yet another subpanel thread

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  #1  
Old 12-11-14, 01:54 PM
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yet another subpanel thread

i have read many of the others to learn, but want to write out my plan to get signoff - measure twice, cut once

metered service box is on outside of garage - one split is to a 200amp breaker on outside of garage - it runs to inside of garage where a multi-breaker 200amp panel sits that feeds the house

i would like to drop a 100amp subpanel next to the 200amp panel to wire up the garage - this will include a few high amp items (compressor, lift, welder), lights and several outlets to plug in tools, etc.

researching the threads here, i have read that when you are dropping a sub into the "same building", you do not need a separate grounding rod - would i be correct that this qualifies and that no grounding rod is needed? - to be clear, on the outside of the same building (i.e., the garage), there is a grounding rod and the metered box is grounded there

if so, i would need black red from new 100 amp breaker in existing panel to 100 amp switch in new subpanel - white from neutral bar to neutral bar - green from ground bar to ground bar - is that all correct?

from the threads, it appears i will need 4 gauge copper wire - does something like (3) 4 AWG and (1) 6 AWG Bare Ground, SER, 600V, Copper Conductor, PVC Jacket sound correct?

the existing panel is in the wall - so the above wiring would leave the existing panel and travel about a foot within the wall and then it exits the wall and a foot or two on the surface of the wall until it enters the new subpanel - the new subpanel will be on the surface of the wall - am i correct that the portion inside the wall is fine loose (meaning no conduit) and the portion outside the wall needs to be in conduit?

- and is it ok to use the same bundle of wires inside the conduit (even though not required)?

thanks!
 
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  #2  
Old 12-11-14, 02:17 PM
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Some clarification is needed. Are you thinking about adding a new breaker near the meter or running a new cable to a second service panel in the garage?
 
  #3  
Old 12-11-14, 02:30 PM
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sorry not to have been clear

inside a garage, i am trying to run a 100 amp sub panel next to an existing 200 amp panel
 
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Old 12-11-14, 02:42 PM
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So the feed breaker will be in the existing panel in the garage? Have you done a demand load calculation? Is the existing panel full necessitating the sub for breaker space?
 
  #5  
Old 12-11-14, 03:01 PM
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yes, the feed breaker will be in the existing panel in the garage



yes, i have done a very rough demand load calculation - if everything on the existing panel and new subpanel ran, i would fly to the moon - but, that will never happen - and i will be the sole user in the garage - there should be enough headroom

yes, the existing panel is full necessitating the sub for breaker space
 
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Old 12-11-14, 03:04 PM
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it appears i will need 4 gauge copper wire - does something like (3) 4 AWG and (1) 6 AWG Bare Ground, SER, 600V, Copper Conductor, PVC Jacket sound correct?
No, you will need either #3 or #2 copper (depending on the exact wiring method and code revision) for a 100A panel. Protection such as conduit may or may not be required based on your description. Could you post a picture?
 
  #7  
Old 12-11-14, 04:25 PM
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what would drive the #2 v. #3 decision?

in terms of wiring method, i am not exactly sure what that means, but.... i would get the appropriate gauge bundled (black, red, white, green (bare)) in a pvc casing, put a 100 amp breaker in the existing panel, run red and black from that breaker to the incoming lugs/breaker of the new subpanel, run white and ground from existing to new (one of my questions below is whether i need a grounding rod...I don't think so but would appreciate confirmation)

part (maybe 2 feet) of the run is in the wall (so no pvc conduit there) and part (maybe 2 feet) is along the wall - where i exit the wall i will put a box and then conduit to the new panel

is there any issue to running sheathed cable inside conduit?

thanks
 
  #8  
Old 12-11-14, 04:48 PM
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You are talking about using a cable like SER. You are going to have a hard time finding it with copper conductors. Aluminum is more common.

A ground rod is not needed for the new panel.
 
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Old 12-11-14, 06:43 PM
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sorry not to have been clear

inside a garage, i am trying to run a 100 amp sub panel next to an existing 200 amp panel
No, from your existing 200 amp subpanel in the garage you are wanting to feed a 100 amp subpanel also in the garage.

metered service box is on outside of garage - one split is to a 200amp breaker on outside of garage - it runs to inside of garage where a multi-breaker 200amp panel sits that feeds the house
That 200 amp breaker outside the garage is the main and all panels afterward are subpanels. I am going to recommend you also take this opportunity to bring your grounding up to current code by installing a #4 copper conductor from the neutral bus at the main breaker to the water service within 5 feet of where it enters the house, jumping around any meters and/or pressure reducing valves with a continuous length of wire and terminating with appropriate water pipe clamps.

what would drive the #2 v. #3 decision?
I would use #3 THHN/THWN in conduit between the two subpanels. Although copper SER cable can be used, you'll never find it in local stock and it's doubtful a piece that short can be ordered through a supply house.
 
