Transformer conductor/circuit questions

[Steelhead]

I need some clarification on some things:

A breaker in a subpanel feeding the primary of a transformer - this is considered a branch circuit - correct?

Secondary conductors with no OCPD at their point of supply need to follow 240.21(C) without exception - correct?

These conductors are still "secondary conductors" up to the first OCPD - correct?

So even if you size the secondary conductors at 125% of the transformer secondary current rating you still have to follow 240.21(C) - correct?

In our facility we have a 112KVA transformer feeding a machine with OCP integrated into the disconnect of the machine. The seconday conductors are sized to 125% of the FLA of the transformer and travel about 50 feet to the machine disconnect. My interpretation of the code says this is a violation - correct?

Thanks in advance for your help!

 

[charlie b]

"Yes" to all of your questions.

 

[petersonra]

I need some clarification on some things:

A breaker in a subpanel feeding the primary of a transformer - this is considered a branch circuit - correct?

yes. As long as nothing else is on the circuit and it feeds the transformer primary without going thru some other OCPD. It would be a feeder otherwise.

Secondary conductors with no OCPD at their point of supply need to follow 240.21(C) without exception - correct?

yes

These conductors are still "secondary conductors" up to the first OCPD - correct?
yes

So even if you size the secondary conductors at 125% of the transformer secondary current rating you still have to follow 240.21(C) - correct?
yes

In our facility we have a 112KVA transformer feeding a machine with OCP integrated into the disconnect of the machine. The seconday conductors are sized to 125% of the FLA of the transformer and travel about 50 feet to the machine disconnect. My interpretation of the code says this is a violation - correct?

Thanks in advance for your help!

take a close look at 240.21 (C) (1).

There is some chance it might meet this provision.

 

[Steelhead]

take a close look at 240.21 (C) (1).

There is some chance it might meet this provision.

The transformer is 3 phase wye at the secondary.

Thanks.

 

[david luchini]

A breaker in a subpanel feeding the primary of a transformer - this is considered a branch circuit - correct?

I would think in most cases this would be considered a feeder, not a branch circuit.

 

[charlie b]

I would think in most cases this would be considered a feeder, not a branch circuit.

I disagree. The primary of the transformer is essentially a piece of utilization equipment. There is no additional overcurrent device between the upstream breaker and the transformer's primary windings. The fact that there will be additional overcurrent devices beyond the secondary windings means nothing. At that point, you are into a separately derived system, and you start the concepts of feeders and branch circuits all over again.

 

[Steelhead]

I would think in most cases this would be considered a feeder, not a branch circuit.

Even considering the NEC definition of a branch circuit vs a feeder? I would also consider the primary winding of the transformer the "load".

 

[david luchini]

I disagree. The primary of the transformer is essentially a piece of utilization equipment. There is no additional overcurrent device between the upstream breaker and the transformer's primary windings. The fact that there will be additional overcurrent devices beyond the secondary windings means nothing. At that point, you are into a separately derived system, and you start the concepts of feeders and branch circuits all over again.

We will have to agree to disagree. A transformer does not conform to the Code's definition of "Utilization Equipment."

Even considering the NEC definition of a branch circuit vs a feeder? I would also consider the primary winding of the transformer the "load".

The definition of a Feeder is

All the circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the FINAL branch-circuit overcurrent device.

You cannot, by definition, have a feeder "after" a branch circuit. Nor would I consider a transformer to be the "load." The load is the utilization equipment that is connected to the transformer.

 

[Smart $]

...

You cannot, by definition, have a feeder "after" a branch circuit. Nor would I consider a transformer to be the "load." The load is the utilization equipment that is connected to the transformer.

I agree your interpretation as quoted above. However, it is possible for a load to be supplied by a transformer without any OCPD after the transformer. In these [rare] cases, all conductors after the transformer primary OCPD will be branch circuit conductors.

 

[david luchini]

I agree your interpretation as quoted above. However, it is possible for a load to be supplied by a transformer without any OCPD after the transformer. In these [rare] cases, all conductors after the transformer primary OCPD will be branch circuit conductors.

I agree completely.

 

[Smart $]

...

Secondary conductors with no OCPD at their point of supply need to follow 240.21(C) without exception - correct?

...

In our facility we have a 112KVA transformer feeding a machine with OCP integrated into the disconnect of the machine. ...

If this qualifies as a supervised industrial installation, see 240.92(C).

 

[Steelhead]

If this qualI'llies as a supervised industrial installation, see 240.92(C).

You just might have a point there. I'll have to check out the specifics to see if the install qualifies.