How many 3-12MC cables can I fit into a 2" PVC sleeve?

[billp65]

I am trying to calculate the number of 3-12 MC cables that can be pulled in a 2" PVC sleeve underslab. Any suggestions?

 

[infinity]

There are a few factors that would apply, for one is the slab on grade? If so then you'll need a MC cable listed for wet locations. Second depending on who you ask derating factors may apply. Third, as many as you can fit.

Welcome to the Forum.

 

[Buck Parrish]

​How long is the sleeve?

 

[infinity]

You would likely be limited to 20 CCC's so if you're pulling 12/3 MC cables that would 10 cables if from a 120/240 volt system. Not sure if 10 cables would even fit.

 

[billp65]

There are a few factors that would apply, for one is the slab on grade? If so then you'll need a MC cable listed for wet locations. Second depending on who you ask derating factors may apply. Third, as many as you can fit.

Welcome to the Forum.

If I'm using the 2" PVC conduit as a sleeve, would I still have to derate the conductors inside the MC cable? Wouldn't the MC jacket be the conduit and not the PVC sleeve?

 

[kwired]

To answer this question one has to assume all cables of the same type and number of conductors will be same dimension. Though they are all probably close to same dimension they certainly don't have to be.

 

[infinity]

If I'm using the 2" PVC conduit as a sleeve, would I still have to derate the conductors inside the MC cable? Wouldn't the MC jacket be the conduit and not the PVC sleeve?

If the sleeve is longer than 24" (MC cable is not a conduit) then you may need to derate the conductors but as I said prior that depends on who you ask. IMO within a sleeve the bold portion of 310.15B()(3) applies. Having said that since you have #12 AWG MC cable then (4)&(5) would apply also which gives you up to 20 CCC's without derating. Is the slab on grade?

310.15(B)(3) Adjustment Factors.
(a) More Than Three Current-Carrying Conductors.
Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or
multiconductor cables are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) and
are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(3)(a).
Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.

310.15(B)(4) Adjustment factors shall not apply to Type AC cable
or to Type MC cable under the following conditions:
a. The cables do not have an overall outer jacket.
b. Each cable has not more than three current-carrying
conductors.
c. The conductors are 12 AWG copper.
d. Not more than 20 current-carrying conductors are
installed without maintaining spacing, are stacked, or are
supported on “bridle rings.”

310.15(B)(5) An adjustment factor of 60 percent shall be applied
to Type AC cable or Type MC cable under the following
conditions:
a. The cables do not have an overall outer jacket.
b. The number of current carrying conductors exceeds 20.
c. The cables are stacked or bundled longer that
600 mm (24 in) without spacing being maintained.