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Old 12-11-14, 06:54 PM
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Many panels have a bus stab limit. You may need to remove two breakers across from the 90 amp breaker.
 
  #11  
Old 12-11-14, 07:56 PM
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PC Boss - i am afraid i don't follow your post - sorry ... amateur here
 
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Old 12-11-14, 08:00 PM
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Casual Joe

- yes, what you said

- to be clear, you are suggesting i get a conduit in the wall somehow and connect it the existing 200a subpanel? - what drives that suggestion? - i thought that if it was inside the wall conduit was not required?
 
  #13  
Old 12-11-14, 08:05 PM
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ibpooks

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Old 12-11-14, 09:23 PM
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Wow, those pictures certainly changed my idea of this job. I thought this was a residential garage.

Whether you can use cable or not now depends on the type of garage and whether any classified locations are involved. You are going to need to tell us more about the garage.
 
  #15  
Old 12-12-14, 05:00 AM
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It is residential - garage is 19x19 - attached to house - contractor was commercial and had this stuff left over
 
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Old 12-12-14, 07:37 AM
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I had the same reaction pcboss did! Looks kinda like a strip mall service entrance. Good clean work though.

Anyway, I would run some conduit between the existing panel and the new panel and use #3 copper THHN wires. Something like flexible metal conduit could be a good option, or a custom made PVC offset bend with a heat gun.

The situation doesn't sound like a good fit for SER cable unless you're able to make the entire run inside the finished wall, and your local supplier has a good selection of sizes.
 
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Old 12-12-14, 08:22 AM
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If the SER is not subject to damage it should be fine on the surface before going into the wall.
 
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Old 12-12-14, 09:45 AM
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thanks guys...

i have attached a drawing

maybe this helps

keep in mind that the new box will be mounted on the surface of the wall - the existing box is inset into the wall

so the options seem to be either come out and go around the corner to the box - i was leaning toward this because it is easier to go straight into the box

the other might be to go around the corner inside the wall - but that seems tricky to fish - also, how would you do conduit inside the wall in that scenario??

i guess the other thing is i how do I bend such thick wire? - i am thinking i don't, but come out low from the existing box and do a junction below the new box and then come straight in from the bottom?

thanks in advance for the guidance
 
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Old 12-12-14, 09:54 AM
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ibpooks - does #3 copper THHN come in a bundle sheathed? - or do you just use individual pieces?

i have see something called 2-2-2-4 AL SER which is aluminum...is that an option?
 
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Old 12-12-14, 10:23 AM
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- to be clear, you are suggesting i get a conduit in the wall somehow and connect it the existing 200a subpanel? - what drives that suggestion? - i thought that if it was inside the wall conduit was not required?
You were wanting to use copper SER cable which would work, but where will you find #3 copper SER cable in a length less than 10 feet long? Your options could be aluminum SER cable or individual conductors in conduit to connect the two panels. Individual conductors cannot be run inside a wall without being in conduit. IBPooks suggested flexible metal conduit, a good option.

Looking at the pictures you provided, the neutral in the 200 amp disconnect is technically not properly grounded. Assuming all three disconnects are similar, you need a #4 grounding conductor (for 200 amp) to be run from a lug on the metal panel box to the grounding lugs adjacent to the neutral lug, that is what that small lug is for. As it is now, the metal panel box is being used as a conductor which is a code violation.

http://www.ecmag.com/section/codes-s...opper-and-more

The first question and answer covers this neutral grounding issue. This link used to have a nice illustration, but it's obviously been dropped from the archives.
 

Last edited by CasualJoe; 12-12-14 at 12:20 PM.
  #21  
Old 12-12-14, 10:40 AM
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Home Depot has 3-3-3-5 Copper SER by the foot - would this work?

If it does, and given that it is in pvc sheathing, is a conduit still necessary?



Southwire 3-3-3-5 Copper SER Wire (By-the-Foot)-27757499 - The Home Depot
 
  #22  
Old 12-12-14, 12:00 PM
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The #3-3-3-5 Cu SER would be okay as long as it's in an uninsulated wall and/or protected from damage where exposed.
 
  #23  
Old 12-12-14, 12:16 PM
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thanks

if i do end up needing conduit, can i put this inside a conduit? - or, if using a conduit, should i have loose conductors, not inside a pvc sheathing?
 
  #24  
Old 12-12-14, 12:33 PM
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You can put the SER in conduit, but that is not a typical installation. Individual conductions are typically used in conduit.
 
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Old 12-12-14, 06:19 PM
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The bus stab limits are how many amps of breakers can be connected to the fingers of the bus. The bus is where the breaker connects in the panel to provide power to the breaker. Both the left and right sides need to be under the stab limit.
 
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Old 12-12-14, 07:42 PM
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thanks guys.........................
 
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