Transformer questions

[JES2727]

I am installing a 75 KVA dry-type transformer, 480 primary/120-208y secondary. The transformer will supply a 200A panel that will serve a new water treatment system, some production equipment, and "future needs". The transformer and panel will be located in a large storage room adjacent to the water room. I've read article 450, but I'd like some clarification on a few things. Am I required to enclose the trans & panel to comply with 450.8? Right now the transformer is about 4' from a freezer and 10' from an exit door, with no fencing or barriers. Is 450.8(b) calling for a seperate enclosure, or is it referring to the outer case of the transformer? Also, I see no requirement for a local disconnecting means so am I safe to use a 100A breaker in the 480v distribution panel (150' away)with no further protection? Is #3 cu adequate for the primaries?
Thanks for the help.

 

[cripple]

Transformer questions

Article 450 is talking about the transformer which is the windings and the core, 450.8 is talking about how to protect the winding and the core. Section 450.8(B) is giving option on how the winging and core can be protected. An enclosure dry-type transformers does not need an additional enclosure, but it will have to be installed to prevent physical damage to the transformer. As for the location of the disconnecting means and the protection of the transformer secondary conductor you will have to comply with section 240.21(C)

 

[bsh]

transformer primary

transformer primary

The primary current for a 480 volt, 3 phase, 75 KVA transformer is 90 amps. Per table 450.3(B) you can protect the primary up to 250% of the primary current if you have secondary protection for the transformer(90 X 2.5=225). Your secondary panel should have a main breaker per section 408.36 since the "future needs" are not known. If the breaker for the primary is 100 amps then size the cable based on the 60 degree C column in table 310.16. Since the breaker is 100 amps you must use the 60 C column (article 110.14(C)(1)(a)). If you use a larger ampacity breaker then you can use the 75 C column (article 110.14(C)(1)(b))

 

[cpal]

The primary current for a 480 volt, 3 phase, 75 KVA transformer is 90 amps. Per table 450.3(B) you can protect the primary up to 250% of the primary current if you have secondary protection for the transformer(90 X 2.5=225). ))

You can but the100 A breaker is fine.

Your secondary panel should have a main breaker per section 408.36 since the "future needs" are not known. ))

in 408.36 mains are only required if it is a lighting and appliance BC panelboard. Future needs may be addresed in the future.

Since the breaker is 100 amps you must use the 60 C column (article 110.14(C)(1)(a)). If you use a larger ampacity breaker then you can use the 75 C column (article 110.14(C)(1)(b))

Most breakers mfg since 1987 have a dual 60/75deg rating

 

[JES2727]

Article 450 is talking about the transformer which is the windings and the core, 450.8 is talking about how to protect the winding and the core. Section 450.8(B) is giving option on how the winging and core can be protected. An enclosure dry-type transformers does not need an additional enclosure, but it will have to be installed to prevent physical damage to the transformer. (C)

That's exactly what I thought it was saying. Just wanted to be sure I was reading it the right way. Thanks.