480v 3 phase from two panels with 240v High Leg Delta 3 Phase

[mrmike99]

Hello, we have a property that one had a laundromat. I am not a electrical expert but have basic understanding. They had three 240v panels. Two of the service panels are set up with 3 hots and a neutral and I believe are 240v high leg 3ph Delta panels. There are 3 phase breakers on the A-B-C slots, 240 on A-C slots, and single 120's but not on the B slots. A third panel has 2 hots and 1 neutral and it looks like it is setup for single phase 120 and 240 breakers. We have a new 460v Lennox HVAC unit on the roof and we need heat now in Chicago. Other than 1) new expensive 480 service just for the HVAC and 2) a 240v to 480v step up transformer, is there any way to get 480v 3ph power? I doubt it, but some people involved insist that you can so I am asking.Two electricians said no but they are not the brightest stars. And if a transformer is the only way, which of the following is best for a HVAC unit with a sophisticated control board:

1) 240v Delta to 480v Delta with isolation
2) a multi tap using 240v to 480v no isolation But we like for future proofing and having options
3) 240v Delta to a 480v Wye

The unit draws little less than 30 amps - 26A with 24v transformer step down circuits. It does not specifically mention any type of 480v 3 ph like120v or 240v legs or 277v. However the blower motor has an inverter as I understand it and the more balanced load the better. Yes, I have been calling
Lennox technical for weeks but because of Covid and very limited staff, no one answers the phone! Any help ASAP is greatly appreciated, thanks in advance. I tried to attach a photo of the HVAC name plate but it will not load.

 

[mrmike99]

Photo tried again as a pdf

 

[winnie]

Your electricians are correct, you can't get 480V from your 240V panels.

Have your electrician install a 240V delta to 480/277 wye step up transformer.

Note: someone might suggest installing a 480V to 240V step down transformer 'in reverse'. Do not do this.

Jon

 

[hillbilly1]

Your electricians are correct, you can't get 480V from your 240V panels.

Have your electrician install a 240V delta to 480/277 wye step up transformer.

Note: someone might suggest installing a 480V to 240V step down transformer 'in reverse'. Do not do this.

Jon

Buying the wye secondary transformer would be the correct way to do it, using a 480 to 120/208 volt transformer on a 240 volt delta service would produce close to 575 volts, and unless your in Canada, not a good choice! LOL!

 

[mrmike99]

Thanks for the replies. Is there an advantage or is it more stable/balanced to go Delta to Wye vs Delta to Delta? That was my first choice and thinking and Wye also seems to be more modern and widely used.

One transformer rep tells me since it is 4 wires and not a large motor, we would be fine with a multi-tap transformer, but we must go Delta to Delta on it.

Funny, Lennox offers this model in 208/230v, 460v, AND 575v!

Maybe I am missing something, but why would we go down to 120/208? And we don't have the 480 - that's what we are trying to get. Not sure how you would get 575v from that.

 

[LarryFine]

Funny, Lennox offers this model in 208/230v, 460v, AND 575v!

Maybe I am missing something, but why would we go down to 120/208? And we don't have the 480 - that's what we are trying to get.

You just answered your own question. You should get the 208/230v model because it matches your available power.

 

[winnie]

A wye secondary is preferred for any inverter driven load. The neutral point of the wye gets grounded, and this gives balanced voltage relative to ground.

All transformers have multiple taps on their primary to adjust to small variations on the input voltage.

When you say 'multi-tap' transformer, what are you describing, and what does it give you that you _might_ want? Which other voltages?

Motors are internally transformers, so it is trivial for Lennox to sell different models of the same unit to work at different voltages. You probably should have purchased the 208/230V unit, which would _probably_ work with your existing service directly. (I say probably because the delta grounding might have caused issues.)

-Jon

 

[texie]

My first question would be why someone would install a 480 volt unit when the correct unit for 208/230 is available. That said, if you really want to do this and as others have said, use a 240 delta primary X 480Y secondary transformer. Without going into a lot of technical details as to why, it will prevent a whole host of other issues by doing so. Keep in mind it will need proper OCP and a GES. The whole idea of boosting the voltage to correct someone's mistake is a waste of money now and in future operating cost.

 

[Jraef]

Assuming you have a 480V unit already (because you got it cheap?) and have to adapt what you have, get a transformer with a 480Y277V output, at least 25kVA, larger if you want future capacity capabilities. You want the wye secondary because even if your equipment does not have VFDs on it now, it might some day. The primary side is irrelevant as to delta or wye, but because you want 240V, it will most likely be delta.

Don't let the transformer salesmen talk you out of the wye on the 480V side, they just care about moving iron and copper that is sitting in inventory. Most of them have designs available for a 480V wye output, they just don't likely have them already made. There are companies, like MGM Transformer, that specialize in getting you the transformer you want with low lead times.

 

[hillbilly1]

Thanks for the replies. Is there an advantage or is it more stable/balanced to go Delta to Wye vs Delta to Delta? That was my first choice and thinking and Wye also seems to be more modern and widely used.

One transformer rep tells me since it is 4 wires and not a large motor, we would be fine with a multi-tap transformer, but we must go Delta to Delta on it.

Funny, Lennox offers this model in 208/230v, 460v, AND 575v!

Maybe I am missing something, but why would we go down to 120/208? And we don't have the 480 - that's what we are trying to get. Not sure how you would get 575v from that.

