This is a fairly common situation: A 200 amp 480V meter/main w/breaker panel that needs to feed a 50 KVA stepdown transformer. The breaker lugs are rated down to #6 wire and the 100 amp primary protection fused disconnect lugs only accept up to #1/0 wire. Is there a good reason why there is not an exception in the tap rule that would allow feeding the disconnect from the breaker with #2 instead of having to go full sized and use pin terminals? A fused 200 amp meter/main solves the problem with 110 Amp fuses but they are not always available.

I may not be understanding you but if you are saying the 2ga conductors are protected by 100 a fuses on the load end, that sounds like a tap to me. You just need to follow the appropriate tap rules.
I may be misunderstanding the question tho.

Greg, there are no provisions in the tap rules to feed a
smaller wire from a breaker but you can feed a smaller wire from a feeder as a tap. It doesn't make sense that there is
no provision in the code to allow feeding a smaller wire
from a breaker than what the breaker is rated at.

The tap rules are basically saying a tap conductor can be protected at the load end at it's rated ampacity. You are describing a feeder tap. The issues are just that you need to follow the appropriate tap rules for the length and wiring method.

If this is 25' or less we use 240.21(B)

(2) Taps Not over 7.5 m (25 ft) Long. Where the length of the tap conductors does not exceed 7.5 m (25 ft) and the tap conductors comply with all the following:

(1) The ampacity of the tap conductors is not less than one-third of the rating of the overcurrent device protecting the feeder conductors.

OK it is half of the main


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

Yes


(3) The tap conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.


This is the open question, is it?

I agree the "tap" is actually the only load on the "feeder" but I don't see anything that prohibits that and it would be possible to add another load later.


I am open to another opinion tho.

The rules allow you to tap a feeder conductor only and not a breaker and the definition of a feeder does not include the feed breaker.

If you have to go with full sized 3/0 wire, what are the options for termination at the 100 amp disconnect with only
1/0 lugs. Would the UL listing be compromised if you could find lugs bigger lugs that fit? Thanks for the input!

Read Feeder

If there was any question you could put an inch or two of 3/0 and "tap" that with Polaris connectors but that only points out the silliness of trying to say this is not a legal tap.

Can't do the Polaris thing because it says the tap shall not feed another conductor.

I just rethought that scenario. If you call the 3/0 stub of wire from the breaker a feeder and then tap the feeder
with the Polaris and reduce it there I guess that would meet the rules.

OK lets go a little farther. What if you had a dual lug breaker and maybe even another tap to another transformer? Is that then the feeder?
Now if you just step back a little and see what we are accomplishing you see the stub of 3/0 and the Polaris is unnecessary. The "feeder" is just the lug on the breaker.

At the end of the day the important thing is that the conductor is adequately protected from overload and we have done that with the load side fuses. Short circuit protection is adequately provided from the line side O/C device and we have the conductor in a raceway to deal with the momentary heating until the line side breaker opens.

But the definition of Feeder is: 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. It specifically states
conductors and not lugs. I think they need to change the wording because you can tap the secondary on a transformer and it's obvious there that you need to use lugs.

It does not say wire, it says conductor. What is a conductor?
If a piece of conduit is a conductor, why can't a lug be a conductor? It is really undefined.

An inspector who would insist on a stub of 3/0 and a Polaris connector, simply to settle a semantics problem is why we lose respect in the community.

Greg

I agree 100% but in the NEC definitions they lean towards a
conductor being a wire. A conductor is a conductor of
electricity in the dictionary. Excellent point!!

The "good reason" you can't use undersized cables is because the OCP won't protect it in case of a fault. If there was a fault, the cable could burn up before the OCP trips. Allowances for bus taps are highly restrictive because of this.

However, if full ampacity (#3/0) cable is used, it's not a tap- in fact, the #3/0 can be considered a bus just as well as if it was a solid piece of bus-bar inside an enclosure. You can safely legally feed a bus-tap from the end of this cable, so even if you consider the polaris to be a bus-tap, it's OK because it's only a few inches long and meets all the other requirements of 240.21(B).

If you're going to feed it from 200A OCP, I'd recommend you use #3/0 and polaris lugs. It's safe, simple, and would be able to withstand fault conditions long enough for the breaker to open and protect it.

