45kva transformer OCPD question

[embryo3]

I have a 45kva 480v to 208/120v 3ø transformer that is suppliedby a 150amp existing breaker. The 45kva transformer in turn supplies asecondary is a 100amp disconnect that is within 10’ of the transformer

480vac3ø 45kva Primary OCPD (NEC 450.3(b) Primary OCPD at 250%. = 54amp x 2.50 =135amp
Next size up is 150amp breaker (NEC240.4(b).

PrimaryConductors: are 1/0 THHNconductors – (NEC 310.15 (b) = 1/0 awgrated for 150amp @ 75°c


Thesecondary OCPD is a 600vac 208vac3ø 100amp fused disconnect within10’ of the 45kva transformer.

Secondaryconductors are sized for 100amp disconnect= #2 THHN (NEC 310.15(b) #2 THHN rated for 115amp @75°c

Is this installation to code or am Imissing something?

 

[don_resqcapt19]

Table 450.3(B) does not permit rounding up to the next standard size for the 250% primary OCPD.

 

[Tony S]

I get 124A for the secondary

 

[ADub]

I've never once sized up 250% for transformer ocpd. At my work this would get a 70 amp feed on the primary and 150 on the secondary


Sent from my iPad using Tapatalk

 

[don_resqcapt19]

I get 124A for the secondary

Yes, but there is not requirement that the secondary conductors be sized for the full output of the transformer as long as they are protected per one of the rules in 240.21(C). In this example the secondary conductors are rated at 115 amps and protected with a 100 amp fuse at the load end of the conductors. This is compliant with the rules in the NEC.

 

[jojo]

I will size the OCPD (primary and secondary) at 125% full load amps.

45kVA 3-phase transformer 480-208Y/120V
Primary:
OCPD - 70A
Conductors - 3#4 and 1#8Gnd

Secondary:
OCPD - 150A
Conductors - 3#1/0 and 1#6Gnd

 

[embryo3]

Transformer OCPD be above 7'-6"?

Transformer OCPD be above 7'-6"?

Can the OCPD (fused disconnect) servicing the transformer be above 7'-6" based on 240.24 (A) 4? It is with in site and accessible with a potable ladder?

 

[petersonra]

450.14 Disconnecting Means. Transformers, other than
Class 2 or Class 3 transformers, shall have a disconnecting
means located either in sight of the transformer or in
a remote location. Where located in a remote location,
the disconnecting means shall be lockable, and the location
shall be field marked on the transformer

In Sight From (Within Sight From, Within Sight).
Where this Code specifies that one equipment shall be “in
sight from,” “within sight from,” or “within sight of,” and
so forth, another equipment, the specified equipment is to be
visible and not more than 15 m (50 ft) distant from the other.

I don't see anything about a height requirement or that it be readily accessible, or even accessible at all.

You might have some issues with working space though.

 

[embryo3]

Transformer Disconnect location

Transformer Disconnect location

The thing I was struggling with is that 240.24 (A) (4) states that overcurrent protection devices can be adjacent to utilization equipment that they supply, access shall be permitted by portable means. Also, under switches (404.8 (A) EX2, it gives the same exception. The disconnect is supplying the transformer power and is mounted within site.

Is the transformer defined as utilization equipment?

Cant find any other articles that say you cant do this?

 

[petersonra]

The thing I was struggling with is that 240.24 (A) (4) states that overcurrent protection devices can be adjacent to utilization equipment that they supply, access shall be permitted by portable means. Also, under switches (404.8 (A) EX2, it gives the same exception. The disconnect is supplying the transformer power and is mounted within site.

Is the transformer defined as utilization equipment?

Cant find any other articles that say you cant do this?

Utilization Equipment. Equipment that utilizes electric energy
for electronic, electromechanical, chemical, heating,
lighting, or similar purposes.

It would appear a xfmr is not "utilization equipment" from the code definition.