25 foot XFMR secondary conductors 240.21(3)

[Isaiah]

If my transformer secondary conductors are 25’ or less to the switchboard, do I really need a MCB? Can I use 6 disconnects in lieu of the Main if all other conditions are met?


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[ActionDave]

No. You have to land the secondary in a single disconnect. You could have six sets of secondary conductors out of the transformer to six disconnects.

 

[Isaiah]

No. You have to land the secondary in a single disconnect. You could have six sets of secondary conductors out of the transformer to six disconnects.

This shows no MCB is needed


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[wwhitney]

No. You have to land the secondary in a single disconnect.

That's true for 240.21(C)(6) but doesn't appear to be true for 240.21(C)(3), which I understand the subject to be referring to.

Cheers, Wayne

 

[ActionDave]

That's true for 240.21(C)(6) but doesn't appear to be true for 240.21(C)(3), which I understand the subject to be referring to.

Cheers, Wayne

You have a point. I never got to use that section before.

View attachment 2569550
This shows no MCB is needed


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Might be legit. Do you meet all the criteria?

(3) Industrial Installation Secondary Conductors Not Over 7.5 m (25 ft) Long
For the supply of switchgear or switchboards in industrial installations only, where the length of the secondary conductors does not exceed 7.5 m (25 ft) and complies with all of the following:
Conditions of maintenance and supervision ensure that only qualified persons service the systems.
The ampacity of the secondary conductors is not less than the secondary current rating of the transformer, and the sum of the ratings of the overcurrent devices does not exceed the ampacity of the secondary conductors.
All overcurrent devices are grouped.
The secondary conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.

 

[Isaiah]

That's true for 240.21(C)(6) but doesn't appear to be true for 240.21(C)(3), which I understand the subject to be referring to.

Cheers, Wayne

I should have mentioned I was looking at the 2017 NEC


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[Isaiah]

You have a point. I never got to use that section before.

Might be legit. Do you meet all the criteria?

(3) Industrial Installation Secondary Conductors Not Over 7.5 m (25 ft) Long
For the supply of switchgear or switchboards in industrial installations only, where the length of the secondary conductors does not exceed 7.5 m (25 ft) and complies with all of the following:
Conditions of maintenance and supervision ensure that only qualified persons service the systems.
The ampacity of the secondary conductors is not less than the secondary current rating of the transformer, and the sum of the ratings of the overcurrent devices does not exceed the ampacity of the secondary conductors.
All overcurrent devices are grouped.
The secondary conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.

Yes sir. The installation would meet all this criteria.


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[augie47]

What about 408.36 ???
408.36 Overcurrent Protection. In addition to the requirement of 408.30, a panelboard shall be protected by an overcurrrent protective device having a rating not greater than that of the panelboard. This overcurrent protective device shall be located within or at any point on the supply side of the panelboard.

 

[ron]

It is tough to comply with Note 2 in Table 450.3(B)

 

[david luchini]

It is tough to comply with Note 2 in Table 450.3(B)

View attachment 2569559

Provide primary only protection

 

[don_resqcapt19]

What about 408.36 ???
408.36 Overcurrent Protection. In addition to the requirement of 408.30, a panelboard shall be protected by an overcurrrent protective device having a rating not greater than that of the panelboard. This overcurrent protective device shall be located within or at any point on the supply side of the panelboard.

That only applies to panelboards, it does not apply to switchboards or switchgear. The OP specified a switchboard.

 

[augie47]

That only applies to panelboards, it does not apply to switchboards or switchgear. The OP specified a switchboard.

Thanks...
Never noticed that distinction

 

[Isaiah]

That only applies to panelboards, it does not apply to switchboards or switchgear. The OP specified a switchboard.

That is correct Don. This is a switchgear application


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[zooby]

You have a point. I never got to use that section before.

Might be legit. Do you meet all the criteria?

(3) Industrial Installation Secondary Conductors Not Over 7.5 m (25 ft) Long
For the supply of switchgear or switchboards in industrial installations only, where the length of the secondary conductors does not exceed 7.5 m (25 ft) and complies with all of the following:
Conditions of maintenance and supervision ensure that only qualified persons service the systems.
The ampacity of the secondary conductors is not less than the secondary current rating of the transformer, and the sum of the ratings of the overcurrent devices does not exceed the ampacity of the secondary conductors.
All overcurrent devices are grouped.
The secondary conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.

man...that second condition is a tough one if I am reading that correctly. I just happen to be floating this idea here but were are not true industrial and I believe a fused disco would help ( here ) with sccr.