Sub-panel - Conduit vs NM options

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Old 07-24-13, 09:24 AM
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Sub-panel - Conduit vs NM options

I am in the process of finishing off my basement and I want to put a sub-panel in.

I only plan on requiring a 35-40 amps (per my load calc) to be fed from the sub-panel initially but would prefer to put in at least a 60 amp panel (breaker).

The feeder to the sub panel would run up a studded/sheetrocked wall, into my garage attic and across to the opposite wall, down this opposite wall and through studs/floor joists and into the basement.

As I see it, my four options are.

1. Run NM 6/3 from main service panel to sub-panel. I understand the NM is only rated for 55 amps but in my research I can round up to 60 and protect this with a 60 amp breaker in the main service panel if my intended load will be no more than 55 Amps. This is definitely the easiest solution but it limits any future expansion to 55 Amps. If I later add a kitchenette in the basement I would be in the 55-59 Amp range when accommodating for the additional circuits (range, small appliances, etc.).

2. Run #6 THHN (6-6-6--8) in 3/4" EMT conduit from the main service panel to the sub-panel. This is my preferred method since it gives me a true 60 Amps. 75 really... which could possibly be later rounded up to 80; if more than 60 (but less than 75) is needed. My concern with this is I believe I have to run the conduit from service panel to service panel. The gotcha with this is that my interior garage wall sits directly over my basement poured concrete wall. So I would need to bend/offset the 3/4" EMT inside a bored hole in order to run it down through the wall to the basement and to the sub-panel. I've never bent EMT so I'm not sure how difficult this is going to be.

3. Run #4 THHN (4-4-4-8) in 1" EMT. This would definitely allow for any future expansion but unless my inter-wall offset will be relatively easy with 1" EMT, this would likely be a complete PITA.

4. 1. Run (2) NM 6/3 cables from main service panel to (2) sub-panels protected by 40 breakers in the main. May be the easiest route to get 60-80 Amps in the basement?


Any feedback, suggestions or alternative solutions?

Edit: I've attached a very crude picture of the situation.
 
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Old 07-24-13, 11:05 AM
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Welcome to the forums!

I only plan on requiring a 35-40 amps (per my load calc) to be fed from the sub-panel initially but would prefer to put in at least a 60 amp panel (breaker).
How did you do your load calculation?

Run #6 THHN (6-6-6--8) in 3/4" EMT conduit from the main service panel to the sub-panel. This is my preferred method since it gives me a true 60 Amps. 75 really... which could possibly be later rounded up to 80; if more than 60 (but less than 75) is needed.
#6 AWG is rated for 55 amps, AFAIK, unless there's an exception for feeders.

If you want more than 55 amps in the future, run #4. But I'm not sure why you'd need that much.

See if you can buy a pre-bent offset in 1" EMT (my local big box store stocks them), or run PVC.

You can run 4-3/G cable and protect it outside the walls. My primary concern in trying to do what you've described would be getting past/through the sill plate and beam that I imagine are sitting on top of the poured concrete wall.

How would building a chase on the interior side of the "opposite" wall work for you?
 
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Old 07-24-13, 11:27 AM
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You will never get non-flexible conduit through the proposed holes as shown in your two sketches. That leaves you with either using flexible conduit or a cable.

BTW, number 6 THHN is rated at a maximum of 65 amperes but ONLY when the terminations are also rated at 75 degrees C. The Ampacity shown in the 90 degree C. column is ONLY used for derating purposes.
 
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Old 07-24-13, 11:28 AM
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If you go with the conduit, you coulld use fittings to change from EMT or PVC to flex to get you through the problem area. And although it's not required, you could change back to conduit to get down the concrete basement wall. If it's going to be exposed, the flex is kind of sloppy looking.
 
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Old 07-24-13, 12:51 PM
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I'm guessing I can't directly quote a previous post since I'm a new member...

How did you do your load calculation?
I used this link, which came out to 36 A.
Service and Panel Size Calculator

I also did a load calc following the formulas in my NEC book based on the equipment I intend to install and the 3VA/sq foot rule. That came out at ~31 A.

#6 AWG is rated for 55 amps, AFAIK, unless there's an exception for feeders.

