Using High-Leg Delta for Japanese Appliances?

[00crashtest]

I was reading Electrical Wiring Commercial 17th Edition, which is based on the 2020 National Electrical Code, and page 284 said,

The voltage between “B” and “N” is 208 volts. The “B” phase is called the high leg and cannot be used for lighting or other line-to-neutral purposes.

However, I could not find any code references prohibiting it. I searched online and could only find on forums that one could not use it because they would not be able to find a single-pole breaker rated 208 volts and that the voltage would be unstable from unbalancing the three-phase high-leg delta transformer.

The reason why a high-leg to neutral single-phase circuit would be useful is precisely because it provides 208 volts between conductors, and Japanese split-phase appliances use 200 volts without also requiring 100 volts for the controls (unlike how split-phase appliances in North America require 120 V for the controls in addition to 240 V for the heating loads). The voltage imbalance on the transformer can be mitigated by having only a small fraction of loads be high-leg to neutral, because one wouldn't typically be using Japanese appliances in North America anyways.

However, a lodging facility popular with tourists from Japan or a community in North America with a high concentration of people who frequently travel between Japan and North America would benefit greatly from having 208 V power outlets to power their 200 V small kitchen appliances as intended by the manufacturer, especially if the equipment is bought in Japan west of the Fuji River, including the Kansai Region for Osaka, where the grid also runs on 60 Hz. This is especially useful because small kitchen appliances involving heating can easily fit within checked baggage. This is also especially helped by the fact that Japanese 200 V 15 A and 200 20 A plugs can be plugged into NEMA 6-15 and 6-20 receptacles respectively. Anyway, most appliances are typically rated for both 50 and 60 Hz in order to also be sold in the largest metropolitan area, which is the Kanto Region for the city of Tokyo, where they use 50 Hz. Granted, I see on travel and expatriate forums that most 200 V appliances from Japan work just fine on both 220 V 50 Hz European and 240 V 60 Hz North American as long as they are not on the highest setting. However, one would want their appliance to work as design intended on all settings.

https://www.plugsocketmuseum.nl/JP/Meikosha-15A-250V_plug.jpg

In Article 210 for branch circuits, I could only find section 210.21 for Outlet Devices stating,

(B)(1) Single Receptacle on an Individual Branch Circuit. A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.

and

(B)(3) Receptacle Ratings. Where connected to a branch circuit supplying two or more receptacles or outlets, receptacle ratings shall conform to the values listed in Table 210.21(B)(3), or, where rated higher than 50 amperes, the receptacle rating shall not be less than the branch-circuit rating.

In Article 240 for overcurrent protection, I could only find section 240.83 for Marking stating,

(E) Voltage Marking. Circuit breakers shall be marked with a voltage rating not less than the nominal system voltage that is indicative of their capability to interrupt fault currents between phases or phase to ground.

So, can't one just use supply NEMA 6-20 receptacle(s) (which also accept NEMA 6-15 plugs and consequently both 200 V 15 A and 200 V 20 A JIS plugs) on a branch circuit that is 208 volts from high-leg to neutral (making it not a multi-wire branch circuit in this case) and is rated 20 A using a single-pole breaker rated for 20 A at 277 volts (or also 347 volts for Canada, the Pacific Northwest, and the US South) as long as they keep the branch circuit load under a relatively small proportion, such as 25% of the service transformer current rating?

 

[jim dungar]

Because the 208V uses 1/2 of the center tapped coil the transformer sees it as part of the possible 120V single phase load. The majority of 240/120V 4wire transformer banks are not sized taking the 208V load into account.

 

[winnie]

As far as I know, there is no explicit code prohibition to using the high leg to neutral, but as @jim dungar says it makes very bad use of the transformer, and thus not a good practice.

Yes, you could use a 277V or 240V straight rated breaker for this.

High leg delta is also a getting rarer, and IMHO would not be a good choice for a new installation.

Using a 6-20 receptacle for 208V is not compliant if 6-20 is also used for 240V in the same facility.
NEC 406.4(F) Noninterchangeable Types
Receptacles connected to circuits that have different voltages, frequencies, or types of current (ac or dc) on the same premises shall be of such design that the attachment plugs used on these circuits are not interchangeable.

IMHO if there were a building where it made sense to provide power for 200V Japanese appliances, it would make more sense install standard 208/120V three phase, or custom 100/200V single phase. But probably the best approach would be to install standard 120 and 240V receptacles, and have plug in transformers available for the 'foreign' voltage.

