12 awg 25 amp breaker

xguard said:
I'm struggling with the load side terminals being considered separately from the overcurrent protection. If that's true then it seems like a case with a breaker with interchangeable lugs could be viewed differently than one where the terminals that are not interchangeable. What do you think of this distinction?
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Not following the difficulty. You have a piece of #12 conductor. It has just two ends, and connections at each of those ends (assuming it actually participating in a circuit). One of those ends will be its point of supply. If that end is landed on a breaker doing the supplying, that breaker is "ahead of its point of supply."

Cheers, Wayne
 
In response to the deleted post: the "point" of supply is a point. So it is not the breaker itself, that is much bigger than a point.

Rather, it is the point where the conductors connect to the breaker's terminals. That means the breaker itself is ahead of this point.

Cheers, Wayne
 
wwhitney said:
In response to the deleted post: the "point" of supply is a point. So it is not the breaker itself, that is much bigger than a point.

Rather, it is the point where the conductors connect to the breaker's terminals. That means the breaker itself is ahead of this point.

Cheers, Wayne
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Thank you for the explanation. It looks like they added language in 240.21 (B) to clarify this.

from 2020 NEC
1746635360865.png
from 2017 NEC
1746635460484.png
 
david luchini said:
Wayne pointed out in post #4, that condition could be acceptable if the installation meets the requirements of 240.21(B)(3).
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It should be acceptable as a feeder tap even if it does not meet 240.21(B)(3)(3).
I believe that particular feeder tap rule was originally for pole transformers, particularly those with MV primaries.
 
xguard said:
I've ran into a few examples recently of 12 awg installed on a 25 amp breaker supplying the primary of a 15 kva dry-type transformer. Is this allowed? I couldn't find an exception that would allow it but that doesn't mean there's not one.
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240.4(D)(7) would seem to indicate a 10 AWG conductor, and 30Amperes. Which makes sense for 15KVA @ 480V ( 31.25A)

I don't see how we get this to be a Tap Conductor ?
 
milmat1 said:
I don't see how we get this to be a Tap Conductor ?
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It's a tap conductor because #12 is normally protected by a 20A ocpd. So #12 protected by a 25A ocpd, and not allowed to be protected by a 25A ocpd by some other Code section, is a Tap Conductor.
 
240.3 sends us to art 450 for overcurrent protection of transformers. I don't believe the small conductor rule of 240.4(D) applies to conductors supplying a transformer because transformers are in the list of 240.3 items and basically bypasses the rest of 240 other than where specifically mentioned in 240.21(B)(3).

Based on T450.3(B) 25 amp OCPD would be a pretty common possibility on primary conductors for a transformer with input rating of 18 amps, but depending on secondary could be up to 250% of transformer rated current.

Nothing in 450 addresses conductors, if small conductor rule does not apply then a 12 AWG 75C conductor is good for 25 amps without ever needing to consider what tap rule of 240.21(B)(3) may allow beyond 25 amps.
 
kwired said:
240.3 sends us to art 450 for overcurrent protection of transformers. I don't believe the small conductor rule of 240.4(D) applies to conductors supplying a transformer because transformers are in the list of 240.3 items and basically bypasses the rest of 240 other than where specifically mentioned in 240.21(B)(3).
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No. 240.3 tells you about OCPD protection of equipment in accordance with other articles. It does not relieve the conductors supplying the equipment from compliance with the rest of Article 240.

In other words, the requirements of those other articles are in addition to Article 240, not instead of Article 240.

Cheers, Wayne
 
This is no special tap conductor situation.
A tap (240.2 definition) has overcurrent protection ahead of it's point of supply that exceeds the wire's appropriate value. These #12's have overcurrent protection at their point of supply. This is a normal feeder.

As for it feeding a transformer, the wires have little do with the overcurrent selection. 240.3 does not allow you to undersize wires, it simply tells you where/how to size the breakers feeding different equipment.

I believe 240.4 (D) (5), which limits #12s to 20A overcurrent protection, is the final rule here. I would use #10s instead.
 
HarrySlother said:
I believe 240.4 (D) (5), which limits #12s to 20A overcurrent protection, is the final rule here. I would use #10s instead.
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If 240.4(D)(5) limits #12s to a 20A overcurrent protection, then #12s protected by a 25A overcurrent protection would either be a violation or be a tap and would have to follow one of the tap rules. In this case, 240.21(B)(3).
 
