60A Subpanel Feed Questions

[TurboEuro88]

(This is in the US, specifically Ohio)

In short, I have about a 40' run that I need to install to feed a new subpanel in my garage from my main breaker box from a 60A dual-pole breaker. Unfortunately the garage is detached and there will be about a 5ft section of that run that will be inside buried PVC between my house and the garage structures. After a great conversation with my local building inspector, I was told I need to run THHN wire as the conduit will be buried and thus a "wet location". The issue I am running into is that while NM-B wire can be bought bundled in the proper 6/3 flavor, I seemingly can only buy THHN wire individually for each conductor. This is confusing me as for the part of the runs where this feed will be in the studs, I assume the 4 conductors should be bundled in some way, yet nothing THHN exists. I can only find it in NM-B Romex which by code I can't run in the conduit.

Am I confusing something about the job that would make this a whole lot easier? What would be the right material for this kind of a job?

I know, just have a pro do it - I am waiting to hear back on getting a guy out to quote it... But having had plenty of experience with electrical over the years and having family members with even more experience I figure I can tackle it once I iron out the important details. Any suggestions or insight is appreciated.

Thanks!

 

[joe--h]

What's the problem? If that's all you can get, just tape it together and pull it.
Joe H

 

[wyliesdiesels]

You are confused a bit.

individual wires must be in conduit everywhere.

NM-b is permitted in conduit indoors. However, unless its for protection i wouldnt do it.

In your situation, you could either run NM-b for the indoor portion and transition to THEN in a box or run conduit for the entire length and pull THWN.

Several ways to skin a cat as they say.

 

[wyliesdiesels]

What's the problem? If that's all you can get, just tape it together and pull it.
Joe H

Wtf



THWN or any other type of loose conductor cannot be taped together and pulled. It must be in conduit.

 

[ddawg16]

NM-B is not rated for wet locations....I don't think.

In fact, you do not want to use THHN...but rather THWN. But all the THHN you get at Home Depot is most likely going to be THHN/THWN anyway.

Just do the conduit....PVC.....and I'd make it at least 1".

You will need 2 blacks, 1 white and a ground. The black and white should be #6 AWG and the ground #10 AWG. And it can be bare solid copper.

Additionally, because your garage is detached, you are going to need 2 ground rods at the garage....at least 6 or 8' apart....and do NOT tie the neutral to the ground.

On your sub-panel, if you want more than 6 breakers, you will need a disconnect breaker. I have a 60A sub in my garage....it has 8 spaces....I just left 2 of them unused (for inspection). Or you can put in a double breaker and backfeed through it. But then you're back to just 6 breakers.

 

[Charlie K]

I see 2 easy solutions to your problem. 1 is to run conduit from the existing panel to the new sub and use thwn wire. The other is to use type UF cable.

 

[mike93lx]

Put in a much larger main breaker panel, something at least 12 spaces if not 20. Main breaker size doesn't matter and can be larger than the breaker at the house main panel.

I would run stranded wire, not solid, and would pull 2AWG aluminum instead. It will be cheaper than 6 copper and allow for up to 90a. I believe the right rating is USE-2

 

[pattenp]

Put in a much larger main breaker panel, something at least 12 spaces if not 20. Main breaker size doesn't matter and can be larger than the breaker at the house main panel.

I would run stranded wire, not solid, and would pull 2AWG aluminum instead. It will be cheaper than 6 copper and allow for up to 90a. I believe the right rating is USE-2

Wire rated only USE-2 is not allowed by the NEC to be installed inside. Wire insulation rating needs to be THHN/THWN or RHH/RHW/USE or XHHW for inside installation.

 

[TurboEuro88]

Unfortunately I can't run conduit from the main panel to the sub panel due to the number of bends that would be required to get there. I think I would be over 900° which exceeds the code just a bit lol

I've had breaking up the run between THHN/THWM and NM-B where suitable (former in the conduit, latter in the walls to the panels), but I don't know that I am comfortable/experienced enough with making that kind of connection. At least not yet. Ideally I'd not have to splice, but I know it's an option.

My plan is to install a 16-space box, even though I don't need that much for my garage. I think as of this writing I am planning to install 5 or 6 circuits into the subpanel, all of which at 120v. However I wanted to leave myself some room in case I need to upgrade to a 240v breaker down the road, add another circuit, etc.

I've been doing some additional research into this and it was suggested that I get what's referred to as "Service Entrance Cable". I found what I think I'd need over at Lowes but really don't know for certain if a) it'd work, b) code permits it.