-Jon

 

[00crashtest]

Because the 208V uses 1/2 of the center tapped coil the transformer sees it as part of the possible 120V single phase load. The majority of 240/120V 4wire transformer banks are not sized taking the 208V load into account.

But most 3-phase distribution transformers can be made by connecting three single-phase transformers together, particularly when overhead. In alternating-current theory class, I already learned that the single-phase transformer in a 4-wire delta bank that has its load-side winding centre grounded has higher loads because of the single-phase 120 V loads in addition to any 240 V single-phase and 240 V three-phase loads. In that case, if the other 2 transformers are at full current capacity, then the centre-tapped transformer has to be upsized moderately anyway. So, can't one just upsize the A-B transformer and B-C transformer (with phase B being the high-leg as required by 408.3(E)(1)) slightly and upsize the A-C centre tapped transformer significantly?

This way, 208 V 1 ph 60 Hz can be supplied for Japan, along with the standard 120 V 1 ph required for the general-purpose receptacle; the typical 120/240 V split phase for North American ranges, ovens, and dryers; the typical 240 V 1 ph for North American, European, British, and Australian welders; and the typical 240 V 60 Hz 3 ph for synchronous and induction motor loads -- all without requiring any additional transformers. The beauty of the centre-tapped high-leg delta transformer is that it allows the highest number of different voltages while minimizing conversion steps, which minimizes energy loss to increase efficiency.

Of course, I know that at any given current and given frequency, as long as the voltage is at or higher than the voltage the equipment being fed is rated for, it can run at full power, only requiring a step-down transformer if the supply voltage is higher than the upper tolerance of the equipment. However, using an additional transformer means an additional step of conversion is required, which needlessly increases energy loss to reduce efficiency.

 

[00crashtest]

Yes, you could use a 277V or 240V straight rated breaker for this.

Thanks for letting me know!

 

[00crashtest]

As far as I know, there is no explicit code prohibition to using the high leg to neutral, but as @jim dungar says it makes very bad use of the transformer, and thus not a good practice.

...

High leg delta is also a getting rarer, and IMHO would not be a good choice for a new installation.

It is not bad use for percentage capacity purposes if the centre-tapped individual transformer forming part of the 3-phase bank is sized substantially larger than the 2 others. In my honest opinion, high-leg delta is the best type of transformer by far in the world because it provides the greatest number of voltages using standard individual pieces of equipment while requiring no additional conversion steps that lead to reduced energy efficiency. I am very glad that the high-leg delta is common in North America (and used to be one of the standard practices and is still common because of all the old installations, with the transformers lasting so long because they have no moving parts and consequently no abrasion).

 

[Birken Vogt]

I recently vacationed all across the Western states, and looking at power lines is more interesting than looking at the road, and I saw plenty of open delta installations around, not just in California either.

We have open high leg delta at my shop and I like it, as noted above.

 

[00crashtest]

Using a 6-20 receptacle for 208V is not compliant if 6-20 is also used for 240V in the same facility.
NEC 406.4(F) Noninterchangeable Types
Receptacles connected to circuits that have different voltages, frequencies, or types of current (ac or dc) on the same premises shall be of such design that the attachment plugs used on these circuits are not interchangeable.

Then I will use NEMA 14-20 for the 120/240 V receptacles and NEMA 6-20 for the 208 V receptacles. Since the NEC does not require receptacles to be listed [by an NRTL recognized by OSHA], then a JIS 200 V 20 A receptacle can be used, as long as the 240 V receptacles are not NEMA 6-15 or 6-20 in order to prevent JIS 200 V plugs to be accidentally inserted, because their yokes also mount in the same wall boxes. However, since all JIS 15A and 20A 200V plugs can fit into all NEMA 6-20R but not all NEMA 6-20P can fit into JIS 200V 20A receptacles, it would be foolhardy to install those JIS receptacles, especially with the lack of parts availability here.

In North America, where the split-phase transformer is readily available, whenever a receptacle supplying 240 V is to be provided, I will not provide just that voltage. I will also add the neutral to supply 120 V because I learned that wires are fairly cheap but transformers are comparatively very expensive. If one wants to power a cord-and-plug-connected appliance requiring only 2 hots such as a NEMA 6-50 welder, then they can just use a plug adapter. That way, the NEMA 14-50 receptacles in the workshop installed for welders, compressors, or Level 2 EVSEs can also power a range, dryer, or big rig RV if need be.

