Article 450 has had very few changes to it. I believe table 450.3 is still the same.I am looking to get information on the code requirerments for installing an 112.5 KVA transformer. The transformer was installed in 1996, thus I need to obtain code info from 1996. I believe the original installation was sized improperly.
Wasn't it in the 90's that the NEC let an odd situation out for a cycle.....
112.5 KVA
4.5 % IZ
HV-480, HA-135
Lv-240, LA-271
Class AA
150 C
If the code hasn't changed much and my math is correct:
Primary OC protection should be 168.75 or 175 breaker size
112.5 KVA
4.5 % IZ
HV-480, HA-135
Lv-240, LA-271
Class AA
150 C
If the code hasn't changed much and my math is correct:
Primary OC protection should be 168.75 or 175 breaker size
I have 350 for the secondary OCPD, and I agree with 175 for primary. But is this a 240 delta secondary, or is it one of those wierd high leg thingys that I have never (fortunately) had to deal with? :-? :wink:Assuming the unit has secondary protection (it should) I come up with an NEC maximum primary overcurrent protection value of 338 amps or a 350 breaker size.
I have 350 for the secondary OCPD, and I agree with 175 for primary. But is this a 240 delta secondary, or is it one of those wierd high leg thingys that I have never (fortunately) had to deal with? :-? :wink:
Doesn't matter when sizing a 3-pole circuit breaker.But is this a 240 delta secondary, or is it one of those wierd high leg thingys that I have never (fortunately) had to deal with? :-? :wink:
Is this the correct math?
PRI
122,500va / (480x1.732)= 135a
135a x 1.25= 169
next higher standard = 175a
SEC
112,500va / (240x1.732) = 270a
270a x 1.25= 337.5A
next standard 350amp
Bob wheres the 2.5 come from???? Or is it one of those reversed math tricks - like 80% of 125% is the same....I have to try again. :smile:
I get this
PRI
122,500va / (480x1.732)= 135a
135a x 2.5 = 337 amps
next higher standard = 350a
I get the same for the secondary.
Is this not correct?
bc -I believe the original installation was sized improperly.