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

[kwired]

Something else not mentioned - is this replacing something of similar electrical load ? If not can your service handle the additional load?

That unit may need 30 amp circuit @ 480 volts, but should need about 70 amp circuit if same capacity @ 208 volts. The feed to the transformer still draws that same amount from the 208 input.

If service needs upsized you are spending some $$ anyway.

 

[oldsparky52]

Something else not mentioned - is this replacing something of similar electrical load ? If not can your service handle the additional load?

That unit may need 30 amp circuit @ 480 volts, but should need about 70 amp circuit if same capacity @ 208 volts. The feed to the transformer still draws that same amount from the 208 input.

If service needs upsized you are spending some $$ anyway.

You read my mind.

 

[winnie]

Something else not mentioned - is this replacing something of similar electrical load ? If not can your service handle the additional load?

That unit may need 30 amp circuit @ 480 volts, but should need about 70 amp circuit if same capacity @ 208 volts. The feed to the transformer still draws that same amount from the 208 input.

If service needs upsized you are spending some $$ anyway.

Questions like this are the reason that we don't permit DIY answers on this forum. We never know what the poster doesn't even know to ask. I was comfortable with (and I presume the mods permitted) this thread because there are professional electricians involved doing the actual installation.

-Jon

 

[mrmike99]

So, the only savings is in needing thinner wires and smaller conduit and lower amp breakers? And on a short single run, its not all that much. But, isn't there is also less energy loss from resistance? And, it takes a bigger increase in current to get a higher power output than increasing the voltage. Doesn't 480v give you more than twice the power of 208v with the same current? And if no savings, why don't so many businesses, warehouses, industrial places use just the 208 electricity and units instead of 480 most use especially with 277 lighting? It seems to me they use it especially for machines because they can get more power more efficiently. I would think they save significantly in the long run on lighting too, but that is probably all changing with LED lighting. And it looks like they often go the other direction- adding step down transformers to 208v for the smaller 120/240 circuits. However, you know more about this than me and I am the first to admit there is a lot to keep learning and understanding.

 

[mrmike99]

Questions like this are the reason that we don't permit DIY answers on this forum. We never know what the poster doesn't even know to ask. I was comfortable with (and I presume the mods permitted) this thread because there are professional electricians involved doing the actual installation.

-Jon

I am a general contractor, but the owner had 2 of his own electricians who I both don't think are experienced and qualified. I am trying to confirm what I initially thought of going Delta to Wye and to understand more of the situation BEFORE bringing in and making sure the new electrician understands and knows what they are doing. One thing I know for sure, 480v 3 phase with a transformer is not something to play around with as a DIYer or even an inexperienced "professional" electrician.

 

[mrmike99]

Something else not mentioned - is this replacing something of similar electrical load ? If not can your service handle the additional load?

That unit may need 30 amp circuit @ 480 volts, but should need about 70 amp circuit if same capacity @ 208 volts. The feed to the transformer still draws that same amount from the 208 input.

If service needs upsized you are spending some $$ anyway.

Please re read my post. There is no 208v feed. There are two 3 phase 240v high leg Delta feeds and another single phase 120/240v feed left from a former laundromat. Its now just a 3,000 sq foot retail store, so we can use one of the Delta feeds solely for the hvac unit with the transformer. Plenty of electricity, but we need the right electricity to the unit.

 

[LarryFine]

Please re read my post. There is no 208v feed. There are two 3 phase 240v high leg Delta feeds and another single phase 120/240v feed left from a former laundromat. Its now just a 3,000 sq foot retail store, so we can use one of the Delta feeds solely for the hvac unit with the transformer. Plenty of electricity, but we need the right electricity to the unit.

Thus, you need a 240 delta to 480 wye transformer.

 

[winnie]

So, the only savings is in needing thinner wires and smaller conduit and lower amp breakers? And on a short single run, its not all that much. But, isn't there is also less energy loss from resistance? And, it takes a bigger increase in current to get a higher power output than increasing the voltage. Doesn't 480v give you more than twice the power of 208v with the same current?

480V delivers power more efficiently than lower voltages, but in the end 'watts is watts'.

Imagine a motor that is consuming 10kW of electricity. If designed for 240V, it will consume 10kW at 240V. If designed for 480V, it will consume 10kW at 480V, half the current and twice the voltage for the same power.

As you note the savings is is smaller wire for the same power delivered, or smaller losses for the same wire used. Especially in large facilities the losses in the wire can add up.

