Did I miss anything

[wireday]

Ive got 3/4 EMT leaving the panel for 5', then switching to MC. Each MC run if feeding a dedicated 20amp recetacle.I have 6 #10s in the 3/4 EMT,3 blacks,3 whites ,3 greens, So if Im understanding it correctly,I have 4 current carrying conductors,for a deration at 80%. Im thinking #12 would be just fine up to six CCC. My run is around 100' total.So I went to #10 wire.Im new at this derating(doing it the right way) so thats why I posted this, Thanks

 

[charlie b]

If I understand the installation, you have three separate circuits, each with a black, a white, and a green. So the EMT has a total of 9 wires, and 6 (not 4) of them are current-carrying, for the purposes of derating. Assuming the #10's have 90C insulation (e.g., type THHN), then you start the derating with the value for #10 wire in the 90C column. That value is 40 amps. You then derate by 80%, since you are in the range of 4 to 6 CCCs. 80% of 40 is 32 amps. Since you will be using a 20 amp breaker, and since the ampacity of the wires is at least 20 amps, your installation is acceptable. Do not forget that the EGC also has to be a #10, since you upsized the ungrounded wires from #12 to #10.

By the way, I think you could have shared the green wire for the three circuits, from the panel to the point of connection to the MC cables.

 

[wireday]

yes thank you Charlie, I guess also that at this point the 3/4 EMT is full,Table 9 states 10 conductors total.

 

[kwired]

You could have used 12 AWG unless you needed larger conductors for voltage drop or something or for some reason have 60 deg C conductors.

A 12 AWG 75 deg conductor is good for 25 amps. Derate that at 80% and you are good for 20 amps.

You did not need any more than one equipment grounding conductor, and unless you are dealing with health care facilities and patient care areas, could really be code compliant by using the metal raceway as the sole EGC.

 

[arion]

last i looked multiple egc were counted as 1 conductor when doing fill calc for boxes or conduit

 

[wireday]

thank you for the Response, Yes I am running 10s for Voltage drop.

 

[arion]

vd is only a concern on the phase legs the egc can be #12 and shared for all the 20A conv outlets as long as there is a ground tail tied to the box and the egc screw on the recept and these are tied to the egc at each box this will meet code

 

[GoldDigger]

vd is only a concern on the phase legs the egc can be #12 and shared for all the 20A conv outlets as long as there is a ground tail tied to the box and the egc screw on the recept and these are tied to the egc at each box this will meet code

Even though voltage drop is not an issue on the EGC, the code specifically states that a wire EGC. must be up sized in proportion to the increase in the current carrying conductors.
If you look at the ungrounded wire and the EGC as a voltage divider under fault current, having the EGC proportionally smaller than the phase conductors will both reduce the fault current and increase the voltage on exposed metal until the fault is cleared.

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[arion]

the conduit and egc in parallel using the specifications i posted if properly bonded at all points. should be able to handle a fault of up to 85A without any rise of surface potential

 

[GoldDigger]

True, but that is not what the language of the NEC requires.
It does not make an exception for not upsizing a wire EGC when a raceway EGC is also present.
If there were no wire EGC, it would be fine.

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[mwm1752]

last i looked multiple egc were counted as 1 conductor when doing fill calc for boxes or conduit

Chapter 9 Notes to Tables

(3) Equipment grounding or bonding conductors, where installed, shall be included when calculating conduit or tubing fill. The actual dimensions of the equipment grounding or bonding conductor (insulated or bare) shall be used in the calculation.

 

[arion]

im used to the jnec i just now received my copy of usa 2014 nec am reading it now (faceplant)