Transformer tap

[hhsting]

I have two sets of secondary conductors from 75kva three phase 480v to 208/120v feeding two panels. Each panel main circuit breaker is 225A. So 225x2 = 450a which is 216% of transformer secondary full load amps.

The primary breaker is sized within 125% of full load amps.

Customer says transformer is protected by primary breaker. No need for secondary breakers at all in terms of transformer protection. The secondary breakers provided for secondary conductor and in accordance with tap rules. The secondary two sets feeding panels demand load is less than 75kva rating now.

The demand load of both panels is less than transformer 75kva rating at present but can exceed if in future they add load to panels to exceed that of the 75kva transformer since btoh panels have room and can add in future.

Is the above allowed in code?

 

[jim dungar]

As described, your installation meets the code requirements of articles 240, 408, and 450.

 

[hhsting]

As described, your installation meets the code requirements of articles 240, 408, and 450.

Yes but what about the part where demand load can exceed transformer capacity in future?

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[jim dungar]

Yes but what about the part where demand load can exceed transformer capacity in future?

The NEC does not address the sizing of transformers.

 

[hhsting]

The NEC does not address the sizing of transformers.

So any transformer secondary conductors and secondary side panelboard size can be big as one wants, no limit so as long as the nec 2014 articles 450, 240.21 are met?
Nothing in code to prevent overloading the transformer.

 

[jim dungar]

So any transformer secondary conductors and secondary side panelboard size can be big as one wants, no limit so as long as the nec 2014 articles 450, 240.21 are met?

Yes.

 

[kwired]

The NEC does not address the sizing of transformers.

It does address overcurrent protection of transformers though. I don't see anything that allows 216% protection of this secondary, I do see it can be 125%, then allows next higher standard size overcurrent device.

 

[david luchini]

It does address overcurrent protection of transformers though. I don't see anything that allows 216% protection of this secondary, I do see it can be 125%, then allows next higher standard size overcurrent device.

I see that the secondary protection is allowed to be "not required."

 

[kwired]

OK, note 2 - where secondary protection is required.... where is it required?

What protects a multiwire secondary should you have severe imbalance if you have primary only protection?

 

[jim dungar]

OK, note 2 - where secondary protection is required.... where is it required?

Secondary protection is required when the primary protection exceeds the table value for primary protection only, such as 125% for a 480V primary and 208V secondary.

 

[hhsting]

I read the following post which points to NEC 2014 Article 110.3(B) if manufacturer of the transformers allows it use to be way over rating then ok if not then no

https://www.google.com/url?sa=t&sou...AzATegQICRAI&usg=AOvVaw1pzS18sdlfrnyt5FAtoDRO


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[david luchini]

I read the following post which points to NEC 2014 Article 110.3(B) if manufacturer of the transformers allows it use to be way over rating then ok if not then no

https://www.google.com/url?sa=t&sou...AzATegQICRAI&usg=AOvVaw1pzS18sdlfrnyt5FAtoDRO


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110.3(B) doesn't say what most people think it says.

 

[hhsting]

110.3(B) doesn't say what most people think it says.

Dont follow

Nec 2014 Article 110.3(B) says:

Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.



The 75kva transformer manufacturer instructions says do not load beyond 75kva then installation which does have potential to go beyond 75kva not comply per nec 2014 110.3(B). Am I missing something?

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[jim dungar]

I read the following post which points to NEC 2014 Article 110.3(B) if manufacturer of the transformers allows it use to be way over rating then ok if not then no

https://www.google.com/url?sa=t&sou...AzATegQICRAI&usg=AOvVaw1pzS18sdlfrnyt5FAtoDRO

Every manufacturer I know of wants to know your loading profile, ambient temperature, cooling, and desired life before they will tell you if the chosen transformer can be used. It is all about the internal heat build up and removal in the core and coils.

 

[david luchini]

Dont follow

Nec 2014 Article 110.3(B) says:

Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.



The 75kva transformer manufacturer instructions says do not load beyond 75kva then installation which does have potential to go beyond 75kva not comply per nec 2014 110.3(B). Am I missing something?

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Listing and labeling don't involve the manufacturer.

 

[hhsting]

Listing and labeling don't involve the manufacturer.

Ok so

The 75kva listed or labeled transformer instructions says do not load beyond 75kva then installation which does have potential to go beyond 75kva not comply per nec 2014 110.3(B).


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[david luchini]

Ok so

The 75kva listed or labeled transformer instructions says do not load beyond 75kva then installation which does have potential to go beyond 75kva not comply per nec 2014 110.3(B).


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Do you know of any transformer that is listed with those conditions?

 

[hhsting]

Do you know of any transformer that is listed with those conditions?

The other post points to UL listing.

Besides manufacturer instruction say max loading then who would go against it and load more than max kva. AHJ cannot say anything about manufacturer instruction?

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[david luchini]

The other post points to UL listing.

Besides manufacturer instruction say max loading then who would go against it and load more than max kva. AHJ cannot say anything about manufacturer instruction?

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Do you know of any transformer with a UL listing or with manufacturers instructions that says you cannot load it beyond it's rated kVA?

It may exist, but I've never seen a transformer with that type of instructions.

 

[hhsting]

Do you know of any transformer with a UL listing or with manufacturers instructions that says you cannot load it beyond it's rated kVA?

It may exist, but I've never seen a transformer with that type of instructions.

What is the purpose of primary breaker? In theory would not the primary breaker if sized 125% protect the transformer from overloads?

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