Subpanel install

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  #1  
Old 10-20-10, 10:16 PM
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Subpanel install

Just wanted to run this scenario by licensed electricians:

Sub to be installed in residential attached gargage, 3 ft from existing main. Main is 200a, 1p, 120/240 service fed by 2/0 cu in a QO 40/40 with no available slots.

The plan is to run 1" emt up above main into attic, over and down into new panel. Running inside will be (3) #3 cu thhn (2 legs and neutral) into another QO main lug 32/32. In existing main, replace two slots with tandems and install a 100a 2 pole breaker. According to nec 358.6 the emt counts as grounding method so no ground wire. Neutral will remain unbonded in subpanel.

Q1: Have I got it right so far?

I don't own a hickey so I am going to have to cobble with fittings - from top of main ->emt connector -> 45 sweep ->coupler -> to another 45 sweep to make an offset to get from left top of panel to right to clear attic obstructions (about 10") -> coupler -> 90 degree -> coupler -> straight 3' -> coupler -> 90 -> straight 2-3' -> connector. pheww If there wasn't finished ceilings to contend with I think with all those connectors I could pay for a bender!

Q2: - Are 3 #3 going to be pullable through all this mess?
Q3: - For the short stretch in the attic (literally just a few feet) should I
worry about derating? Attic temp can get to 110
I would use the next size up, but I am at capacity in the gutter of the existing panel and its going to be hard working in the new cables as it is. I don't even have an accessible large lug to put my neutral under! I am in the process of looking for a bus bar kit for QO for larger wire size.

Subpanel will have 11 circuits:
Lighting on separate 20a circuit, 5 20a circuits for misc. power tools, 2 30a 240v circuits for larger power tools, 1 30a 240 reserved for potential future a/c.

Your thoughts, thanks
 
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  #2  
Old 10-21-10, 05:24 AM
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The first thing I will say is that the tandems cannot be used in the panel. You will need to remove two circuits from the original panel and move them into the new subpanel. The 2 spaces freed up will allow the double pole breaker to be installed.

Why do you need to use conduit? SER cable would be much easier.

As far as the loads, you have not stated the ampacity requirements of the machines and if the possiblitiy of more than one being used at one time.
 
  #3  
Old 10-21-10, 06:14 AM
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Thanks PCBoss, why are you saying the tandems can not be used? I ask because they do make tandems in the QO series. To move them into the sub would require splicing in the gutter so its not a huge deal. I am able to free up some ground bar locations because the panels ground bars are rated for up to 2 #12 for each ground connection (not neutral). Not that it's necessarily correct, but there is a tandem installed already in the panel.

The reason behind the conduit is because SER would be derated to the 60 chart (315.16b IIRC) and would require me to bump up two wire sizes in cu. In Al it would have to be three wire sizes up and I just don't have the physical space in the gutter for it. Also SER in 1-1-1-3 in Cu is not readily available in my area - to order its a $25 cut charge plus shipping to local supply house, aluminum is out of the question.

There are three loads that would be continuous and have been uprated by 25% according to NEC. And the two larger ones would be phased opposite of each other.
 

Last edited by chopnhack; 10-21-10 at 06:36 AM.
  #4  
Old 10-21-10, 06:54 AM
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You said the panel was a 40/40. That means no tandems. If the panel was a 30/40 tandems could be used.

According to the NEC a load in only continuous if it is on for more than 3 hours. Does this really apply?

Any 240 volt circuit is pulling from both legs of the panel. There is no worry about opposite phasing. This is also a single phase panel.

The difference between a #3 CU THHN and SER would only be 10 amps. The SER would be 90 amps, the THHN would be 100.

How did you determine your gutter fill would be too much? It takes quite a bit to fill the gutter space.
 
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Old 10-21-10, 07:30 AM
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Your right, I guess the inspector let that one slide, because its a 40 slot main panel all slots were used and they ran out of room and put in a tandem in the bottom. Will have to cut and splice into new box to correct that.

