Secondary Protection on transformers
- Thread starter mbhorton
- Start date
- Status
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Keep in mind that there are four separate things that all need protection from overcurrent.
1. Transformer primary windings. They would be protected by the primary OCPD.
2. Transformer secondary windings. In one specific circumstance, and your installation does not fit that circumstance, you do not need separate OCPD for the secondary. See table 450.3(A).
3. Secondary conductors from the transformer to the panel it serves. In limited circumstances, and your installation is not one of them, they can be protected by the primary OCPD. See 240.21(C)(1). Otherwise, you need an OCPD at the transformer location or within the locations allowed by 240.21(C).
4. The panel(s) served by the transformer. They must be protected by an OCPD either integral to the panel or located upstream.
Welcome to the forum.
1. Transformer primary windings. They would be protected by the primary OCPD.
2. Transformer secondary windings. In one specific circumstance, and your installation does not fit that circumstance, you do not need separate OCPD for the secondary. See table 450.3(A).
3. Secondary conductors from the transformer to the panel it serves. In limited circumstances, and your installation is not one of them, they can be protected by the primary OCPD. See 240.21(C)(1). Otherwise, you need an OCPD at the transformer location or within the locations allowed by 240.21(C).
4. The panel(s) served by the transformer. They must be protected by an OCPD either integral to the panel or located upstream.
Welcome to the forum.
dana1028
Senior Member
- Location
- San Francisco Bay area
Can only speak from my own experience.
The types of installations that I have seen have supplied condominiums, condo/multi-use [condos with some retail space on 1st level], or apartments.
The secondaries have come in underground [thus considered outside the building] to a vault room and have entered the bottom of switch gear with a main disco sized for the total load.
From this main switch gear I have seen multiple feeders sized at 600-800A which feed banks of meters...each meter has its own disco which feeds the individual units. All the meter/discos have been in the same vault as the service equipment.
The types of installations that I have seen have supplied condominiums, condo/multi-use [condos with some retail space on 1st level], or apartments.
The secondaries have come in underground [thus considered outside the building] to a vault room and have entered the bottom of switch gear with a main disco sized for the total load.
From this main switch gear I have seen multiple feeders sized at 600-800A which feed banks of meters...each meter has its own disco which feeds the individual units. All the meter/discos have been in the same vault as the service equipment.
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