3-phase split load design

[podz]

We are having our electric redone in order to support, among other things, my brewing hobby!

I am designing and putting together the main panel and two sub-panels. If you are interested in how things are done here in europe, just follow the thread. I'll post some photos here soon.

My feed from the transformer is 3x25A phase conductors plus a neutral. My main board has three isolated rails for mini-circuit-breakers (MCB), so I'll just run a phase conductor from the main switch to a breaker on each rail and then use a floating bus system to connect the first MCB to the rest of the MCBs and residual-current-devices (RCDs) in the row. RCD is what you north american people like to call GFCI.

 

[lschiavo]

I'm in. Very curious to see this. Lykkyä tykö!

 

[The10mmKid]

Sub'd

You guys at 50 or 60Hz?

 

[podz]

230v, 50Hz.

I will get to the photos here in a few hours. Expecting visitors soon.

 

[bonsai4tim]

3phase makes motors/pumps much easier (probably smaller too). Can you pull different current loads down each of the 3 phase feeds?

 

[podz]

Can you pull different current loads down each of the 3 phase feeds?

Yes, but it's in the electric contract that the customer is responsible for phase balancing. If you overload one phase constantly, the price per kilowatt hour rises progressively - therefore, a poorly balanced panel can end up costing you a few hundred extra per month, permanently.

I have some preliminary photos now, but dammit I have to install iPhoto to this new Macbook so I can get the photos off of my phone. Over a mobile connection. At least I have LTE ;-) Still needs half an hour, seems that the Apple servers are slower than my LTE connection.

 

[podz]

I don't know why photos always end up sideways and upside down, but here is the first photo of the entire panel:

 

[The10mmKid]

Curious about the missing RCD on the third row (phase)?

'da Kid

 

[ajdelange]

Yes, but it's in the electric contract that the customer is responsible for phase balancing. If you overload one phase constantly, the price per kilowatt hour rises progressively - therefore, a poorly balanced panel can end up costing you a few hundred extra per month, permanently.

That's interesting (but reasonable). What's the criterion? Neutral ampere hours or actual imbalance between watt-hours on each of the phases?

 

[podz]

Curious about the missing RCD on the third row (phase)?

'da Kid

Yeah, good eye. I just forgot to buy it yet. The panel layout was still a bit under planning and experimentation.

Basically, the 10 amp circuits are for ceiling lamps only. Those can be wired with 1.5mm cable and don't need RCD. The 16 amp circuits are for wall sockets and need to be behind RCD and wired with 2.5mm cable.

If you notice, I also have 2 x 20 amp breakers per phase. Those will feed 2 sub-panels - 1 in the kitchen and 1 the basement. Due to my house layout, installing sub panels is far cheaper than buying lots of cable.

So, when my feed fuses are 25 amps, I can put 20 amp breakers in my main panel and feed them down to 16 amp breakers in the sub panels. This is the requirement to maintain discrimination.

 

[podz]

That's interesting (but reasonable). What's the criterion? Neutral ampere hours or actual imbalance between watt-hours on each of the phases?

Actual watt-hour imbalance. The meters we have measure per-phase and they have built-in GSM SIM cards which communicate in real-time with the electric company. We can log into their website and see what's going on at any moment.

You will be financially punished for phase imbalances.

 

[podz]

This is a closeup for the main switch and the L1 rail. For those of you not familiar with 3-phase, the live wires are called L1, L2, and L3.

Sorry the photo is again upside down.

The main switch is 3-pole, 40 amp. Next to that are two 20 amp MCBs - each of those will be the first out of 3 phases feeding the two sub-panels. Then, there are three 10 amp MCBs for ceiling lamp circuits. After that, two 16 amp RCDs to protect the two 16 amp MCBs that come last (those are for wall sockets).

So basically, this main panel will feed the ground floor and outside of my house, with the exception of the kitchen, as well as feeding 3-phase to two sub-panels.

The black phase conductor cable is 6mm2 cross-section, i.e. between 9 and 10 AWG. I'll use the same cable for the neutral to the RCDs, except that it's blue (European Standard).

 

[ajdelange]

Actual watt-hour imbalance. The meters we have measure per-phase and they have built-in GSM SIM cards which communicate in real-time with the electric company.

If I had a 1 kW load and ran it for an hour on phase A, then moved it to phase B for an hour and then to phase C for an hour the meter would read 1 kW hour on each of the three phases i.e. perfectly balanced loading based on that criterion alone when in fact you have been badly imbalanced for 3 hours (i.e. have drawn 0 and negative sequence currents over that whole time period). Would you be penalized for this? We could argue that 0 and negative sequence currents are detrimental to the network at any instant they exist but on the other hand we could argue that as long as the phase of your negative sequence current is moving around temporally and your neighbor's is too with any angle as likely as any other that the total on the network is small (this may be getting too technical).

