Residential Feeders 215 or 225

[tryinghard]

I notice many electricians minimize the sizing of a feeder to ?good enough, it?ll be fine? rather than qualifying it. Often these items are not on drawings. Which causes me to wonder do you see plan check red lined drawings noting ?submit circuit calculation?? Do you experience or notice inspectors making sure feeder circuits are correctly sized (requiring the designer/electrician to submit calcs)? Am I the only one noticing this and am likely off my nut? :-?

 

[Dennis Alwon]

For a residence I find it very hard to undersize a feeder. I have never, ever been asked for a calculation and I am not sure they even check. They do, however, check wire size with OCPD to make sure it matches.

 

[tryinghard]

For a residence I find it very hard to undersize a feeder. I have never, ever been asked for a calculation and I am not sure they even check. They do, however, check wire size with OCPD to make sure it matches.

How would the correct wire size be known, just and only tabel 310.16? In rural areas feeding outbuildings are common i.e. barns, shops, garages, buildings..., these often over 250' from supply. The wealthy here had a trend for a while to serve a meter main to a well house then feed the whole house underground to avoid metering on the house and aerial visibility.

 

[Dennis Alwon]

How would the correct wire size be known, just and only tabel 310.16?

Yes, they match the wire size to what T. 310.16 states is allowed exceptions a/c's etc.

 

[tryinghard]

What about voltage drop (310.15(A)(1) FPN No. 4 & 215.2(A) with FPN No. 2 of (3))?

A very notable electrician is considering 125a circuit with #1/0AL feeding 300? UG to a barn that happens to include an apartment, shop, & office at a calculated load of 124A (per III 220).

I personally would account for this circuit & load to respect up to 3% voltage drop (VD = 2x(KxQ)xIxD/CM). Meaning his 125A limited circuit at this distance with 1/0AL can experience over 6.25% VD and if 3% can only be around 143? long ? not 300?. With this load & distance I come up with 3-3/0 & 1-2 CU, am I being too analytical or beyond code to accommodate voltage drop?

 

[Dennis Alwon]

FPN is not code and therefore an inspector cannot fail you for that. Sure I think most EC do consider it however, it is not really a code issue.

 

[Dennis Alwon]

A very notable electrician is considering 125a circuit with #1/0AL feeding 300? UG to a barn that happens to include an apartment, shop, & office at a calculated load of 124A (per III 220)

Any EC who would pull a 125 amp feeder for a 124 amp load is suspect esp. with a 300 feet distance. IMO, they should pull a 250kcm al for that load. Not sure it can be turn down however he probably will have problems with that feeder.

 

[tryinghard]

Any EC who would pull a 125 amp feeder for a 124 amp load is suspect esp. with a 300 feet distance. IMO, they should pull a 250kcm al for that load. Not sure it can be turn down however he probably will have problems with that feeder.

Dennis, there you go respcting the 3% with 250's :grin: that's what I'm talking about. But if you continue with this respect how does one terminate??

 

[Dennis Alwon]

Dennis, there you go respcting the 3% with 250's :grin: that's what I'm talking about. But if you continue with this respect how does one terminate??

??? Do you mean because the wire is to large for the lug??? I would just split bolt a smaller size wire at the panel.

 

[Jim W in Tampa]

Just because the load calc is 124 does not mean it will in reality ever come near it. Voltage drop might be issue and he will have very unhappy customer to explain this to. Would be smart to let customer know in advance and give him 2 prices.

 

[iwire]

Dennis, there you go respcting the 3% with 250's :grin: that's what I'm talking about. But if you continue with this respect how does one terminate??

Considering the limited space in a 'load center' I would hit a j-box at the far end and splice on 'normal' size conductors to bring into the load center. This might have to be done at each end.

We all know ... or should know that an NEC load calculation that says 124 amps is unlikely to actually draw more than 60 amps.

 

[Strife]

Some things require load calcs, some don't if I'm adding an outlet, or light is part of the sq feet area. If I'm doing a kitchen remodel and now I have 7 receptacles on the 2 small appliances circuits instead of the previous 4, it doesn't matter. If I'm replacing an AC is most likely a more efficient one, therefore less load. In general if you're not changing the square feet area and the designation of the building, there's not much change in the demand if looking at a 20-35 YO building. I've had some plan reviewers asking me for load calcs in situations like these and after pointing out what I said above they were satisfied.
Now, if you're talking a new building, I've always been asked, and always provided load calcs, feeder, breaker, etc.

I notice many electricians minimize the sizing of a feeder to ?good enough, it?ll be fine? rather than qualifying it. Often these items are not on drawings. Which causes me to wonder do you see plan check red lined drawings noting ?submit circuit calculation?? Do you experience or notice inspectors making sure feeder circuits are correctly sized (requiring the designer/electrician to submit calcs)? Am I the only one noticing this and am likely off my nut? :-?

 

[tryinghard]

Okay sounds like I?m overanalyzing and putting too much emphasis on 215.2(A)(1) & 225.5, one can apply something as long as it aligns with best practices. I do understand the calculated load is a projection and may never take place but I see it as the load when required, my belief with this is challenged. One could operate - best as can anyway - full load to prove the circuit or just let it unfold with the occupant. Maybe 215 & 225 needs two exceptions added

• (1)If the results are conductors too large to terminate or bend then a smaller conductor that can shall be used
  (2)If the occupant experiences noticeable voltage drop the feeder must be increased in size

:grin:

 

[tryinghard]

Considering the limited space in a 'load center' I would hit a j-box at the far end and splice on 'normal' size conductors to bring into the load center. This might have to be done at each end.

We all know ... or should know that an NEC load calculation that says 124 amps is unlikely to actually draw more than 60 amps.

If this were a sub feed calculation in a non-dwelling environment would you employ the same as above?

 

[suemarkp]

Look at what the power company typically runs for service conductors. My 400A service is fed from the POCO with 1/0 aluminum, and that overhead drop is 110' long. Seems way too small to me, but the line hasn't melted, and the flicker really isn't bad.

 

[Dennis Alwon]

IMO, this all really depends on the type of load. If a large part of the load is heat strips and heat pump etc. Then there is no question in my mind that a larger conductor is needed. If the load is most recep. & lighting it may not be as big an issue.

What type of load is at this structure?

 

[tryinghard]

I view the Article 220 load calc in this case as thee load because of it's referencing through the feeder articles - I still believe in this and it's why I'm less inclined to ignore the calc results - although this particular case adds concern regarding voltage drop but only within 3% and a 220 calc. I do understand fine print notes, but these are the only portal NEC addresses voltage drop through, I also believe best practices need some structure as well or we may be leaving too much to instinct. I know tapping would work and it now appears NEC leaves this wide open; or does it? Anyway to answer you question here a snapshot of the calc: