NEC Tap Conductor

[timm333]

I have a question about tap conductor as per NEC 240.21(B)(5). The service conductor cannot be tapped; however automatic transfer switch (ATS) has service conductor (service lateral) only on the incoming side.

Can the outgoing copper feeder of a service-entrance rated automatic transfer switch (ATS) be tapped as shown in the attached sketch? Thanks

 

[Carultch]

Once you are on the load side of the main service disconnect/OCPD, you no longer call them "service conductors", and they are treated just as any other feeder, rendering this to be a feeder tap.

There is an exception to their sizing algorithm, allowing them to maintain the same size as the service conductors (which take credit for the 83% rule) when they are a direct extension of the service conductors. In your situation, the 83% rule wouldn't apply anyway, given that your service is over 400A.

 

[timm333]

Thanks. Will the sketch (attached) be Ok if the tap conductor (conductor # 1) is placed in steel conduit? Do we also need to put the other conductor (conductor # 2) in the steel conduit?

 

[Carultch]

Thanks. Will the sketch (attached) be Ok if the tap conductor (conductor # 1) is placed in steel conduit? Do we also need to put the other conductor (conductor # 2) in the steel conduit?

For conductor #1:
Depends on if you are following the context rules of the 10 ft tap or the 25 ft tap rule. Given the relative ampacities, you'd probably go with the 10 ft tap rule, so you only need 60A of wire for the tap instead of 200A. The 10 ft tap rule states must be in a raceway, which would exclude a pre-manufactured cable assembly and a cable tray. In otherwords, it would have to be in a wiring structure that fully encloses the conductor, as wireways and wire troughs also count as raceways in addition to conduit & tubing. The 25 ft rule states must be protected from physical damage, which is more open to interpretation about how you choose to build it. Most people would use a raceway anyhow, without thinking about it.

For conductor #2:
Any wiring method appropriate for the environment of the circuit would work. No specific rules apply because it is a tapped feeder, instead of a feeder in general.