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Old 15-09-2009, 11:30   #31
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Sorry, I misunderstood your earlier comment on the Tableís provenance.
Youíre right about extropolation from the particular (1 table) to the general (whole code), even when the table represents fundamental principles within the whole.

Notwithstanding, the ampacities given (in your representative table & ABYC tables) are higher than I (& I thought you) would recommend.

Since THHN is 75 deg insulation, the free air rating of #12 would be 35A, thoí it still requires OCP at 20A.
Lapp Online Catalog: National Electrical Code Allowable Conductor Ampacity

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They are standard tables (off the net) but they are in conformance with my copy of the Chicago Electrical Code...
Festoon, festoon, feshtume (as I bespoke the word whilst typing).
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Old 15-09-2009, 12:42   #32
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Quote:
Originally Posted by GordMay View Post
Sorry, I misunderstood your earlier comment on the Table’s provenance.
You’re right about extropolation from the particular (1 table) to the general (whole code), even when the table represents fundamental principles within the whole.

Notwithstanding, the ampacities given (in your representative table & ABYC tables) are higher than I (& I thought you) would recommend.

Since THHN is 75 deg insulation, the free air rating of #12 would be 35A, tho’ it still requires OCP at 20A.
Lapp Online Catalog: National Electrical Code Allowable Conductor Ampacity



Festoon, festoon, feshtume (as I bespoke the word whilst typing).
You're correct, I would not recommend the free air ampacities for application work.(all code free air ampacities are abnormally high for what we do).

I'd limit #12 to under 20A fused ( around 15A nominal currrent). If the branch circuit would be fused at anything over 20, I'd raise the conductor size #10. (Under 50' run, bundled). For safety's sake, it's necessary to use the enclosed ampacities if one's checking a table.

Festoon.
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Old 15-09-2009, 15:34   #33
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Quote:
Originally Posted by S&S View Post
You're correct, I would not recommend the free air ampacities for application work.(all code free air ampacities are abnormally high for what we do).

I'd limit #12 to under 20A fused ( around 15A nominal currrent). If the branch circuit would be fused at anything over 20, I'd raise the conductor size #10. (Under 50' run, bundled). For safety's sake, it's necessary to use the enclosed ampacities if one's checking a table.
Festoon.
We seemed to have hijacked this thread, so Iíll limit myself to these last supporting comments on THIS particular topic.
1. Free Air ampacities are limited by such a large number of technical constraints, that the NEC tables must be applied with considerable expertise.
2. Iíve never seen a Free Air application on a yacht.
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Old 15-09-2009, 15:39   #34
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We seemed to have hijacked this thread, so I’ll limit myself to these last supporting comments on THIS particular topic.
1. Free Air ampacities are limited by such a large number of technical constraints, that the NEC tables must be applied with considerable expertise.
2. I’ve never seen a Free Air application on a yacht.
1. Agreed.

2. Closest thing(still, not quite) is a shore power cord
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