View Full Version : Maximum size conductors in 3/4" conduit


IONH
02-20-2012, 07:17 PM
I have a 3/4" conduit going from my house to my detached garage, approx 6 foot space between the buildings.

Currently, there is what looks like a 10/3 with ground running a 30 amp sub panel including no main breaker. The panel is wired to my 200 Amp service in the main house at a 30 Amp double pole breaker.

I was wondering if I could fit a larger wire through that conduit to potentially add more circuits. Right now I have 2 double pole breakers and two single pole breakers. The double pole go to my compressor and welder. The single pole go to lights and outlets. I would also like to add another circuit or two for more lights and such, but probably shouldn't with the 30 amp max I have right now.

ishiboo
02-20-2012, 07:42 PM
I have a 3/4" conduit going from my house to my detached garage, approx 6 foot space between the buildings.

Currently, there is what looks like a 12/3 with ground running a 30 amp sub panel including no main breaker. The panel is wired to my 200 Amp service in the main house at a 30 Amp double pole breaker.

I was wondering if I could fit a larger wire through that conduit to potentially add more circuits. Right now I have 2 double pole breakers and two single pole breakers. The double pole go to my compressor and welder. The single pole go to lights and outlets. I would also like to add another circuit or two for more lights and such, but probably shouldn't with the 30 amp max I have right now.

12/3 is good for 20A, not 30A. Given the short run length, I would run #6 THWN giving you 31% fill.

IONH
02-20-2012, 07:48 PM
12/3 is good for 20A, not 30A. Given the short run length, I would run #6 THWN giving you 31% fill.

Sorry, I meant 10/3. Edited my OP.

How many #6 THWN can I fit in that conduit? What amperage will that net me?

Figure 6 feet between buildings and maybe another 10 vertical length into each building total.

Also, it's about 60 feet from the inlet into the main house to the 200 Amp panel, but I can transition to something else once inside.

pattenp
02-20-2012, 08:20 PM
You can put four #6 CU THHN/THWN in 3/4" Sch 40 PVC conduit. That gives you 60A. You could push it to 70A, but I suggest you stay at 60A.

Note: 3/4 " Sch 80 PVC conduit is good for three #6 THHN/THWN conductors. 3/4" Rigid Metal is good for four #6 THHN/THWN

DSLTRK
02-20-2012, 08:44 PM
Sorry, I meant 10/3. Edited my OP.

How many #6 THWN can I fit in that conduit? What amperage will that net me?

Figure 6 feet between buildings and maybe another 10 vertical length into each building total.

Also, it's about 60 feet from the inlet into the main house to the 200 Amp panel, but I can transition to something else once inside.

Maximum of four no 6 AWG wire in a 3/4 conduit

Thruxton
02-21-2012, 06:15 AM
This calculates raceway fill capacity for different size conductors (even mixed), different insulation, Al/Cu, and different raceway types. Very useful.

http://www.electrician2.com/calculators/rf_calculator.html

IONH
02-21-2012, 07:33 AM
The conduit is some type of PVC if that matters. It is gray in color.

pattenp
02-21-2012, 09:24 AM
It does matter what the type of conduit is. Fill rates are different in PVC Sch40 vs PVC Sch80. 3/4" ENT is three #6 THHN/THWN. The type of conductor makes a difference in fill rates too.

The conduit is some type of PVC if that matters. It is gray in color.

IONH
02-21-2012, 09:30 AM
Okay, I will get back to you on the type of PVC. I expect it will have writing on the outside of it.

As I am not home to check it right now, could you list the fill capacities for each?

How difficult is it going to be to pull three #6 THHN or THWN through the two 90 degree bends underground?

Falcon67
02-21-2012, 09:46 AM
# 6 is not too bad. I would use the existing to pull through a pull cord with at least 100lbs tensile strength, then use a wire lube to grease up the conductors and work them through the pipe. Two people makes it easier, one pulling on command and one feeding. Got my wife to help with the 2-2-2-4 pull for the shop - that was 36' in 2" PVC.

pattenp
02-21-2012, 09:55 AM
Your grey conduit is most likely PVC. PVC conduit comes in Sch40 and Sch80. Sch40 is used in areas not subject to damage such as when buried. When the PVC conduit exits the ground and goes up the side of a building then it should be switched to Sch80. Even though the run may have both Sch40 and 80 the fill needs to be based on Sch80.

