Conductor Ampacities

[iwire]

If supervised location under engineering supervision
most cases I would guess

Well if you are playing that card all bets are off.

 

[Smart $]

Well if you are playing that card all bets are off.

I know many engineers believe they can supersede code ampacities with their own calculations as prescribed by 310.15(A)(1) and (C), or 310.60(B) and (C). However, that only applies to Article 310 ampacities. It does not apply to termination temperature limitations imposed under either 110.14(C) or 110.40.

 

[Smart $]

Not sure if I am the one who missed it lol
The mv SW without question is rated for use with 105 cable
105 cable does not de-rated to use it

And all I am asking is for you to link us to the manufacturer's documentation which clearly states that. Then it qualifies as UOI...

 

[iwire]

I know many engineers believe they can supersede code ampacities with their own calculations as prescribed by 310.15(A)(1) and (C), or 310.60(B) and (C). However, that only applies to Article 310 ampacities. It does not apply to termination temperature limitations imposed under either 110.14(C) or 110.40.

If you can pick your own ampacity of the cable you can get around the termination temps.

Correct?

In other words I just claim the cable is rated X amps at 75C.

 

[Smart $]

If you can pick your own ampacity of the cable you can get around the termination temps.

Correct?

In other words I just claim the cable is rated X amps at 75C.

No, you cannot. Article 110 specifies the use of the appropriate Table. No option for engineering supervision.

 

[Ingenieur]

Well if you are playing that card all bets are off.

Not mine, the codes
better to have a justfication or basis for the decision
if 125 is good for lv, seems reasonable and prudent for mv

as far as the 100% non + 125% cont load nugget
Usually not worth the effort to seperate and identify
usually not a factor when std sizing and expansion is considered

if you have a 225 loaded to 160 continuous (considering all loads cont)
does reducing it to 150 buy you anything?

 

[Ingenieur]

If you can pick your own ampacity of the cable you can get around the termination temps.

Correct?

In other words I just claim the cable is rated X amps at 75C.

can't pick ampacity for a given type/size, it's predetermined by tables/calc
only the way the load/ampacity ratio is determined

edit
clarification
there is a little room for 'engineering supervision'
like determining amb temp, etc

again, scraping to find savings by downsizing cables in a mv project/system is imo not a good approach
good layout
flexibility of equip mfgr
clear documents
getting a good bid response

 

[wwhitney]

No such 125% continuous factoring requirement for MV.

What about this:

215.2(B) Feeders over 600 Volts [ . . . ]

(2) Feeders Supplying Transformers and Utilization Equipment. The ampacity of feeders supplying a combination of transformers and utilization equipment shall not be less than the sum of the nameplate ratings of the transformers and 125 percent of the designed potential load of the utilization equipment that will be operated simultaneously.

Seems like all non-transformer loads get 125%, unless you go to part (3) Supervised Installations.

Cheers, Wayne

 

[Smart $]

What about this:

...125 percent of the designed potential load of the utilization equipment that will be operated simultaneously.

Seems like all non-transformer loads get 125%, unless you go to part (3) Supervised Installations.

The "will be..." lets it be highly subjective. Not the same as "may be..."

Also, note there is no requirement to include the non-coincidental load... so that 125% of the simultaneously-operated load may still be less than the total designed load.