I can certainly see how this would be a concern for and industrial consumer but your max load is only 17 kVA here.

 

[podz]

If I had a 1 kW load and ran it for an hour on phase A, then moved it to phase B for an hour and then to phase C for an hour the meter would read 1 kW hour on each of the three phases i.e. perfectly balanced loading based on that criterion alone when in fact you have been badly imbalanced for 3 hours (i.e. have drawn 0 and negative sequence currents over that whole time period). Would you be penalized for this? We could argue that 0 and negative sequence currents are detrimental to the network at any instant they exist but on the other hand we could argue that as long as the phase of your negative sequence current is moving around temporally and your neighbor's is too with any angle as likely as any other that the total on the network is small (this may be getting too technical).

I can certainly see how this would be a concern for and industrial consumer but your max load is only 17 kVA here.

Yes, you would be penalised for that.

Maybe it is too technical for me to understand how or why the electric company runs it's network the way it does.

I do know this: If you have 3 x 25A feeds and you consistently draw 20A from L1, 5A from L2, and 5A from L3, your monthly electric bill will be around 3 times as high as if you had consistently drawn 10A each from L1, L2, and L3. I don't know exactly why, but that's the way they bill. I am also not sure what their statistics period is - but I am guessing nowadays that it is per minute since they have already had real-time access to the meters for about 8 years now and have had sufficient time to refactor their billing systems.

They do anything and everything to get as much money as they can.

Good electricians take the time to balance the phases. Bad ones do the job as quickly as they can and don't care too much. If they do a really bad job, though, the electric company will send someone to fix it and in turn send the invoice to the contractor in question.

 

[ajdelange]

Maybe it is too technical for me to understand how or why the electric company runs it's network the way it does.

...


They do anything and everything to get as much money as they can.

That explains it satisfactorily to me.

More seriously though and without getting too technical (I hope) a three phase system can be described by three currents: positive sequence, negative sequence and 0 sequence. The last is the neutral current. If it is appreciable the system can launch 'strays' which can, for example, shock cows connected to milking machines. If the three loads (phases A, B and C) are balanced 0 sequence current is 0. That's a good thing. Negative sequence current rotates in the opposite direction of the supplied voltages. IOW if the utility supplies the sequence A,B,C,A... negative sequence current is C,B,A,C.... This results in a field component in connected machines (motors, generators) running in the opposite directions of those machines' rotors which results in double frequency eddy currents and excess heating. Not a good thing. If the loads on phases A, B and C are equal the negative sequence current is 0.

..the Good electricians take the time to balance the phases.

Understood but I'd be sitting there wondering every time I turned on a table lamp whether I would be better off turning on two more.

Interesting topic though. I've only ever been to one place in the world (Mauritius) where the houses were wired for three phase. We never worried about balance, other than in the sense that we were good (I hope) engineers, but then we didn't pay the electric bill.

 

[lschiavo]

Good electricians take the time to balance the phases. Bad ones do the job as quickly as they can and don't care too much. If they do a really bad job, though, the electric company will send someone to fix it and in turn send the invoice to the contractor in question.

I like the fact that the electrician is actually accountable for his/her work. There seems to be no working model of that around here unless maybe through negligence someone is injured or property is damaged.

Understood but I'd be sitting there wondering every time I turned on a table lamp whether I would be better off turning on two more.

I was thinking the same. It seems it would be difficult, as an electrican, to guess which receptacle or lighting loads may be used at the same time in a residential situation. There must be a resonable allowance given for imbalance.

 

[podz]

Interesting topic though. I've only ever been to one place in the world (Mauritius) where the houses were wired for three phase.

There are approximately 100 million homes in the 28 countries European Union that are directly wired with three-phase power. That is a little less than half of the total number of residences (approximately 210 million) in the entire European Union. It is more common in central and northern EU and less common in the southern countries.

Main benefit: saves a whole lot of copper.

All household stoves and ovens that are sold in the EU are capable of operating on 3-phases and most of them even require it.

Every household in Finland that has an electric heater in the sauna and/or the house, the heater is 3-phase. Luckily I have a wood burning stove in my sauna - much nicer ;-)

Every household that has underfloor heating (very common), this is also 3-phase.