The link Thruxton posted for conduit fill calculation provides the wire type and conduit types.

ishiboo
02-21-2012, 10:17 AM
Okay, I will get back to you on the type of PVC. I expect it will have writing on the outside of it.

As I am not home to check it right now, could you list the fill capacities for each?

How difficult is it going to be to pull three #6 THHN or THWN through the two 90 degree bends underground?

You need to pull a ground as well, don't forget.

IONH
02-21-2012, 12:18 PM
You need to pull a ground as well, don't forget.

I thought the garage would need its own grounding rods and should not be connected to the main house.

pattenp
02-21-2012, 12:26 PM
Oh yes.. you need four wires to your garage. I didn't catch you asked how hard was it to pull three wires. The ground wire doesn't need to be as large, that can be a #10 CU if the feed is no more than 60A.

You need to pull a ground as well, don't forget.

pattenp
02-21-2012, 12:27 PM
The garage also needs the two ground rods. Remember the grounds and neutrals are separate in the garage sub-panel. For the grounding electrode(rod) wire, you can use #8 bare copper. Note: electrode ground conductor smaller than #6 must be protected in conduit or cable armor. You should just use #6 and run it in a manner that is not subject to damage.

IONH
02-21-2012, 07:19 PM
I took a couple of pictures of the conduit tonight for you guys. I did not see any marking on the outside of the exposed portion of it. I believe it is the far right one in the picture which is heading to the garage.

pattenp
02-21-2012, 08:50 PM
I thought you said it was PVC(plastic), looks like metal ridge in the picture.

IONH
02-21-2012, 09:05 PM
I thought you said it was PVC(plastic), looks like metal ridge in the picture.

The cover is metal, but the pipe is gray plastic.

pattenp
02-21-2012, 09:49 PM
Without markings I don't know how to tell you the difference between sch40 vs sch80. The O.D. is the same, it's the I.D. that is smaller on sch80. If you know for sure it's 3/4" then go with 3 #6 for the current conductors and 1 #10 for the ground.

IONH
02-22-2012, 09:52 AM
So 3 x #6 and 1 x #10 will work for even SCH40?

60 amps would be great, that's double my current (pun?) capacity.

So I can understand, the #10 would be to protect the conduit. The garage would still need its own grounding rods and those would be what is connected at the sub panel and not the lead from the house as they should be isolated from each other... Correct?

pattenp
02-22-2012, 10:42 AM
You can put up to 4 #6's in a 3/4" sch40 pvc, so 3 #6 and 1 #10 will fit just fine. The sch80 pvc is where you run into trouble it has a smaller I.D. than the sch40. All 4 wires need to be THHN/THWN.

Being that the conduit is plastic the ground isn't needed to protect it. The ground wire running from your sub-panel back to the main panel is one of those things required by NEC to provide better fault current protection up and above whats provided by the two ground rods at the garage.

The equipment ground (ground wire to main panel) lands on the ground bar in the sub-panel. The ground wire from the 2 ground rods (ground electrodes) lands on the ground bar in the sub-panel, so both ground wires connect to the same bar in the sub.

The neutrals and grounds are isolated from each other in the sub. You will most likely need to add a separate ground bar in the sub to do this. The main breaker panel is the only place that both the neutrals and grounds are connected to the same bar or in other words "bonded".

You are going to upgrade the sub-panel to a main breaker panel to handle the 60A.... right?

http://www.garagejournal.com/forum/picture.php?albumid=1735&pictureid=16967

IONH
02-22-2012, 11:34 AM
You can put up to 4 #6's in a 3/4" sch40 pvc, so 3 #6 and 1 #10 will fit just fine. The sch80 pvc is where you run into trouble it has a smaller I.D. than the sch40. All 4 wires need to be THHN/THWN.

Being that the conduit is plastic the ground isn't needed to protect it. The ground wire running from your sub-panel back to the main panel is one of those things required by NEC to provide better fault current protection up and above whats provided by the two ground rods at the garage.

The equipment ground (ground wire to main panel) lands on the ground bar in the sub-panel. The ground wire from the 2 ground rods (ground electrodes) lands on the ground bar in the sub-panel, so both ground wires connect to the same bar in the sub.

The neutrals and grounds are isolated from each other in the sub. You will most likely need to add a separate ground bar in the sub to do this. The main breaker panel is the only place that both the neutrals and grounds are connected to the same bar or in other words "bonded".