-Jon

 

[winnie]

I am a general contractor, but the owner had 2 of his own electricians who I both don't think are experienced and qualified. I am trying to confirm what I initially thought of going Delta to Wye and to understand more of the situation BEFORE bringing in and making sure the new electrician understands and knows what they are doing. One thing I know for sure, 480v 3 phase with a transformer is not something to play around with as a DIYer or even an inexperienced "professional" electrician.

IMHO doing your due diligence so that you know you have an electrician qualified to do the work is a great approach.

-Jon

 

[kwired]

Please re read my post. There is no 208v feed. There are two 3 phase 240v high leg Delta feeds and another single phase 120/240v feed left from a former laundromat. Its now just a 3,000 sq foot retail store, so we can use one of the Delta feeds solely for the hvac unit with the transformer. Plenty of electricity, but we need the right electricity to the unit.

Everything I said is still applicable, change the 70 amp @ 208 to 60 amp @ 240. Bottom line is VA is still the same. You get billed for watt hours not amps.

Why not 208 or 240? A lot of places do have that for service voltage if VA capacity is lower. Medium capacity kind of can go either way.

Yes you get twice the VA out of same size conductors if you go with 480 instead of 240.

Where it starts to save to go with the highe voltage is over about 80-100 KVA, unless the bulk of the load is 120 and/or 240 volt loads that are not commonly available in 277 or 480 volt versions.

Over 25 to 50 HP motors require lesser expensive motor controllers, fuses, breakers, disconnects, conductors simply because all those items are ~ half amps capacity @ 240 volts then it is @ 480. But sometimes 600 volt gear is a little pricier than 240 volt gear, but over about 50 HP still usually going to be less cost for 600 volt gear.

Resistance of conductor can add to operating losses, but increasing conductor size compensates but at same time adds to initial installation cost.

 

[mrmike99]

I have an electrician questioning why we want a Delta-WYE 240 to 480 transformer which is more expensive. He says that the Delta-Delta is just as balanced as a Delta-Wye as long as the Neutral on the Delta is not used which he says makes it a 'high leg" delta. He also says that the Delta is more stable vs the Wye- something about the primary and secondary windings in the transformer . Everyone here says to use the Delta-Wye and no one said the Delta-Delta. So, I ask, can we go with the Delta-Delta without issues? What really is the advantage with the Delta-Wye, if any, in this particular setup? I argued that I thought it would be better for the blower and inverter (VFD) and more balanced and stable. Then he said that he was able to get a Lennox Tech on the phone when I have been trying for weeks with no luck. He explained the set up to the Lennox tech with the potential Delta- Delta transformer to get the 460v, and the tech said it was fine to do that.

 

[oldsparky52]

I have an electrician questioning why we want a Delta-WYE 240 to 480 transformer which is more expensive. He says that the Delta-Delta is just as balanced as a Delta-Wye as long as the Neutral on the Delta is not used which he says makes it a 'high leg" delta. He also says that the Delta is more stable vs the Wye- something about the primary and secondary windings in the transformer . Everyone here says to use the Delta-Wye and no one said the Delta-Delta. So, I ask, can we go with the Delta-Delta without issues? What really is the advantage with the Delta-Wye, if any, in this particular setup? I argued that I thought it would be better for the blower and inverter (VFD) and more balanced and stable. Then he said that he was able to get a Lennox Tech on the phone when I have been trying for weeks with no luck. He explained the set up to the Lennox tech with the potential Delta- Delta transformer to get the 460v, and the tech said it was fine to do that.

Re read post #13. Winnie knows what he is talking about. Yes, the Lennox tech said it was fine to use Delta-Delta, but I have come across techs that have given out wrong answers. I would trust the guys on this site before a tech even if they work for the manufacturer. Ask that Lennox tech if he will send you an email saying that feeding his unit with a Delta-Delta transformer is okay.

Then, are you going to corner ground the secondary Delta? Are you going to install a phase monitor? Are you going to mid ground one of the secondary windings (I've never heard of this being done on a 480V secondary, but it doesn't mean it's not possible)?

You are very fortunate that the monitors have let you continue since you are not the electrician. The members in the know have given you very good advice. I do not have the experience with VFDs to comment on whether the voltage to ground should be the same, but if the guys on this forum say that typically a VFD does not like the different voltages to ground and the tech says no problem, ... I think I'm going with what the guys on this forum are saying.

It is great that you were not shut down on your questions, I'm learning more and I am sure others are too. Good luck getting this resolved, I hope you will be kind enough to let us know the final resolution.