Electric hot water heaters, for those people who have them, are all 3-phase. Mine is heated by an oil burner which also circulates hot water through pipes and to radiators for my heating.

Finally, the electric log splitters that some of us have in our yards - they are also 3-phase.

 

[ajdelange]

Then I would have to revise my statement: I've only been to one place in the world where I noticed that the power to houses was three phase.

Three phase distribution does save some copper and produces much better ripple out of rectifiers without filters (I worked in the electroplating rectifier industry for a couple of summers) but far and away the biggest advantage is the simplicity it lends to motor design.

 

[podz]

Moving along further in this project, I bought 50 meters of 5x6 mm2 (cross-sectional area) cable to connect my two sub-panels to the main panel. I tried to find a conversion chart, so I guess that this is 5 x 10 AWG insulated copper conductors. This cable should easily handle a 30 amp load per phase.

So, I will run three phases plus neutral and ground between the main panel and sub-panels.

I'll get a photo of the new sub-panel for the basement/garage soon. I put a three-phase (3-pole) 16 amp breaker in there as well for my upcoming electric brew rig which will naturally feature a three-phase heating element. I am still deciding whether to change that out for 3 separate breakers on 3 separate phases. Safety vs convenience...

 

[podz]

Subpanel for the garage / basement. Just put it together this morning and didn't wire up the inside yet.

There is a 16 amp 3-phase simultaneous-trip breaker right next to the main power switch. That's what I'll use for my electric brew rig. Next to that are 2 x 16 amp and 2 x 10 amp circuits without RCD (GFCI). All the rest of the 16 amp circuits each have their own RCD device in order to eliminate nuisance tripping of multiple circuits.

I'll put the ceiling lights on the unprotected 10 amp circuits. My water pump and oil burner will go on the unprotected 16 amp circuits, probably.

Total cost to build this unit was 200 EUR.

 

[schematix]

Good electricians take the time to balance the phases. Bad ones do the job as quickly as they can and don't care too much.

A good electrician follows the print they were given. Leave the balancing up to the electrical engineers. Shame on the engineer if they mess it up.

 

[lschiavo]

A good electrician follows the print they were given. Leave the balancing up to the electrical engineers. Shame on the engineer if they mess it up.

I have never seen any sort of electrical design done on the prints for residential jobs I have been part of. Hell, half the small commercial jobs we do have a foot-note at best for electrical. It seems everything down to the pipe hangers is spelled out for the other trades but not for electrical. Maybe electricians are just assumed to be smarter. I do have a BSEE from going on 20 years back but nobody seems to care as long as the light comes on when they flip the switch.

 

[schematix]

I've never seen a residential electrical drawing beyond an architectural diagram that showed where different types of receptacles were to be installed.

However, given the nature of residential 2-phase electrical vs 3-phase industrial, this isn't as much of an issue. In general the single phase loads tend to be much much smaller so an imbalance is less of a concern. In a residence if you split your large breakers between the left and right side of the breaker box, and then continue to fill top to bottom you'll naturally balance your system.

 

[ajdelange]

The utility doesn't care one whit whether your biphase system is balanced or unbalanced. If you are pulling 20 kVA there system sees a 20 KVA load on whichever phase they have connected you to whether your draw it perfectly balanced or all from one side of your panel. Their concern is to balance the houses fed from a particular substation so that the substations phases are balanced. You, on the other hand, should shoot for balance as you don't want to be generating strays etc.

In North America 3ø usually goes to manufacturing facilities and office buildings where the major loads (machinery, air conditioning, lighting...) etc. are usually 3ø so that the load is more or less balanced to begin with. Yes, offices and factories do have single phase loads like fax machines, copying machines, desk lamps but with a large number of occupants those would probably naturally distribute themselves more or less equally among the three phases. In a single family home it is a different story just because there are fewer loads and many of them are single phase though OP did mention that things like ovens in countries that use 3ø distribution are often wired for 3ø. But how often is the oven on compared to the computer, TV, washing machine, table lamps etc?

 

[podz]

In a single family home it is a different story just because there are fewer loads and many of them are single phase though OP did mention that things like ovens in countries that use 3ø distribution are often wired for 3ø. But how often is the oven on compared to the computer, TV, washing machine, table lamps etc?

Nearly all stoves, hot water heaters, and electric sauna heaters where I live are 3-phase. Any nearly all sub-panels will also have 3 phases doing down to them.

The meter on my service panel measures and reports activity on all three phases to the electric company, in real-time over a mobile connection.

