NM in conduit ?

[yeldogt]

What's the rule for length allowed -- is there one?

Currently -- have two controls for the light in my pool (inside/outside). Inside is by window with view of pool -- because of recent changes the outside is no longer within the pool area and can't see the pool. The light can dim and is often not all the way up -- seeing the pool is important.

I drilled though the brick/ block wall of the garage at 50" high -- want to run a length of 3/4 PVC pipe to a single gang box with clear cover and another controller -- maybe 10' of straight pipe and one 90 up. Since the garage is not drywalled == just studs.... my plan was to use regular 12/3 thought the PVC and run directly to the the junction box where the light controller is located -- that' s on the other side of the garage wall outside .. 25' away I was going to drill another hole to match up with a knock out on the box and have a stub-out to protect the wire through the brick and block on that wall. I could do that with one length and no splicing

 

[dscheidt]

There isn't a limit, but romex is not allowed outside. Even in conduit. So you'll need to put a box inside, splice and then run thwn to the device.

 

[yeldogt]

There isn't a limit, but romex is not allowed outside. Even in conduit. So you'll need to put a box inside, splice and then run thwn to the device.

Never gave that a thought .... all the other controls are on the outside garage wall -- The wires enter the outside boxes directly though the wall.

Installed a slightly higher fence -- so now blocked from view.

Thanks for the info! I will do the junction box.

 

[75gmck25]

UF-B is rated for wet locations, and its just as easy to run as NM-B. It can also be run in conduit for protection.

Bruce

 

[yeldogt]

UF-B is rated for wet locations, and its just as easy to run as NM-B. It can also be run in conduit for protection.

Bruce

There is another idea ... want to use the conduit as it's neater looking. I have all the other stuff .. but it may be easier to just get 50' of the UF 3 wire.

 

[BreeStephany]

There is a limit on length based upon the size of the conductor, based upon NEC 210.19(A) Informational Note No. 4 which states

"Conductors for branch circuits as defined in Article 100, sized to prevent a voltage drop exceeding 3 percent at the farthest outlet of power, heating, and lighting loads, or combinations of such loads, and where the maximum total voltage drop on both feeders and branch circuits to the farthest outlet does not exceed 5 percent, provide reasonable efficiency of operation"

To calculate voltage drop, use the formula V=I*R where I is the amperage draw of the circuit and R is the resistance of the conductor, based upon Table 8 - Conductor Properties of NEC 2017. The resistance values in the table are based upon 1000', so be sure to take that resistance value and divide it by the length of your conductor. Once you calculate V, which is the total voltage drop, divide that by the total voltage present at the circuit - i.e. 120V, 240V, 208V, etc. which will give you the percentage drop. As long as this value is within 3%, you are fine.

With that said, I don't think you will have issues for a 25' ~ 50' conductor, as voltage drop calculations and conductor upsizing generally do not come into play until the length of the branch circuit conductor begins to exceed 200+ ft.

Just my two cents.

 

[alfredeneuman]

There is a limit on length based upon the size of the conductor, based upon NEC 210.19(A) Informational Note No. 4 which

Informational Notes (which were called Fine Print Notes in the past), are just what title implies. Informational only and as such are totally unenforceable.

 

[Firebrick43]

There is another idea ... want to use the conduit as it's neater looking. I have all the other stuff .. but it may be easier to just get 50' of the UF 3 wire.

Also conduit fill with a wire is based on Romex or UF width of the largest outside dimension of the cover and not the size/number of conductors in the sheath.

So UF 12/3 has a width of .626". This gives it a cross section of .310 sq in

3/4 emt has a cross section of .530 sq in
.310 divided by .530 equals a 58% fill which is above the allowable 40%

1" emt has a cross section of .850 sq in
.310 divided by .850 equals a 36 percent fill which is acceptable.

However if you used 12ga THWN in 1/2 emt you could run 9 12 ga conductors and 16 in 3/4" emt (if more than 6 conductors in a raceway requires derating to table 310.15 (B)(3)(a) which will still normally give you 20 amps with 12 ga THWN/THHN

You can easily purchase 12 ga THWN from most box stores off the reel and any electrical supply house.

 

[BreeStephany]

Informational Notes (which were called Fine Print Notes in the past), are just what title implies. Informational only and as such are totally unenforceable.

Yes, they are an informational note and are considered unenforceable, but that doesn't mean that they shouldn't be followed... just my two cents.

 

[nh_yota]

Don't overthink it. Run the whole circuit in 12g UF and sleeve it in conduit as needed.

 

[02vito]

OP:

Keep in mind that stranded conductors are easier to pull through conduit than solid conductors + a cable jacket.