No secondary over current protection?

[pfalcon]

Thats my point as well, it is listed and manufactured as a grounded system transformer. Two of the ungrounded conductors can be 120v to ground therefore it requires grounding and would be in violation if ungrounded.

In my industrial circles most of our 240v delta's are grounded systems, our ungrounded systems are 480v.

Without the pages I can't confirm for this transformer but typically it won't be listed as a grounded system transformer. It will be listed as a three phase 480/240 transformer with optional 120V midtap to reference on one phase. Use of the midtap is normally listed as optional. Use of ground rather than a reference voltage is normally listed as optional.

I concur with your common usage. Ungrounded systems in the US are usually 480V buss supply to machinery. Ground is frequently pulled from the building steel or a fourth bar. 240V is normally a motor supply and thereby requires a transformer ground.

 

[pfalcon]

... 480 volt panel > 45 amp breaker > 30 kva transformer > 8 AWG > non fused 60 amp disconnect > 175? 8 AWG > 60 amp receptacle > 60 amp plug > 75? 8/4 rubber cord > refrigeration unit. ...

Back to the OP.
Secondary fusing of the transformer will be required since 8awg is 50A. Minimum primary is 45A requiring a minimum secondary conductor ampacity of 90A to avoid the secondary fuse.

Since secondary fusing is required, due to the secondary conductor if nothing else, then primary fusing can run from 45A to 100A (next size up from 90A) dual element. 45A/50A being recommended from Bussman fuse. Increasing the fuse size up to the 100A is done to avoid nuisance trips.

Load current is currently 60FLA so 60A secondary fusing should be good. 90A (100A next size up) can be used. It's recommended to use the lowest fuse size required for best protection. You can increase it later.

How did we get to an 8awg for 60A? Don't we need a 6awg? Doesn't change the need for secondary fuses on the transformer.

This is going to a receptacle and therefore premises wiring. Ground is required.

What else is missing?

 

[augie47]

Back to the OP.
Secondary fusing of the transformer will be required since 8awg is 50A. Minimum primary is 45A requiring a minimum secondary conductor ampacity of 90A to avoid the secondary fuse.

Since secondary fusing is required, due to the secondary conductor if nothing else, then primary fusing can run from 45A to 100A (next size up from 90A) dual element. 45A/50A being recommended from Bussman fuse. Increasing the fuse size up to the 100A is done to avoid nuisance trips.

Load current is currently 60FLA so 60A secondary fusing should be good. 90A (100A next size up) can be used. It's recommended to use the lowest fuse size required for best protection. You can increase it later.

but, not on a #8 secondary conductor, correct ?

How did we get to an 8awg for 60A? Don't we need a 6awg? Doesn't change the need for secondary fuses on the transformer.

This is going to a receptacle and therefore premises wiring. Ground is required.?

Can you give me a Code refernce on that requirement ?

What else is missing?

 

[tryinghard]

I do not see that at all, any transfomer can be grounded or not.

I could use a delta wye transformer to supply an ungrouned delta simople by not using XO.

IMO in your case you would be ignoring the listed equipment lable that shows X4 as a winding center tapped to ground, as well as the phisical lug as it say's is provided for such.

 

[iwire]

IMO in your case you would be ignoring the listed equipment lable that shows X4 as a winding center tapped to ground, as well as the phisical lug as it say's is provided for such.

For what it's worth it is grounded.

That aside I see absolutely nothing that says I have to ground X4.

Can you tell me where you see such an instruction?

 

[tryinghard]

For what it's worth it is grounded.

That aside I see absolutely nothing that says I have to ground X4.

Can you tell me where you see such an instruction?

The secondary delta symbol includes the X4 as drawn, the label secondary (x) notes 120V. IMO these noted on the label is the listed instruction of this equipments use.

 

[iwire]

The secondary delta symbol includes the X4 as drawn, the label secondary (x) notes 120V. IMO these noted on the label is the listed instruction of this equipments use.

Yes it shows an X4, it does not say I have to use it.

Would you also say I must connect single phase 120 loads to this transformer that presently only supplies a 3 phase motor unit?