 

[mike93lx]

Wire rated only USE-2 is not allowed by the NEC to be installed inside. Wire insulation rating needs to be THHN/THWN or RHH/RHW/USE or XHHW for inside installation.

Thanks

 

[mike93lx]

Use AL 2-2-2-4 SER indoors without conduit and then transition to individual pieces of RHH/RHW/USE or XHHW in conduit for outdoors

 

[Innovate1]

Use AL 2-2-2-4 indoors without conduit and then transition to individual pieces of RHH/RHW/USE or XHHW in conduit for outdoors

What type cable are you suggesting? MHF can be called out that way but has to be in conduit indoors.

 

[mike93lx]

What type cable are you suggesting? MHF can be called out that way but has to be in conduit indoors.

Wow, I'm on a roll. SER is what I intended. I'll edit

 

[klassenl]

You will get there. Keep plugging away at it.

Where I live there would be essentially ways of doing this: 1) Run an direct burial cable (here it's called NMWU - non metallic wet underground) from the main panel to the sub panel protecting in in PVC or EMT where necessary. Probably a 6/3. If you used some form.of armoured cable no protection would be needed. 2) Run EMT inside to the exterior wall. Mount a PVC box on the exterior, run the PVC on the exterior/underground to the panel, maybe changing back to EMT if that works better.

No extra ground rods or plates would be needed since the bonding conductor comes from the main panel. As an aside - I don't undertand why the American code calls for rods at the garage it doesn't make much sense.

There would be other ways of course but they don't make sense economically or labour-wise.

 

[TurboEuro88]

The inspector I talked to said I wouldn't need ground rods at the garage - simply connect the ground in the 4-wire 6/3 run to the ground in the main panel. I may need to clarify that with him, but he definitely mentioned it.

I think the best bet I've found so far is SER cable. My only real question is whether its OK to run in the studs of both structures as well as the conduit. From what I'm reading the SER cable I linked above has THWN wire which is exactly what I'd have to run in the conduit anyway, but has the benefit of being bundled so I can run it in the studs. Is that right?

 

[pattenp]

Detached structures need electrode grounding system. The ground to the main is an equipment ground and is not the same thing. SER is not to be installed underground.

 

[TurboEuro88]

Okay if SER can't be installed underground (even in a conduit) what would be the right product for the job? Admittedly I am a little confused since I've been given a number of suggestions, some of which conflict with others and I don't really know what is or isn't right. At this point I am working with what I've been told so you'll have to forgive me if I sound dumb. Ideally I'd like to avoid having to splice together NM-B and THWN to do the run just for sake of simplicity for me, but understand that to be a viable option.

As far as the grounding goes, I now understand the need for the electrode and will make sure that's done as part of the subpanel install. Sill focused on trying to find the right wire(s) for what I need to do.

 

[ddawg16]

Can you post pics?

When you say 900 deg of bends, do you mean 10 90 deg corners? If you put an LB or pull box after 4 bends....you are good for another 4. LB's are your friend.

 

[dscheidt]

No extra ground rods or plates would be needed since the bonding conductor comes from the main panel. As an aside - I don't undertand why the American code calls for rods at the garage it doesn't make much sense.

It's for lightning protection. If the detached structure is struck, it is much better to have current going into the earth at the structure, rather than through the remote panels ground rods.

 

[brewchief]

You can buy uf cable in 6-3, it's similar to nm-b but is rated for underground usage, it's normally a flat wide cable so it's not the most fun to work with. It can be run in conduit for protection underground or direct buried, conduit needs to be pretty decent sized.
6-3 would be rated at 55 amps but i belive you could upsize to the next larger common size breaker and meet code.

Sent from my SM-G965U using Tapatalk

 

[TurboEuro88]

At ddawg16's request, here's an overview of the run in its entirety. I'll describe what you're looking at here:

#1 -
This is the main panel box inside in my home. The main feed into the panel box comes from the top. Theres only one or two wires exiting the panel at the bottom leaving me plenty of room to work with. The wires would exit down, then make a 90° towards the corner, then another 90° in the corner, then another 90° down into the crawlspace of my house. It would then make one last 90° (likely by way of a junction box) towards the exterior of the house (final arrow). See this link to explain why the wire has to be run in this fashion: https://m.imgur.com/nntMqsV



#2
This is the part of the run where it goes outside. Ignore the existing 1/2" conduit you see - this is the existing 20A circuit that currently feeds the garage and will be replaced by what I am running. The new conduit will follow much the same path as the shown conduit. The stairs you see will be removed for the conduit install and rebuilt afterward. I am planning to put LB boxes on either end of the conduit against the siding of each structure to make this part of the pull easiest.



