double check of sub panel plan b4 i start

[amolaver]

hoping for some feedback before i start down this path...

i've got 200 amp service to my shop's main panel. the main panel is on one end wall, near one corner. i'd like to put a subpanel on the same end wall, but the opposite corner. they will be ~35' apart horizontally, with ~10' vertical run up to the ceiling, and another 10' down. (~55' total).

i'm planning on putting a 50amp double pole breaker in the main panel feeding 6ga hot legs, 6ga neutral, and a 10ga ground to the subpanel. i know i need to make sure the neutral and ground are kept separate at the subpanel. ideally, i'd like to also include a 14ga hot/neutral/gnd for an exterior light in the same conduit, which i'll break out at a junction box near the roof peak. i'd like to fit all this in 3/4 EMT. i know it will be a tight fit (and probably a bear of a pull), but based on my math (which i would appreciate a double check on), it does meet the NEC fill chart. this is all thhn/thwn copper.

i do not believe i need a breaker or ground rods on the subpanel since this is one structure, and no walls between the two panels.

anyone see any issues with the plan? any comments? i can take pictures if that would help visualize it.

ahm

 

[pattenp]

The only thing I question is the fill on the 3/4" EMT. 3 #6, 1 #10, and 3 #14 seem to be too much. If you're doing 50A with THHN, why not use #8? I think that will work better in the 3/4" EMT with the other 14's. I'm too lazy to do the exact fill calculations.

 

[kd3pc]

what requires the use of a sub-panel? Why not serve the device directly from the existing panel?

I am missing something?

 

[amolaver]

nothing 'requires' the subpanel. hell, nothing 'requires' the building but it will make providing volts to anything on the matching long wall MUCH easier than pulling from the main panel. its strictly a convenience factor.

i don't have time to look up / do the fill calcs again, but i'll try and post them later tonight.

#8 is good for 50A (code-wise)? i thought i'd need #6 (although it seems like that could be breakered as high as 60a).

ahm

 

[pattenp]

#8 THHN in conduit is good to 50A. If using NM-b then #6 would be needed for 50A. The THHN can be sized by 75 deg C, but NM-b is sized by 60 deg C.

 

[amolaver]

based on chapter 9 (http://records.jonesboro.org/Technical Codes/Electrical Code/Chap_9.pdf), i calculate i'm good NEC / fill wise as follows:

3+ conductors == 40% max fill

table 4 says total area for 3/4 EMT is .533sq inch. 40% of that is .213sq inch

THHN / THWN area per conduction:
14ga == .0097"
10ga == .0211
6ga == .0507

add 'em up:

.1521 == 3x 6ga (3x .0507)
.0211 == 1x 10ga
.0291 == 3x 14ga (3x ..0097)
==
.2023

.2023 < .213 (40% of .533)

Looking at the ampacity table (310-16) i see you (patttenp) are absolutely right re: 8ga being sufficient for 50a. not sure why i 'knew' i needed 6ga. now the question is, do i use 6ga and breaker it at 60, or take the easy way out and use 8ga. nothing wrong with a little overkill, but i imagine the pull is going to **** with 8ga, never mind 6.

assuming THHN in EMT, is there anything special NEC-wise that would differentiate receptacle runs ampacity/gauge wise? perhaps that's too broad - specifically, i'm going to run at least two and perhaps 3 50amp receptacles. one will almost certainly be a welder (which i know have some weird exceptions), but excluding that fact... is 8ga good for 50a receptacles as well? that would certainly make my life easier (and cheaper) thanks!

ahm

 

[pattenp]

#8 THHN is okay to use for a 50A circuit with 50A outlets. If you are considering of putting multiple 50A outlets on a circuit you should check with your local AHJ for local code restrictions. As an example there was another post that brought up the fact that Virginia residential construction code restricts multiple outlet circuits to 20A. I'm not aware of any code section in the NEC that restricts circuits greater than 20A from having multiple outlets.

 

[Charles (in GA)]

I'll reprint this here, as it might be of some use. From the NEC.

210.21 Outlet Devices. ..... snip.......

(A) Lampholders. ....... snip ........

(B) Receptacles.
(1) Single Receptacle on an Individual Branch Circuit.
A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.

Exception No. 1: A receptacle installed in accordance
with 430.81(B).