If you want more than 55 amps in the future, run #4. But I'm not sure why you'd need that much.
#6 THHN is listed at (in Col C where it is the only place THHN is listed) at 75 A. The cable itself that I am looking to purchase states it is rate at 70 A.

You can run 4-3/G cable and protect it outside the walls. My primary concern in trying to do what you've described would be getting past/through the sill plate and beam that I imagine are sitting on top of the poured concrete wall.
Yeah but 4/3G (if your referring to NM) is only rated at 55A.

How would building a chase on the interior side of the "opposite" wall work for you?
Unfortunately I cannot since the opposite side of that wall is the kitchen which has the refrigerator, cabinets and range on that wall.
 
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Old 07-24-13, 12:55 PM
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If you go with the conduit, you coulld use fittings to change from EMT or PVC to flex to get you through the problem area. And although it's not required, you could change back to conduit to get down the concrete basement wall. If it's going to be exposed, the flex is kind of sloppy looking.

What type of flexible conduit is acceptable for THHN through this trouble area?

I would really prefer using THHN and conduit since it is better protected and provides more amperage.
I'm not necessarily looking for the easy way out... otherwise I would simply run NM (for the load I currently plan to have and be done with it)
 
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Old 07-24-13, 12:59 PM
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BTW, number 6 THHN is rated at a maximum of 65 amperes but ONLY when the terminations are also rated at 75 degrees C. The Ampacity shown in the 90 degree C. column is ONLY used for derating purposes.
This table (attached) lists THHN 6 AWG at 75 A and the cable itself lists a spec of 70 A. Yes, it's in column C. But that is the only column that lists THHN. I understand the table refers to the conductor itself and (according to the verbiage) I must consider the termination as well but I cannot find any table referencing termination ratings/limits.

BTW, this exact table is in all 4 electrical wiring books I have.
 

Last edited by gmanvbva; 07-24-13 at 01:47 PM.
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Old 07-24-13, 01:20 PM
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VA Code also lists the same table.
 
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Old 07-24-13, 01:33 PM
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I'm guessing I can't directly quote a previous post since I'm a new member...
Disabled for all members to prevent excessive quoting. The way you did it is just fine.
 
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Old 07-24-13, 02:02 PM
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More research seems to indicate that I should nearly always reference column B...

Not sure why... but several places state this!


So that nullifies my earlier statement of
75 really... which could possibly be later rounded up to 80
 
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Old 07-24-13, 02:06 PM
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More information on how the circuits will be run for the basement. All circuits are run using NM 12-2.

Circuits powered directly from main service panel.
(12-2 has already been run for these).
I'm debating on running the Small appliance GFI ckts to the sub-panel (based on the rating I can achieve on the sub-panel).

Bathroom GFCI
Bathroom Light/Heater/Fan (Broan-Nutone 659 Bathroom Heat/Fan/Light)
Wetbar Refrigerator
Small Appliance GFCI #1 (Run but may pull back and terminate on sub-panel
Small Appliance GFCI #2


Circuits to be powered directly from sub panel.
Family Room Receptcles
Family Room Lights

Home Theater Receptacles
Home Theater Lights

Storage Room, Utility Room & 1 Outdoor GFCI Receptacles
Storage Room & Utility Room lights
 
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Old 07-24-13, 02:11 PM
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Disabled for all members to prevent excessive quoting. The way you did it is just fine.
Thank you for the clarification! The FAQ explains how to quote and multi-quote so I thought perhaps it was due to my new membership status.
 
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Old 07-24-13, 03:29 PM
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Originally Posted by Nashkat1
#6 AWG is rated for 55 amps, AFAIK, unless there's an exception for feeders.

If you want more than 55 amps in the future, run #4. But I'm not sure why you'd need that much.
Originally Posted by gmanvbva
#6 THHN is listed at (in Col C where it is the only place THHN is listed) at 75 A. The cable itself that I am looking to purchase states it is rate at 70 A.
From reading later posts I think this has been clarified. The tables you posted show #6 AWG copper @ 55A and #4 AWG copper @ 70A. So does Table 310.15(B)(16) in the NEC.