Yes, the NEC defiinition apply. There are 3 120v circuits that would be continuous. There would be a 12-13a draw from an air cleaner that would run ~4-8 hours and a lighting circuit that would be on (~8a) at the same time. There could be an a/c draw as well that would be continuous and that would be ~19a. The machinery would typically be intermittent and doubtful of any past three hours straight. I was referring to the 120v circuits being on opposite legs to balance each other(used the wrong term (phase) sorry).

I'm not sure I follow you on the difference between #3 thhn and what guage SER? If both are #3 I see the difference between the two wires being 100 for thhn and 85 for ser using the 60 column for ser and 75 for thhn.

Gutter fill ---> mostly by gut feel, that is, will I will be able to snake the conductors in or not :O It looks like the panel was installed by pro's, but the one thing I would have done differently would have been to have mounted the unit with the main breaker on the bottom, that way you didnt have 3 2/0 filling up the 240v gutter side! In addition to that side having the main feed, there are also 2 10/3 circuits, 2 6 ga circuits, I believe an 8ga is in there as well. That side is kinda no go for pulling three large conductors. The 120 side is a little lighter with only 2 6 ga circuits coming in, but there are about 12 12ga. circuits on that side too. Here are some pics to show what I am describing.




Thanks for your input, pcboss
 

Last edited by chopnhack; 10-21-10 at 09:14 AM. Reason: added photos of gutter/confirmed 40/40
  #6  
Old 10-21-10, 09:22 AM
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Originally Posted by chopnhack View Post
Does square d's bus design prohibit you from installing a tandem in a 40/40?
It's supposed to, but people often break off or file down the rejection tab.

I'm not sure I follow you on the difference between #3 thhn and what guage SER?
#2 copper SER would be okay for 100A. 60 ampacity is 95A, round up to 100A (next standard breaker size).

Gutter fill
Have you thought about just removing a small piece of drywall and running the subpanel feeder in the wall? Patching a 3' x 1' piece of drywall would take a lot less effort than cobbling a bunch of EMT fittings together in the attic. You could also come out the bottom of this panel quite easily without crowding the top. Flex conduit would also be an option through the wall if you didn't want to mess with SER.

Comments:
EMT is a legal ground, but I personally do not like to rely on it especially with set-screw fittings (compressions are more reliable). Steel eventually rusts and with it goes the quality of your ground. I always pull a copper ground. #8 would be the required size in your case.

I also always do at least 1-1/4" pipe for 100A. Some types of 1" might be okay if you run the numbers, but 1-1/4" is more pleasant to work with.

edit: just saw your edit. I assumed the panel was flush mount not surface mount. Where is the new sub relative to this one? Is it possible to just run the EMT horizontally into the side of the new panel?
 
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Old 10-21-10, 10:31 AM
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This is possible, I would have to take a good look at the guts to see if this happened.
Originally Posted by ibpooks View Post
It's supposed to, but people often break off or file down the rejection tab.
I would love to remove some drywall , but the wall is block. Thanks for the input on the emt, I was looking for more seasoned in the field experiences with it, just cause its code doesnt mean its the best of situations. I like your idea of using flex conduit. That might be a possibility I will chase down the tables for fill and see if the size can be accomodated. Running emt on the outside horizontally would be nice, but would require a lot of rework - there is an existing 1/2 emt feeding a 2 gang, and a doorbell transformer in the same corner where the emt exits. I will have to look at the trade off in time vs material in that instance. Going from the bottom would be the shortest route and would allow the larger conductors to tie right in at the bottom, allowing the entire top open for branch circuits on the new sub.
 