Not going down, but going up by feeding it backwards. 480 to 120/208 wye is an extremely common transformer unlike a 480 to 240 delta. Using that transformer (480 to 120/208) on a delta system (240 volt) will produce 575 volts, I know of one I installed about 26 years ago for a sheet metal duct manufacture, which is still in use today. The machinery was from Canada, and 575 volt three phase. Georgia Power gave an outrageous estimate to supply the plant with 575 volts, I think it was something like $60,000+ for a 200 amp service. Don’t blame them though, because the revenue would have never paid off.

 

[mrmike99]

You just answered your own question. You should get the 208/230v model because it matches your available power.

Ok, you are saying the 208/230 model could run on 240V high leg Delta? The main reason we the 480V unit was bought was because it was $7,000 cheaper! And the owner's electrician said he could get the 480v up to the roof but he was wrong. I told the owner even with the transformer, he is still about $5,000 ahead. I can get the transformer for $1500 + wires, shut off , and fused sub panel protection. The 480v is also more efficient with higher voltage and lower amps.

 

[LarryFine]

Ok, you are saying the 208/230 model could run on 240V high leg Delta?

Absolutely, as long as it's not expecting a neutral with equal voltage to all phases.

The 480v is also more efficient with higher voltage and lower amps.

Only on the 480v portion of your circuit. You want minimum primary circuit length and maximum secondary circuit length.

You also need to consider losses, wasted energy, heat, etc., due to idling current/magnetizing energy, inefficiency, etc.

 

[winnie]

Ok, you are saying the 208/230 model could run on 240V high leg Delta? The main reason we the 480V unit was bought was because it was $7,000 cheaper!

Very likely. The only potential gotya is that some inverter drives are not happy with uneven phase to ground voltages. This would be something to check with Lennox prior to purchase. But no longer relevant for you.

Jon

 

[mrmike99]

Thanks for everyone's input. I was just trying to have others confirm with what I initially thought and that was to go with the Delta to Wye transformer. As I said above, this unit was $7,000 less expensive. The multi tap unit was this one from American Rotary here:

Three Phase Transformer Archives - American Rotary

UL and CUL Listed 60 Hz Multiple knockouts for easy installation Dimensions are listed in (L x W x H) Note: Transformer inventory levels can change quickly, for live inventory please call us! 888-743-6832. It is recommended to size a transformer 20% larger per motor starting loads. We carry...

www.americanrotary.com

3 Phase Multi Tap (600, 480, 400, 240, 208) Auto Transformer Delta - Delta or Wye - Wye 60hz - American Rotary

www.americanrotary.com

The multi tap option was attractive only for the future for any possible changes and having options. For example, if they update the electricity with 208 3 phase down the road and were replacing the vac unit but hell, who knows what the scenario 20 years down the road will be, so it's not that important right now.

Their rep now concurs with the delta to wye setup you all suggest. And that unit is about $1000+ more so why wouldn't he? But, I can get one for $1500 from another source. I calculate that we need a 30kva unit.

As Winnie pointed out, we really want balanced voltage relative to ground and using the 240 or 480v Delta would be very questionable vs the 480 wye.

BTW, it does have a variable frequency drive and thus my desire to get the most balance voltage relative to ground to the unit. It would really suck to buy a Delta to Delta transformer and have issue because of this when we could just spend a little more and have the Delta to Wye transformer to solve the potential added problem.

 

[mrmike99]

Just found this from Lennox literature on the unit:

VIII-Belt Drive Supply Air Inverter
NOTE - Units equipped a Variable Frequency Drive (VFD) are designed to operate on balanced, three-phase power. Operating units on unbalanced three-phase power will re duce the reliability of all electrical components in the unit. Unbalanced power is a result of the power delivery system supplied by the local utility company. Factory-installed in verters are sized to drive blower motors with an equivalent current rating using balanced three-phase power. If unbal anced three-phase power is supplied; the installer must re place the existing factory-installed inverter with an inverter that has a higher current rating to allow for the imbalance. Refer to the installation instructions for additional informa tion and available replacements.

 

[winnie]

So you would be stuck with a transformer in any case. The 460V unit is thus the correct choice

 

[winnie]

Check out Fargo transformers. They make drive isolation transformers with wye output and multiple voltage input voltages. So you would be future proof if your supply changed to 208V wye

 

[hillbilly1]

Changing to 208 from 240 can be more difficult than you imagine. One of our salesmen sold a conversion job on an old wine and liquor store. Lots of 240 volt only compressors and RTU’s. Ended up with quite a few buck/boost transformers. Didn’t make no money on that one.

 

[mrmike99]

Check out Fargo transformers. They make drive isolation transformers with wye output and multiple voltage input voltages. So you would be future proof if your supply changed to 208V wye

Thanks, I also just came across Maddox Transformers who seem to be very reasonably priced considering American Rotary wants about $2650 for a 30 kva and Acme was about $3100 and a seller who used one for less than 30 hours on a specific project would sell it to me for around $1500-1600- it pays to shop around:

3-Phase 240V Delta - 480 Y 277 (Step Up Transformer)

This transformer is designed to convert 3-phase 240v to 3-phase 480 Y 277 to run equipment such as panels, motors, CNC machines, welders, conveyor systems, pumps, printing equipment, fabrication tools, and other business machines. Primary Voltage: 240 Delta Secondary Voltage: 480 Y 277 (Step Up...

store.maddoxtransformer.com

 

[Jraef]

...The 480v is also more efficient with higher voltage and lower amps.

No, that is not true. You do not pay for amps, you pay for watts. Higher voltage, lower amps, but the watts stay the same, plus not you have introduced losses in the transformer which are also watts, so in actuality exactly the OPPOSITE is true.