#3
This is the garage. When the LB exits into the garage, it'll go into another junction box, then go up the wall, over top the door, then down to where I am planning to install the subpanel. I've measured all studs and this is the closest spot with 16"OC to install the panel.

 

[ddawg16]

Piece of cake.

Your imgur link is not working...but I think I have the gest of it.

Basically, you are going to replace those 1/2" LB's with 1". I'm kinda thinking you might be ahead if you can find a box to fit in that spot where the LB's are.

Since you have a crawl space, I'd be inclined to punch a hole through the concrete foundation for the wire....but then you would have to patch up our vinyl siding in that area.

Is there are reason you don't want to put the panel on the other side of the door? Don't let the studs be the issue.....you just box around it. But if you are going to be running a lot of ckts into the garage from your proposed loc...then stick with that loc.

I'm kinda thinking your adding an outlet for an EV charger.

 

[TurboEuro88]

Updated the link...

I can actually punch a hole through the exterior floor joist above the foundation to gain access to the crawl space without having to drill through concrete. Would make it easier to seal up. One thing to note about the line coming out the house right now (right side of picture #2) is that I can't use that location for this new run. It actually sits above the bottom plate of the exterior studwall, an inaccessible location. I'm going to replace that corner pull with an exterior outlet so it's not a waste of a circuit.

The thought about an EV did cross the mind which is why I wanted to have a bit of extra space in the panel box. Just in case. Though I don't see myself getting one that soon. Overall I have plans for definitely 6 circuits in the garage and want to have space should I want to power a 240v compressor, etc. Just trying to think ahead a bit.

Overall, though, are you thinking I can actually conduit the whole thing if I put in LBs strategically? That would simplify things by being able to just get THWM by the foot.

 

[ddawg16]

Yes on the conduit.

You are ahead if you have a continuous run. Each connection is a potential point of failure.

 

[TurboEuro88]

You are ahead if you have a continuous run. Each connection is a potential point of failure.

That was why I was hoping to do this as a continuous run. That, and splicing together wires with products like the Polaris IT-4 Insulated Connector can get pricey quick.

I think knowing now that I can, in theory, run conduit for the entire run I should be able to use THWN wire. Just a matter of figuring out how exactly I'll make that inside 90° turn in the studwall below my panel box. Worst case I suppose I can just build out the wall a bit so the 90° bend fits. TBD once I open the wall up

 

[ddawg16]

That was why I was hoping to do this as a continuous run. That, and splicing together wires with products like the Polaris IT-4 Insulated Connector can get pricey quick.

I think knowing now that I can, in theory, run conduit for the entire run I should be able to use THWN wire. Just a matter of figuring out how exactly I'll make that inside 90° turn in the studwall below my panel box. Worst case I suppose I can just build out the wall a bit so the 90° bend fits. TBD once I open the wall up

Don't be afraid of using pull boxes/LB's.

 

[TurboEuro88]

Thats we're I am stumped at the moment - how would I run the conduit through the inside corner of the interior studwall next to my panel box (see here: https://i.imgur.com/G7xBdP3.png)? I really won't know what I am up against until I cut away the drywall, but trying to dive in with some semblance of an idea that I know what to do.

 

[ddawg16]

your imgur link is not working

 

[TurboEuro88]

Thats strange... Try this link? https://imgur.com/G7xBdP3

 

[ddawg16]

Never mind....I figured out the link

As mentioned early on, NM can be ran in conduit....it just needs to be rated for wet conditions.

We need one of the experts to chime in to tell us at what point you can run un-sheathed cables.

In that wall space, besides PVC conduit, MC? Flex?

 

[ddawg16]

Thats strange... Try this link? https://imgur.com/G7xBdP3

I replaced the //i.imgur with //m.imgur

 

[TurboEuro88]

I had only thought about running conduit the whole way between the main and subpanels, using various junction boxes and LBs, as a means to only have to buy THWN wire that wouldn't need to be spliced in the middle. I think that based on all the conversations I've had to this point if I can just get conduit all the way from panel box to panel box, that would be the best and easiest way to wire in the subpanel. The only part I don't fully understand yet is how I'd get the conduit to route through the corner of the above linked wall.

It would seem that any other alternative would require splicing wires which I'd prefer to not do. If any of this is wrong, let me know.

