Sizing new power feed to small garage

[AntonLargiader]

I'm replacing the old (long gone) underground power to an 18x18 detached garage. It's not a shop; it's just parking although I do want a 240 outlet for whatever comes up. Basically lights (maybe 200W total) and a few outlets. I occasionally use a portable air compressor out there, and the car's block heater runs in the early morning which is 1000W. We may plug in a Volt at times which can draw 12A. Worst case we see now is the Volt and the block heater running together but code might feel otherwise. Other outlet loads are pretty rare, and would be when the cars aren't plugged in. It's not a shop.

It's about 100' from the main panel in the house across the basement, down, underground and back up to the garage panel which is at this point an 8-position Eaton MLO.

The heater and the Volt look like 20A sustained. Would 10/3 UF do the trick? They are both 120V and could be on separate legs but of course that would be up to me.

Complicating this is that if we buy a Leaf in the future it could demand up to 6.6kW, requiring a 40A circuit. I don't know if it's worth doing that now.

 

[rockwithjason]

imho, it's not worth running a feeder less than 60a. most people will never outgrow that and the cost is reasonable.

 

[pattenp]

I agree with rock, do at least a 60A feed.

 

[AntonLargiader]

That may be the real answer, then. It's been mentioned before.

In that case, what's the most cost-effective way? The actual distance is about 35' inside and then 50' outside. I have a bunch of 6 that I think will do the distance three times. I'm not home so I can't say if it's THWN or whatever. Last time I was working on this (last summer maybe) I was evaluating pulling that through some conduit but never got around to pricing it out. Direct-bury UF seems so much easier, although it's 6" more digging.

 

[theoldwizard1]

... I have a bunch of 6 that I think will do the distance three times. I'm not home so I can't say if it's THWN or whatever.

I needs to be THWN, but most THHN is dual rated.

Last time I was working on this (last summer maybe) I was evaluating pulling that through some conduit but never got around to pricing it out. Direct-bury UF seems so much easier, although it's 6" more digging.

Yes, the conduit will cost some money and you will have to run THWN in conduit inside the building.

Most people around here recommend conduit under ground, mainly for easy of replacement or adding additional wires. Best price on UF-B is about $2.30/foot. That would buy a lot of conduit !

 

[AntonLargiader]

I'll have to verify the lengths and rating.

If I can use that 6 wire, what size ground do I need to run with it? I see the grounds on the UF-B are sometimes smaller than the main conductors.

 

[AntonLargiader]

The 6 wire I have is TW. "Hatfield Hatvinol 6 AWG TW 600V Oil resistant"

From Republic wire: "Type TW insulated wire are designed to operate at conductor temperatures of 60oC (140oF) in wet and dry locations."

 

[pattenp]

TW is okay. TW is 60 deg C wire whereas THWN is 75 deg C wire. The TW will be fine for no more than 60A. It does need to be in conduit for the whole run.

 

[wyliesdiesels]

I'll have to verify the lengths and rating.

If I can use that 6 wire, what size ground do I need to run with it? I see the grounds on the UF-B are sometimes smaller than the main conductors.

For 60a breaker u will need a #10 green insulated wire for the EGC.

Dont forget ground rods and make sure the neutral bar is isolated in the subpanel.

 

[AntonLargiader]

Thanks! That was the missing part. Time to cost it out.

MHF 2-2-4-6 is a suitable alternative, right? In case the lengths I have don't work? It's less than $2/foot, plus conduit all the way (although not technically needed outdoors I would do it anyway).

 

[AntonLargiader]

BTW the MHF would obviously be harder to pull, especially at the main panel, due to size. Is there a smaller all-in-one cable like that that would be as cheap?

 

[pattenp]

BTW the MHF would obviously be harder to pull, especially at the main panel, due to size. Is there a smaller all-in-one cable like that that would be as cheap?

Not really. If you just want wire large enough for 60A then just buy #4 XHHW-2 in the length you need for the 4 conductors. If you buy a #6 or smaller for the EGC then you need to get a green wire so it's just easier to use the same #4 for the ground and tape the ends green.
https://www.wireandcableyourway.com/XHHW-2/

Edit: The XHHW-2 is not a direct bury wire so it needs to be in conduit the whole run.

