480V Wye stepped down for residential 120/240V 1PH?

[jim dungar]

Scott-T connected transformers are not very common. They may be in a very small region, but I have never come across one in the past 50 years.

I would go with 208Y/120V as my primary 'low voltage'.

 

[MD Automation]

My 2 cents is to KISS this - meaning keep it simple and get yourself a 480Δ to 208Y/120 Step Down transformer.

If I had 140 amps of 208/120 single phase load, and had 3 phase 480 coming into the facility from the POCO, I would definitely get a 3 phase step down xfmr.

It's possibly the single most common transformer you will run across. So that's means relatively inexpensive and easy to find.

Loads are going to inevitably "creep up" in the future as new equipment wanders in. It will be nice to have a transformer already in place to handle them.

 

[norcal]

For us, EU, we use residential. It is just simpler - all 230V

In Germany they use 400V 3Ø for domestic ranges.

 

[Jpflex]

We've been in the middle of a big 3PH upgrade at a facility and am complete with Phase I. We are up and running with a 480V Wye configuration (400A) into our main building and panel.

Now we need to step it down so we can ultimately turn on the lights and power single phase 120/240V equipment.

I'm not a 3PH commercial electrician so hoping for some help here. Always been on the residential side.

What is the proper way to do this? I keep getting totally different answers from "experts" including transformer suppliers.

Some suggested going with a 480V to 208V step down and then pulling a leg off the 208V for 120V secondary.
Some suggesting a series of transformers to balance the loads correctly (making our utility company happy).

Very much appreciate you former experience and how you would meet these electrical needs. We want to install a 200A residential panel for these purposes.

Thanks.

Although you’ll get a usable 120 volt secondary, I would not go with a 208Y /120 volt transformer because the 208 volt option has limited usage for equipment unless you have equipment calling for this. In a 208Y/120 transformer you connect to any two legs of y secondary to feed a single phase panel A and B. However 1 phase could be left off (balance issue possibility). Or use all three phases of Y secondary on three phase panel while using each phase to neutral for 120 volt loads

Rather go 120/240 standard transformer

 

[Besoeker3]

I am well aware, having occasionally visited our daughter, her husband the Geordie, and their two daughters over the past 15 years or so. It never occurred to me to ask, is there a 3-phase system in the UK?

Hi Charlie B. UK residential systems are (almost) single phase 230Vac. Industrial systems are 400V/11kV/132kV/400kV.

In Germany they use 400V 3Ø for domestic ranges.

"Homes in Europe and the UK have standardized on a nominal 230 V between any phase and ground.Homes in Europe and the UK have standardized on a nominal 230 V between any phase and ground."

That includes Germany.

 

[jim dungar]

Although you’ll get a usable 120 volt secondary, I would not go with a 208Y /120 volt transformer because the 208 volt option has limited usage for equipment unless you have equipment calling for this. In a 208Y/120 transformer you connect to any two legs of y secondary to feed a single phase panel A and B. However 1 phase could be left off (balance issue possibility). Or use all three phases of Y secondary on three phase panel while using each phase to neutral for 120 volt loads

Rather go 120/240 standard transformer

The first thing to do is find out how distributed the Low Voltage loads are. If they are all in a single building and 220kVA my recommendation will be different than if they are in 10 locations of 22kVA each.

A 208Y/120V 3 phase 4 wire transformer is probably the most common 120V to ground system in the US, for non-residential installations. It is also likely the most common for multifamily residential where the service is 1200A or larger. It is even being found in some mega-mansions. Balancing loads across multiple 120/208V 3w panels is hardly ever an actual problem except when the L-L loads are large motors and fed from only 2 panels.

 

[tortuga]

I would go with 208Y/120V as my primary 'low voltage'.

Sure if the job specifications allow 120/208, but if the bid specifications were supply120/240 I'd submit and RFI before just installing a voltage the customer did not specify.

 

[ruxton.stanislaw]

"Homes in Europe and the UK have standardized on a nominal 230 V between any phase and ground.Homes in Europe and the UK have standardized on a nominal 230 V between any phase and ground."