 

[oldsparky52]

He explained the set up to the Lennox tech with the potential Delta- Delta transformer to get the 460v, and the tech said it was fine to do that.

Did the tech understand that the voltages to ground might not be stable nor the same?

 

[hillbilly1]

Millions of RTU’s are running on the delt-wye configuration, if you go delta-delta, you WILL have to do one of two things for a proper installation, ground one phase to make it a corner grounded system or a fault detector. Corner grounding leaves the other two phases 480 volts to ground, which can be dangerous to unqualified electricians.

 

[kwired]

Re read post #13. Winnie knows what he is talking about. Yes, the Lennox tech said it was fine to use Delta-Delta, but I have come across techs that have given out wrong answers. I would trust the guys on this site before a tech even if they work for the manufacturer. Ask that Lennox tech if he will send you an email saying that feeding his unit with a Delta-Delta transformer is okay.

Then, are you going to corner ground the secondary Delta? Are you going to install a phase monitor? Are you going to mid ground one of the secondary windings (I've never heard of this being done on a 480V secondary, but it doesn't mean it's not possible)?

You are very fortunate that the monitors have let you continue since you are not the electrician. The members in the know have given you very good advice. I do not have the experience with VFDs to comment on whether the voltage to ground should be the same, but if the guys on this forum say that typically a VFD does not like the different voltages to ground and the tech says no problem, ... I think I'm going with what the guys on this forum are saying.

It is great that you were not shut down on your questions, I'm learning more and I am sure others are too. Good luck getting this resolved, I hope you will be kind enough to let us know the final resolution.

Not likely found in a single core unit. Can do so with multiple single phase units that are made into a three phase bank.

POCO's around here do this often with small limited load services and in open delta configuration with only two transformers. High leg is 416 volts.

Main problem with VFD's is surge protection built into them is designed for 277 volts to ground. With corner ground system and 480 volts to ground you will be clamping overvoltage continuously until the surge protection fails on two of the input lines. With a high leg system you clamping overvoltage on high leg continuously. On ungrounded system there is no ground reference and capacitive effects can result in a wide range of voltage to ground, plus when there is a ground fault on one line it essentially becomes the same thing as a corner ground system at that point.

 

[winnie]

A delta secondary will be as balanced as a wye secondary line to line. Possibly more so.

A delta secondary cannot be grounded in a balanced fashion. It must either be corner grounded, center tap (high leg) grounded, or left ungrounded.

The issue that inverters might have with any of the delta setups is that the unbalanced line to ground voltage can trip/damage surge suppression elements on their input. These surge suppression elements are ground referenced. Not all inverters have them, and inverters can be designed to operate with unbalanced line to ground voltages.

Bottom line: if Lennox has in writing that a delta supply with specified grounding is acceptable, then you could go delta:delta without issues. But if they don't provide that assurance, I would go with delta:wye.

-Jon

 

[kwired]

I have an electrician questioning why we want a Delta-WYE 240 to 480 transformer which is more expensive. He says that the Delta-Delta is just as balanced as a Delta-Wye as long as the Neutral on the Delta is not used which he says makes it a 'high leg" delta. He also says that the Delta is more stable vs the Wye- something about the primary and secondary windings in the transformer . Everyone here says to use the Delta-Wye and no one said the Delta-Delta. So, I ask, can we go with the Delta-Delta without issues? What really is the advantage with the Delta-Wye, if any, in this particular setup? I argued that I thought it would be better for the blower and inverter (VFD) and more balanced and stable. Then he said that he was able to get a Lennox Tech on the phone when I have been trying for weeks with no luck. He explained the set up to the Lennox tech with the potential Delta- Delta transformer to get the 460v, and the tech said it was fine to do that.

Voltages to ground reference is about the only thing that is not balanced in a delta. Wye has a true neutral point that is same voltage to all other lines and the neutral is typically what gets grounded.

Outside of that as long as it is a full delta and not an open delta, current/power gets balanced equally if your load is divided equally. A true three phase load will be divided equally. Any single phase aux loads (like a condenser fan) will throw some imbalance to the load on both delta and wye sources.

 

[winnie]

Oh, the electrician you are working with is more than welcome here; always happy to learn from different perspectives!

-Jon

 

[electrofelon]

The transformer in post #14 might be an auto transformer - it is not clear to me if it is or not. I know Hammond makes a line of autos that do all the common voltages. OP does not want an auto.