I suppose you know that puts you at odds with 240.21(B).
As long as the tap is protected at the load end from overload they believe the larger line side breaker will protect you from overcurrent (short circuit) faults in the tap.
That is why there are different rules for 10 foot and 25 foot taps.

If you can tap a feeder you ought to be able to feed a tap from a
breaker if its lugs are listed for the smaller wire. This seems common sense
to me. I cannot find the wording to allow exception or provision in the code for a
breaker to feed a smaller wire than the breaker rating unless perhaps if you
consider the breaker lug a conductor. If so then the code also says the
tap shall feed no other conductor so where does that leave us? Anyone have
experience submitting revisions to the NEC committee? Am I missing something
in the interpretation? Steve, how is feeding the tap with a breaker more
dangerous than feeding it from a feeder protected by the same size breaker?
Your input is appreciated!

Absolutely you can connnect a smaller wire to the load lugs of a breaker.
Example 1: Start with a 100A protective device feeding #3CU @75°, go 300' and terminate them in a 200A breaker, leave the 200A with #3 conductors and go 20' to a 100A breaker.

Example 2: Start with a 200A protective device feeding 3/0, again go 300' and terminate in a 200A device, leave the 200A with #3 conductors and go 20' to a 100A breaker.

In my examples, the oversized breaker is acting as nothing more than a very expensive method to 'butt splice' the conductors together.

Can you please cite the exact verbiage in the NEC that allows you to do that
while simultaneously complying with 240.21?

240.21(B) says conductors may be tapped to a "feeder".
The article 100 defines a "feeder" as all circuit conductors between the source and the final branch overcurrent device.

No where in the definition of feeder does it ever specifically mention either main or feeder circuit overcurrent devices, but we know these devices must exist (see 215.3). So breakers are either considered 'conductors' or they are ignored when defining feeder circuits.

As far as UL and breaker manufacturers go, they clearly allow 'taps' directly from circuit breakers as there are Listed power distribution lugs for many industrial breakers (typically up to 6 #14-4AWG openings).

In the Tap rules it mentions The overcurrent protection/breaker that the tap terminates in
but does not mention the overcurrent device at the origination. You are correct that the
lugs on a circuit breaker are conductors however throughout the code the use the word conductor
is such that it seems to apply exclusively to wire. I like the way you're thinking though!

Article 240 defines a conductor a 'tap' when it is smaller than the protective device at its source/origination.

In-line splices, terminal blocks, panelboard bus bars, and disconnecting/isolating switches are all found in feeder circuits, but none of them are specifically called 'conductors' either.

The best example is a tap off of feed through lugs in a panelboard. There is no "wire" between the breaker and the tap but we all know it is OK if the rest of the tap rules are followed. The important thing about taps is the length and the protection of the conductors. Longer taps (10-25') require a smaller ratio between the line side breaker and the tap ampacity because voltage drop might not allow a short to operate it fast enough to protect the wire. Overload protection still comes from the load side breaker.

NFPA has decided if this tap is outside, we treat it like a service conductor (the disconnect/OC protection reads like 230.70) and we don't really care much about it burning up. I should read the ROP and see where that came from.

Panelboard feed thrus are not taps>
The conductor size must remain the same unless
a breaker is installed??
Feed thurs are just that Feed thrus??

Did a buss tap get it's name because of tapping the
buss to install a conductor or because of using a tap
and die set to install the lug?

Why can't you tap from the lugs on a panelboard rail? (load side of the main)

Generically many, if not most, people call any connection of a "spur" conductor to a "main run" conductor a tap. The NEC article 240 has a specific and narrow definition of a tap as a reduced size conductor.

The Tap Rule thinking is inre fire hazard.

Outside the building = incased in a raceway surrounded by 2" of concrete.

If aerial, outside the building also means free air available to cool.

INRE 'Conductor'

For myself, I've always regarded any path of conduction to be a CONDUCTOR.

To my mind, that is why the Code does not use the term WIRE.

Compression terminals -- conductors

Ilsco taps -- conductors

Mechanical lugs -- conductors ( they even have temp ratings )

etc.

Wa-a-ay back in the day, the first significant taps were in electro-chemical smelters. (Copper & Aluminum)

The main conductors were bus-duct.

Hence, term of a bus-tap got started. It was soon carried to heavy industry -- particularly Big Auto.

