What makes a tap not a feeder or branch circuit conductor?

[arussthur]

Trying to understand what the difference is between the 3, especially as applies to 240.4(B).

I always thought a tap was where you spliced a feeder to serve multiple disconnects without additional overcurrent protection.

 

[petersonra]

Trying to understand what the difference is between the 3, especially as applies to 240.4(B).

I always thought a tap was where you spliced a feeder to serve multiple disconnects without additional overcurrent protection.

The code tells you what a tap conductor is.

Tap Conductor. A conductor, other than a service conductor,
that has overcurrent protection ahead of its point of supply
that exceeds the value permitted for similar conductors that
are protected as described elsewhere in 240.4.

I don't see that whether the conductor is a tap, feeder, or branch circuit is relevant to 240.4(B). It applies to all of them.

 

[LarryFine]

A tap is a conductor that is smaller than its source OCP would normally protect, and is instead protected at its load end.

Technically speaking your service is an example, because it's protected from overload at its terminus.

A feeder generally supplies power to one or more OCPDs, while a BC supplies only one load or one grouped set of loads.

 

[arussthur]

I've gotten confused by some on the job voices.

240.4(B) relevance-we have an existing 800a disconnect. No load wires, but hot. Need to power a 7a pump 150ft away.

One boss says we need to run parallel 500s to a panel and then come off that to a motor starter.

Another boss says 500s are too small and we need to run 600s because it's potentially a branch circuit if they put multiple loads on the panel.

Another said it's neither but a tap. Another says ultimately everything downstream of OCP is a tap.

It's got me pretty confused at this point.

 

[arussthur]

A tap is a conductor that is smaller than its source OCP would normally protect, and is instead protected at its load end.

Technically speaking your service is an example, because it's protected from overload at its terminus.

A feeder generally supplies power to one or more OCPDs, while a BC supplies only one load or one grouped set of loads.

Ok. So Meter to panel is a tap. What about Disconnect to MLO panel? Which is that?

 

[augie47]

You calculate your conductor ampacity and look at 240.4 to see if the conductor is protected by the device (breaker/fuse).
If the conductor is smaller than the device is designed to protect (per 240.4) then it's a tap.
In your example the parallel 500s on a 800 amp breaker would not be a tap because their ampacity (760 amps) is covered by the 800 amp breaker. The same is true for the 600s.
If you "tapped" off the 500s say with a 3/0, then the 3/0 is a tap as the 800 amp is larger than normally needed for a 3/0.

 

[retirede]

Ok. So Meter to panel is a tap. What about Disconnect to MLO panel? Which is that?

Does the disconnect include OCP?

 

[arussthur]

You calculate your conductor ampacity and look at 240.4 to see if the conductor is protected by the device (breaker/fuse).
If the conductor is smaller than the device is designed to protect (per 240.4) then it's a tap.
In your example the parallel 500s on a 800 amp breaker would not be a tap because their ampacity (760 amps) is covered by the 800 amp breaker. The same is true for the 600s.
If you "tapped" off the 500s say with a 3/0, then the 3/0 is a tap as the 800 amp is larger than normally needed for a 3/0.

That's always been my understanding.

Like if you ran a 500mcm and tapped off of it to feed 3 100a disconnects.

Those are taps. The 500mcm is not.

Does the disconnect include OCP?

Yes. Fused at 800a. Not a cb. It is possible while closed to lose a phase and keep power on the others.

 

[petersonra]

I've gotten confused by some on the job voices.

240.4(B) relevance-we have an existing 800a disconnect. No load wires, but hot. Need to power a 7a pump 150ft away.

One boss says we need to run parallel 500s to a panel and then come off that to a motor starter.

Another boss says 500s are too small and we need to run 600s because it's potentially a branch circuit if they put multiple loads on the panel.

Another said it's neither but a tap. Another says ultimately everything downstream of OCP is a tap.

It's got me pretty confused at this point.

I would point out that the 800 amp overcurrent protection device the tap is coming from limits the tap conductor size. Depending on where the tap goes the ampacity rating of the conductors could be as low as 10% of 800, but probably has to be at least a third.

80 A is #4 awg iirc.

 

[bwat]

Like if you ran a 500mcm and tapped off of it to feed 3 100a disconnects.

Those are taps. The 500mcm is not.

Depends if those conductors that you’re using from the 500s to the discos are protected at ampacity or not.

Think “is the upstream breaker or fuse protecting this wire at the wire’s ampacity”. If yes, then not a tap. If no, then it is a tap (unless it’s a service).