You are going to upgrade the sub-panel to a main breaker panel to handle the 60A.... right?

http://www.diychatroom.com/attachments/f18/8175d1234414074-need-install-sub-panel-garage-4-wire-subpanel-detached.jpg

That makes much more sense now, thanks.

Yes, I plan on upgrading the sub panel as it is only 6 slots and having 2 240 volt breakers took up the majority of the box already.

Your diagram did not make mention of needing either a "main" breaker or a disconnect in the garage between the box and the conduit feeds. Is this correct?

My current sub panel does not have a "main" breaker in it, nor do others which are also ~8.75" wide which is the space I have to work with.

In case you were curious, the 8.75" one I am looking at is 8 slot 16 circuit capacity. I do not believe my current 6 slot supports tandem breakers at all.

pattenp
02-22-2012, 11:39 AM
The diagram does make reference to a disconnect. See the note NEC 225.31, 32 & 33 beside the sub-panel image. The disconnect is not required to be a main breaker in the sub-panel, but the main breaker meets the code requirement for the disconnect.

Your diagram did not make mention of needing either a "main" breaker or a disconnect in the garage between the box and the conduit feeds. Is this correct?

IONH
02-22-2012, 11:42 AM
The diagram does make reference to a disconnect. See the note NEC 225.31, 32 & 33 beside the sub-panel image. The disconnect is not required to be a main breaker in the sub-panel, but the main breaker meets the code requirement for the disconnect.

Thank you again. I had followed the hot legs and did not see anything obstructing them.

Is this disconnect a requirement because of the 60A service or should my 30A also have one (it does not today). If it is because of the 60A, what is the largest which would not require a disconnect?

pattenp
02-22-2012, 11:47 AM
Actually the disconnect is only required if the sub-panel has more than six breaker handles in the panel. So your old panel didn't need a disconnect if it only had 4 breakers in it.

I suggest you put in a 100A main breaker panel with 12 to 20 spaces. It doesn't matter that the main breaker is a 100A because you'll be feeding it with a 60A breaker in the main house panel.

This is a 20 space Square-D 100A main breaker panel served with 60A in my detached garage.
http://www.garagejournal.com/forum/picture.php?albumid=1643&pictureid=14783

IONH
02-22-2012, 03:14 PM
Actually the disconnect is only required if the sub-panel has more than six breaker handles in the panel. So your old panel didn't need a disconnect if it only had 4 breakers in it.

I suggest you put in a 100A main breaker panel with 12 to 20 spaces. It doesn't matter that the main breaker is a 100A because you'll be feeding it with a 60A breaker in the main house panel.

Ahh, the 6 breaker limit to not require a disconnect makes sense.

The problem is that my space is on the corner of the garage and only about 9" of clearance. The existing box is a tiny one with no disconnect as mentioned. I can get a replacement box which allows 8 spots/16 circuit max, but it has no disconnect. I could put a disconnect below it in the same section of wall.

Or, since I'd be running another line (probably the #6 we talked about), I think I could still come out of the far corner cavity to use the same conduit in my foundation but then move over one cavity to the left and go straight up into a *standard* width box (~14"). That would give me the disconnect plus the box as you mentioned.

One concern, let me paint this picture. I have the corner 9" cavity, a full cavity, and another small cavity before the rear door of my garage. This exterior door opens inward. The hinges are on the breaker box side. Are there any laws about how close to a door the breaker box can be?

I am the one who installed that door and mounted it facing in due to snow reasons as I do not shovel out there unless I have to.

pattenp
02-22-2012, 03:43 PM
No, there is no problem with the panel being located where the door opens and covers the panel. As long as when the door is closed you have clear access to the panel you're ok.

http://www.ashireporter.org/photos/thumbnails/2011_02/The-Word-19-art-panel-clearance.jpg

pattenp
02-22-2012, 03:52 PM
If you move the panel over you will need to extend the conduit to the box because you have to run single conductors in conduit. The only other way is to use a junction box and switch to a SER cable which can be run through the wall without conduit.

IONH
02-22-2012, 04:14 PM
I looked at the conduit again just now and it is in fact galvanized steel. Sorry about the confusion I caused earlier.

The space to the right of the door is 44" to the door frame.

Right now, from memory, whatever type of 10/3 is coming out of the conduit in the garage goes straight up into the panel. You are saying that this is allowed with non-SER but only if it goes straight into the box? Otherwise, as I would be crossing stud cavities, I need to junction it to SER type wire (what I'd be using in the house as well) in order to then go to the new main panel.