 

[Bert_]

Underground wire like the #2 MHF is commonly availiable down to a #6

I would do at least a #4 which gets you 60A. In my area I get 4-4-4 plus adding a #6 ground for less than a dollar a foot.

 

[wyliesdiesels]

Underground wire like the #2 MHF is commonly availiable down to a #6

I would do at least a #4 which gets you 60A. In my area I get 4-4-4 plus adding a #6 ground for less than a dollar a foot.

MHF is NOT available in sizes smaller than 2-2-4-6

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet15

 

[theoldwizard1]

MHF 2-2-4-6 is a suitable alternative, right?

The 4 AWG conductor for neutral should be pre-approved by your building department before purchase. In GENERAL, a smaller neutral is allowed if there are a "large" percentage of 240 circuit (i.e. circuits that do NOT use neutral).


Check the price on 2-2-2-4. Probably worth the cost difference.

 

[Bert_]

MHF is NOT available in sizes smaller than 2-2-4-6

I used the MHF term because it seems most people are familiar with it. Your right that it isn't the correct name, but it is equivalent.

And yes the wire in the photo is triple-rated (USE-2 or RHH or RHW-2) even though it doesn't say it. You would also have to add a ground wire or get it in quadruplex when using it for a sub feed.

 

[wyliesdiesels]

I wouldnt even bother with that.

 

[Bert_]

I wouldnt even bother with that.

Why? The OP seems to have decided on a 60A feeder, #4 would fit the bill perfectly.

Heck, originally he talked about 10/3 UF. This would give him 2X the power at a similar cost

 

[AntonLargiader]

Thanks everyone for the info. I am actively wondering about the same wire choices that you are discussing. Looking for MHF (easily ordered online from Home Depot for instance) I see a host of other inexpensive options such as SEL but I simply don't know what's appropriate and what's not.

The 10-3 was (is?) a totally viable option, it's just for a different need. Much easier to install but it doesn't give me the 40A EVSE circuit that I will probably want. I didn't realize how inexpensive these heavier wires could be. Or, I suppose, how expensive UF-B is relative to these.

I think I want the easiest-to-handle cable that will give me a 40A circuit. Preferably without conduit indoors, but it's not that big a deal. Access to the main panel is a bit tight. I suppose I could run a jacketed line from the panel to a junction box at the outside wall, and then conduit from there.

Speaking of the main panel, I need to audit that. It's a 1930 house to which 200A service was added, so the new main has a 50A double breaker feeding the original. During some recent renovation the remainder of the knob & tube was decommissioned and replaced with Romex. The 200A panel is full except for one double opening, but many of the circuits seem to feed very light loads (like a single string of LED lights). I'm not sure what's in the small panel.

 

[AntonLargiader]

...In GENERAL, a smaller neutral is allowed if there are a "large" percentage of 240 circuit (i.e. circuits that do NOT use neutral).

If I go with 60A, I will have a 40A 240 circuit.

 

[bczygan]

It seems these discussions always start out with a small feeder to supply just a light and one small load.

Usually they end up with either a 60 or 90A feed to a sub, with conduit sized properly.

This gives future proofing and is always a good idea.

Bill

 

[AntonLargiader]

To avoid poisoning this thread with the issues specific to my house, I will start a new one about how I can get 50A or 60A out of my existing panel. I started mapping it out and what a mess. There are breakers that serve only one receptacle, and the older portion of the wiring has j-boxes that house multiple circuits with paper-wrapped wires in galvanized BX. I need to remove some unused circuits and pretty much rewire the basement. It's small.

 

[bandlaw]

I would suggest considering a 100A panel, assuming you have the space for a double-pole 100A breaker in your existing panel, and that won't overload it, per code, etc. Again - you'll only want to run it once, and power needs are probably only going up for the foreseeable future (more toys to play with, etc.) so go ahead and run 100A and be done.

I ran #2 wire in LTMC from my main to my sub, then am running a 1" main line until I get to the junction box to begin breaking out individual circuits. I'm dealing with a fully finished in garage at this point, so I refuse to open the drywall after what I've been.