Now that CalGreen in California's 2022 Building Code requires receptacle outlets [on individual branch circuits as required by NEC 625.40] capable of supplying low-power Level 2 EVSE (defined as a 208 V or 240 V circuit providing 20 A) to be installed in new construction for other than single-family and two-family dwellings (including multi-family, lodging, and retail facilities) as part of the 2035 ICE ban for new vehicles, the use of NEMA 14-20 will suddenly increase exponentially. The requirement is waived for single-family and two-family homes because the owners have total control over the interior of their garages, but the requirement to add a raceway and outlet box sized for at least low-power Level 2 EVSE still holds in order to make future installation of the conductors quick, easy, and affordable.

In some of my previous posts, I had asked about the availability of ranges and dryer that require only 2 hots because I had no idea how much wires costed versus transformers and uncommon appliances. Now that I have completed many electrician courses, especially working with equipment hands-on, I know much more.

 

[LarryFine]

The high-leg delta is a 120/240v 1ph source and a 240v 3ph source, superimposed on each other.

The open delta actually began as a 3ph modification to existing 1ph services to serve new machines.

 

[00crashtest]

IMHO if there were a building where it made sense to provide power for 200V Japanese appliances, it would make more sense install standard 208/120V three phase, or custom 100/200V single phase. But probably the best approach would be to install standard 120 and 240V receptacles, and have plug in transformers available for the 'foreign' voltage.

I think otherwise because using a plug-in transformer means requiring an extra conversion step, which increases energy loss to increase energy consumption overall and reduce energy efficiency. While not big, the extra energy losses are not insignificant given that powerful appliances are used. This is important in states adopting the California Air Resources Board standards, Canada, the European Union, and the European Free Trade Association, where reducing CO2 emissions in order to minimize global warming, especially from electricity generation, is more important than saving money.

Granted, one could say that a passenger's share of even a single intercontinental flight emits way more CO2 than the additional losses over an entire year from requiring an extra transformer. However, if one were to travel between Japan and the US/Canada/Mexico regardless of whether they would use Japanese split-phase appliances here or not, which is the case with virtually all travellers, then there would be a not-insignificant net CO2 savings for using an intentionally asymmetrical high-leg delta transformer, especially if a 3-phase transformer were to be required anyway for the large building that the Japanese appliances are used in. I was thinking of like an office building-sized Japanese tourist/expat centre (in San Francisco, New York, Los Angeles, Toronto or whatever) with elevators to have the closed high-leg delta 120/208/240 V transformer bank with the grounded centre-tapped 120/240 V individual transformer intentionally oversized to supply 208V loads, which would require a 3-ph transformer anyway for its elevators, food courts, and HVAC systems.

 

[00crashtest]

The high-leg delta is a 120/240v 1ph source and a 240v 3ph source, superimposed on each other.

The open delta actually began as a 3ph modification to existing 1ph services to serve new machines.

I am so glad for the unknown genius who invented this and for the subsequent property owners (especially dining, big box retail, and industrial establishments that are power-hungry by necessity) who made it one of the standard setups, which is especially useful for energy efficiency purposes. They also created the unintended benefit of being able to power 200 V Japanese appliances in the US and Canada without extra equipment, not even plug adapters because all 200V 15A and 20A Japanese plugs can fit into any NEMA 6-20 receptacle.

 

[winnie]

I think otherwise because using a plug-in transformer means requiring an extra conversion step, which increases energy loss to increase energy consumption overall and reduce energy efficiency. While not big, the extra energy losses are not insignificant given that powerful appliances are used. This is important in states adopting the California Air Resources Board standards, Canada, the European Union, and the European Free Trade Association, where reducing CO2 emissions in order to minimize global warming, especially from electricity generation, is more important than saving money.

You do understand that when you connect a load 'high leg to neutral', that you are using the utility supply transformer less efficiently, in essence adding an additional conversion step?

Consider an 'open delta high leg' system, because it is easier to analyze. Connect a 10A 208V load from B to N. That 10A has to flow through the full 240V leg of the stinger transformer and 120V of the lighting transformer, so while you are feeding 2080 VA to the load, the transformer coils are experiencing 3600 VA of loading.

On top of this, your neutral is now no longer 'balanced' and your 4 wire service and feeders would have to count as 4 current carrying conductors for purpose of ampacity calculations.

