Are the wires feeding a transformer primary considered feeders or branch circuits?

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rojodo3030

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I was having a conversation with someone on my job and we ran into an unspecified area in the Nec (2023). The question is are the wires feeding the primary of a transformer (served from a switch board) considered branch circuits or feeders? Transformers have primary ocpd... so that, for the sake of argument, is your final ocpd. The secondary is a separately derived system, so that leaves the primary windings to be the final part of the system. Nec 2023 art 100 has 5 types of branch circuits. The one that stood out to me was individual branch circuits. This states that there are branch circuits that supply utilization equipment. I would say a transformer isn't utilization equipment because it doesn't use electrical energy as power but only to transform voltage (minus eddy currents and hysteresis). Am I missing something here or does the code just leave this out?
 
What do you mean, "Transformers have primary ocpd..."? Feeder vs. Branch circuit is pretty straight forward. If the wires terminate at or before overcurrent protection, they are feeders. If they feed an outlet, they are branch circuits. Two things. Make sure you read and understand the definition of an outlet as the point between the building wiring and utilization equipment, and that overcurrent protection that is part of the equipment is not overcurrent protection as required for feeders.
 
Welcome to the forum.

Interesting question. I would say that the supply to a single transformer primary is a branch circuit.
 
Are you saying there is a built in primary overcurrent protective device in the transformer? If so that overcurrent protective device would be considered supplemental protection and then the load would be a branch circuit. IMO...

It is an interesting question and I am not sure it is addressed in the NEC
 
My general understanding is that the circuit supplying the primary of a transformer is a feeder and not a branch circuit because the transformer is _not_ utilization equipment.

I see the point however that for a transformer you have a circuit supplied by OCPD and that circuit terminates at the single transformer.

I support this position as follows:
1) The transformer is not utilization equipment, but rather an intermediate on the way to the utilization equipment.
2) Some types of transformers allow the primary OCPD to protect the secondary conductors (2 wire single phase and 3 wire delta:delta transformers). Consider a circuit which is OCPD->primary conductors->transformer->secondary conductors->panelboard. The secondary conductors are clearly feeder conductors protected by the primary OCPD. That says to me that the primary conductors are also feeder conductors

Aside: Imagine a 2 wire transformer (primary OCPD protects secondary), where the transformer is small enough to serve a single piece of utilization equipment, with no secondary OCPD needed. Wouldn't that make the entire circuit (primary, transformer, secondary, and outlet) a branch circuit?
 
Strathead said:
What do you mean, "Transformers have primary ocpd..."? Feeder vs. Branch circuit is pretty straight forward. If the wires terminate at or before overcurrent protection, they are feeders. If they feed an outlet, they are branch circuits. Two things. Make sure you read and understand the definition of an outlet as the point between the building wiring and utilization equipment, and that overcurrent protection that is part of the equipment is not overcurrent protection as required for feeders.
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I see from other posts that my response is not as cut and dry as I first thought. I agree, that a transformer isn't utilization equipment.
winnie said:
My general understanding is that the circuit supplying the primary of a transformer is a feeder and not a branch circuit because the transformer is _not_ utilization equipment.

I see the point however that for a transformer you have a circuit supplied by OCPD and that circuit terminates at the single transformer.

I support this position as follows:
1) The transformer is not utilization equipment, but rather an intermediate on the way to the utilization equipment.
2) Some types of transformers allow the primary OCPD to protect the secondary conductors (2 wire single phase and 3 wire delta:delta transformers). Consider a circuit which is OCPD->primary conductors->transformer->secondary conductors->panelboard. The secondary conductors are clearly feeder conductors protected by the primary OCPD. That says to me that the primary conductors are also feeder conductors

Aside: Imagine a 2 wire transformer (primary OCPD protects secondary), where the transformer is small enough to serve a single piece of utilization equipment, with no secondary OCPD needed. Wouldn't that make the entire circuit (primary, transformer, secondary, and outlet) a branch circuit?
Click to expand...
After realizing my mistake, I think you are 100%. From a code perspective in this instance, the transformer is no different than a switch.
 
All conductors and bus bars between the load side of the service OCPD and the breaker that directly feeds the utilization equipment are feeders.
The branch circuit starts at the load side of the final OCPD that directly feeds the equipment.

I guess if you have the rare case where the primary OCPD is permitted to protect the transformer primary winding, transformer secondary winding, the secondary conductors and the load, then all of the conductors, on the load side of the primary OCPD would be branch circuit conductors, but other than that very limited case, the primary and secondary conductors for a transformer will always be feeder conductors.
 
Strathead said:
What do you mean, "Transformers have primary ocpd..."? Feeder vs. Branch circuit is pretty straight forward. If the wires terminate at or before overcurrent protection, they are feeders. If they feed an outlet, they are branch circuits. Two things. Make sure you read and understand the definition of an outlet as the point between the building wiring and utilization equipment, and that overcurrent protection that is part of the equipment is not overcurrent protection as required for feeders.
Click to expand...
Just as you need to understand that an OCPD is required for transformers. They are installed separately from transformers. They can be installed within sight of a transformer, or at a remote location (where the OCPD would then need to be marked on the transformer as to where the disconnecting means is, NEC 2023 450.14) This means that the wires feeding the transformer can be branch circuits, or feeders, depending on your interpretation of what constitutes 'Utilization Equipment'. Read through Art. 100... there are 5 different types of branch circuits. A transformer is NOT an appliance branch circuit, general purpose branch circuit, motor branch circuit, or multi-wire branch circuit. This leaves one type of branch circuit left: an individual branch circuit, which defines itself as a branch circuit that supplies one piece of utilization equipment. So, the question I ask now is, can the wires going to a transformer by definition BE a branch circuit? The answer is yes, if transformers are considered utilization equipment. Flip to utilization equipment: Equipment that utilizes electric energy for electronic (not a transformer), electromechanical (no), chemical (no), heating (no), lighting (no), or similar purposes (hmmm, maybe, but I would say no). I would say no because a transformer doesn't UTILIZE electric energy, it just changes the voltage. You could argue hysteresis and eddy currents but that isn't utilizing, that is just a side effect. That is where I am confused by the code. It is incomplete in its specification.
 