To further my project, I just bought 50 meters of 5x6mm2 cable (6mm2 cross-section is like 9 or 10 AWG). That is some heavy-ass cable to go between my main fuses and main panel, also between the main panel and the two sub-panels. 5 wires are needed - 3 for the phases, 1 for neutral, and one for ground.

When I get the sub-panel in the garage, I expect to be putting a 6kW 3-phase heating element into my brew rig. That should pull about 10.5 amps, which is fine since I will be feeding it with 3x16 amp breakers (on 3 separate phases). Seeing how electricity is far more efficient than gas, this should bring 20 liters to a full rolling boil in equal or less time than a high-end gas burner.

My TV is LED, all of our laptops have LED displays, and all of the lamps in our house are LED. Our oven is on daily and our washing machine is on twice weekly. I do have a server room in my basement that is all on a single phase, and those stay on 24-7 and are big servers. They will be balanced soon.

 

[ajdelange]

The meter on my service panel measures and reports activity on all three phases to the electric company, in real-time over a mobile connection.

That's pretty bizarre. The cell phone company must have lots of spare bandwidth in your area. To accomplish their goals all they would need to do is report kW-hrs on each phase (for billing) and ampere hrs on the neutral (your integrated imbalance for penalty calculation) once a month or at most a couple of times a day if they are trying to implement tight load management (adjusting regulator taps, bringing on additional generation, buying from another utility, brownouts....).

 

[podz]

That's pretty bizarre. The cell phone company must have lots of spare bandwidth in your area.

It's not just my area; it's the entire country. For 8 or more years already.

 

[orangehero]

That's pretty bizarre. The cell phone company must have lots of spare bandwidth in your area.

Or the US is a decade behind Finland.

 

[motobrewer]

smart meters / advanced metering infrastructure has started to be rolled out in the US (namely cali)

wouldn't use cell here, some of them are zigbee, some of them are PLC.

 

[podz]

Or the US is a decade behind Finland.

In many ways, it is.

One of the biggest reasons for that is that there are no "state" governments here - everything is national or municipal. It's pretty easy for the national government to pass a mandate that residential fibre trunks will be laid nationwide, and they did that for example more than 10 years ago. Smaller countries are more agile.

The smart meter stuff comes from business, though - it's a lot cheaper to roll out smart meters than it is to keep meter reading people on staff.

 

[podz]

Taking a break on this project since I fell down and broke my hand yesterday. Fourth metacarpal snapped like a twig. Cast for a month.

 

[podz]

So I just hired an electrician to come and finish the job. Got three panels installed and going hot today.

Three phase socket and RCD (GFCI) for my brew rig will also be installed today!

 

[lschiavo]

Glad you found a way to make some progress. Hope you are healing up well.

 

[podz]

Preparing for phase two: yesterday bought 100 meters (325 feet) of lamp cable and 200 meters (650 feet) of socket cable. That should be enough for SWMBO to do the rest of the cabling (our entire installation is surface-mounted).

 

[Facinerous]

Good luck with your project Podz.

Just wanted to chime in as to why panel load balancing is... and isn't important for a utility.
In the USA most home power has two phases. Technically though it is only one phase as far as the utility is concerned, which is split in the middle to produce two phases via the transformer on the nearest pole outside your house. The utility doesn't give two hoots about panel balancing in this case because your home is only pulling power from one of the utilities three phases.

It is good practice, as an electrician though, to balance a panel between its available phases because you never know when the home owner is going to decide they want to add another 50 amp breaker in their panel for home brewing or other purposes. In that case if the panel is unbalanced, that could cause the main breaker to trip unnecessarily even though your total power use is below its tripping value.

The phase balance is more important, from a utilities perspective, in buildings that have multiple phases. The reason why is much like what I just stated above.

Lets say there are 50 buildings that have three a three phase service, but for some reason or another out of those 50 the L1 or A phase is loaded more than the other two. Maybe by 20%. In what a utility would consider a peak demand time, the circuit that runs out from a substation to those 50 buildings will be considerably loaded, maybe to 90%. That A phase though. Its drawing 20% more, so the breaker back at the substation see excessive current over a period of time, and trips. Now all 50 buildings are out of power.

If all the panels were balanced then all three phases would have been below max capacity. Now imagine a circuit that is supplying 100 thousand buildings. Same thing.

I may have been a little wordy, but that is the reason why utilities care.

 

[ajdelange]

Just wanted to chime in as to why panel load balancing is... and isn't important for a utility.

