Had lunch yesterday with a contractor who had just returned from 2 years in Korea building military facilities. Some things surprising , such as #14 rated @ 30A., #12 @ 40A. & #10 @ 54A. These ratings are based on AWG.
Rowdy

I can't speak for Korea, but the USA is almost unique in it's particular wiring practices. As such, one really has to "leave the USA behind" when leaving the borders.

The ampacity tables are, simply put, our best judgment call. One can always make a case for a higher, or lower, number. It's not at all surprising that different places have slight differences in opinion.

Code issues are not the only places where countries differ. Local construction methods, and lifestyle, have a great effect.

Military and Federal facilities are not under the NEC for the most part, but only guided by industry standards - depending on contract. (This one not being 'standard' for this country....) You also don't mention the insulation - they might be using silicone - which has a much higher temp rating.

Right out of our own NEC, #14 THHN is rated at 25A, #12 @ 30A, and #10 @ 40A. It is only the hyperconservative limits of 240.4(D) that make our normal limits so much lower.

Even these restrictions do not entirely prevent fires from overloaded branch circuits. But they do manage to do a pretty good job of it.

I thought #14 AWG was only rated at 25 amps for derating purposes. That rating is in the 90º column. My understandng is that #14 is good for 20 amps but in only in applications described in 240.4 (G).

[This message has been edited by ShockMe77 (edited 01-26-2007).]

[This message has been edited by ShockMe77 (edited 01-26-2007).]

[This message has been edited by ShockMe77 (edited 01-26-2007).]

30A for #14 sounds real heavy!
2.5mm2 is larger than #14 and has an absolute maximum rating of 26A in free air, 25 degrees Celsius ambient temp. So considering #14 is smaller AND Korea most likely has a higher ambient temperature... scary!

2.5 is rated 30A absolute max. here, free air, 2-core cable, same ambient/conductor temperatures. Clipped direct to a surface it's still 27A.

Which just goes to show how little agreement there is!

Definitely!
By the way, in general purpose installs said 2.5mm2 is usually protected by a 16A breaker or fuse... so there's another difference between max. rating and real life.

The US military has adopted the NEC for facilities in lieu of older MIL-SPECs and other codes that are just easier to use existing industry standards for. Anything built on a US base *should* be conforming to NEC and a number of other MIL-HDBKs that often exceed NEC requirements. We have much wider authority for deviation then in the civilian sector, though, as a single entity is generally responsible for funding, building and approving a project and isn't always as heavy-handed as a city inspector when it comes to failing things for non-compliance!

I think in Mexico its ok to use #14 for a 200 amp service as long as you use white pipe.

White pipe? I've always seen orange. It's the wire that's white. It looks like zip cord, but I think it's #12. Enclosing it in conduit is optional. I've seen the stuff on roofs, where exposure to UV makes it blister and bubble.

What are the grounding requirements for a service done in zipcord?

Steve,
Are any of these Mil_Spec codes online or available to the average citizen? I'd be interested in how much they go above the NEC, weird practices, etc.

Mike

Yes, almost all the MIL-HDBKs and Tech Manuals dealing with facilities are unclassified and approved for public release. None of these are anything like NEC, though. In fact, I've never actually seen the specs that were used before IBC and NEC were invoked by UFC 1-200-01! But I've only been working power for about a year now; I worked electronics before this and never had to worry about it. (Edit: Nobody else here remembers it either- we've been using UFC for quite a while!)

Here's a site with a large # of MIL-HDBKs related to facilities: http://65.204.17.188//report/doc_ufc.html

I reference MIL-HDBK-1004/2-4, MIL-HDBK-419A and MIL-HDBK-411B a lot; I think they're all part of the UFC now, I just know them by their old numbers. There's a lot of good stuff in MIL-HDBK-1012/1 "ELECTRONIC FACILITIES ENGINEERING" too: http://www.wbdg.org/ccb/NAVFAC/DMMHNAV/1012_1.pdf

I use MIL-HDBK-1003/3 for HVAC, too, even off-base as it's free and I don't own a copy of Manual-J or Manual-S, lol...

It's almost all good practice and makes a lot of sense- NEC is not a design guide, it's a set of minimum standards- these are design guides, compiled in a form to keep consistant design good practice throughout the government. But the key is that every military command is its own AHJ, and all this guidance is merely that- guidance. There are very few hard and fast requirements we HAVE to follow, just a lot of recommendations we SHOULD follow, so in practice, we're free to approve/disapprove whatever we want, regardless of what UFC or NEC says. It's good to be your own AHJ, let me tell ya!

[This message has been edited by SteveFehr (edited 01-30-2007).]

ROFLOL!!!

My favorite Mexican wiring method is they will grease a piece of garden house, and put in a concrete pour. After the concrete cures a bit they pull it out (so they can re-sue it), and there you have it, a custom concrete wireway.

Back on topic:
Take a look at NEC 2005 310.60 (C) Engineering Supervision.
Under engineering supervision, conductor ampacity shall be permitted to be calculated by means of the following general formula.

[formula]

Basically if you have the engineering wire specs, excel, and can get the PE for the project to sign off on it, then you can pretty much throw T31016 out the window.

Using that formula for some wire manufactures 54A with #10 AWG THHN does not sound to far off.

Granted it won’t happen in general construction here in the US for #10, but there have been times when I have used it for special circumstances in installations that access or space made it a viable solution. Like an under slab feeder for a remodel that was too small for the new service in an existing 6 story building.

Grounding? What's that Senor?