A lot of smaller homes and apartments indeed have single phase service from a three phase network, however, three phase is extremely common in Germany, as well as other countries in Europe and South America. My kitchen appliances have a 400Y/230 V "MWBC" for example. If something ever mishappens with that neutral wire, it will be an expensive month... The most common 380 - 415 V rated appliances that I see are VFD air conditioners, electric stove tops (sometimes smaller models using two phases and a neutral, interestingly), larger hot water tanks and UPSs.

 

[ruxton.stanislaw]

As Phase II of the project (2025), we will be erecting a 10,000 SF building. Most my 1PH needs remains associated more with residential type loads. Power tools, lights, etc. All our high load stuff is 3PH 240V and 3PH 480V. This building is for a millwork, woodworking shop. But I can address these power needs at a different time, if needed. Just an input to consideration in terms of looking across all our power needs.

Option 1 is likely more cost effective at that capacity (~50 KVA or more) and also allows you to tap near 220 V nominal whilst staying within specification for 120 V appliances. Anecdotal knowledge, but the voltage in China where they manufacture and test these things is usually around 220 V, albeit 50 Hz.

Tortuga is very knowledgeable. Scott-T is going to be the ultimate way of balancing a three phase system with single phase loads when converting voltage, but it is more rare of a transformer, so difficult to source and probably more expensive. It also won't support your three phase motor loads.

Like the other posters mentioned, using 277 V lighting or for other appliances where possible is the way to go. You can also use small buck boost transformers to get 240 V where needed, if you find any situations where that makes more sense to do.

As for Phase II, my recommendation would be to obtain a large 250Y/144 V or 240Y/139V transformer for those motors if they are rated 240 V three phase. That way, you do not need to worry about delta grounding issues. Use the X0 neutral of that transformer system exclusively for grounding purposes (no 120 V circuits).

You may also be able to wire the motors with a lower tapped 480Y/277 V transformer (e.g. 440Y/254 V) if the motors are dual rated. In fact, if the utility can provide 440Y/254 V or thereabouts (the less, the better in this case), it can help with a lot of your project and not having to buy as many transformers.

 

[Besoeker3]

A lot of smaller homes and apartments indeed have single phase service from a three phase network, however, three phase is extremely common in Germany, as well as other countries in Europe and South America. My kitchen appliances have a 400Y/230 V "MWBC" for example. If something ever mishappens with that neutral wire, it will be an expensive month... The most common 380 - 415 V rated appliances that I see are VFD air conditioners, electric stove tops (sometimes smaller models using two phases and a neutral, interestingly), larger hot water tanks and UPSs.

As far as I am aware most of the residences in the EU are 230V. These include the ones I have visited like France, Belgium, Germany, Netherlands,, Sweden, Spain etc.

 

[ruxton.stanislaw]

As far as I am aware most of the residences in the EU are 230V. These include the ones I have visited like France, Belgium, Germany, Netherlands,, Sweden, Spain etc.

This will definitely be a YMMV experience. I have less experience in Europe, other than Germany. I usually pay attention to the meters/overhead lines when I go on walks in Paraguay, Uruguay and Argentina. In Argentina, single phase service is more common especially to homes or businesses with gas appliances. Most small homes and apartments that I noticed have a single phase 25 A service, with the exception of one home I was staying in. However, EVERYTHING in Paraguay that I have seen, with the exception of shacks in underdeveloped regions, is three phase. They like to run small wires in the service entrances, from what I can tell usually a set of four 10 AWG or ~ 4mm^2 conductors , no heavy pulling.

 

[jim dungar]

Sure if the job specifications allow 120/208, but if the bid specifications were supply120/240 I'd submit and RFI before just installing a voltage the customer did not specify.

I understood the OP as being about the design decision for the specifications not value engineering after the fact.

