Grounding secondary of a 30KVA single phase transformer 480 to 208

[kwired]

I don't see a 120/208v Secondary as an option.

Am I missing it somewhere?

JAP>

because it is physically impossible with a single phase transformer. You could have one with 240 end to end and a 208 tap, but the other end to that tap is only 32 volts. All they need to do is get right turns ratio and they can build about any primary to secondary voltages imaginable and physically possible - 120/208 is only physically possible with three phase wye system or electronically derived system like an inverter.

208 winding is not common stock item much of the time. May be catalog number for some of them, some may be common enough they may be in manufacturer's stock but still are not high volume like a similar kVA unit with 120/240 winding would typically be.

 

[jap]

Your best guess?

Just doing a Google search for a 22 KW 1ph 208V cooking appliance I ran across this unit.

Commercial Convection Ovens

Shop: <a href="/14185/conveyor-ovens-and-impinger-ovens.html" target="_blank">conveyor ovens</a> | <a href="/43745/bakery-deck-ovens.html" target="_blank">bakery deck ovens</a> | <a href="/14625/combination-ovens.html" target="_blank">combination ove

www.webstaurantstore.com

https://cdnimg.webstaurantstore.com/documents/specsheets/markv-200_specsheet.pdf

Unit shall be electrically heated with three tubular heaters.

Each heating element Individually fused? Both ungrounded phases of each element fused?

$22,086.00..... I think I would contact the manufacturer before I grounded one leg of the transformer.

Who bought the transformer? Who in the end will be responsible for wiring the transformer and connecting it to the appliance?

I don't think the piece of equipment cares where it gets its single phase 208 volts from, or , whether that voltage comes from a line to line or line to grounded line source.

The fused protection for the elements should still operate on overcurrent seeing as how the secondary current will rise with the primary current.

The grounding of the transformer is a separate issue.

it's required, and, creates a return path for a fault path.

without the grounded line you loose that.

At least that's the way I see it.

JAP>

 

[jap]

because it is physically impossible with a single phase transformer. You could have one with 240 end to end and a 208 tap, but the other end to that tap is only 32 volts. All they need to do is get right turns ratio and they can build about any primary to secondary voltages imaginable and physically possible - 120/208 is only physically possible with three phase wye system or electronically derived system like an inverter.

208 winding is not common stock item much of the time. May be catalog number for some of them, some may be common enough they may be in manufacturer's stock but still are not high volume like a similar kVA unit with 120/240 winding would typically be.

Exactly.

Sometimes best to pose as a question to bring out the best answer.

JAP>

 

[kwired]

I don't think the piece of equipment cares where it gets its single phase 208 volts from, or , whether that voltage comes from a line to line or line to grounded line source.

The fused protection for the elements should still operate on overcurrent seeing as how the secondary current will rise with the primary current.

The grounding of the transformer is a separate issue.

it's required, and, creates a return path for a fault path.

without the grounded line you loose that.

At least that's the way I see it.

JAP>


Correct. You also need separate grounded and equipment grounding conductors beyond the system bonding point, which is likely going to be within the transformer housing on this one. So even if a fuse would happen to blow within appliance in the grounded conductor it isn't really that dangerous of an issue to the user, might be more risk to someone troubleshooting problems that don't understand what they have to work with.

 

[jap]

Agreed.

That's why on this particular transformer, one of the legs should be grounded and 3 wires brought to the equipment, not just 2.


JAP>

 

[LarryFine]

I don't see a 120/208v Secondary as an option.

Am I missing it somewhere?

No, because it can't be done.

 

[LarryFine]

Agreed.

That's why on this particular transformer, one of the legs should be grounded and 3 wires brought to the equipment, not just 2.

I did not mean to suggest that a separate EGC is not necessary. As with a typical 120v circuit, there should be an EGC, too.

The main reason for grounding a conductor is so an EGC can function.

 

[jap]

I did not mean to suggest that a separate EGC is not necessary. As with a typical 120v circuit, there should be an EGC, too.

The main reason for grounding a conductor is so an EGC can function.

Exactly.

We're with you.

JAP>

 

[Jamesco]

120/208 is only physically possible with three phase wye system

Really?

I called TEMCo and left a message asking them for a price to build a 480V to 104/208V 30KVA single phase transformer. If they manufacture a 480V to 208V transformer what makes you think the company is unable to build a 480V to 104/208V single phase transformer. All they need to do is split the secondary winding and bring out a center tap lead. They don't have to split the winding for the center tap connection. Are you saying it can't be done?

Remember special order

Built to Order 14 to 21 days.

You got the money, they got the time.

 

[Jamesco]

We don't know what the KW rating of the cooking appliance is. Who in their right mind would have ordered a 480v to 208v 1ph transformer to fed the the cooking appliance to begin with? For a few more dollars he/she could have special ordered a 480 to 120/208V 1ph transformer and wired the secondary as a 120/208v grounded power system.