What is your preference in this case?

I'm guessing a new 100 Amp main panel. Does it matter if the main breaker is placed toward the top or bottom of the main panel? The wire will be coming in from below of course so I would think the breaker would be best to be on the bottom.

pattenp
02-22-2012, 07:23 PM
If the conduit does not run fully from panel to panel the best thing to do is put junction boxes on each end of the conduit and switch (do a splice) from the individual THHN/THWN wires to Service Entrance cable (SER) for going to the panels. Since the conduit is metal and doesn’t run panel to panel you will need to use metal junction boxes and you will need to ground the boxes with the equipment ground wire. The grounding can be done by making a pigtail at the ground wire splice and connect the ground wire pigtail to the junction box. You can bore holes in the studs and run the Service Entrance cable directly to the panels. This way you don’t have to deal with getting the conduit to the panels. Running SER to the panels from the ends of the conduit with junction boxes may be easier than getting the conduit extended all the way to the panels in order to use single THHN/THWN wires from end to end. I don’t have a preference; it’s what works the best for the situation. Either way will work, it’s just a matter of what you feel like doing.

If you do decide to connect the conduit to the panels, use metal conduit; that way there will be no junction boxes or splices or any need to connect the ground wire to the conduit. It will be grounded by its connection to the panel.

If the existing 10/3 comes out of the end of the conduit and then runs to the panel I assume it must be type UF cable. But technically type UF is not supposed to be run within the interior of buildings.

As far as the panel install direction. It does not matter which end is up on the panel, most are made to be positioned either way.

IONH
02-22-2012, 08:55 PM
If the conduit does not run fully from panel to panel the best thing to do is put junction boxes on each end of the conduit and switch (do a splice) from the individual THHN/THWN wires to Service Entrance cable (SER) for going to the panels. Since the conduit is metal and doesnít run panel to panel you will need to use metal junction boxes and you will need to ground the boxes with the equipment ground wire. The grounding can be done by making a pigtail at the ground wire splice and connect the ground wire pigtail to the junction box. You can bore holes in the studs and run the Service Entrance cable directly to the panels. This way you donít have to deal with getting the conduit to the panels. Running SER to the panels from the ends of the conduit with junction boxes may be easier than getting the conduit extended all the way to the panels in order to use single THHN/THWN wires from end to end. I donít have a preference; itís what works the best for the situation. Either way will work, itís just a matter of what you feel like doing.

If you do decide to connect the conduit to the panels, use metal conduit; that way there will be no junction boxes or splices or any need to connect the ground wire to the conduit. It will be grounded by its connection to the panel.

If the existing 10/3 comes out of the end of the conduit and then runs to the panel I assume it must be type UF cable. But technically type UF is not supposed to be run within the interior of buildings.

As far as the panel install direction. It does not matter which end is up on the panel, most are made to be positioned either way.

Awesome added information here pattenp! Thank you so much. I'll post back once I get to work on this little project.

pattenp
02-22-2012, 09:20 PM
Use this type of connector for splicing the wires together, but one for #6.

http://www.lowes.com/pd_34311-12704-46-404_0__?productId=3379022&Ntt=splice+kit&pl=1&currentURL=%2Fpl__0__s%3FNtt%3Dsplice%2Bkit&facetInfo=

http://images.lowes.com/product/converted/783250/783250580316xl.jpg

IONH
02-23-2012, 05:26 AM
Use this type of connector for splicing the wires together, but one for #6.

http://www.lowes.com/pd_34311-12704-46-404_0__?productId=3379022&Ntt=splice+kit&pl=1&currentURL=%2Fpl__0__s%3FNtt%3Dsplice%2Bkit&facetInfo=

Sounds good pattenp.

sberry
02-23-2012, 07:59 AM
Now is the time to relocate the panel if you are not happy, nothing has to be in the same place it was? Put it where you want it, not where it is.

IONH
02-23-2012, 08:06 AM
Now is the time to relocate the panel if you are not happy, nothing has to be in the same place it was? Put it where you want it, not where it is.

I definitely agree. I won't be buying a new panel until I am ready to run the new wire though.

Thankfully, when I rebuilt the rear wall, I had thought about moving the box over one bay so I left about 20" of slack on the new wires in the attic space.