Transformer Secondary Conductors, 240.21(C)

[Isaiah]

Client has an 300kVA power transformer, 3Ph 2400-480V (installed outdoors) with secondary conductors that terminate directly onto switchrack bus, i.e. "A" (primary windings are protected with a properly sized, fused disconnect switch). Switchrack A feeds a 100HP motor and a sub-switchrack, i.e. "B" that has a 200AT/250AF MCB protecting it. It seems the Xfmr secondary windings are protected per 450.3(A) but not sure about the xfmr secondary conductors per 240.21(C)(4).

 

[david luchini]

It seems the Xfmr secondary windings are protected per 450.3(A) but not sure about the xfmr secondary conductors per 240.21(C)(4).

The secondary conductors are not properly protected per 240.21(C)(4), Perhaps one of the other sections of 240.21(C) applies.

 

[Isaiah]

Is it possible the xfmr secondary conductors to Swrk "A" are protected by the 200AT MCB on Swrk "B"?

 

[jim dungar]

The secondary conductors are not properly protected per 240.21(C)(4), Perhaps one of the other sections of 240.21(C) applies.

But they may be protected using 240.92(C), if this installation is considered a Supervised Industrial Installation and the systems involved are feeding manufacturing or process

 

[Isaiah]

It's a process application (refinery) and is considered to be supervised, but I am not seeing the necessary criteria to meet 240.92(C)(1), (2) and (3).

 

[Dale001289]

Table 450.3(A), Note 2 allows up to 6 operable disconnects as long as the sum of their ratings don't exceed that allowed by the secondary protective device required.
For a 300kVA Xfmr, that would be 360A x 1.25 = 450A. Looks to me you only have a 150A MCP and a 200A?, thermal mag CB....but its very difficult to see on your screen shot
The part that may be questionable is if they're actually "grouped in one location". That's subjective language, but the intent is they're supposed to be grouped in close proximity to one another, not several feet away from each other. But, that would be the AHJs call.

.

 

[Isaiah]

Table 450.3(A), Note 2 allows up to 6 operable disconnects as long as the sum of their ratings don't exceed that allowed by the secondary protective device required.
For a 300kVA Xfmr, that would be 360A x 1.25 = 450A. Looks to me you only have a 150A MCP and a 200A?, thermal mag CB....but its very difficult to see on your screen shot
The part that may be questionable is if they're actually "grouped in one location". That's subjective language, but the intent is they're supposed to be grouped in close proximity to one another, not several feet away from each other. But, that would be the AHJs call.

.

I thought article 450 was only to protect the transformer windings, not the secondary conductors. Also, they are not grouped together. They are at least 150 feet apart.

 

[david luchini]

I thought article 450 was only to protect the transformer windings, not the secondary conductors. Also, they are not grouped together. They are at least 150 feet apart.

You are correct, 450 is for transformer protection and 240 is for conductor protection. Can't actually read your posted image, but it doesn't seem like it would comply with 240.92 either.

 

[Isaiah]

You are correct, 450 is for transformer protection and 240 is for conductor protection. Can't actually read your posted image, but it doesn't seem like it would comply with 240.92 either.

Thanks David. I also believe the secondary is not protected per 240.92.

 

[Dale001289]

Thanks David. I also believe the secondary is not protected per 240.92.

I thought the 2ndary would be ('sort of') protected under section 240.21(C )(4), but after looking at it again, I'd have to agree with you/David. One has to assume the CB to the motor is a MCP and provides NO thermal protection where the cable ties to the bus. That leaves the 200A MCB to protect both cables, which it cannot do due to location in circuit, therefore the transformer secondary conductors are by default, also inadequately protected.