LarryFine said:
Welcome to the forum.

Interesting question. I would say that the supply to a single transformer primary is a branch circuit.
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I thought the same thing... but then I looked at the different types of branch circuits: appliance (no), multiwire (no), motor (no), general purpose (no), individual... maybe. Individual branch circuits feed one piece of utilization equipment which is equipment that utilizes electric energy for electronic (I assume this means computers, not electrical), electromechanical (no), chemical (no), heating (no), lighting (no), or similar purposes (maybe, but I would say no). I'd say no to that because a transformer doesn't UTILIZE energy in the first place. it just changes voltage. You could argue that it utilizes energy in the process of its operation via hysteresis and eddy currents but that energy isn't being used by anything, its just an occurrence from transforming voltage. By this logic, I would say they are feeders.
 
don_resqcapt19 said:
All conductors and bus bars between the load side of the service OCPD and the breaker that directly feeds the utilization equipment are feeders.
The branch circuit starts at the load side of the final OCPD that directly feeds the equipment.

I guess if you have the rare case where the primary OCPD is permitted to protect the transformer primary winding, transformer secondary winding, the secondary conductors and the load, then all of the conductors, on the load side of the primary OCPD would be branch circuit conductors, but other than that very limited case, the primary and secondary conductors for a transformer will always be feeder conductors.
Click to expand...
Correct, and I agree that they are feeders. I am curious why you don't think transformers are utilization equipment. The primary conductors are the final load in the system, and they are protected by OCPD. By that logic they could be branch circuits, no?
 
Dennis Alwon said:
Are you saying there is a built in primary overcurrent protective device in the transformer? If so that overcurrent protective device would be considered supplemental protection and then the load would be a branch circuit. IMO...

It is an interesting question and I am not sure it is addressed in the NEC
Click to expand...
No I am saying that transformers require OCPD on their primary windings. The primary windings are the last load in that given system. There is OCPD, and a final load in a system. Logically, if transformers are utilization equipment, the wires feeding them could be branch circuits.
 
winnie said:
My general understanding is that the circuit supplying the primary of a transformer is a feeder and not a branch circuit because the transformer is _not_ utilization equipment.

I see the point however that for a transformer you have a circuit supplied by OCPD and that circuit terminates at the single transformer.

I support this position as follows:
1) The transformer is not utilization equipment, but rather an intermediate on the way to the utilization equipment.
2) Some types of transformers allow the primary OCPD to protect the secondary conductors (2 wire single phase and 3 wire delta:delta transformers). Consider a circuit which is OCPD->primary conductors->transformer->secondary conductors->panelboard. The secondary conductors are clearly feeder conductors protected by the primary OCPD. That says to me that the primary conductors are also feeder conductors

Aside: Imagine a 2 wire transformer (primary OCPD protects secondary), where the transformer is small enough to serve a single piece of utilization equipment, with no secondary OCPD needed. Wouldn't that make the entire circuit (primary, transformer, secondary, and outlet) a branch circuit?
Click to expand...
I agree with your positions. A transformer doesn't utilize electrical energy (minus hysteresis and other losses of power) but transformers electric energy. As for the scenario you provided, by my own logic I would say that would be a branch circuit.
 
rojodo3030 said:
Correct, and I agree that they are feeders. I am curious why you don't think transformers are utilization equipment. The primary conductors are the final load in the system, and they are protected by OCPD. By that logic they could be branch circuits, no?
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Transformers are not a load.
 
Just my $0.02 worth:

I see it as a branch circuit because the secondary (SDS) starts a new "system" complete with new electrode requirements, etc.

To me, the transformer's primary is a load. The primary source from the panel to the primary is a single circuit from that panel's perspective.

The primary circuit doesn't change depending on whether the secondary supplies a single load (circuit) or a panel with many loads (feeder).
 
A branch circuit is between the final overcurrent device and the outlet(s). A transformer is not an outlet, so it doesn't create a branch circuit. Notwithstanding that primary and secondary conductors are different conductors, the Article 100 definitions don't get specific on whether the conductors 'between' various points have to be electrically continuous. The primary and secondary conductors on each side of a transformer are still physically and schematically 'between' the power source and any either a) branch circuit overcurrent device(s), in which case they are feeders, or b) a branch circuit overcurrent device and an outlet(s). So whether or not the conductors in and out of a transformer are feeders or branch circuit conductors depends entirely on the same things as in any other circuit, and the presence of a transformer makes no difference.
 
Like the feeder-vs-circuit debate about the conductors between an A/C circuit breaker and the disconnect.
 
As far as the conductors between a breaker and an AC disconnect if the AC disconnect has fuses or breaker in it the the conductors between the panel and the ac disconnect are a feeder. If the AC disconnect is unfused the everything is a branch circuit IMHO.

As far as the transformer goes it's a feeder because the transformer is not utilization equipment and has no outlets
 
I'm going to turn the question around: What difference does it make if the primary conductors are considered a feeder vs a branch circuit?

Do different rules come into play which would mean a different installation, or do you end up with the exact same requirements other than the name?
 
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