I repeat, as far as I know there is not explicit prohibition in code to using high leg to neutral loading. But it is not an accepted practice and you would have to go over every detail of the installation to ensure that you didn't violate some aspect of the code.

You would need to ensure that the power company doesn't prohibit that use of their transformers, or you would need to use your own transformers. Of course you can get anything you want in a transformer, but custom add $$$$.

You would need to deal with having the correct breaker ratings. You couldn't use ordinary 120/240V 'slash' rated breakers commonly used at these voltage ranges. Of course you can use ordinary 480/277V panels and breakers, but they are more expensive.

You would need to deal with proper conductor sizing, including considering the neutral as a CCC. Bigger conductors adds $$$.

If you are talking about residential units with individual metering, you are now putting in 3 phase meters where normal usage would be single phase meters. Again more $$$$.

Every single one of these issues can be answered, through careful understanding of all the codes and laws involved. But every non-standard thing you do will add $$$ and confusion.

What exactly are you trying to accomplish, and why won't ordinary 208/120V three phase achieve that same end while remaining blog standard?

-Jon

 

[jim dungar]

But most 3-phase distribution transformers can be made by connecting three single-phase transformers together, particularly when overhead. In alternating-current theory class, I already learned that the single-phase transformer in a 4-wire delta bank that has its load-side winding centre grounded has higher loads because of the single-phase 120 V loads in addition to any 240 V single-phase and 240 V three-phase loads. In that case, if the other 2 transformers are at full current capacity, then the centre-tapped transformer has to be upsized moderately anyway. So, can't one just upsize the A-B transformer and B-C transformer (with phase B being the high-leg as required by 408.3(E)(1)) slightly and upsize the A-C centre tapped transformer significantly?

Yes, a high leg system could be designed taking the 208V L-N voltage into account, but no POCO does this as a standard practice. It takes special engineering, so it would likely need to be customer owned and maintained.
Remember just because you can, doesn't mean you should.

 

[kwired]

High leg delta is not becoming less common everywhere. Rural POCO's still installing new services around here that are high leg delta. Full delta high leg systems are common on farms with a lot of three phase motor load. Why use 208 wye when 240 delta gives you a little more bang for your buck so to speak? Plus any single phase motors you do have still get the 240 they are rated for instead of 208.

There is also limited load applications - services supplying a center pivot and basically nothing else. These are machines on a 30 amp or less 480 volt three phase supply. Supplying them with a two transformer open delta @ 480 volts is pretty common, the high leg is 416 volts to ground. The machine has no neutral load so to some extent we don't even care which position the high leg is connected to.

Then there is still many remote locations where they only have brought two phase conductors plus the neutral to the location. Open delta is about the only option if you have three phase need in those places. If you have enough demand then all three phases becomes more important to the POCO but if you have what they see as limited load they may only give you open delta or want more in construction costs if you still want all three phases. Though it was more that way in the past than it is now, but those locations still exist. The past 20-25 years have improved to having all three phase lines kind of near to a lot more locations than they used to be.

 

[zbang]

Using high leg to neutral..... seems to come up almost every month. AFAICT the answer never changes ("it's a bad idea, here's why"); search the forums and you'll find the threads.

IMHO, if you want to provide 200v for Japanese devices, just get a transformer and the matching receptacles and mark everything in both Japanese and English.

 

[tortuga]

Japanese split-phase appliances use 200 volts without also requiring 100 volts for the controls (unlike how split-phase appliances in North America require 120 V for the controls in addition to 240 V for the heating loads).

If US appliances were made that way we that would be a cool fix for legacy 3 wire range circuits. Instead of having to rewire them to 4-wire you could just swap a 10-50 to a 6-50.

However, a lodging facility popular with tourists from Japan or a community in North America with a high concentration of people who frequently travel between Japan and North America would benefit greatly from having 208 V power outlets to power their 200 V small kitchen appliances as intended by the manufacturer, especially if the equipment is bought in Japan west of the Fuji River, including the Kansai Region for Osaka, where the grid also runs on 60 Hz. This is especially useful because small kitchen appliances involving heating can easily fit within checked baggage. This is also especially helped by the fact that Japanese 200 V 15 A and 200 20 A plugs can be plugged into NEMA 6-15 and 6-20 receptacles respectively.

Keep in mind you *technically* can't provide receptacles over 120 volts in a dewlling for an appliance that takes less than 1440 watts.

