Transformer Secondary protection with Panel OC protection

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WattsOn70

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I have 7 150KVA transformers 480-208/120V in delta-star configuration. All transformers located in the ground floor Electrical room of a six story hotel. Each transformer feeds a remote 600A Distribution Panel located in different floors. Distance from transformers to Panel is more than 100' all.

Question: Considering al panels have a 500A MCB, do I need to install an additional OC protection right at the transformer secondary?

What of the NEC rules should refer to?

Thanks in advance.
 
II. Location
240.21 Location in Circuit. Overcurrent protection shall be
provided in each ungrounded circuit conductor and shall be
located at the point where the conductors receive their supply
except as specified in 240.21(A) through (H). Conductors supplied
under the provisions of 240.21(A) through (H) shall not
supply another conductor except through an overcurrent protective
device meeting the requirements of 240.4.

The conductors need protection.
 
(2) Transformer Secondary Conductors Not over 3 m
(10 ft) Long. If the length of secondary conductor does not
exceed 3 m (10 ft) and complies with all of the following:
(1) The ampacity of the secondary conductors is
a. Not less than the combined calculated loads on the
circuits supplied by the secondary conductors, and
b. Not less than the rating of the equipment containing
an overcurrent device(s) supplied by the secondary
conductors or not less than the rating of the overcurrent
protective device at the termination of the
secondary conductors.
 
As others have noted, OCP meeting the appropriate 240.21(C) tap rule needs to be installed (in this case, the 25ft rule). Compared to most hotel jobs I've seen this one is a strange situation in that, from a installation cost standpoint, the transformers are normally located at the secondary panel. Are you confident the plans call for all the transformers to be at the service panel.
 
WattsOn70 said:
I have 7 150KVA transformers 480-208/120V in delta-star configuration. All transformers located in the ground floor Electrical room of a six story hotel. Each transformer feeds a remote 600A Distribution Panel located in different floors. Distance from transformers to Panel is more than 100' all.

Question: Considering al panels have a 500A MCB, do I need to install an additional OC protection right at the transformer secondary?

What of the NEC rules should refer to?

Thanks in advance.
Click to expand...

OCPD required within 25' if 240.21(C)(6) applies.
 
WattsOn70 said:
I mean OC protection to the Panel. I'm confused about the allowed distance from the secondary to the OC protection.
Click to expand...

Note there are three required things going on:

1. Conductor protection (240.21)
2. Transformer protection (450.3(B))
3. Panelboard protection (408.36)

Most commonly, a panelboard main breaker takes care of all 3, but there are other arrangements. Note also that #1 is the only one that requires the protection be at a specified distance.
 
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