Originally Posted by Nashkat1
You can run 4-3/G cable and protect it outside the walls. My primary concern in trying to do what you've described would be getting past/through the sill plate and beam that I imagine are sitting on top of the poured concrete wall.
Originally Posted by gmanvbva
Yeah but 4/3G (if your referring to NM) is only rated at 55A.
#4 @ 55A? Is this a typo? I don't see any listings specifically for Type NM.

Originally Posted by Nashkat1
How would building a chase on the interior side of the "opposite" wall work for you?
Originally Posted by gmanvbva
Unfortunately I cannot since the opposite side of that wall is the kitchen which has the refrigerator, cabinets and range on that wall.
Yep, that's out. Given that, I would pipe it down the inside wall of the garage to an LB and punch straight through the beam to a second LB or a big box in the ceiling of the basement. EMT with compression fittings.
 
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Old 07-24-13, 03:32 PM
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For the flex part of the conduit run you could use flexible metal conduit(FMC) if you're running metal conduit or electrical non-metallic tubing(ENT) if you're running PVC. For EMT there are fittings to changeover or you could put together a flex connector, a EMT connector and a threaded conduit coupling to make the conversion. For ENT use an ENT connector instead of the EMT connector.
If I were doing it, I'd run flex from the top of the garage wall and fish it down the wall. Might need a hole in the sheetrock at the bottom of the wall, but that would be a lot easier that patching the whole wall from top to bottom.
 
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Old 07-24-13, 03:41 PM
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And I would run it on the face of the wall, with no flex, and punch through the beam under the wall. The main reason is that I can't figure out how to get from the inside of the wall into the basement without seriously chewing into the sill plate and beam.
 
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Old 07-24-13, 04:35 PM
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I' not sure we're looking at a beam in the drawing.
If there's a sill on top of the concrete and the floor joists sitting on top of that, it might be that he can drill down through the garage wall plate and the subfloor that the plates sitting on and end up in the void between two joists.
 
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Old 07-24-13, 05:31 PM
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I' not sure we're looking at a beam in the drawing.
If there's a sill on top of the concrete and the floor joists sitting on top of that, it might be that he can drill down through the garage wall plate and the subfloor that the plates sitting on and end up in the void between two joists.
That's a good point, gari. Y'know, I thought the OP had said there was a beam there, but I just looked back and couldn't find it.

A sill plate over a subfloor over open joists which end at a rim joist would be a much more standard framing for this wall, and makes going down through it much easier to do.
 
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Old 07-24-13, 06:39 PM
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Attaching a couple pictures.

I have already drilled through this portion for some refrigerant lines. It wasn't too bad to drill through. It would just be pretty tricky to fit some type of rigid conduit.

First on is of the base of the wall in the garage and the second is looking up between the joists coming down into the basement.

Edit: Added another crude mspaint picture to depict how the base is constructed.
 
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Old 07-24-13, 06:45 PM
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#4 @ 55A? Is this a typo? I don't see any listings specifically for Type NM.
Yup it was a typo. I meant 6/3 (which is all I could find locally). Anything larger would apparently have to be THHN.
 
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Old 07-24-13, 07:11 PM
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How about 2-2-2-4 Aluminum service entrance cable? Good for 90A...
 
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Old 07-24-13, 07:29 PM
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Here a few things I feel I should clarify:

6/3 NM-b cable has THHN wires installed in it. You can use the 90 degree for derating, (75 amps) however you can not go higher than the 60 degree for your final amp rating with NM cable, which is 55 amps. As was mentioned, you may use the next higher rated breaker (60 amps) since there is no 55 amp breaker available.

Individual wires installed in ANY conduit may use the full amp rating of that wire, unless the conduit has a temperature rating less than the wire. So that means that THHN wires installed in PVC, EMT, FMC (Flexible Metal Conduit) can be protected by a breaker sized to the 90 degree column, which is 75 amps. Again, there is no 75 amp breaker, so you may go to the next size which is 80 amps.

However, The screw terminals on breakers are normally only rated at 75 degrees or less. So then you have to go by that column which would only be 65 amps. Guess what? There is no 65 amp breaker, so we are back to 70 amps.

Bottom line:
60 amps for NM-b cable
70 amps for THHN in conduit

I hope that clears up a few things.
 
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Old 07-24-13, 08:09 PM
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Thank you for the clarification Tolyn.

