tap rule clarification for less than 25 ft.

[winslowfam]

Our client would like to tap his existing switchboard bus for a new feeder. The switchboard has no more space for additional feeder breakers. My reading of the Tap Rule makes it seem pretty straight forward for taps not more than 25 ft in length, but I wanted to put up this post to see if there is any other possible interpretation. My understanding is that the tap conductors' ampacity must not be less than 1/3 of the rating of the switchboard's main breaker, which is the overcurrent device protecting the feeder conductors (main bus of this switchboard). The problem we are having is that the main breaker is rated 4000A, so any tap we install will require over 1300A of wire...more than we need for our new load.

 

[kwired]

Can you get the tap length down to 10 feet?


What is the plan for next time additional taps would be needed? Maybe you make that 1300 amp tap now and use it again for future loads.

Outdoor taps can be unlimited in length if you can make that work for you.

 

[petersonra]

sometimes putting in a CB or fused switch is less expensive than running the big wire. just depends on how much current you need.

is there anywhere inside the switch gear to install some fuses? some times the way switchboards are made you can actually bolt the fuses right on to the bus. the manufacturer might be of some help in that respect.

 

[winslowfam]

Thanks...something for me to consider. The real problem is that this client has an existing tap for a power factor cap bank that he would like to re-use for feeding his new load..it is less than 25 ft but the conductors and the breaker at the end of the tap are both rated 600A. I've told our client that this is likely not possible to be re-used, but I wanted to check it from every angle first before solidifying that position.

 

[petersonra]

Thanks...something for me to consider. The real problem is that this client has an existing tap for a power factor cap bank that he would like to re-use for feeding his new load..it is less than 25 ft but the conductors and the breaker at the end of the tap are both rated 600A. I've told our client that this is likely not possible to be re-used, but I wanted to check it from every angle first before solidifying that position.

do you need more than 600A?

 

[infinity]

As Kwired asked if you can get the tap down to 10' then you'll only need a minimum of 400 amp conductors. Are these feeder taps or is this a service switchboard?

 

[NetNathan]

You can locate the OCPD at 10' or less under tap rule, then make the rest of the run at OCPD rating.