Transformer/Panel Wire Sizing/Conduit Fill

[infinity]

What Augie said. Back to the drawing board.

 

[augie47]

Sorry, can I ask you what code section this is so I can read about it more.

So the Panel can be sized for 600AMP but the total demand load still needs to be around 400AMP only

As for Transformer protection 450.3
As for conductor size (secondary) 240.21(C)

 

[Electricalhelp]

As for Transformer protection 450.3
As for conductor size (secondary) 240.21(C)

Based on Table 450.3(B)
For the 112.5 kVA, I get the primary protection to be 135AMP x 1.25 = 169AMP, the next size up is 175AMP.

If the breaker size on the primary is only 150 AMP, how does this meet the Primary protection for the secondary to have a 600 AMP Panel.

Since there is a Primary and Secondary protection, do I use 250% for primary and 125% for secondary protection [Table 450.3(B)]

 

[augie47]

You somewhat answered your own question
The transformer can be protected by primary protection only if that protection does nor exceed 125% pf the primary current.
In your case that would be 169 amps and the breaker is 150 amp so it is within the 125% allowable range.
It allows a 175(next size up) but doesn't preclude any lesser value.
Anything less than 175 and the transformer is considered to be protected.

You can exceed that 125% primary and go up to 250% but, if you do so, the secondary would need to be protected at 125%

 

[Electricalhelp]

You can exceed that 125% primary and go up to 250% but, if you do so, the secondary would need to be protected at 125%

I wouldn't have interrupt the table that way. I would have make the primary 250% and the secondary be protected by 125%
Meaning my OCP device would have been a lot larger if I have design this project

When doing so, it will only need protection so it does not exceed 250%. So a 150AMP breaker will still work for the primary protection and there is a secondary protection of 125%.

 

[augie47]

IF you have 125% primary protection, the secondary can be any value

 

[Knightryder12]

You somewhat answered your own question
The transformer can be protected by primary protection only if that protection does nor exceed 125% pf the primary current.
In your case that would be 169 amps and the breaker is 150 amp so it is within the 125% allowable range.
It allows a 175(next size up) but doesn't preclude any lesser value.
Anything less than 175 and the transformer is considered to be protected.

You can exceed that 125% primary and go up to 250% but, if you do so, the secondary would need to be protected at 125%

From what I have read in the code, (240.21(C)(1)), on this type of transformer (delta to wye)you will always be required to have secondary protection.
240.21(C)(1) states that "Single phase (other than 2-wire) and multiphase (other than delta-delta, 3-wire) transformer secondary conductors are NOT considered to be protected by the primary overcurrent protective device".

 

[augie47]

I was referencing Art 450 Transformer protection only....
Trying not to muddy the water
I agree Art 240 requires secondary protection and Art 408 requires line side protection on the panels but I was attempting to shed light on Art 450 without going further.

(you are correct...I should have prefaced my comment with 'as far as Art 450 is concerned' )

 

[Electricalhelp]

When combing both Art 240 and Art 450, all transformer need primary and secondary protection.

 

[Knightryder12]

I was referencing Art 450 Transformer protection only....
Trying not to muddy the water
I agree Art 240 requires secondary protection and Art 408 requires line side protection on the panels but I was attempting to shed light on Art 450 without going further.

(you are correct...I should have prefaced my comment with 'as far as Art 450 is concerned' )

I get your point. But what you gave to the OP was not a correct response as you can clearly see that his question was about a transformer that requires secondary protection.

 

[infinity]

I get your point. But what you gave to the OP was not a correct response as you can clearly see that his question was about a transformer that requires secondary protection.

Is it the transformer itself that requires the secondary protection or is it the secondary conductors that require the protection?

 

[jim dungar]

When combing both Art 240 and Art 450, all transformer need primary and secondary protection.

Not really.

Panel boards need to be protected per 408. This protection may be remote from the panel.

Transformer secondary conductors need to be protected per 240. This protection is irrespective of the transformer size.

The transformer primary must be protected per 450. The primary protection size is dependent on if appropriately sized secondary side protection is present.

Any protective device can provide protection under several NEC sections.

I usually recommend to start selecting equipment at the load and work back towards the source.