Transformer secondary taps

[Davebones]

480V 3 phase to 208V / 120V transformer indoors in a manufacturing building.112.5 Kva.Is it permissible to feed from transformer to wireway and them tap off to 3 disconnects from the wireway with no ocp in secondary before the wireway.The disconnects are each fused.My understanding is this is not allowed now?

 

[don_resqcapt19]

Dave,
That has never been allowed, but the code was changed to make it very clear that it is not permitted. You can bring 3 sets of conductors off the transformer and run them to the OCPDs, but you can't bring a single set off and then "tap" that set to the OCPDs.

 

[jim dungar]

480V 3 phase to 208V / 120V transformer indoors in a manufacturing building.112.5 Kva.Is it permissible to feed from transformer to wireway and them tap off to 3 disconnects from the wireway with no ocp in secondary before the wireway.The disconnects are each fused.My understanding is this is not allowed now?

Your multiple disconnects are acceptable per 240.21(C), however you cannot tap a tap. So you need to run conductors from each disconnect all the way back to the transformer or run one conductor from the transformer using the same size "tees" to each disconnect.

 

[Davebones]

480V 3 phase to 208V / 120V transformer indoors in a manufacturing building.112.5 Kva.Is it permissible to feed from transformer to wireway and them tap off to 3 disconnects from the wireway with no ocp in secondary before the wireway.The disconnects are each fused.My understanding is this is not allowed now?

So this would not be allowed in a industrial plant.We have a few setups like this as this building was built in 1981.

 

[charlie]

So this would not be allowed in a industrial plant.We have a few setups like this as this building was built in 1981.

It has never been permitted to "tap a tap" but the code was not as clear then as it is now.

 

[don_resqcapt19]

Your multiple disconnects are acceptable per 240.21(C), however you cannot tap a tap. So you need to run conductors from each disconnect all the way back to the transformer or run one conductor from the transformer using the same size "tees" to each disconnect.

Jim,
I am not sure that you can make a tap even when using the same size "tee" conductors to each disconnet. That would still be tapping a tap to me.

 

[jim dungar]

Jim,
I am not sure that you can make a tap even when using the same size "tee" conductors to each disconnet. That would still be tapping a tap to me.

Don,

As far as the definition of Tap Conductors, in 240.2, is concerned a "tap" is a connection of a reduced size conductor without overcurrent protection. If the conductors remain the same size a tee connection is not a tap, otherwise "wire nuts" would have no purpose, every splice would require an OCPD.

 

[don_resqcapt19]

Jim,
The size of the "tee" conductors is not what makes them a "tap". It is the fact that they are not protected at their ampacity at the point of supply. The wires used on normal "tee" connections are protected at their ampacity and are not taps.
There is nothing in the defintion of tap that says anything about the size of the conductors. It is still my opinion that a full or even larger size conductor "teed" to the main would be a tap as the conductor is not protected at its ampacity at its point of supply.

 

[jim dungar]

It is still my opinion that a full or even larger size conductor "teed" to the main would be a tap as the conductor is not protected at its ampacity at its point of supply.

Don,

If you have a single 11' long conductor that qualifies under the tap rule 240.21(C)(3), would you say that it could not be "spliced" and extended to 20' in length using an identical conductor?

 

[iwire]

Interesting, anytime I have done multiple disconnects to a single transformer we ran separate conductors, at times this can be very difficult to fit it all in the transformer.

I also thought it was the NEC required way.

But Jim's question, sure has me thinking.

If you have a single 11' long conductor that qualifies under the tap rule 240.21(C)(3), would you say that it could not be "spliced" and extended to 20' in length using an identical conductor?

IMO the direct answer to Jim's question is, yes I could extend that conductor to 20'.

 

[don_resqcapt19]

Don,

If you have a single 11' long conductor that qualifies under the tap rule 240.21(C)(3), would you say that it could not be "spliced" and extended to 20' in length using an identical conductor?

Jim,
The wording of the code makes that second conductor a tap conductor and if the first is also a tap conductor that is a violation of the code section.

 

[jim dungar]

Jim,
The wording of the code makes that second conductor a tap conductor and if the first is also a tap conductor that is a violation of the code section.

I believe you can easily support your position, using the strict definition of a tap conductor in 240.2 and considering that all conductors installed under 240.21(C)2, or greater, are tap conductors.

I am having a hard time convincing myself that I need to consider two lengths of wire joined by an "in-line" splice as two separate conductors.

 

[don_resqcapt19]

Jim,
Yes, I too, have a tough time with a single spliced condutor being a tap, but as you said it is based on the wording in 240.2.
That being said, I don't think an inspector would have a problem with a splice, but I think that he would with a "tee" connection.

 

[jim dungar]

Jim,
Yes, I too, have a tough time with a single spliced condutor being a tap, but as you said it is based on the wording in 240.2.
That being said, I don't think an inspector would have a problem with a splice, but I think that he would with a "tee" connection.

You are probably right. Now, how about a daisy chain (device to device looping into and out of a double barrel lug)?

 

[don_resqcapt19]

Jim,
That is still a tap. The conductor is not protected at its ampacity at its point of supply.

 

[Pierre C Belarge]

I do not see that the wording in the definition of a "Tap Conductor" as provided in Art 240 would preclude the use of splicing one conductor to another of the same size, as long as they comply with the conditions set forth in 240.21(C).
Sorry Don, I do not see the wording as saying what you say.

But...
The wording of 240.21(C) is now (2008), specific as to the installation of conductors.

" A set of conductors feeding a single load, or each set of conductors feeding separate loads, shall be permitted to be connected to a transformer secondary, ...

 

[iwire]

" A set of conductors feeding a single load, or each set of conductors feeding separate loads, shall be permitted to be connected to a transformer secondary, ...

What is a set of conductors?


No paralles?

 

[sandsnow]

I don't think they are tap conductors. They are secondary conductors.

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

I think the old tap rules talked about conductors tapped to a transformer secondary.

In 240.21(C)(3)(!) it states in part ....the sum of the ratings of the overcurrent devices does not exceed thae ampacity of the secondary conductors.

That would seem to me that one set of conductors would be feeding multiple OCPD. How could you do that without "tapping" (for lack of a better word) the conductors that connect directly to the xfmr terminals?

All the other rules require that the conductors terminate in a single set of fuses. That removes all doubt in my mind about "tapping" those conductors.

IMO extending a conductor with the same size would not be a tap no matter where you do it. If I understand the point correctly.

Oh yeah, I'm reading from the 2005.

 

[don_resqcapt19]

I do not see that the wording in the definition of a "Tap Conductor" as provided in Art 240 would preclude the use of splicing one conductor to another of the same size, as long as they comply with the conditions set forth in 240.21(C).
Sorry Don, I do not see the wording as saying what you say.
...

Before and after you make the splice you have two conductors. If the first conductor (supply end) is not protected at its ampacity it is a tap conductor. If you connect the second (load end) conductor to the first without overcurrent protection, it is also a tap conductor and you are not permitted to tap a tap.

 

[don_resqcapt19]

IMO extending a conductor with the same size would not be a tap no matter where you do it. If I understand the point correctly.

Larry there is nothing in 240.2 that says anything about the size of the conductor in the defintion of "tap". If the conductor does not have overcurrent protection equal to or less than the rated ampacity, then that conductor is a "tap" conductor. The fact that the connected or "teed" conductor is of the same size or even bigger than the "main" conductor does not even enter into the discussion...it is all based on the overcurrent protection.