanced, right?

Well, they don't always run at the same time, so no. In fact, only the vampiric loads ever all run at the same time and they're pretty small. When humans are involved, you never know what's going to run or when.

I also recently discovered that my 4 prong 240V devices are really a combination of 240V and 120V devices, and that my drier is particularly bad at balancing the load, here's a sample of the amps on L1 and L2 while it was the only thing running:

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While I might not be able to do anything about the dryer, I have noticed a kW imbalance at 4 A.M on Saturdays. At that time it should just be vampiric loads and things that don't typically get turned off (e.g., the refrigerator). I suspect this particular case, since it doesn't happen every day, is the freezer's defroster:

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Those with circuit-level monitoring (e.g., IotaWatt) can probably run some sort of time analysis with the data to optimize the load, possibly @MurphyGuy and @FilterGuy and tell us if they ever took it to the load balancing step.

But electricians have been load-balancing panels for years, so figured a number of you might have some tips.

 

[RCinFLA]

Everyone's use case is different.

Most common heavy 120vac loads are in kitchens with microwave ovens, toaster ovens, coffee pots, etc. Different wall outlets should be on different phases to avoid too much on single side. Most kitchen outlets go to 20 amp breakers in main panel.

There are some dumb cases of a large water pump wired for 120vac. Should be rewired for 240vac if greater than half HP.

Teenagers with big hair dryers are wild card.

 

[zanydroid]

But electricians have been load-balancing panels for years, so figured a number of you might have some tips.

Not for residential, I don’t think. For 120/208 there are many more bad combinations of heavy loads, for 120/240 the big 240 loads are always balanced inherently.

If you are on-grid, to my knowledge the only important cases for balancing are:
- make sure both legs of MWBC are on opposite phases
- when the service or feeder is close to being maxed out

It’s only been recently with full electric homes or EVSE where we are close to maxing out. Even then, keep in mind that most 120V loads are short lived. There are very few loads that last a long time without cycling or turning off. Things in the kitchen are usually only drawing 1800W for 5-10 min.

Worst appliance I can think of is 120V HPWH which is absolutely going to be a continuous load.
Second worse is dishwasher, mine uses 1kWh or so for a 1 hour cycle.

I think you mentioned something about 120/240 appliances. For the most part the 240 dominates that, except for special cases like spin dry low where the motor is the only thing doing work.

 

[zanydroid]

Teenagers with big hair dryers are wild card.

Hahaha this was outside my mental model for 120v loads

 

[MurphyGuy]

Load balancing in my home is only an issue when we start plugging in electric space heaters for winter, and even then, I just make sure they're on different breakers rather than worry about different L1 or L2 lines at the box.

The only time our house really sees more than 800 watts being used is when a 240volt appliance is operating (electric dryer, air conditioner, welder, plasma cutter, etc) , and load balancing isn't relevant with that.

I would think that load balancing is only an issue for big houses with large families. Five bedrooms, three or more kids, etc.

 

[zanydroid]

So, if it was always balanced all the time L1 would equal L2 which would minimize consumption thereby reducing costs if on-grid, or reducing demand if off-grid.

On-grid the only cost difference is in extra voltage drop on the service conductors and feeders from the difference between a fully balanced load and the imbalanced load. Unless you have the odd residential power plan that penalizes you for the extra imbalance at the utility transformer. Service and feeder conductors are much bigger than 120v branch circuit conductors so I would expect the extra voltage drop to be kind of in the noise in practice. But by all means, try to save that energy if you have the motivation to do so!

Off grid you may hit inverter power limits sooner on one leg or on autotransformer if there is an imbalance.