Last edited by chopnhack; 10-21-10 at 11:15 AM.
  #8  
Old 10-21-10, 11:58 AM
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Originally Posted by chopnhack View Post
but the wall is block.
Well that makes it a little tougher.

there is an existing 1/2 emt feeding a 2 gang, and a doorbell transformer in the same corner where the emt exits.
You could replace the existing 1/2" EMT with a new piece and kick some saddle bends into it to make a straight path for the 1-1/4" subpanel feeder. You can probably rent/borrow a bender or even buy a cheap one for $25. I would think you could even put a quick saddle into a length of EMT in the aisle of the big box store using one of the benders they usually have standing in a bin.

Three Bend Saddles
 
  #9  
Old 10-21-10, 01:12 PM
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The breaker with the green button is not a tandem. It is either a GFI or AFCI breaker.

The white pigtail goes to the neutral buss and the circuit neutral connects to the breaker along with the circuit hot.
 
  #10  
Old 10-21-10, 05:43 PM
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Originally Posted by pcboss View Post
The breaker with the green button is not a tandem.
Not that one, keeping going down to the last breaker on that side. The picture is not the greatest but you can see two poles.

Originally Posted by ibpooks View Post
Well that makes it a little tougher.
LOL, yeah I will have to check the bottom of the panel for available locations to pop out a 1-1/4" hole. But I think it might be easier to use what you mentioned earlier - liquidtite and go up and over. I have to think this through some more, thanks for the tip on the flex nm, that gives me a few more options.
 
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Old 10-21-10, 05:58 PM
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John,

What I see below the breaker with the green button are three more two pole breakers. I will look on my larger monitor but i don't see any tandems.

A tandem is two breakers that fit into one space, typically the width of a single pole breaker. A double wide breaker like shown on the top right is called a double pole breaker. These are for 240 volt circuits or for a multiwire branch circuit.

Never mind, I was looking on the right side of the panel. I see the old QO tandem on the bottom left. Thanks Scott.
 

Last edited by pcboss; 10-21-10 at 06:22 PM. Reason: clarification
  #12  
Old 10-21-10, 06:08 PM
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Bottom left breaker is the old style of QO tandem breakers which is why it fits. The old style QO tandems did not have the rejection tab. Also, the old style has the poles side by side instead of top and bottom.
 
  #13  
Old 10-21-10, 06:37 PM
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Originally Posted by Tolyn Ironhand View Post
Bottom left breaker is the old style of QO tandem breakers which is why it fits. The old style QO tandems did not have the rejection tab. Also, the old style has the poles side by side instead of top and bottom.
Ah, there it is, sneaky, sneaky! And I was wondering why in a young box there was this old looking tandem! Thanks for the clarification.
 
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Old 10-21-10, 07:35 PM
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Let me know if this sounds like a good plan of attack:

Bring in thhn thru top left pop out via flex with , 3 #3 cu and 1 #8. Neutral will go under available lug right next to main service neutral, other two legs will go to left side of panel, where the first two existing breakers are. Those breakers will be pulled and replaced with the 100a breaker. The old breakers will go into the sub panel and the circuits that were fed will be spliced/nutted in gutter and brought over via romex. Ground wire should fit under any of the recently vacated neutral/ground locations. Replace tandem with a single 20a breaker and bring other circuit over into subpanel.
 
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Old 10-22-10, 08:31 AM
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Sounds good except the relocated circuits should be piped too -- can't have exposed romex on a block wall. One 1/2" conduit can accommodate four 20A circuits with #12 THHN, so that should be plenty. Your feeder conduit should be 1-1/4" if it's flex, 1" would be okay if you go with EMT or sch.40 PVC.
 
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Old 10-22-10, 05:32 PM
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The old breakers will go into the sub panel and the circuits that were fed will be spliced/nutted in gutter and brought over via romex
Will this be inspected? The inspector may frown upon transferring the existing 120 volt circuits this way (although it is commonly done). What you are proposing to do is to route the circuits through the main panel and on to the subpanel. Might be a good idea to consult the inspector first if it will be inspected.
 
