Mightymite47
New member
- Location
- Rustburg,va.
I'm having a hard time understanding the requirements when feeding a motor from a jbox,disconnect or vfd to a motor to size the wire.How is tap rule applied?Any help would be appreciated. Thanks
Clarification of tap rule
- Thread starter Mightymite47
- Start date
- Status
- Location
- Illinois
- Occupation
- retired electrician
There are no tap rules involved for a single motor on the load side of the motor branch circuit overcurrent protective devices.
publicgood
Senior Member
- Location
- WI, USA
How would serving a motor be a feeder?
publicgood
Senior Member
- Location
- WI, USA
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Tap rule would be a situation where you "tap" from a feeder and end up in an overcurrent device to protect the branch circuit on the load side of that device.
Say you ran a 100 amp feeder across the plant to an area where you had a group of motors. Near those motors you maybe place a gutter or splice box and make taps to that 100 amp feeder to several 30 amp fused disconnects each to supply a motor circuit of 30 amps or less.
Tap rule covers any conductor between the feeder and each overcurrent device that has lesser ampacity then the feeder.
See 240.21(B)
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
More specifically, IMHO, it covers any situation where a conductor (other than a service conductor) is protected at its rated ampacity only at the downstream end rather than at the upstream end.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Yes.
If the "Tap" conductor is the same ampacity as the feeder conductor, the "Tap" is not really a "Tap", so the tap rule should not apply. The rule only applies when the tap is at a smaller ampacity than the feeder conductor, to avoid any overheating issues of the tap, since there isn't an over current device protecting the smaller wire.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
For completeness, there are some "tap rules" in 430 where one can use a tap for the control wiring. I would have to look, its been a while, but I don't think those require any protection. The protection is they are short and don't leave the enclosure.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
It is in 430.72. There is still overcurrent protection requirements, it just relaxes the general rules for those control circuits. In such cases you just have a few VA of a load being supplied (contactor coil in many cases) so overloading isn't really a concern, but they still want short circuit/ground fault protection level that isn't so high that the control conductor ends up being the fuse link.
Couple examples from the table there - motor circuit with 100 amp OCPD - you can tap 14 AWG control conductors directly from that 100 amp protected circuit if none of the control circuit conductors leave the enclosure. Extend the control circuit conductors outside the enclosure and you can still tap the motor circuit if not over 45 amps OCPD. Want leave enclosure but have 60 amp OCPD, increase control circuit conductors to 12 AWG is allowed.
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