Re: Maximum Size Breaker for #12 Branch
A picture is worth a 1000 words this string must be getting close; I?m fairly certain this post will insure the 1000 is hit with it?s length and hot topic. I sure could use a prop to convey my message though. I actually do have a JPEG image but cannot get it uploaded to the code forum. So I will try to script through this application again:
Application is: existing contract for a public agency, a ?TI?, through a General Contractor. The initial contract drawings have been value engineered some by a Mechanical Contractor who is specifying the replacement HVAC equipment.
Problem: the inquisitive Client?s (public agency) Superintendent is asserting the existing #12?s will suffice. I have submitted my scope based on information received from the Mechanical Contractor and I will ?Feed? with 10?s rather then ?Branch? with 12?s.
New HVAC unit in question specification: 14 FLA, fused disconnect at unit required (again, this is the requirement from the Mechanical Contractor)
?Source? circuit: panelboard with existing 25A 3P breaker and existing source circuit is 3 #12?s (130? source breaker>new local fused disconnect at unit)
Question: is the source circuit a feeder or branch circuit?
Article 100: "Feeder: All circuit conductors between?source and the final branch-circuit overcurrent device." (overcurrent device see 240-1 & 6(A))
A possible normal route to collect proper conductor sizing (the route I picked) could start and end as follows: 310-16 & *240-4(D) & while in view of 215-3. This route would qualify a feeder NOT branch and reveals the conductors are to be #10?s
Further investigation: 310-6 & *240-4(D) & (G) & 440 parts III, VI (440 parts III, VI are both
?Brancb-Circuit? related therefore my investigation returns to *240-4(D) and stops if the source circuit is a feeder).
This now evolves to question: is the HVAC fused disconnect a "final branch-circuit overcurrent device" as described in Feeder definition?
Again *240-4(D) references 440 parts III, VI
440 III ?
Branch-Circuit Short-Circuit and Ground-Fault Protection?
440-21 General ??devices intended to protect the
branch-circuit conductors?and motors...against
overcurrent due to short circuits and grounds"
440 VI ?...
Branch-Circuit Overload?, this section qualifies the overloads (heaters) if existing.
Answer: 440-21 clearly calls this a
branch-circuit overcurrent device.
So the source circuit is a feeder qualified by the criteria of 440 parts III, VI & 240-1 & 6(A) (overcurrent device)
Does branch circuit exist?
Article 100, "Branch Circuit: "?conductors between final overcurrent device protecting the circuit and the outlet."
Branch size: 310-16 & 240-4(G) & 440 parts III, VI reveals the conductors are to be #12?s
Answer: If the HVAC fused disconnect is a final branch-circuit overcurrent device then this is a branch between the load of this disconnect to the unit and the disconnect line circuit is a feeder.
Well guy?s I gotta say (although I?m bias) I agree with my All Summarized statement (feed with 10?s) and disagree with #12?s branch (source) circuiting from a remote breaker to the local fused disconnect at the HVAC unit. It really does boil down to the HVAC unit having a ?final branch-circuit overcurrent device? qualification and my investigation reveals this scenario does.
?Ga-ahead? make me eat my words, if I have to eat these words I?ll NEVER go hungry!
All Summarized: because the source circuit is a feeder the conductor size will be #10?s.
Notice
web page & navigate to/NEC/General Information/Conductor Sizing, he states ?The National Electrical Code requirements for conductor sizing and overcurrent protection have always been confusing and complex?? At least this site supports our head scratching!