 

[arussthur]

So if the upstream OCP is a 400a, the 500 is not a tap, but if it's a 1200a CB next upstream they're all basically taps?

 

[augie47]

 

[don_resqcapt19]

I've gotten confused by some on the job voices.

240.4(B) relevance-we have an existing 800a disconnect. No load wires, but hot. Need to power a 7a pump 150ft away.

Unless the tap conductors are outside, you can't run a tap that is a 150' long. The only real solution is a short tap to an overcurrent device and they run conductors on the load side of the overcurent device based on the load, the rating of the overcurrent device, and any consideration for voltage drop.

One boss says we need to run parallel 500s to a panel and then come off that to a motor starter.

Another boss says 500s are too small and we need to run 600s because it's potentially a branch circuit if they put multiple loads on the panel.

Unless the load will exceed 760 amps, the parallel 500's would be fine. Not sure why you would even think about running 150' of parallel 500s for a 7 amp load.

Another said it's neither but a tap. Another says ultimately everything downstream of OCP is a tap.

It's got me pretty confused at this point.

If the conductors on the load side are protected at their ampacity, or above their ampacity, using 240.4(B), they are not tap conductors. Tap conductors have a supply side overcurrent protective device that has a rating that exceeds the rating of the conductors.

 

[Carultch]

Unless the load will exceed 760 amps, the parallel 500's would be fine. Not sure why you would even think about running 150' of parallel 500s for a 7 amp load.

If the conductors on the load side are protected at their ampacity, or above their ampacity, using 240.4(B), they are not tap conductors. Tap conductors have a supply side overcurrent protective device that has a rating that exceeds the rating of the conductors.

Tap conductors are an exception, where 240.21(B) overrides 240.4(B). Each of the sections in 240.21(B), and the analogous rules in 240.21(C), has a criteria for conductors to have an ampacity not less than the trip rating of the overcurrent device to which the tap conductors terminate. This leads to a situation where you have an inconsistent size between the tap, and the feeder immediately downstream of the overcurrent device to which the tap conductors terminate. Such as #1 on the feeder and #1/0 on the tap, for the example of a 150A tapped circuit that only utilizes 130A of it.

 

[GoldDigger]

Since by its definition a tap conductor is not protected at its rated ampacity at its origin but instead by OCPD at the far end, no tap can be a branch conductor. It can however originate from a branch conductor (which is as a result then both a branch conductor and a feeder!)
Note that there is vigorous dispute on this forum at to whether a section of wire can be both a feeder and a branch conductor. I clearly think it can.

 

[LarryFine]

Note that there is vigorous dispute on this forum at to whether a section of wire can be both a feeder and a branch conductor. I clearly think it can.

An A/C circuit with a fused disconnect comes to mind.

 

[don_resqcapt19]

Tap conductors are an exception, where 240.21(B) overrides 240.4(B). Each of the sections in 240.21(B), and the analogous rules in 240.21(C), has a criteria for conductors to have an ampacity not less than the trip rating of the overcurrent device to which the tap conductors terminate. This leads to a situation where you have an inconsistent size between the tap, and the feeder immediately downstream of the overcurrent device to which the tap conductors terminate. Such as #1 on the feeder and #1/0 on the tap, for the example of a 150A tapped circuit that only utilizes 130A of it.

Parallel 500s supplied by an 800 amp OCPD are not tap conductors and 240.4(B) applies to them.

 

[petersonra]

An A/C circuit with a fused disconnect comes to mind.

Where would any part of that circuit be both a feeder and a branch circuit? It is pretty clear from the definitions that they are mutually exclusive.

Branch Circuit. The circuit conductors between the final overcurrent
device protecting the circuit and the outlet(s).

Feeder. All circuit conductors between the service equipment,
the source of a separately derived system, or other power
supply source and the final branch-circuit overcurrent device.

 

[LarryFine]

Where would any part of that circuit be both a feeder and a branch circuit? It is pretty clear from the definitions that they are mutually exclusive.

I meant as a topic of discussion.

 

[wwhitney]

Where would any part of that circuit be both a feeder and a branch circuit? It is pretty clear from the definitions that they are mutually exclusive.

The definitions do not result in mutual exclusivity. You can have the following arrangement:

OCPD 1 - Conductors A - Outlet 1 --- OCPD 2 --- Outlet 2.

Then Conductors A are a feeder with respect to OCPD 2 / Outlet 2 and a branch circuit with respect to Outlet 1.

E.g. run a circuit for a 208Y/120 HVAC unit with an unfused disconnect. Tap the circuit for a 20 amp OCPD for a service receptacle.

Cheers, Wayne