The reason utilities are concerned was discussed in #15. In case you didn't see it:

More seriously though and without getting too technical (I hope) a three phase system can be described by three currents: positive sequence, negative sequence and 0 sequence. The last is the neutral current. If it is appreciable the system can launch 'strays' which can, for example, shock cows connected to milking machines. If the three loads (phases A, B and C) are balanced 0 sequence current is 0. That's a good thing. Negative sequence current rotates in the opposite direction of the supplied voltages. IOW if the utility supplies the sequence A,B,C,A... negative sequence current is C,B,A,C.... This results in a field component in connected machines (motors, generators) running in the opposite directions of those machines' rotors which results in double frequency eddy currents and excess heating. Not a good thing. If the loads on phases A, B and C are equal the negative sequence current is 0.

The reason the home owner should care about panel balance is that if his loads are unbalanced badly enough neutral voltage can depart from ground voltage. Also I'm sure code requires it. This assumes you are on a biphase system. If you are a 3 phase customer you don't want imbalance because you don't want negative sequence currents over heating your motors any more than anyone else does.

The utilities have lots of ways of dealing with imbalance when it occurs. If, for example, there is a single phase to ground fault in a distribution system the protective fuses/cutouts/breakers for that phase open which removes that phase from the system although the other two phases may still be hot. This would happen, for example, if a tree branch falls across the primary line in my neighborhood taking it off line. If my neighborhood is on phase A obviously the relative loads on phase B and C go up. There is neutral sequence current and there is negative sequence current in those cases and the utility doesn't like that, of course, so they try to clear the fault. Their fault management strategies depend on monitoring of those currents.

 

[Facinerous]

I'm sorry ajdelange I missed your post for some reason. I did have a few last night though so that is probably why.

I agree with you having an event where one of the phases had low voltage it would stress motors and the like. I have never seen that happen as of yet though. I have seen motors burn up from locked rotors and such, and I have seen 3 phase motors lose one phase and cause the overload protection to operate. I have never seen a poorly balanced system cause an undervoltage to such a degree though, unless it is in the event of a single line to ground like you stated. Granted these are probably lessons the electric industry has learned over time.

Maybe I haven't seen this stuff because I have learned from good electricians, and we fix the problems that others leave.

Either way thanks for the explanation.

Podz. I will not hijack your thread so this is the last post I will put that is not related to your project.

 

[podz]

It's all good, all discussion welcome!

 

[ajdelange]

I agree with you having an event where one of the phases had low voltage it would stress motors and the like. I have never seen that happen as of yet though.

Imbalanced loads result in negative sequence voltages which result in negative sequence currents which cause motors and generators to heat more than they would otherwise. If the plant manager's secretary plugs in a single phase electric heater in her office that's not likely to cause sufficient negative sequence voltage to burn out all the motors in the plant or even enough to cause a measurable temperature rise. But remember that we got started looking into this from the POV of the utility when OP posted that his utility micromanages the balance of each customer. The utility definitely wants to present its generators with balanced loads because when their machines are running at 105% rating (summer, peak load) they don't have any margin. So they monitor balance throughout the network. If a substation finds that one distribution phase is drawing more current on average than another I would guess that the utility (talking US now) would reassign neighborhoods to different phases. For example, if the local substation found Phase A persistently relatively overloaded they might move my neighborhood (and some others) to Phase B - only have to move/replace one wire to do that.

I have seen motors burn up from locked rotors and such, and I have seen 3 phase motors lose one phase and cause the overload protection to operate. I have never seen a poorly balanced system cause an undervoltage to such a degree though, unless it is in the event of a single line to ground like you stated.

Maybe I haven't seen this stuff because I have learned from good electricians, and we fix the problems that others leave.

No engineer will design a plant that presents an imbalanced load to the utility (because the utility will be on him if he does). Thus imbalances, within a plant, are small (the secretary's heater, the fact that one department leaves its lights on when another doesn't) except in the case of a fault and faults are cleared as quickly as possible. It is the utility's perspective that we are focused on here. From the customer's perspective the only time that imbalance may be at issue is when, as in OP's case, the utility monitors and charges for imbalance. The other case might be in sizing backup generating equipment. In my house I have three panels and I have thought about installing a backup generator. It sort of seems to make sense that I hook up each panel to one of the phases of a 3ø generator. Clearly, here, the generator would not be presented a symmetrical load since two of the panels have air conditioners on them and one doesn't. Thus, in cooling season, that generator would have to deal with considerable negative sequence current, would experience additional temperature rise and would have to be de-rated.

 

[The10mmKid]

Hey Podz,
Could you please post some images of your completed panel guts?
I'm curious about how the branch circuits are jumpered back to the mains.

Thanks,
'da Kid