For a few more dollars he/she could have special ordered a 480 to 120/208V 1ph transformer and wired the secondary as a 120/208v grounded power system.

That should read 480V to 204/208V 1 phase transformer.

 

[jim dungar]

I called TEMCo and left a message asking them for a price to build a 480V to 104/208V 30KVA single phase transformer.

You changed the parameters of the discussion.

120/208V single phase input to single phase output are not possible.

Yes, every manufacturer should be able to build a 104/208V center tapped output.

 

[LarryFine]

I called TEMCo and left a message asking them for a price to build a 480V to 120/208V 30KVA single phase transformer.

You can not obtain 120v L-N and 208v L-L from a single transformer core. 208v with a CT, yes.

 

[winnie]

I called TEMCo and left a message asking them for a price to build a 480V to 104/208V 30KVA single phase transformer. If they manufacture a 480V to 208V transformer what makes you think the company is unable to build a 480V to 104/208V

A 480V to 104/208V single phase transformer is certainly possible, simply requiring a center tap.

A symmetric 480V to 120/208V single phase transformer is not possible without some sort of phase shift hardware. Thus kwired comments about needing a 3 phase system. IMHO it could be done with something like a small rotary converter built into the transformer. But it would be a truly bizarre equipment design to strictly require 208V single phase from a 120/208V wye system without actually requiring the neutral.

-Jon

 

[Jamesco]

No, because it can't be done.

Agree. But you can have a 480V to 104/208V transformer made. jap used 120/208V in his question he can't find. No a split phase secondary winding would not be possible at 120/208. I should have caught that but I missed it. My bad. A 120/208V secondary is not needed. The neutral will be ground but not used as a circuit conductor.

 

[Jamesco]

A 480V to 104/208V single phase transformer is certainly possible, simply requiring a center tap.

A symmetric 480V to 120/208V single phase transformer is not possible without some sort of phase shift hardware. Thus kwired comments about needing a 3 phase system. IMHO it could be done with something like a small rotary converter built into the transformer. But it would be a truly bizarre equipment design to strictly require 208V single phase from a 120/208V wye system without actually requiring the neutral.

-Jon

Don't need 120/208V. 104/208V is all that is needed.

I just got off the phone with TEMCo. Yes they can build a 480V to 104/208V single phase transformer for a small added charge. No big deal.

 

[Jamesco]

Agree. But you can have a 480V to 104/208V transformer made. jap used 120/208V in his question he can't find. No a split phase secondary winding would not be possible at 120/208. I should have caught that but I missed it. My bad. A 120/208V secondary is not needed. The neutral will be ground but not used as a circuit conductor.

Actually I am the guilty party. My bad! Brain fart moment!

We don't know what the KW rating of the cooking appliance is. Who in their right mind would have ordered a 480v to 208v 1ph transformer to fed the the cooking appliance to begin with? For a few more dollars he/she could have special ordered a 480 to 120/208V 1ph transformer and wired the secondary as a 120/208v grounded power system.

To date the OP has not provided any info on the cooking appliance other than it is 208v 1ph.
It appears the OP has left the building.

Should be 104/208V. My apologies to all. Especially jap and kwired.

 

[jap]

Actually I am the guilty party. My bad! Brain fart moment!



Should be 104/208V. My apologies to all. Especially jap and kwired.

I love it when people apologize to me when there's absolutely no reason to whatsoever.
I should agree with K-wired more often.

JAP>

 

[kwired]

Agreed.

That's why on this particular transformer, one of the legs should be grounded and 3 wires brought to the equipment, not just 2.


JAP>

Same rules apply to any grounded conductor. Corner ground delta - you separate EGC from "grounded" beyond the service or system bond point of separately derived system. Exactly what we do with systems with neutral as the grounded conductor.

 

[jap]

Same rules apply to any grounded conductor. Corner ground delta - you separate EGC from "grounded" beyond the service or system bond point of separately derived system. Exactly what we do with systems with neutral as the grounded conductor.

I know you work on farms and irrigation, and I on feed mills and industrial plants, but, you can have all of the corner ground delta's, for that matter any Delta secondaries.,,,,,I've about flamed out on em.

JAP>

 

[kwired]

I know you work on farms and irrigation, and I on feed mills and industrial plants, but, you can have all of the corner ground delta's, for that matter any Delta secondaries.,,,,,I've about flamed out on em.

JAP>

I don't run into as many as I once used to. But one has to lose the mentality that a grounded conductor must be a neutral conductor- it can be any conductor of any system. NEC just happens to require that systems that have a neutral conductor must ground the neutral conductor.

Even in your industrial settings, how many 120 volt two wire secondaries do you have for control volts on various machines? There is no neutral on those, pick one side and ground it, pick both sides and you are blowing control fuse or letting smoke out of the transformer if done ahead of any overcurrent devices.