 

[jim dungar]

The secondary delta symbol includes the X4 as drawn, the label secondary (x) notes 120V. IMO these noted on the label is the listed instruction of this equipments use.

The diagrams on this nameplate meet the ANSI/IEEE standards. If a ground was required on X4 it would have been indicated on one of the diagrams.

 

[pfalcon]

The secondary delta symbol includes the X4 as drawn, the label secondary (x) notes 120V. IMO these noted on the label is the listed instruction of this equipments use.

We use equipment like sensors all over our facility that show both PNP and NPN wiring methods on the same label. Nobody wires both. To find the correct answer you have to go to the installation sheet shipped with the device. The label is just a helper not the listing.

 

[pfalcon]

but, not on a #8 secondary conductor, correct ?

Can you give me a Code refernce on that requirement ?

I'm thinking a #6 from the transformer to the secondary OCPD is required. Sizing of wires after the secondary OCPD is load dependant. The secondary OCPD can be a 90A with following wires smaller than #6 provided they have the correct OCPD for their wire size.

Refrigerators require grounding per 250.114

 

[mivey]

...Applying Table 450.3(B) the protection must be a maximum of 250%.

But with no secondary protection wouldn't we be limited to 125%?

Most likely I will recommend replacing the unfused disconnect on the secondary side with a fused disconnect equipped with 50 amp fuses.

That would be my recommendation as well.

Yes it shows an X4, it does not say I have to use it.

You are correct here too.

 

[tryinghard]

Yes it shows an X4, it does not say I have to use it.

Would you also say I must connect single phase 120 loads to this transformer that presently only supplies a 3 phase motor unit?

These items noted on the label qualify it as it's listed, simple as that. It can be ignored; but it can be grounded in such a way to cause two of the phase conductors to have 120v to ground whereas an ungrounded transformer cannot, because there would not be a termination point, no X4.

I am saying this transformer should be grounded and if not would be violating it's label and listing at minimum. I am saying a 240v ungrounded system transformer would be furnished as such (rare as it would be) rather than using a grounded system transformer.

 

[mivey]

These items noted on the label qualify it as it's listed, simple as that. It can be ignored; but it can be grounded in such a way to cause two of the phase conductors to have 120v to ground whereas an ungrounded transformer cannot, because there would not be a termination point, no X4.

I am saying this transformer should be grounded and if not would be violating it's label and listing at minimum. I am saying a 240v ungrounded system transformer would be furnished as such (rare as it would be) rather than using a grounded system transformer.

Please indicate the ground on the transformer diagram iwire provided.

We install power transformers all the time with a center tap and NOTHING says that tap has to be grounded in all cases.

 

[tryinghard]

Please indicate the ground on the transformer diagram iwire provided.

We install power transformers all the time with a center tap and NOTHING says that tap has to be grounded in all cases.

You intentionally purchase grounded system transformers and use them as ungrounded?

 

[iwire]

You intentionally purchase grounded system transformers

I have never heard the term 'grounded system transformers'

Transformers are transfomers, how we apply them is up to us in many regards.

 

[tryinghard]

Thats fine but my point is buy what you need and use it the way it's designed & listed.

 

[mivey]

You intentionally purchase grounded system transformers and use them as ungrounded?

Not what I said. Again, show me the ground in the diagram.

You can have a transformer with a terminal tied to the transformer housing. That is not what iwire has in his picture.

 

[mivey]

Thats fine but my point is buy what you need and use it the way it's designed & listed.

It looks like they bought what they needed. This transformer can serve more than one purpose. Making a multi-purpose transformer can reduce manufacturing costs. It does not make sense to build a separate type transformer for every type application.

PS: Where is iwire's transformer not being used as listed?

 

[Pierre C Belarge]

I have never heard the term 'grounded system transformers'

Transformers are transfomers, how we apply them is up to us in many regards.

I think there is some confusion, maybe based on typical usage for people who perform their work differently (not wrong) than others may perform their work. "there is more than one way to skin a cat", sort of statement.

 

[iwire]

Thats fine but my point is buy what you need and use it the way it's designed & listed.

Show me anything at all that indicates grounding X4 is part of or required by the listing.