What to use

[codequestion]

I have 30kva transformer hung above suspended ceiling. Primary is in electrical room 50 amps breaker. I have disconnecting non fused switch 60 amp next to primary of transformer above celing in sight. Secondary conductor feed panelboard below room. The secondary conductor would require overcurrent protection if more than 10 feet and in case less than 10 feet?

Table 450.3 (b) says not req but 240.21 (C)(2) or (6) says less than 10 feet not req more than 10 feet needs circuit breaker.

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[petersonra]

I have 30kva transformer hung above suspended ceiling. Primary is in electrical room 50 amps breaker. I have disconnecting non fused switch 60 amp next to primary of transformer above celing in sight. Secondary conductor feed panelboard below room. The secondary conductor would require overcurrent protection if more than 10 feet and in case less than 10 feet?

Table 450.3 (b) says not req but 240.21 (C)(2) or (6) says less than 10 feet not req more than 10 feet needs circuit breaker.

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You are required to provide primary and secondary transformer protection. You are ALSO required to provide protection for the primary and secondary conductors.

There is no requirement to have a disconnect on a transformer "within sight".

240.21 is about conductor protection.

450.3 is about transformer protection.

Read carefully what these sections actually say. Like a lot of the code, it is not written to make it easy to understand.

 

[codequestion]

If its 30kva xfmr and primary is 50amps thats 1.25xFLA. So why would secondary be req?

Also 450.14 says disconnecting means shall be in sight other than class 2 or 3 xfmr. So in my case would not apply?

You are required to provide primary and secondary transformer protection. You are ALSO required to provide protection for the primary and secondary conductors.

There is no requirement to have a disconnect on a transformer "within sight".

240.21 is about conductor protection.

450.3 is about transformer protection.

Read carefully what these sections actually say. Like a lot of the code, it is not written to make it easy to understand.

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[petersonra]

Also 450.14 says disconnecting means shall be in sight other than class 2 or 3 xfmr. So in my case would not apply?

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this is what 450.13 says.

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.

If the disconnect is in a remote location it has to be lockable and a marking applied to the xfmr indicating where the disconnect is located. so a disconnect "in sight" just is not a requirement.

 

[petersonra]

If its 30kva xfmr and primary is 50amps thats 1.25xFLA. So why would secondary be req?

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Regarding overcurrent protection

Based on your numbers I am guessing you have a 480V primary 3 phase xfmr. A 50 A CB does indeed protect both the primary and the secondary of the transformer per table 430.5(B). But this provision only protects the transformer and not the conductors.

450.3 Overcurrent Protection.
Informational Note No. 1: See 240.4, 240.21, 240.100, and
240.101 for overcurrent protection of conductors.

240.4(F) allows the xfmr secondary conductors to be protected by the primary ONLY if it is a single phase 2 wire circuit or a delta-delta xfmr. I don't know what you have.

(F) Transformer Secondary Conductors. Single-phase (other
than 2-wire) and multiphase (other than delta-delta, 3-wire)
transformer secondary conductors shall not be considered to
be protected by the primary overcurrent protective device.
Conductors supplied by the secondary side of a single-phase
transformer having a 2-wire (single-voltage) secondary, or a
three-phase, delta-delta connected transformer having a 3-wire
(single-voltage) secondary, shall be permitted to be protected
by overcurrent protection provided on the primary (supply)
side of the transformer, provided this protection is in accordance
with 450.3 and does not exceed the value determined by
multiplying the secondary conductor ampacity by the
secondary-to-primary transformer voltage ratio.

240.21 is about tap conductors. if the secondary conductors are properly protected by the primary protection IAW 240.4(F), they are not tap conductors. If not protected IAW 240.4(F) they are tap conductors and the OCPD has to be within ten feet as noted.

240.100 and 240.11 don't apply here because they are for circuits over 1000V.

 

[codequestion]

I have 480/277v primary to 120/208v secondary. The secondary panel has 100 amps main breaker. Can it not use to protect both secondary xfmr and conductor or would have to provide another ocpd? I assume i would look at 240.21 (c)(2) or (6).

Regarding overcurrent protection

Based on your numbers I am guessing you have a 480V primary 3 phase xfmr. A 50 A CB does indeed protect both the primary and the secondary of the transformer per table 430.5(B). But this provision only protects the transformer and not the conductors.



240.4(F) allows the xfmr secondary conductors to be protected by the primary ONLY if it is a single phase 2 wire circuit or a delta-delta xfmr. I don't know what you have.



240.21 is about tap conductors. if the secondary conductors are properly protected by the primary protection IAW 240.4(F), they are not tap conductors. If not protected IAW 240.4(F) they are tap conductors and the OCPD has to be within ten feet as noted.

240.100 and 240.11 don't apply here because they are for circuits over 1000V.

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[petersonra]

I have 480/277v primary to 120/208v secondary. The secondary panel has 100 amps main breaker. Can it not use to protect both secondary xfmr and conductor or would have to provide another ocpd? I assume i would look at 240.21 (c)(2) or (6).

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The primary OCPD can protect the primary and secondary of the xfmr and the primary conductors but because it is not a delta-delta circuit the secondary conductors are not protected by the primary OCPD. the main in the panelboard can indeed protect both the secondary and the secondary conductors. But the secondary conductors are considered tap conductors so the ten or 25 foot rule applies.

 

[codequestion]

Ten foot rule? 240.21 (c)(2) or 240.21(c)(6)?

The primary OCPD can protect the primary and secondary of the xfmr and the primary conductors but because it is not a delta-delta circuit the secondary conductors are not protected by the primary OCPD. the main in the panelboard can indeed protect both the secondary and the secondary conductors. But the secondary conductors are considered tap conductors so the ten or 25 foot rule applies.

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[petersonra]

Ten foot rule? 240.21 (c)(2) or 240.21(c)(6)?

(C)(2) is the rule when the secondary conductors < 10 feet.

(C)(6) is for secondary conductors < 25 feet.

 

[codequestion]

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[codequestion]

Attached is what I have. Going from left to right 480/27v 3 phase panel, xfmr 60 amp disco primary, 480/120/208 secondary, secondary fused disco and secondary panel.

Secondary fused disconnect downstream panel has 100 amp main breaker. The transformer is hung from ceiling and panel below ceiling. Is the transformer secondary fused disco required per code?

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[don_resqcapt19]

Attached is what I have. Going from left to right 480/27v 3 phase panel, xfmr 60 amp disco primary, 480/120/208 secondary, secondary fused disco and secondary panel.

Secondary fused disconnect downstream panel has 100 amp main breaker. The transformer is hung from ceiling and panel below ceiling. Is the transformer secondary fused disco required per code?

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That is all compliant with the NEC and actually goes beyond what the NEC requires. However plans and specs are part of the contract and must be complied with.

 

[jap]

Attached is what I have. Going from left to right 480/27v 3 phase panel, xfmr 60 amp disco primary, 480/120/208 secondary, secondary fused disco and secondary panel.

Secondary fused disconnect downstream panel has 100 amp main breaker. The transformer is hung from ceiling and panel below ceiling. Is the transformer secondary fused disco required per code?

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All that aside, I'm not used to seeing notes on prints like this...... "Appox. 500'"...... "If secondary conductors are longer than 10'".....
I'm also curious as to why they bumped up the EGC in the flex to the Transformer to #6.

Oh well.

JAP>