Exception No. 2: A receptacle installed exclusively for the
use of a cord-and-plug-connected arc welder shall be permitted
to have an ampere rating not less than the minimum
branch-circuit conductor ampacity determined by 630.11(A)
for arc welders.

Informational Note: See the definition of receptacle in
Article 100.

(2) Total Cord-and-Plug-Connected Load. Where connected to a branch circuit supplying two or more receptacles or outlets, a receptacle shall not supply a total cord-and-plug connected load in excess of the maximum specified in Table 210.21(B)(2).

Table 210.21(B)(2) Maximum Cord-and-Plug-Connected
Load to Receptacle

Circuit Rating(Amperes)..Receptacle Rating(Amperes)..Maximum Load(Amperes)

15 or 20......................15....................................12
20..............................20....................................16
30..............................30....................................24

(3) Receptacle Ratings. Where connected to a branch circuit supplying two or more receptacles or outlets, receptacle ratings shall conform to the values listed in Table 210.21(B)(3), or, where rated higher than 50 amperes, the
receptacle rating shall not be less than the branch-circuit rating.

Exception No. 1: Receptacles for one or more cord-and plug-connected arc welders shall be permitted to have ampere ratings not less than the minimum branch-circuit conductor ampacity permitted by 630.11(A) or (B), as
applicable for arc welders.

Exception No. 2: The ampere rating of a receptacle installed for electric discharge lighting shall be permitted to be based on 410.62(C).

Table 210.21(B)(3) Receptacle Ratings for Various Size Circuits

Circuit Rating(Amperes).....Receptacle Rating(Amperes)

15.....................................not over 15
20....................................15 or 20
30....................................30
40....................................40 or 50
50....................................50

ARTICLE 100—DEFINITIONS

Receptacle. A receptacle is a contact device installed at the
outlet for the connection of an attachment plug. A single
receptacle is a single contact device with no other contact
device on the same yoke. A multiple receptacle is two or
more contact devices on the same yoke.

 

[amolaver]

appreciate the reference material Charles! i don't foresee having multiple 240v receptacles per circuit - those i am running individually. i did read the thread with virginia's multi-receptacle restriction, but its not applicable to my situation - thanks for the heads up on it though!

i decided i'm going to try and pull the 6ga for the subpanel so i can breaker it at 60a. its a more flexible solution than pulling 8ga/50a, but it will depend on how the pull goes. if it is truly miserable, i may retreat and fall back to the 8ga. the fill calc is sooo close to the max (w/6ga), i imagine it is going to be less than fun. will post back and let you know how it goes.

thanks for the advice!

ahm

 

[wyliesdiesels]

appreciate the reference material Charles! i don't foresee having multiple 240v receptacles per circuit - those i am running individually. i did read the thread with virginia's multi-receptacle restriction, but its not applicable to my situation - thanks for the heads up on it though!

i decided i'm going to try and pull the 6ga for the subpanel so i can breaker it at 60a. its a more flexible solution than pulling 8ga/50a, but it will depend on how the pull goes. if it is truly miserable, i may retreat and fall back to the 8ga. the fill calc is sooo close to the max (w/6ga), i imagine it is going to be less than fun. will post back and let you know how it goes.

thanks for the advice!

ahm

Dont forget wire snot aka lube!!

 

[MTW]

In my experience, your pull will depend on your conduit bending skills. Just cause the NEC says it's legal, doesn't make it desirable. If you have more than a couple of 90's with some offsets, you will experience a tough pull. Keep you bends as gradual as possible, and use a pull box to turn a corner if you need multiple bends. I do lots of industrial 3 phase work and learned to never use 3/4" for three #6 AWG. For my customers time and money I always use 1" EMT for this application. It can be done, but if you let the wires get twisted while pulling into the conduit, your in for a headache. The small conductors will be immaterial, the twisted #6's will be your problem.

 

[amolaver]

just to circle back on this one... two separate attempts, both failures with the 6ga. made the pull through one offset, but when the bundle got to the 90 turning onto the ceiling, fail. one guy pushing at the panel, one pulling at the far end and no joy. 1/2 a bottle of lube, MANY pull-backs of a couple inches and go at it again, about half a dozen returns of the head of the snake to the panel and various push/pull techniques, all no joy

will probably just run the 8ga and deal with it until i feel like there is enough of a capacity problem to justify changing it.

appreciate everyone's help (and advice to not waste my time trying to do this ). will report success when the 8ga is done.

ahm