Hope this helps and good luck!

 

[wyliesdiesels]

Why? The OP seems to have decided on a 60A feeder, #4 would fit the bill perfectly.

Heck, originally he talked about 10/3 UF. This would give him 2X the power at a similar cost

Because for the same price or cheaper he can have more ampacity.

Thanks everyone for the info. I am actively wondering about the same wire choices that you are discussing. Looking for MHF (easily ordered online from Home Depot for instance) I see a host of other inexpensive options such as SEL but I simply don't know what's appropriate and what's not.

The 10-3 was (is?) a totally viable option, it's just for a different need. Much easier to install but it doesn't give me the 40A EVSE circuit that I will probably want. I didn't realize how inexpensive these heavier wires could be. Or, I suppose, how expensive UF-B is relative to these.

I think I want the easiest-to-handle cable that will give me a 40A circuit. Preferably without conduit indoors, but it's not that big a deal. Access to the main panel is a bit tight. I suppose I could run a jacketed line from the panel to a junction box at the outside wall, and then conduit from there.

Speaking of the main panel, I need to audit that. It's a 1930 house to which 200A service was added, so the new main has a 50A double breaker feeding the original. During some recent renovation the remainder of the knob & tube was decommissioned and replaced with Romex. The 200A panel is full except for one double opening, but many of the circuits seem to feed very light loads (like a single string of LED lights). I'm not sure what's in the small panel.

Theres no such cable as SEL. Perhaps u meant SER?

SER is not allowed to be used underground even in conduit.

 

[AntonLargiader]

I would suggest considering a 100A panel, assuming you have the space for a double-pole 100A breaker in your existing panel

As I mentioned, it's not a shop. It's a 1.5 car garage that may or may not get a 40A EVSE. Without the EVSE I could probably get away with no panel at all, as before, but the EVSE is the future-proofing that is appropriate for this outbuilding. More of a shed really.

Believe it or not, some people actually just park cars in their garages. I have another outbuilding that would be a workshop if I need it, but my mechanical workspace isn't on my property at all. I don't really want that intruding on my home life (heresy, I know!).

 

[AntonLargiader]

Theres no such cable as SEL. Perhaps u meant SER?

I'm sure you're right. And I was also wrong about the subpanel breaker in the main panel; it's 90A feeding the original knob/tube/BX panel.

 

[pattenp]

I used the MHF term because it seems most people are familiar with it. Your right that it isn't the correct name, but it is equivalent.

And yes the wire in the photo is triple-rated (USE-2 or RHH or RHW-2) even though it doesn't say it. You would also have to add a ground wire or get it in quadruplex when using it for a sub feed.

Be aware that Stabiloy is one of the few that has wire listed as URD which is triple rated. Southwire's URD is only single rated as USE and is not to be used inside of the structure, it's for outside only. Be sure of what you buy.

 

[Bert_]

^^ A good point whatever wire you choose make sure it has the correct ratings

As far as splicing to a cable for the inside portion of the run it would probably be easier to just run a bit of PVC/ect. rather than having to deal with another box and and splices. Unless the inside run is very long or a difficult path.

 

[AntonLargiader]

The inside portion is just low-ceiling basement, and the obvious run is right in the walking path, so I'd prefer to not have a conduit hanging below the joists. But I'll have a better look as I do some clean-up work down there soon.

 

[theoldwizard1]

I used the MHF term because it seems most people are familiar with it. Your right that it isn't the correct name, but it is equivalent.

And yes the wire in the photo is triple-rated (USE-2 or RHH or RHW-2) even though it doesn't say it. You would also have to add a ground wire or get it in quadruplex when using it for a sub feed.

Also note that URD 4-Stabiloy "Vassar" only has 3 conductors according to picture (says 4-4-4)

 

[wyliesdiesels]

Also note that URD 4-Stabiloy "Vassar" only has 3 conductors according to picture (says 4-4-4)

Thats why Bert said a ground wire would need to be added.

I used the MHF term because it seems most people are familiar with it. Your right that it isn't the correct name, but it is equivalent.

