# Transformer Secondary conductors



## Jkrauss (Feb 27, 2014)

The ? I have is what length can the secondary conductor from a Y transformer be with out a over current protection ? The job I am on is a commercial job conductors are inside the building and are feeding a main breaker panel one panel is over 40 feet from the transformer , The other panel is 100 ft from the transformer that is supplying it . The drawings show no protection on the secondary conductors between the transformer and the main breaker in the panel .240-21(c) says 10 feet


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## Jkrauss (Feb 27, 2014)

Bump


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## kg7879 (Feb 3, 2014)

You have to have an opcd for the secondary conductors. The stipulations just change if the conductors are not over ten feet or over ten feet but less than twenty five feet. 

So the opcd can not be further than 25ft


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## Jkrauss (Feb 27, 2014)

Thank you .


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## manchestersparky (Mar 25, 2007)

Keep in mind that is 25 feet of total conductor length , not 25' from the x-former


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## wildleg (Apr 12, 2009)

read the table in 450 that tells you when you need secondary protection. the secondary can be protected by the primary side.


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## varmit (Apr 19, 2009)

wildleg said:


> read the table in 450 that tells you when you need secondary protection. the secondary can be protected by the primary side.


Code section 240.21 (C) (1) would not allow this as this is a three phase wye transformer.

Yes, 25 feet would be the limit without secondary over current protection.

Also, 450.14 requires a primary disconnect at the transformer.


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## don_resqcapt19 (Jul 18, 2010)

wildleg said:


> read the table in 450 that tells you when you need secondary protection. the secondary can be protected by the primary side.


The rules in Article 450 are only for the protection of the transformer itself. They have nothing to do with the protection of the secondary conductors. The rules for the secondary conductors are in 240.21(C). Both sets of rules have to be complied with.


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## don_resqcapt19 (Jul 18, 2010)

varmit said:


> ...
> Also, 450.14 requires a primary disconnect at the transformer.


It really doesn't require the primary disconnect to be at the transformer. 


> 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 in accordance with 110.25, and its location shall be field marked on the transformer.


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## varmit (Apr 19, 2009)

OK, I should have said FOR the transformer. The OP said that the power was coming from a breaker panel, so the most logical location, in this case, would probably be near the transformer.


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## varmit (Apr 19, 2009)

Remember, by current Code a standard breaker is not a disconnect unless the capability to lock out the breaker remains in place at all times.


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## don_resqcapt19 (Jul 18, 2010)

varmit said:


> Remember, by current Code a standard breaker is not a disconnect unless the capability to lock out the breaker remains in place at all times.


That only applies when the code rule requires that the disconnect be lockable, which is the case if the transformer disconnect is not within sight from the transformer. 

Not all disconnects are required to be lockable. The ones that are will have a reference to 110.25, unless putting that reference was missed when the did the 2014 code.

In general if the disconnect is within sight from the equipment, the NEC does not require the disconnect to be lockable.


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## Carultch (May 14, 2013)

varmit said:


> Code section 240.21 (C) (1) would not allow this as this is a three phase wye transformer.
> 
> Yes, 25 feet would be the limit without secondary over current protection.
> 
> Also, 450.14 requires a primary disconnect at the transformer.



Only if fault currents are guaranteed to align across corresponding windings on the primary/secondary, can you let the secondary be protected exclusively by the primary OCPD.

Examples would be single phase transformers, and delta-to-delta transformers.

If you have a WYE system on either side, then fault currents from two windings on the primary can gang up onto one winding on the secondary. The primary OCPD cannot "see" this happen, and therefore OCPD is required on both sides.


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