450.3(B) multiple secondaries

[lielec11]

So I have a situation where we have a 208V-480V step-up transformer rated 750kVA. On the secondary side the EOR designed it with three (3) OCPDs, 300A, 400A, and 800A. Based on table 450.3(B), including the notes, you are only allowed multiple OCPDs if the total rating of them does not exceed the value for a single device.

750kvA @ 480V = 902A x 1.25 = 1127A ~1200A.

300A + 400A + 800 = 1500A >> 1200A

To me this is a code violation but the DOB missed it in their review and "approved" it. Am I misinterpreting the code here?

 

[infinity]

750kvA @ 480V = 902A x 1.25 = 1127A ~1200A.

Couldn't the bold be up to 250%?

 

[lielec11]

Couldn't the bold be up to 250%?

I read it as the 250% only applies to the primary side OCPD.

 

[jim dungar]

It depends on the value of your primary OCPD. If you stay to no more than 125%, you can ignore any of the secondary protection requirements.

 

[jim dungar]

Couldn't the bold be up to 250%?

The 480V is the secondary side so it is limited to 125%, if the primary is larger than 125%.

 

[infinity]

I read it as the 250% only applies to the primary side OCPD.

I think that you're correct I was just going my memory which is why I got it wrong.

 

[lielec11]

It depends on the value of your primary OCPD. If you stay to no more than 125%, you can ignore any of the secondary protection requirements.

This is what I was looking for. The primary side is currently 3000A, which is greater than 125%. So that would need to change in order to meet code as is, IMO.

Edit: Unless 750kVA @ 208V = 2083A x 1.25 = 2604A .. and then rounding 2604A up to 3000A is ok as it's technically the "next standard size". So.... does it meet code as is?

 

[wwhitney]

Edit: Unless 750kVA @ 208V = 2083A x 1.25 = 2604A .. and then rounding 2604A up to 3000A is ok as it's technically the "next standard size". So.... does it meet code as is?

Seems pretty clearly correct to me.

Cheers, Wayne