I'm curious. Why would the screw terminals be designed/rated at 70 if it would almost always cause you to lose full value of a connected conductor/cable?
 
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Old 07-24-13, 09:06 PM
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You'll need THHN in conduit anyway. No cables in continuous conduit.
 
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Old 07-24-13, 09:07 PM
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Do you REALLY want conductors running at up to 194 degrees Fahrenheit in your walls? Even if they are in conduit? Further, there are NO devices that have terminals rated at 90 degrees Celsius. The 90 degree column is ONLY for derating purposes.
 
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Old 07-24-13, 09:09 PM
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Most loads are equal to or less than the rating of the terminals, so they don't cause a loss. Holding the wires below their max rating is a good way to prevent their overheating, since the installation conditions may not meet all the criteria for them to perform safely at their max rating.
 
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Old 07-24-13, 10:58 PM
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RE: garisilver's idea of snaking a short section of flexible conduit - check the temperature rating printed on the ENT. Some are only listed 50*C. That wouldn't even allow you to use the 60*C amp column. 362.12(4).

FMC is good.

Liquidtight Flexible Nonmetallic Conduit (LFNC) also has a printed temp rating. And it's a b*tch to pull thru it, so use lots of lube.

For holes in wood, any time the edge of the hole is less than 1 1/4 inches from the edge of the wood use a steel plate. 300.4(A) Like this one.

Halex 1-1/2 in. x 2-1/2 in. Nail Plates (50-Pack)-62899 at The Home Depot
 

Last edited by Glennsparky; 07-24-13 at 11:18 PM.
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Old 07-25-13, 06:48 AM
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Do you REALLY want conductors running at up to 194 degrees Fahrenheit in your walls? Even if they are in conduit? Further, there are NO devices that have terminals rated at 90 degrees Celsius. The 90 degree column is ONLY for derating purposes.
As I understand it...

That is the rating at which (generally) the insulation used on that type of conductor is safely rated to run under before the heat would start to cause insulation break down. This insulation breakdown (at those temperatures) would still happen gradually over a long period of time.

It is not a indication of the temperature the conductors reach at the rated amperage.

That is why THHN is listed in column C and TW is listed in column A. The insulation on THHN is much better and is designed to operate safely (without thermal breakdown) at those high temperatures.

I don't really want to derail the thread and I appreciate everyone's assistance and feedback.
 
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Old 07-25-13, 06:52 AM
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For holes in wood, any time the edge of the hole is less than 1 1/4 inches from the edge of the wood use a steel plate. 300.4(A) Like this one.
Thanks for the heads up. I go a little overboard with nail plates! I put nail plates in the basement even when the holes were more than 1 1/4 from the edge.

This concern is also part of the reason I would prefer to run THHN in conduit. I would prefer to have a cable this large and with this much current running through it physically protected.

So someone doesn't come along in a few years and put a shelf up in the garage and run a screw or nail right through a 60A feeder cable (if NM was run inside the wall.
 
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Old 07-25-13, 10:18 AM
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Here is my latest thought/plan based on your suggestions.

Run THHN 6 (3) + THHN 8 through 3/4 EMT until the "choke point", transition to 3/4 FMC through the choke point and then transition back to 3/4 EMT to the service panel.

This would give me a cable/termination rating of 65 Amps and I could protect it with a 60A double pole breaker in the main service panel.

I've attached another "crude" picture to illustrate.

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Below are links of the items I would use (just to make sure I am looking at the correct items and not missing something).

3/4-in Flex 25-ft Conduit

3/4-in EMT 10-ft Conduit

Gampak 3/4-in EMT Coupling
 
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Old 07-25-13, 10:23 AM
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Actually now that I think about (and unless there are any warnings against it)... I think I will run the 3/4 FMC the entire length (height) of the interior garage wall because otherwise I would need to open the entire wall to get the 10" of EMT in there.. So the top coupling would be at the top of the wall (in the garage attic) rather than inside the wall.
 
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Old 07-25-13, 10:26 AM
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Greenfield inside the wall. EMT if exposed.
 
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Old 07-25-13, 11:11 AM
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Greenfield inside the wall. EMT if exposed.
Greenfield = FMC (like what I linked to)?

