Temporary Engine Generator - Portable Conductors - Which Ampacity Table? Free Air?

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Avalon004

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Location
Renton, WA, USA
What is free air?

For a temporary installation of a mobile engine generator with a transfer switch, temporary portable conductors are being implemented.
  • On the line side of the temporary installation, portable conductors could be laying on the ground (or supported in the air) between a disconnect switch and the transfer switch
  • On the load side of the temporary installation, portable conductors could be laying on the ground (or supported in the air) between the transfer switch and a facility panelboard.

Since they go into a disconnect switch and panelboard, is TABLE 310.15(B)(16) used here? Or, could TABLE 310.15(B)(17) be used?
Also, laying on ground vs supported in air?
 
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MrJLH

Senior Member
Location
CO
Avalon004 said:
What is free air?

For a temporary installation of a mobile engine generator with a transfer switch, temporary portable conductors are being implemented.
  • On the line side of the temporary installation, portable conductors could be laying on the ground (or supported in the air) between a disconnect switch and the transfer switch
  • On the load side of the temporary installation, portable conductors could be laying on the ground (or supported in the air) between the transfer switch and a facility panelboard.

Since they go into a disconnect switch and panelboard, is TABLE 310.15(B)(16) used here? Or, could TABLE 310.15(B)(17) be used?
Also, laying on ground vs supported in air?
Click to expand...

Based on what you describe refer to table 400.4 and 400.5
 
iceworm

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
Interestingly, 590.4.B, and 590.4.C limits the installation to multiconductor cables unless you are using hard usage cord in art 400.4. XHHW, THHN are not on the list for single conductors. In fact, none listed in 310.15.B.17 are suitable for single conductor temporary service. Exception for test, emergency, experiment.

Another slight faux pas is 590.4.J
Can't lay the cables on the ground. Yep, that is what it says.

Now that we are by that:

Single conductor hard usage as listed in 400.5.A.2, 75C, Column D, is about the same ampacity as 310.15.B.17

As for getting them off the ground, my norm is to lay out 2x4 or 2x6 and tywrap cables

So, yeah, if you are using 310.15.B.17 conductors, staple/tywrap them to a 2x4 or 2x6, use 75C free air ampacity.
 
hbiss

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
On the line side of the temporary installation, portable conductors could be laying on the ground (or supported in the air) between a disconnect switch and the transfer switch
Click to expand...

Exactly what do you consider portable conductors?

-Hal
 
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zbang

Senior Member
Location
Roughly 5346 miles from Earls Court
jap said:
Where does it say that?
Click to expand...

Actually, it does say that in 590.4(J) "shall not be installed on the floor or on the ground", but is directly followed by "Extension cords shall not be required to comply with 590.4(J)."

Flip then to 525 (Carnivals/circuses/fairs/etc) and the "on the ground" part disappears (525 overrules other articles, which would include 590).

So it depends on circumstances. I'm fairly sure that few AHJs would reject a wad of 4/0 running from a large generator into a building's switchboard for a temporary outage.
 
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