Transformers of Different Voltages Tying Into Same Panel

[Solar Noob]

I have a major question about service transformers and how they tie in together. The job I am working on has a MSP that has two transformers tied into it, however both of the transformers are different voltages. The MSP itself is 480V, and the 75kVA transformer is also 480V, however there is a second smaller transformer that ties into the panel, with the 15kVA transformer with only 240V. How does the smaller transformer affect the 480V transformer? Any specific place in the NEC 450? NEC 450.7 brings up that they may be operated in parallel as long as they obey the 450.3(A) table, but that doesn't actually answer my question. Any help with this would be great.

 

[ggunn]

Why would two transformers with the same primary voltages but different secondary voltages be a problem if their primaries are fed from the same panel?

 

[jaggedben]

I see no issue (although I'm curious if you really meant to say you have a 480/480 transformer). And I don't see what this has to do with solar.

 

[Solar Noob]

My knowledge on transformers is shaky at best, and I am trying to figure out what the kVA is total from the transformers. Since the inverter we are tying into has an AC output of 60kW, with the 75kVA transformer alone I know we will be fine, but I am curious as to how the second smaller transformer ties into determining how much kVA we are actually working with for OCPD calculations, given the secondary voltage being different.

 

[wwhitney]

I am curious as to how the second smaller transformer ties into determining how much kVA we are actually working with for OCPD calculations, given the secondary voltage being different.

If the second transformer is not on the electrical path between the inverter and the service, it is immaterial.

Cheers, Wayne

 

[electrofelon]

My knowledge on transformers is shaky at best, and I am trying to figure out what the kVA is total from the transformers. Since the inverter we are tying into has an AC output of 60kW, with the 75kVA transformer alone I know we will be fine, but I am curious as to how the second smaller transformer ties into determining how much kVA we are actually working with for OCPD calculations, given the secondary voltage being different.

Perhaps a drawing would help, I'm having a tough time understanding the setup.

 

[ggunn]

I have a major question about service transformers and how they tie in together. The job I am working on has a MSP that has two transformers tied into it, however both of the transformers are different voltages. The MSP itself is 480V, and the 75kVA transformer is also 480V, however there is a second smaller transformer that ties into the panel, with the 15kVA transformer with only 240V. How does the smaller transformer affect the 480V transformer? Any specific place in the NEC 450? NEC 450.7 brings up that they may be operated in parallel as long as they obey the 450.3(A) table, but that doesn't actually answer my question. Any help with this would be great.

The total full load primary current for the two transformers is about 108A, if that tells you anything.

 

[Solar Noob]

Perhaps a drawing would help, I'm having a tough time understanding the setup.

I marked this up on paint for a rough drawing, but essentially what's happening is the transformers are connected together on the top where the service voltage is coming down, but they're also crimped together from the wires coming out of the transformer to the MSP we're trying to tie into. I had to reduce the file size a lot, so it definitely isn't as clear as the actual picture itself.

 

[wwhitney]

The secondary of the 480V transformer appears to be grey and goes to that meter and panel on a post in the distance. While the secondary of the 240V transformer connects to the black service wires in the foreground that leave the photo at the bottom right.

So it looks to me that it's two separate services, and that it's not correct that the two services tie into the same panel.

Cheers, Wayne

 

[Solar Noob]

The secondary of the 480V transformer appears to be grey and goes to that meter and panel on a post in the distance. While the secondary of the 240V transformer connects to the black service wires in the foreground that leave the photo at the bottom right.

So it looks to me that it's two separate services, and that it's not correct that the two services tie into the same panel.

Cheers, Wayne

Thank you very much. This helps a lot.

 

[jaggedben]

I thought you were talking about customer owned transformers on the load side of the MSP. You were talking about utility owned transformers. That was really unclear.

Anyway I see the same thing as Wayne.