That interior garage wall (that the FMC would be run in) has drywall on both sides.
 
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Old 07-25-13, 12:44 PM
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Yes, Greenfield = FMC. If you're concerned about whether the coils will stay together through a vertical distance that great with that weight in the pipe, you could use Liquidtight instead - it doesn't always have to be outside.

Me, I would open that section of wall on the garage side, install and support hard pipe, and patch the wall - but it's your call on that. I would also be running 1" pipe, just 'cause I like really easy pulls, but that's your call too.

I don't see your earlier link, BTW.

None of the pipe we're talking about now is nail- or screw-proof, of course. Only rigid provides that. I wouldn't worry too much about it, though. The first thing most of us look for in a wall before we hang something on it is the stud locations. Plus, flexible conduit, if it's not strapped too tightly, will often move aside when a nail or screw contacts it.
 
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Old 07-25-13, 01:07 PM
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I don't see your earlier link, BTW.
I linked the items I listed.

3/4-in Flex 25-ft Conduit

3/4-in EMT 10-ft Conduit

Gampak 3/4-in EMT Coupling

I was considering running 1" (actually even considered 1 1/4") but Lowe's (the only big box in my area) only carries 3/4 FMC and almost any type of coupling.

I spent 45 minutes staring at the shelves the other day trying to find some type of option that would work for 1" or 1 1/4"...
 
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Old 07-25-13, 02:29 PM
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OK, I see them now.

Staring at the shelves... at Lowe's?

I would advise you to go to an electrical supply house, but they tend to sell conduit by the 100' bundle or the 250' roll. You could ask, though.

BTW, you may already know this but, if you install 3/4" flex - or any flex for that matter - be sure to install it so that the inner laps on the coils point in the direction you'll be pulling toward and the outer laps point in the direction you'll be pulling from. You really don't want to try to pull the wire against the grain.

Liquidtight is a lot smoother on the inside.
 
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Old 07-25-13, 02:37 PM
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In the picture it looks like a really short distance of EMT above the subpanel. As long as it's not subject to physical damage you can continue the FMC and not use EMT there. FMC is allowed to run exposed. 348.10
 
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Old 07-25-13, 02:58 PM
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In my area(Fort Lauderdale), flex is available by the foot in 1" and larger and EMT is available by the piece at most supply houses.
If you want to run 1", make a few calls to your local supply house. They don't bite and they don't usually make fun of homeowners. Your money is the same as the pros, even if you have a little trouble speaking the language.
And I would still want to fish the wall if at all possible. When I see a wall cut open, it makes me think it was a lazy electrician or a plumber.
 
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Old 07-25-13, 03:14 PM
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And if you have trouble getting a changeover fitting in 1", here's the other method I had mentioned.
It's a flex connector, a rigid conduit coupling and a EMT connector.
(shown in 3/4",but you get the idea.)
 
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Old 07-25-13, 04:04 PM
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It's a flex connector, a rigid conduit coupling and a EMT connector.
That's probably what I'd use too, but with slightly different components. I would use a compression connector for the EMT. I don't like set-screw connectors in general, although I will use a steel one if I don't have a compression connector on hand and don't want to wait for one. But not a cast zinc connector. I've had too many of those fail, and they don't make it onto the job site or into my materials stash anymore. A steel flex connector too, preferably a saddle grip one rather than a squeeze one. Our rule of thumb for the squeeze type is to tighten the first one until it breaks, and tighten its replacement just a little bit less.

It doesn't matter, BTW, whether you buy the coupling in the electrical aisle or the plumbing aisle. It's the same piece either way and they are often cheaper in the plumbing section for some reason. It can also be black iron if they don't have a galvanized one. It doesn't matter. I like to put a drop of Loctite on the threads when making one of these, but you don't have to. Just be sure you tighten everything really well.
 
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Old 07-26-13, 06:47 AM
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Yes, Greenfield = FMC. If you're concerned about whether the coils will stay together through a vertical distance that great with that weight in the pipe, you could use Liquidtight instead - it doesn't always have to be outside.
Thanks. I saw a 25' length of Titan at Lowe's. It looks like quality stuff. Is it really worth more than twice as much as the Ultratite Alflex in this application?
 
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