And yes the wire in the photo is triple-rated (USE-2 or RHH or RHW-2) even though it doesn't say it. You would also have to add a ground wire or get it in quadruplex when using it for a sub feed.

 

[AntonLargiader]

Can I run the garage 60A sub from the existing 90A sub? Reason I ask is that nearly all of the loads on the current 90A sub (the original house panel) go to the other side of the basement. I could massively clean things up by moving it, and the garage is on that side of the house as well. I could put the 90A sub on the wall toward the garage, making that connection way easier and I would do away with the indoor portion of the run.

The affected wiring is all BX and Romex stapled to the joists, so pretty easy to move. The 90A sub has the well pump (double 15), some lights/outlets, and a 40A receptacle for an electric range that is used maybe once per year. It also has the electric water heater but I can move that to the main panel.

 

[TractorJeff]

Yes you can run the 60 from the 90.

 

[AntonLargiader]

Well, here is a sample of what I have to clean up before I do anything down there regarding power to the garage..

This isn't the only j-box with live cut-off knob & tube hanging out.


This work of art powers the basement lights, j-boxes with cut-off wires sticking out in addition to the Romex that you can see, some old BX that goes upstairs, and... some other stuff that I need to follow.


Time to start tagging and stripping out. The box in the rear of the second pic is actually useful; the basement lights are fairly tidily run to it underneath all of the other spaghetti.

 

[sberry]

There is a difference in quads, I believe HD has the number 2 N and it was cheaper as well. A 4 would be a little cheaper and run in 1 1/4 too which would be easier.

 

[AntonLargiader]

In my second pic, the sole purpose of the mostly-hidden box was to energize the dangling Romex and cloth-wrap. Now it's gone along with some of the other dangling live stuff.

And it's on a 30A breaker just for good measure... :-/

 

[AntonLargiader]

I'm back to planning the basement subpanel move as the first step. It looks like 2-2-2-4 AL SER (which is what serves the current sub) is still allowed to go to 90A if uninsulated, so I would do that. The SER would run across the unfinished basement between or under the joists (the 'under' part is running behind a wooden crossbeam to it's actually pretty well protected). Total length would be just under 40'. As for establishing that 90A is sufficient, I couldn't find a lot about sizing subpanels so I applied a few of the regular load calc techniques and came up with 62A:
- 8100 VA for garage. That's 6600W for an EVSE and 1500W for a block heater. That's worst case. Lights and outlets aren't going to be in use during the moments that the EVSE and block heater are drawing max current.
- 4050 VA for four 15A branch circuits. 3000 VA plus 35% of the other 3000.
- 2025 for the 15A 240V well pump circuit at 75%
- 675 for the other 25% of the well pump because it's the largest motor
- total 14,850 VA divided by 240 = 62 A.

So it looks like even at 90A I have some cushion even if my garage load calc is off. In reality the four branch circuits are very lightly loaded; they're just separated because they are diverse in nature.

Everything look good on the SER and the load?

 

[AntonLargiader]

Oh, and one more question on the sub relocation. The spot I have in mind is between two windows. The concrete there is 12" wide, and then there is a 2x4 on each side (1.75" each) that form the window frame for a total of 15.5". I can maintain 30" clear width in front and I will relocate the water lines that run above it. Like the rest of the basement there's about 6'2" headroom there.

Any issues with that location? I can clean it up and take a pic if it helps.

 

[mike93lx]

I'm back to planning the basement subpanel move as the first step. It looks like 2-2-2-4 AL SER (which is what serves the current sub) is still allowed to go to 90A if uninsulated

edit: Wanted to highlight that SER and MHF (both discussed in this thread) are different and their names are not interchangeable. The distinction is important since SER has specific limitations (like it can't be underground)

 

[AntonLargiader]

I do mean SER. Lowes calls it "2-2-2-4 Aluminum SER Service Entrance Cable (By-the-Foot)" but maybe you know it as #2 SER or something else?

EDIT: Can't staple MHF to the joists. I'm crossing the basement so underground really isn't an issue. Current sub uses the same SER I call out.