 

[00crashtest]

On top of this, your neutral is now no longer 'balanced' and your 4 wire service and feeders would have to count as 4 current carrying conductors for purpose of ampacity calculations.

I repeat, as far as I know there is not explicit prohibition in code to using high leg to neutral loading. But it is not an accepted practice and you would have to go over every detail of the installation to ensure that you didn't violate some aspect of the code.

You would need to ensure that the power company doesn't prohibit that use of their transformers, or you would need to use your own transformers. Of course you can get anything you want in a transformer, but custom add $$$$.

You would need to deal with having the correct breaker ratings. You couldn't use ordinary 120/240V 'slash' rated breakers commonly used at these voltage ranges. Of course you can use ordinary 480/277V panels and breakers, but they are more expensive.

You would need to deal with proper conductor sizing, including considering the neutral as a CCC. Bigger conductors adds $$$.

If you are talking about residential units with individual metering, you are now putting in 3 phase meters where normal usage would be single phase meters. Again more $$$$.

I was thinking about a highly custom case of designing a one-off building, similar to embassy/consulate buildings, airport terminals, 7-star hotels, intercity train stations within major metropolises, central libraries, supertall skyscrapers, and buildings of internationally known universities, where the building would cost at least 200 million dollars (US). So, even having all transformers in the service be owned by the customer would cost proportionally an immeasurable amount in this case. This is why I said "office building-sized". That is also why I said energy efficiency was more important than initial cost. Since the CalGreen section of the California Building Standards Code legally mandates so many efficiency features to be provided, you could also have a needlessly hostile tone about the state's Building Standard's Commission and the Air Resources Board using the argument of $$$$. And yes, since it is a highly custom situation, I would plan to go over every detail of the installation in this thought experiment that deals with a realistically possible case.

 

[00crashtest]

You do understand that when you connect a load 'high leg to neutral', that you are using the utility supply transformer less efficiently, in essence adding an additional conversion step?

Yes, but that is still a single conversion step from the utility distribution lines, albeit a larger one. Also, larger objects are typically more energy efficient than smaller equipment because they have a greater volume to surface area ratio. So, connecting a load directly from the high leg to neutral using the 95%+ efficient three-phase utility transformer to supply a 208 V circuit (which is well within tolerance of 200 V, just like how 120 V is well within tolerance of 110 V) will still be more efficient than first using that same transformer to connect between 2 phases to give a single-phase circuit, and then using a 3000 W plug-in transformer that is probably only 60% efficient just to step down from 240 V to 200 V.

 

[00crashtest]

why won't ordinary 208/120V three phase achieve that same end while remaining blog standard?

An ordinary 208Y/120 volt three phase will achieve the same end of accommodating Japanese split phase appliances. However, that will not enable North American/Taiwanese, British/Irish/Hong Kong/Singapore, European/North African/South Korean, Australian/New Zealand/Chinese, and Indian/South African 220-240 volt appliances (if all of the latter are also rated for 60 Hz) to run at full power. Japan is the odd country out, both for single-phase and split-phase. If Japan had followed either North American or European/British/Australia standards for premises wiring voltage and frequency, then I wouldn't even have considered using the high-leg to neutral in this hypothetical realistic case.

 

[00crashtest]

Keep in mind you *technically* can't provide receptacles over 120 volts in a dewlling for an appliance that takes less than 1440 watts.

Thus is why I mentioned kitchen appliances. That is because the 200V ones in Japan, 240V ones in the British Isles, 220V ones in continental Europe, and 208/240V dual-rated commercial ones in North America all use well over 1440 VA, usually 2000 VA or above. In fact, the standard British and European water kettle is rated 3 kW. With the closed high-leg delta transformer, it will enable high-powered small kitchen appliances and portable space heaters from all over the world to be used on the sane premises supplied by the single service without any extra conversion steps. Of course, if one were to use a 240V British or 220V European appliance that consumed 100W or less like certain electronics equipment that are not intentionally designed for one to take with them unlike mobile phones and laptops, then the additional energy loss from using a tiny plug-in transformer that is only a mere 40% efficient would still be no larger than a rounding error relative to the load of the building's HVAC, even heat pump water heating, loads from commercial all-electric kitchens, and even LED common area lighting all combined. If one were to only accommodate for small loads from playback and recording equipment, then it would be better to just provide wall warts (but with mains voltage AC output instead of low-voltage DC) because the energy loss would be practically nothing.