 

[TurboEuro88]

Looking into wire at local retailers... Is it common for them to label it as THHN, but if you look up the product details it specifically calls out "For use as THWN-2 in wet or dry locations" and rates it as moisture resistant? It all seems rather confusing when I need THWN wire but the retailers aren't specifically naming it as such.

 

[dscheidt]

Looking into wire at local retailers... Is it common for them to label it as THHN, but if you look up the product details it specifically calls out "For use as THWN-2 in wet or dry locations" and rates it as moisture resistant? It all seems rather confusing when I need THWN wire but the retailers aren't specifically naming it as such.

Almost all american made THHN wire is really multiply rated as THHN, and THWN-2. Much of it is additionally listed as MTW and AWM. (for machine tools and appliance wiring, respectively). The makers need to sell those wires too, and it's much simpler to have one product that meets a bunch of very similar requirements, than to have three or four.

Ask your supplier, or if you're buying in person, look at the wire. It's printed on the side.

 

[wyliesdiesels]

The inspector I talked to said I wouldn't need ground rods at the garage - simply connect the ground in the 4-wire 6/3 run to the ground in the main panel. I may need to clarify that with him, but he definitely mentioned it.

I think the best bet I've found so far is SER cable. My only real question is whether its OK to run in the studs of both structures as well as the conduit. From what I'm reading the SER cable I linked above has THWN wire which is exactly what I'd have to run in the conduit anyway, but has the benefit of being bundled so I can run it in the studs. Is that right?

either the inspector doesnt know what he is talking about or you misunderstood.

Ground rods are required and the EGC/ground wire is not the same as a grounding electrode.

for better clarity, read post #3 on this thread:

https://www.garagejournal.com/forum/showthread.php?t=356460

Also, make sure the neutral in your new subpanel is isolated.

Okay if SER can't be installed underground (even in a conduit) what would be the right product for the job? Admittedly I am a little confused since I've been given a number of suggestions, some of which conflict with others and I don't really know what is or isn't right. At this point I am working with what I've been told so you'll have to forgive me if I sound dumb. Ideally I'd like to avoid having to splice together NM-B and THWN to do the run just for sake of simplicity for me, but understand that to be a viable option.

As far as the grounding goes, I now understand the need for the electrode and will make sure that's done as part of the subpanel install. Sill focused on trying to find the right wire(s) for what I need to do.

You will need to either run conduit from panel to panel or SER inside and splice to individual conductors in conduit for the exterior portion of the circuit.

you could run SER inside and switch to MHF/mobile home feeder

 

[TurboEuro88]

wyliesdiesels -

It would appear I misunderstood the inspector unfortunately. Looking at my notes during our conversation, he had mentioned separated the ground buss from the neutral buss as is standard practice for subpanel installs. What I may have misunderstood was when he mentioned connecting the ground buss to the ground wire going back to my main panel. That said, however, he never actually mentioned a grounding rod specifically, presumably by mistake during our conversation. I've now done enough reading on this to know I need at least one ground electrode. I do need to look into the local code to find out if I need 1 or two ground rods, however.

dscheidt -

Thanks for the clarification. Thats what I was guessing was the case based on what I was reading. It just struck me as odd that I couldn't find wire specifically called out as THWN in the product title, rather only as an almost footnote to the product details.

I'll be getting my permit for the job next week and ordering materials ASAP. With ddawg16's advice I believe I can do a conduit the whole way so I can just run THHN/THWN wires, using junction boxes and LBs to "reset" the bend counter and make the pull easier overall. The hardest part of installing the conduit will be right under the panel box given where it's located and how the conduit has to run to reach my home's crawlspace.

 

[mike93lx]

Two rods.

One is only acceptable if you can prove the resistance measures a certain level. It is not easy to do and requires special equipment. Putting in two negates that. Path of least resistance is to do that.

 

[TurboEuro88]

Ground electrodes are cheap enough that it makes sense to go ahead and do it anyway. I'd imagine the inspector would prefer seeing 2 even if one was the requirement.

 

[ddawg16]

If you have only one ground rod, you have to do a ground resistance test to show the resistance is low enough. It's just cheaper to add a second ground rod. And if you use the right clamps on the ground rod, you can burry the rods and wire. A lot of guys will leave it exposed with plenty of wire...then after inspection drive the rods down below ground level.

Turbo....any chance you can do another outline sketch showing the kitchen where the panel is and where the wire is going....all in one view?

 

[TurboEuro88]

I'll do you one better. Created a 3D drawing that will show you what's going on in my place. Here's an overview showing the entire run from the top down:



And here's a 3-Dimensional view of the area showing how the wires would be run: