Industrial xfmr service entrance disconnect

[cukele]

I have a 25kva 480-120/240v, 1 phase transformer located in an industrial plant.
The transformer is feed from a 70A CB located 300' away. The transformer is located outside of a building and feeds a lighting panel with a 125A main. The lighting panel is located inside the building. Should the service entrance disconnect be located on the primary or the secondary side of the transformer? Is an OCPD required at the xfmr or is a disconnect switch suffiecient?

 

[shockin]

I believe you will need to look at 240.21 to determine if overcurrent is required for your application.

 

[barclayd]

That is not a service, it is a feeder. Look at art 450 for transformers.
Your breaker sizes are ok, assuming the wire sizes are correct. You don't need a disconnect on the primary at the transformer, but it makes maintenance a little easier. (Non-Fused) The 125a Main on the panelboard is good. Look at art 250 for grounding a Separately Derived System.
db

 

[cukele]

240.21

240.21

I applied the outside unlimited tap rule in 240.21. Is that correct? What about the service entrance disconnect mentioned in 230? 230 Says that a means of disconnecting the conductors that enter the building is required either outside or immediately inside. Is a disconnection means on the secondary suffiecient?

 

[jim dungar]

There is nothing in article 230 that applies to your installation.

First your 120/240 panel needs to be properly protected per 408.36.
Second the conductors between the transformer secondary and the panel need to be protected using one the the methods in 240.21(C). You may use the protection from step #1 to meet this requirement.
Third your transformer primary protection must be sized per 450.3(b).
Fourth the conductors feeding the transformer primary must be sized based on the device chosen in step #3 unless you are lucky enough to meet 240.21(B)(2).

The 2011 NEC is the first version that would possibly require you to provide a disconnecting means within sight of the transformers primary, but, you would probably qualify for the 'lockable' exception.

 

[barclayd]

The 2011 NEC is the first version that would possibly require you to provide a disconnecting means within sight of the transformers primary, but, you would probably qualify for the 'lockable' exception.

450.14 Where the heck did THAT come from?
It's a great idea, but it's no fun now that it's a rule.
db

 

[dkidd]

9-176 Log #3821 NEC-P09 Final Action: Accept in Principle
(450.14)
_______________________________________________________________
Submitter: James J. Rogers, Bay State Inspectional Agency
Recommendation: Add new text to read as follows:
450.14 Disconnecting Means. Transformers other than listed class 2 or class
3 transformers shall have a disconnecting means located either in sight of the
transformer or remotely provided the remote disconnect is capable of being
locked in the off position. When the disconnecting means is located remote
from the transformer the locking means required shall remain in place whether
or not the locking means is installed.
Substantiation: Requiring a disconnecting means for a transformer is intended
to enhance safety for the qualified individual that is required to work on the
transformer. This is especially true in installations utilizing the requirements of
240.21(B)(3) whereby there may be several transformers in different locations
all tapped from one feeder and it may be impractical to de-energize the entire
feeder system to work on one of the transformers.
Panel Meeting Action: Accept in Principle
Revise the rule to read as follows: ?Transformers, other than Class 2 or Class
3, 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.?
Panel Statement: CMP-9 has made editorial changes to avoid a run-on
sentence, used ?open? instead of ?off? for the disconnect position in
accordance with customary code usage, used ?where? instead of ?when?
because it is a question of place and not time, and removed the listing
limitation on the Class 2 and 3 transformers because it has no bearing on
whether a disconnecting means needs to be installed. The lockable wording
correlates with the task group results reported in Proposal 9-201.
Number Eligible to Vote: 12
Ballot Results: Affirmative: 12
Comment on Affirmative:
YOUNG, R.: The disconnecting means should be lockable in the open
position whether or not the disconnecting means is mounted either within sight
of the transformer or in a remote location.

 

[LarryFine]

... it's no fun now that it's a rule.

"Welcome to the world of the real." ~ Morpheus