240.21(B)5

Status
Not open for further replies.

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
I would like to tap a 100 amp 480V 3 phase feeder to feed a 10HP pump panel that comes with a 30 amp breaker. What is the minimum THHN wire size required?

Am I required to size to the 30 amp breaker? #10?

Or only 125% of my FLA taken from the motor tables? (10HP motor=14 FLA x 125%=17.5 amps) #14?

Thanks.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
240.21(B)(5)(2) requires that the conductors be no smaller than the OCPD.

(2)The conductors terminate at a single circuit breaker or
a single set of fuses that limit the load to the ampacity
of the conductors. This single overcurrent device shall
be permitted to supply any number of additional over-
current devices on its load side.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Yes, as a solution for using #14 instead of #10, which seemed to be the OP'S goal.

He would still need to use #10 tap conductors {10' rule} and then #14 for the pump from there but that would require an additional OCPD at the end of the 10' tap since the control panel will be adjacent to the pump 140' away.
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
The install is all outdoors. I figured it's cheaper to run #10's 150' feet, then install an extra 30A 600V fused 3R disconnect, just to drop down to #14's.
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
He would still need to use #10 tap conductors {10' rule} and then #14 for the pump from there but that would require an additional OCPD at the end of the 10' tap since the control panel will be adjacent to the pump 140' away.

No, he wouldn't need tap #10 tap conductors. The #14 tap would be per 240.21(F) and 430.28(1). He could run #14 taps, 10' or less to an OCPD and then #14 feeder conductors to the pump control panel.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
No, he wouldn't need tap #10 tap conductors. The #14 tap would be per 240.21(F) and 430.28(1). He could run #14 taps, 10' or less to an OCPD and then #14 feeder conductors to the pump control panel.


Would 240.21(F) apply to feeding a pump control panel with an integral 30 amp OCPD and #14 conductors or only a pump?
 

Jljohnson

Senior Member
Location
Colorado
I could be way off base here but here is how I have always interpreted conductor sizing for motors......
- The motor BRANCH CIRCUIT conductors must be sized to a minimum of 125% of table FLA (14 AWG in this instance)
- The tap conductors to the 30 amp fusible disconnect switch must be sized to the maximum potential of the disconnect switch ( # 10 AWG for this instance)

Some confusion comes into play regarding the term "BRANCH CIRCUIT CONDUCTORS". NEC article 100 defines "Branch circuit" as the circuit conductors between the FINAL overcurrent device and the load. This means that the only wires that can be 14 AWG in this case are the conductors from the load side of the fusible disconnect through the controller ( if there is a separate one) and to the motor itself. Here is where I feel it can get a little hairy.... suppose I feed this same motor from a 480 volt panel 150' away, protect it at the panel with 30 amp circuit breaker, then use a NON-FUSED disconnect switch as my local means of disconnecting the motor. NOW all of a sudden I can use 14 AWG all the way from the panel through the entire system since the "last point of overcurrent protection" is in the panel. This has always seemed a bit silly to me.

To the OP's original question, I agree that the tap must be # 10 to the 1st point of disconnect since he is using a 30 amp fusible disconnect but... if he was to put that disconnect near the tap point and an additional non-fused disconnect near the motor, # 14 AWG can be used from the fusible disconnect switch through the balance of the system.
 
Status
Not open for further replies.
Top