Transformer Secondary Protection

[Ed Battle]

NFPA 70 Article 240 Describes Overcurrent Protection
Article 240.4 states that conductors shall be protected against overcurrent in accordance with their ampacities.
There are several exceptions to this rule.
One is article 240.4 (F) for Transformer Secondary Conductors ? There are two exceptions listed in this article:
1. Where the transformers primary and secondary are both connected delta-delta.
2. Single-phase two wire primary and two wire secondary

Article 240.21 (C) Specifically describes Exceptions to Transformer Secondary Protection.
240.21(C) (4) Allows no protection of a transformer secondary conductors if they are located outside.
SPECIFIC APPLICATION
? 1500 kVA Transformer located outdoors. Primary voltage 25 kV, Secondary Voltage 480
? Transformer is Delta-Connected primary, and WYE-Connected Secondary
? There is Primary protection
? Secondary conductors are approximately 75 feet long, and terminate in a set of fuses rated for their ampacity. (All located outdoors, adequately protected, and accessible.)
Question ?
Are we in violation of the code by not having protection of the secondary conductors between the transformer and the fuses?
Article 240.4 (F) suggests that they are required
Article 240.21 (C) (4) suggests that it is not required

 

[augie47]

240.4(F) states that they shall be protected. It does not state how or where.
They are protected per 240.21(C)(4)

 

[scot120]

240.4(F) states that they shall be protected. It does not state how or where.
They are protected per 240.21(C)(4)

Their is a 75' exception for not having protection . If you exseed that length , are you saying you can put protection past that point ? I don't see a length of the secondary , given in the post .
Correct me if I am not reading it right .

 

[david luchini]

Their is a 75' exception for not having protection . If you exseed that length , are you saying you can put protection past that point ? I don't see a length of the secondary , given in the post .
Correct me if I am not reading it right .

240.21(C)(4) permits "outside" transformer secondary conductors to be any length without protection where the conductors receive their supply. Could be 75', 150' or 1500', etc, as long as ALL the conditions in 240.21(C)(4) are met.

 

[scot120]

240.21(C)(4) permits "outside" transformer secondary conductors to be any length without protection where the conductors receive their supply. Could be 75', 150' or 1500', etc, as long as ALL the conditions in 240.21(C)(4) are met.

Sorry , you're right . If you read in the NEC , it doesn't specify length . l was looking at the post instead of checking in my code book .

 

[Ed Battle]

Sorry , you're right . If you read in the NEC , it doesn't specify length . l was looking at the post instead of checking in my code book .

Where does it state that all conditions of 240.21(C) hav eto be met? I interpret this as any one of the conditions of 240.21(C) can be met to allow no secondary protection

 

[david luchini]

Where does it state that all conditions of 240.21(C) hav eto be met? I interpret this as any one of the conditions of 240.21(C) can be met to allow no secondary protection

I don't see that anyone has suggested that all of the conditions of 240.21(C) have to be met.

 

[don_resqcapt19]

Where does it state that all conditions of 240.21(C) hav eto be met? I interpret this as any one of the conditions of 240.21(C) can be met to allow no secondary protection

I don't think anyone said you have to meet all of the conditions of 240.21(C). You pick the one that fits your installation and use it.

Note that the rules in 240.21(C) only apply to the protection of the secondary conductors. The rules for the protection of the secondary of the transformer are found in 450.3. There can be cases where the conductors are properly protected under one of the rules of 240.21(C), but the transfomer secondary is not protected per the rules of 450.3. You have to provide the required protection of both the transformer secondary winding and the conductors that are connected to the transformer.