RE: [CAD_CAM_EDM_DRO] Re: Wire size question...

Dave,

The term "free air" refers to the wire run exposed (without conduit and not
concealed in walls). Depending on the insulation (according to the NEC),
you could use #14 or #12 AWG to carry 30 amperes inside of a cabinet. If
you were enclosing the wire in a conduit system, you would use #10AWG.

The rational behind the higher amperage allowed in open air (like strung
between two telephone poles) is that the heat will dissipate easily (as
compared to being pent-up and building up within a conduit system or behind
a wall).

The questioner was asking about a short length (20 cm if I remember), so I
figured, there was no particular advantage to using a size smaller than #10
regardless. In the real world, there are sometimes significant cost
advantages to engineering towards a smaller wire size.

Example:

I am currently evaluating (for a customer on a design-build) whether the
overall installation is cheaper to use a 600 volt 350 kw (430 kva)
generator, run a distance of 14 floors and use a step-down delta-Y
transformer to 120/208 volts or to do the generator at 120/208 volts and not
use the transformer. Haven't run the numbers yet, but I suspect the cost of
the transformer will be less than the savings in reducing the wire size.

Jeff


-----Original Message-----
From: turbulatordude [mailto:dave_mucha@...]
Sent: Wednesday, April 06, 2005 9:52 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Re: Wire size question...



--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Jeff Goldberg" <jeff@w...>
wrote:

>
> If it enclose in a conduit, then #10 AWG. If in open air, can use

#12. On

> this distance, there is no appreciable price difference, so unless

you have

> an important reason to go smaller, might as well use #10
>
> Jeff

I've seen a lot of numbers tossed around for wire sizes and currents
and such.

I thought that residential wiring was 12ga for a 20 amp service. that
being an insulated wire bundle, NOT in free air, but between walls, and
with a run of less than 100 feet. (increase one ga for over 100 feet
to reduce voltage drop) Kinda fast and loose, not cast in stone stuff.

And, I thought 10ga was good up to 30 amps under the same condioons ?

FREE AIR would be like in an enclosure where the heat of the wire is
easily dissapated, and that increases the wire ampacity. (OK, current
carrying capabilty, but I just like the word Ampacity)

Anyway, are you baseing that on rule of thumb, some standard or code or
something ?

this link clearly states FREE AIR, but I have seen people use it as
gospel for any and all applications.

http://www.allaboutcircuits.com/vol_1/chpt_12/3.html


Dave






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