There are still special Code exceptions for these situations.

-----

Copper was the first industry to use electro-separation. It became evident very quickly that only really pure copper had good electrical properties. Old methods were too costly.

In practice, miners send their ore to crushers to produce a mineralized dust. Next the dust is sent through floatation tanks where a xanthate soap and forced air bubble-lifts the ultra-fine ore to the surface as a film on the bubbles. They slop over and, after drying, are roasted/reduced to crude metals -- mostly copper -- called dore metal.

This dore is then shipped away to where electric power is cheap. ( Mongolian gold an copper is shipped to Canada in one case. ) The dore is rolled/recast into plating sheets surrounded by acids. Pure target copper sheets are placed near. Between them a porous bag/barrier operates as a diaper for the precious metals.

At this point mega-amps of DC current move the copper to the pure target. Voltages being unique to each element -- the gold, silver and what not drop off and sink. Iron and such stays in solution -- which gets refreshed.

The target plates gain weight and are removed, washed, and remelted under a vacuum to out gas any oxygen. Next the copper is shipped out as 'wire-bar' to the wire spinning companies so familiar to us all.

With all of that high power DC to shunt around bright minds came up with massive solid copper bars as in plant conductors. At the low voltage they were using, the original bus-conductors were NAKED.

What had been established for copper purification proved essential for the reduction of aluminum.

Like copper, the mines ship out a purified product that is converted into metal where electric power is cheap. Unlike copper, alumina is so pure that the only metal coming out is aluminum. But the process uses juice like no other!

10-45 Log #4825 NEC-P10 Final Action: Reject
(240.21(B))
_______________________________________________________________
Submitter: Don Ganiere, Ottawa, IL
Recommendation: Add text to read as follows:
(B) Feeder Taps. Conductors shall be permitted to be tapped, without
overcurrent protection at the tap, to a feeder as specified in 240.21(B)(1)
through (B)(5). Feeder taps shall be permitted to originate at the load terminal
of an overcurrent protective device. The provisions of 240.4(B) shall not be
permitted for tap conductors.
Substantiation: This type of installation is permitted in many areas, but the
code does not specifically permit it. The additional wording will make it clear
that this is a code compliant installation. As long as all of the conditions of this
section are complied with the point of origination of the tap conductor does not
create any additional hazard.
Panel Meeting Action: Reject
Panel Statement: The proposed language is not necessary as the present
language permits such installation where appropriate.
Number Eligible to Vote: 12
Ballot Results: Affirmative: 12

WOW! Great research! I totally disagree with the findings but at least I have
something in writing to show an inspector. How about a proposal to include the
NEC definition of a conductor? Did you find that info on the web?

Yes, that information is available on the web, but I did not have to research too much as I submitted the proposal. You can go here to find the Report on Proposals (ROP) and the Report on Comments (ROC) for the NEC. You can go back a number of code cycles.

Thanks for the link. I checked the site out. Amazing how many proposals are rejected.
Don't want the book too thick I guess.

Personally, I wish that more people would take a look at the ROP and ROC for each Code cycle. We came very close to a mandated floor box in a Meeting Room...it died only because enough comments were made to the 2011 draft. (Thanks, everyone).

There are a lot of folks who believe that the NEC is used as a tool to force the purchase of some specific manufacturer's product. Once you see how many time a manufacturer tries that and gets slapped down it makes you realize that the vast majority of the stuff that makes it into the NEC is there for a reason other than marketing.

The problem with reading the ROP is the daunting size of the document and the short time comments are open.

Agreed.
I find that a big part of the bulk is multiple proposals, sometimes verbatim, from multiple people.

I understand that in the name of fairness, they have to include every one of them, but it does make it quite a sizable tome.

I download the file of all 1,200 pages and just keep it open. I read a few pages at break, another few more at lunch, skip past the 50th proposal to mandate some prorietary new product...it takes me about a week of short bursts to get through it. But if it kills stupid stuff before it gets into the book I consider it time well spent.

It's also possible to just keep skipping ahead to the word "accepted" and gloss over all of the things that the CMP already turned down.

Proposals for the 2014 Code cycle are due November 4, 2011.
---HERE WE GO AGAIN---

Yes that is the insanity of this process. We have about 13 months to fix a version of the code that most people have not even seen yet and will not be adopted by most AHJs for over a year.