HarrySlother said:
A tap (240.2 definition) has overcurrent protection ahead of it's point of supply that exceeds the wire's appropriate value. These #12's have overcurrent protection at their point of supply. This is a normal feeder.
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No. The OCPD is ahead of the point of supply of the conductor for purposes of the definition of Tap Conductor. This is slightly clarified in the 2020 NEC's change to 2020 NEC 240.21(B), as shown in post #23.

Really the use of the word "at" in 240.21 should be changed to "ahead of". There is no physics or safety need for the OCPD to be "at" the point of supply.

Taken literally, the "at" requirement would prohibit installing, say, a 20A breaker supplying #10 AWG Cu which is later spliced to #12 AWG Cu. As it seems pretty clear that the #12's point of supply is the end of the #10 connected to the #12, but the OCPD is "at" the other end of the #10, and hence not "at" the point of supply.

Cheers, Wayne
 
david luchini said:
If 240.4(D)(5) limits #12s to a 20A overcurrent protection, then #12s protected by a 25A overcurrent protection would either be a violation or be a tap and would have to follow one of the tap rules. In this case, 240.21(B)(3).
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I think I'm convinced, thanks guys.

My gut hates this though - it seems as though it's just cheating since there's a breaker available for proper protection, and there's no proper protection anywhere else. I'd feel better about it if there was a fused disco ahead of the xfmr.

The only thing that could undo it is the very first word in 240.21(B)(3). It says you can tap from a conductor to the new feeder (the tap), not from a breaker. I don't know how strong that is though - the intent is still the same.. A conductor receiving power without proper overcurrent.
 
Actually, sorry but now I read 240.15. It quite simply says each ungrounded conductor requires a fuse or breaker in series with the conductor. (It does not specify the location of the OCPD).

Then 240.21(B)(3) is titled "Location in Circuit", and will amend the location of the OCPD. It doesn't negate the fact that the tap will need an OCPD at some point. Also 240.21(B)(3)(3) seems to imply the tapped conductors need to be protected for at least a portion of the circuit.

Does this mean the #12s would need to hit a disco with 20A fuses before the transformer?
 
HarrySlother said:
Then 240.21(B)(3) is titled "Location in Circuit", and will amend the location of the OCPD. It doesn't negate the fact that the tap will need an OCPD at some point. Also 240.21(B)(3)(3) seems to imply the tapped conductors need to be protected for at least a portion of the circuit.
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I see no such requirement in 240.21(B)(3)(3). It just says that the secondary conductors have to land on an appropriately sized OCPD. The primary side tap conductors can go directly to the transformer.

Cheers, Wayne
 
Alright I accept it. I see some other tap rules specifically say that the tap has to terminate in an overcurrent device, but 240.21(B)(3) does not say this. Fun times with taps 😅

Cheers Wayne
 
wwhitney said:
No. 240.3 tells you about OCPD protection of equipment in accordance with other articles. It does not relieve the conductors supplying the equipment from compliance with the rest of Article 240.

In other words, the requirements of those other articles are in addition to Article 240, not instead of Article 240.

Cheers, Wayne
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My bad, yes 240.3 is for equipment.

240.4 is for conductors. 240.4(E) along with 240.21(B)(3) can apply to primary side conductors of a transformer even if the ocpd is up to the 250% allowed by table in art 450.3(B) for the transformer as long as all of conditions of 240.21(B)(3) are also in compliance.

So we could have possibly up to a 45 amp breaker per 450.3(B) on this 18 amp rated transformer, still supply it with 12 AWG 75C conductor, and it is over 1/3 the rating of the overcurrent device as required by the tap rule, so kind of comes down to does length of primary and secondary and overcurrent protection on secondary comply along with proper physical protection being all that is left to look into for total compliance here.

Most people are going to use at least 10 AWG but I think 12AWG can be compliant.
 
As the OP maybe I could use my privileges (if I have any) to throw out another real world example I encountered today. I don't see how this one would be okay but here it goes.
45 kva transformer, 100 amp breaker on the primary, 1/0 secondary conductors (thwn-2) landing in panel with 175 amp MCB. Wouldn't the secondary conductors need to be 2/0 minimum?

Thanks for all the help
 
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