CQD Spotlight features questions and answers from NECA and ELECTRICAL CONTRACTOR’s Code Question of the Day program. Whether you’re a seasoned contractor, an apprentice or simply a National Electrical Code enthusiast, you’ll gain knowledge with a nod to the legacy of Charles M. “Charlie” Trout, a true NEC legend

From the archives—Nov. 14, 2024

Is there anything in the NEC that allows for four parallel aluminum conductors to be converted to three parallel copper conductors using an insulated “Polaris” type tap inside of a switchboard to accommodate the lug configuration on a circuit breaker? I don’t believe there is anything that allows this, but I want to make sure I am not overlooking something.

Thanks for the great question. Section 310.10(H) gives us the rules for ungrounded and grounded conductors installed in parallel. The five criteria apply to each parallel set:

1. Must be the same length
2. Consist of the same conductor material
3. Be the same size in circular mil area
4. Have the same insulation type
5. Be terminated in the same manner

The code permits the tapping and splicing of paralleled conductors; what you are describing is essentially a splice. The only restriction would be that termination length is consistent by paralleled set before and after the termination block.

For example:

• A-phase: Could be 4-3/0 aluminum conductors installed end to end, the same length unspliced.
• B-phase: Could be 4-3/0 aluminum conductors all the same length terminated on a Polaris block (spliced) to 3-2/0 copper conductors of the same length and terminated at the circuit breaker. 
• C-phase: Could be 4-3/0 aluminum conductors installed end to end, the same length unspliced.
• Neutral: Could be 4-3/0 aluminum conductors installed end to end, the same length unspliced.

From the archives—Aug. 6, 2025

Are barriers needed in a switchboard to separate the fused and nonfused conductors? My feeling is that the gutter space in a switchboard is not raceway and not subject to NEC 230.7 per the definitions in Article 100.

You are correct. Service conductors are not allowed in the same service raceway or service cable with other conductors as stated in Section 230.7. The space within a switchboard is not a cable or raceway. Consult the cable and raceway type definitions in Article 100, especially the definition for raceway.

From the archives—April 19, 2024

I recently failed an inspection because one of the feeder panels was not rated for the available fault current. The service disconnect ahead of all the feeder panels is a circuit breaker with a 65-kA fault-current rating, which is much higher than the 33 kA of fault-current based on the utility provided information. Why do I now need to have a higher fault-current rating at the feeder panels? Doesn’t the service disconnect circuit breaker provide this protection?

Available fault-current on an electrical system does not end at the service disconnect; it is present at various levels throughout the entire electrical system. Keeping this in mind, Section 110.9 requires equipment intended to interrupt current at fault levels to have an interrupting rating equal to the fault-current available at the equipment.

Additionally, Section 110.10 requires various elements of an electrical circuit (i.e., OCPD) to be sufficiently rated to handle the amount of available fault-current present at the point of the system where it is installed so that during a fault condition the equipment does not get extensively damaged while the fault is clearing. 

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