 

[Besoeker3]

This will definitely be a YMMV experience. I have less experience in Europe, other than Germany. I usually pay attention to the meters/overhead lines when I go on walks in Paraguay, Uruguay and Argentina. In Argentina, single phase service is more common especially to homes or businesses with gas appliances. Most small homes and apartments that I noticed have a single phase 25 A service, with the exception of one home I was staying in. However, EVERYTHING in Paraguay that I have seen, with the exception of shacks in underdeveloped regions, is three phase. They like to run small wires in the service entrances, from what I can tell usually a set of four 10 AWG or ~ 4mm^2 conductors , no heavy pulling.

Yes, but my point was specifically European residential.

 

[tom baker]

Just to give you a few items to consider...
You might look at supplying your warehouse lighting load (40a) at 277 rather than 120 (Some newer lights will operated on either)
The 208Y/120- is still best for balancing so if you have limited equipment that requires 240 you could look at the possibility of a small buck-n-boost transformer (or a small 240/120 transformer) just for that equipment

Agree with 120/208 panel. Considering labor there is a small cost to go from 120/240 to 120/208, but the latter gives more 120 ckts and a lower voltage 3 phase.

 

[gene6]

When I was stationed in Germany all the houses were 63A 400Y230 or 400V L-L 230V L-N 50HZ and the Neutral was not bonded to the Equipment ground at the house. There was always a measurable voltage between neutral and Equipment ground, I remember finding that very odd. Almost nothing used the 400V other than large ranges but 400V was present in every home, however when metered it sometimes reads ~390.

 

[tortuga]

As Phase II of the project (2025), we will be erecting a 10,000 SF building. Most my 1PH needs remains associated more with residential type loads. Power tools, lights, etc. All our high load stuff is 3PH 240V and 3PH 480V. This building is for a millwork, woodworking shop.

For a wood working shop with 3 Phase 240V loads I suggest a 240/120 Hi-leg delta bank sized for phase I and II.
Especially if your LED lighting load can be served from the 277V side.

 

[ruxton.stanislaw]

Yes, but my point was specifically European residential.

When I was stationed in Germany all the houses were 63A 400Y230 or 400V L-L 230V L-N 50HZ and the Neutral was not bonded to the Equipment ground at the house. There was always a measurable voltage between neutral and Equipment ground, I remember finding that very odd. Almost nothing used the 400V other than large ranges but 400V was present in every home, however when metered it sometimes reads ~390.

The latter is my experience with Germany and Liechtenstein as well, though these are limited experiences. I am sure you will see a lot of single phase services based on the required capacity of the service, neighbourhood, local ordinances, alternative fuel sources available to the building etc.

Based on anecdotal experience, I know that UK residential is normally always single phase 230 V to neutral (historically 240 V). Something of interest that I recall is that some higher voltages, like 250 V nominal and as much as 270 V in extreme cases (BigCliveDotCom YouTube reference), are observed on some of the islands.

 

[winnie]

I would advise against any uncommon transformer setups for getting 120/240 volt single phase in a balanced fashion from a 3 phase service.

This includes 'scott t' (which creates 2 phase from 3 phase, and then lets you make 2 separate 120/240V systems), my personal favorite 'hexaphase' (essentially 3 single phase transformers on one frame) or 'leyton' connection (which IMHO doesn't work.

First figure out how much true 240V you need, it sounds like most of your loads would be happy with 208 or 240V. In which case the 208/120 wye system is the way to go.

If you truly have lots of 240V loads, for example a residential appliance testing facility, then go with 3x single phase transformers.

Jon

 

[Besoeker3]

The latter is my experience with Germany and Liechtenstein as well, though these are limited experiences. I am sure you will see a lot of single phase services based on the required capacity of the service, neighbourhood, local ordinances, alternative fuel sources available to the building etc.

Based on anecdotal experience, I know that UK residential is normally always single phase 230 V to neutral (historically 240 V). Something of interest that I recall is that some higher voltages, like 250 V nominal and as much as 270 V in extreme cases (BigCliveDotCom YouTube reference), are observed on some of the islands.

UK was 240V since I was born. More recently it was 230V but a fix for the EU -it remained 240V but the tolerances were adjusted. 270V ? Never heard of it - but what do I know. I'm just an old phart...............