  #17  
Old 10-22-10, 05:39 PM
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Originally Posted by ibpooks View Post
can't have exposed romex on a block wall.
I'm not sure that this qualifies per NEC code, but the pro's that installed the main constructed a chase out of plywood and some 1x pt. The 1x pt was tapconed to the block wall and the various circuits were stapled onto the wood. At the edges of the tapconed wood and perpendicular to the wall, they put 1x4 and screwed this to the tapconed piece and then covered the 1x4 with 1/4" ply. The chase though was left open into the attic, no firestop or anything. Doesn't code say that there are to be no protrusions between xx and the interior cavity unless filled with fire stop or does that only apply to living quarters?
Thanks
 
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Old 10-22-10, 06:45 PM
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From your description this sounds like a vertical chase and IMO should have be sealed to prevent the possible spread of smoke and fire.
 
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Old 10-22-10, 07:07 PM
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Thanks, PCBoss. Is there a section in NEC that describes this or can you tell me the preferred method of sealing it off. The open area is about 3.5"d x 14.5"w x ~24" high, a little too big to hope for spray foam to fill effectively.
 
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Old 10-22-10, 07:32 PM
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This is more of a building code issue than the NEC.

At a minimum I would stuff fiberglass insulation into this. Perhaps an endcap could be made and the end firestopped.

Can you post a pic of this? This would be difficult to seal with firestop given the size of the whole chase.
 
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Old 10-22-10, 08:10 PM
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I can do that. It'll be a couple of days before I am back out there though.
 
  #22  
Old 10-24-10, 06:03 PM
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Originally Posted by CasualJoe View Post
Will this be inspected? The inspector may frown upon transferring the existing 120 volt circuits this way (although it is commonly done). What you are proposing to do is to route the circuits through the main panel and on to the subpanel. Might be a good idea to consult the inspector first if it will be inspected.
What in your opinion would be the solution to this? Is there a better way to decrowd an overfilled panel?
 
  #23  
Old 10-24-10, 10:06 PM
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The alternative would be to remove the cables for the transferred circuits from the service panel and move them to the new sub-panel. If the cables are not long enough then a suitably sized junction box would have to be installed and then new cables from the JB run to the new sub-panel. However, it is unlikely that your service panel is so full that it could not be used as a junction point for new cables running to the sub-panel. If you were in Canada it would be different as I understand that using the service panel as a junction box is prohibited.
 
  #24  
Old 10-25-10, 05:27 PM
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Originally Posted by Furd View Post
The alternative would be to remove the cables....
Thanks Furd, I kinda figured that, just wasn't sure. You are right on just moving the entire circuit out and over to the new sub. That should be much easier than whatever it was I was thinking
Thanks
 
  #25  
Old 10-26-10, 11:26 AM
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Originally Posted by pcboss View Post
Can you post a pic of this? This would be difficult to seal with firestop given the size of the whole chase.
The small cable is for a doorbell and it comes out the right side of the chase. Can you have high and low voltage cables inside the main panel? It would be a cleaner install to just run that through the panel and exit on the bottom.

[IMG][/IMG]
 
  #26  
Old 10-26-10, 11:35 AM
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The doorbell wire should not be run thru the panel.

The connector in the top center and the one immediately to the left are not correct. There are too many cables routed thru them.

I am not sure if the connectors used elsewhere are listed for use with both the round and flat cables at the same time.

RE: the chimney created by the chase, I would stuff the fiberglass near the ceiling and then put a drywall panel over the studs.
 
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Old 10-26-10, 11:43 AM
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Agreed on the connectors, I will have to play with the k.o. configuration. Assuming the other cables stay in place, do you think I will be able to access this k.o.? The front of the chase is covered by 1/4" plywood.

[IMG][/IMG]
 
  #28  
Old 10-26-10, 11:51 AM
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You could remove the staples and finese the cables out of the way and then restaple them within 12" of the panel.
 
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