380v Transformer Install

J.DaSilva24

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Location
Leominster, MA
Occupation
Electrician
I am in the process of getting materials together for a project I have going on.

Essentially the run down is the following:
480v 30KV Delta primary to 380Y secondary for a single piece of equipment. The transformer will be roughly 10-15’ from the panel it is being fed from.

I am going to feed the transformer from the 480/277 distribution panel in the electric room off a 50a breaker which covers the 125% OCP on the primary side.

I was planning on installing a disconnect with 60a fuses on the secondary side to cover the 125% OCP on the secondary side. This transformer is going to feed a single piece of equipment with 40a of OCP.

Does anyone see an issue installing a 2nd disconnect with 40a fuses to feed the new piece of equipment? It would be fed from the 60a disconnect that is connected to the secondary side of the transformer.

I’m trying to avoid installing a main lug load center for 1 piece of equipment to keep costs down for the customer. Or am I overlooking something that could be another option?

Thank you!
 
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Short answer is no. There is no issue with it. So long as the wire is sized to the properly and protected by the secondary OCPD. ..

But if I am understanding everything correctly, there is probably a way to simplify it or at least reduce the wire size if you use 40A fuses instead of 60A fuses.
 
Before anyone else says it, Europe uses 400Y/230 volts only. It is simple. It isn't relevant at all for anything anywhere ever, but I figured I would put that out there.
 
Welcome to the forum.

It sounds Kosher, but redundant. Can't one OCPD function?

Don't forget about bonding the secondary.
 
The secondary will be bonded to building steel at the transformer.

I could use 1 OCPD on just the primary but then it would need to be sized at 250% if I’m understanding correctly. I can’t go lower than 60a on the secondary since 125% of the secondary is 56.98A.
 
480v 30KV Delta primary to 380Y secondary for a single piece of equipment. The transformer will be roughly 10-15’ from the panel it is being fed from.

I am going to feed the transformer from the 480/277 distribution panel in the electric room off a 50a breaker which covers the 125% OCP on the primary side.
Not sure what you mean by the last part, "covers the 125% OCP on the primary side."

I get a rated transformer primary current of 36A, so 125% of that would be 45A. As that is a standard OCPD size, using 50A would put you over the 125% primary only protection option for the transformer. That's actually fine with up to 60A secondary OCPD, as 125% of the rated secondary current is 57A, which is not a standard size, so you are allowed to round up to 60A and still comply with the 125% secondary transformer protection option in 450.3(B).

Cheers, Wayne
 
Not sure what you mean by the last part, "covers the 125% OCP on the primary side."

I get a rated transformer primary current of 36A, so 125% of that would be 45A. As that is a standard OCPD size, using 50A would put you over the 125% primary only protection option for the transformer. That's actually fine with up to 60A secondary OCPD, as 125% of the rated secondary current is 57A, which is not a standard size, so you are allowed to round up to 60A and still comply with the 125% secondary transformer protection option in 450.3(B).

Cheers, Wayne

Yes that was my mistake on the primary side. For some reason I decided to round up but yes I can go with a 45a breaker for the primary side.
 
Does the new piece of equipment come with a main CB or fuses that are listed as branch circuits protection? If so, if the transformer is close enough to meet the tap rules, you can run the xfmr secondary wires right to the equipment and save a bunch.
 
fa0e3ddd4ed451561a884a5849966ac7.jpg

Essentially this is the layout I am going proposing. Just ignore the 50A primary OCPD, I’ll go with a 45a breaker instead.


Sent from my iPhone using Tapatalk
 
Does the new piece of equipment come with a main CB or fuses that are listed as branch circuits protection? If so, if the transformer is close enough to meet the tap rules, you can run the xfmr secondary wires right to the equipment and save a bunch.
It does not. It’s just a cord connected piece of equipment so I need to install an outlet specifically for this machine unless they request it to be hardwired.

My plan was just to simply install a receptacle in a 4-11/16” box nipples directly off the 2nd disconnect with 40a fuses.
 
Before anyone else says it, Europe uses 400Y/230 volts only. It is simple. It isn't relevant at all for anything anywhere ever, but I figured I would put that out there.
South Africa operates on a standard voltage of 230 volts at a frequency of 50 Hz (AC).
 
With individual pieces of equipment like that, I usually run 480 to the equipment, and set the step down transformer they supply at the equipment. Less voltage drop, and smaller wire can be run. The last couple I done had integrated ocp on the secondary, and a rotary disconnect on the primary.
 
With individual pieces of equipment like that, I usually run 480 to the equipment, and set the step down transformer they supply at the equipment. Less voltage drop, and smaller wire can be run. The last couple I done had integrated ocp on the secondary, and a rotary disconnect on the primary.
Unfortunately they are not supplying the transformer. Based on the load they provided me for the equipment they plan on using, I sized the transformer required at 30KV.

They are just asking for a 380v outlet so they can use and test whatever equipment they need to. I am simply trying to provide them a solution at the cheapest cost to them because it seems a bit extreme to spend over $3k for a load center to house 1 single breaker.
 
I meant one OCPD in the secondary. Why both a 60a and a 40a?
40a would put me at less than the 125% on the secondary side so that’s why I was thinking I would need 2.

The disconnect for the secondary would have 60a OCP for the 125% requirement and then the 2nd disconnect with 40a OCP would protect the equipment it is supplying.
 
fa0e3ddd4ed451561a884a5849966ac7.jpg

Essentially this is the layout I am going proposing. Just ignore the 50A primary OCPD, I’ll go with a 45a breaker instead.


Sent from my iPhone using Tapatalk
The different voyages 480V/380V/277V is not what we have in the EU but I do know what you have it in your country.
 
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Why do you think a loadcenter might be required?
Just for the 40a breaker that would be supplying the equipment.

If the secondary requires a 60a OCPD, I don’t want to come off the load side of the disconnect housing the 60a OCPD to protect a piece of equipment rated less than that.

I’m just trying to see if I’m overthinking my design.
 
Just for the 40a breaker that would be supplying the equipment.

If the secondary requires a 60a OCPD, I don’t want to come off the load side of the disconnect housing the 60a OCPD to protect a piece of equipment rated less than that.

I’m just trying to see if I’m overthinking my design.
The secondary can be less than 60A. You can protect the secondary and the single piece of equipment with the same OCPD. If you change the 60A fuses to 40A fuses. You can also use #8 Cu from the secondary side of the transformer rather than needing 60A ampacity of conductor.

Table 450.3(B) is the maximum rating of protection for the transformer.


And to reiterate, there is nothing wrong with your current plan (so long as the wires are sized right). But you could simplify it to save them some more.
 
The secondary can be less than 60A. You can protect the secondary and the single piece of equipment with the same OCPD. If you change the 60A fuses to 40A fuses. You can also use #8 Cu from the secondary side of the transformer rather than needing 60A ampacity of conductor.

Table 450.3(B) is the maximum rating of protection for the transformer.


And to reiterate, there is nothing wrong with your current plan (so long as the wires are sized right). But you could simplify it to save them some more.
Thank you for the help. Never occurred to me that it’s the maximum and we could have gone lower. Since I already stock the material I was just going to wire everything with #6 THHN anyhow but atleast that does cut down on cost of an additional disconnect and 3 fuses.
 
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