Questions about detached garage

[MOD220]

I'm in similiar situation, and could use some help:

Home built in the 1920s, but after major renovation I built a brand new detached garage recently. My electrician said there are two options:

1) dig a line from panel in basement to the garage to get a 240V out there....Garage is probably 60-75' from panel
2) install a brand new service for the garage only

He said the cost would be about the same, $2-3k, which I can't figure out. Option 2 entails a whole new panel, new service, etc. While option 1 is dropping wiring in the dirt (I would be responsible for the trench).

Can someone clarify what other expenses are involved with option 1? We have a 200A main panel, a sub panel, and house is 5k sq ft, two AC/furnaces, etc., so I imagine I'm using a lot of our capacity during peak times. This is why he suggested option 2, which would allow a dedicated 100-200 amp panel just for cars...

 

[mongo]

I'm in similiar situation, and could use some help:

Home built in the 1920s, but after major renovation I built a brand new detached garage recently. My electrician said there are two options:

1) dig a line from panel in basement to the garage to get a 240V out there....Garage is probably 60-75' from panel
2) install a brand new service for the garage only

He said the cost would be about the same, $2-3k, which I can't figure out. Option 2 entails a whole new panel, new service, etc. While option 1 is dropping wiring in the dirt (I would be responsible for the trench).

Can someone clarify what other expenses are involved with option 1? We have a 200A main panel, a sub panel, and house is 5k sq ft, two AC/furnaces, etc., so I imagine I'm using a lot of our capacity during peak times. This is why he suggested option 2, which would allow a dedicated 100-200 amp panel just for cars...

Option 1 seems like a cheaper install and you avoid the reoccurring fee for the second meter.

I reccomend conduit if you go that route.

 

[davewill]

I'm in similiar situation, and could use some help:

Home built in the 1920s, but after major renovation I built a brand new detached garage recently. My electrician said there are two options:

1) dig a line from panel in basement to the garage to get a 240V out there....Garage is probably 60-75' from panel
2) install a brand new service for the garage only

He said the cost would be about the same, $2-3k, which I can't figure out. Option 2 entails a whole new panel, new service, etc. While option 1 is dropping wiring in the dirt (I would be responsible for the trench).

Can someone clarify what other expenses are involved with option 1? We have a 200A main panel, a sub panel, and house is 5k sq ft, two AC/furnaces, etc., so I imagine I'm using a lot of our capacity during peak times. This is why he suggested option 2, which would allow a dedicated 100-200 amp panel just for cars...

The electrician is doing about the same work either way. He puts a new panel in the garage, and wires the circuits you need. The new service requires a more expensive panel with a meter, but the utility is probably responsible for running the service wire to the garage. Running it from the house requires paying for the long wire and hooking it up.

The more important aspect would be whether you have the capacity on your existing service, and whether a second service is going to cost more or less on an ongoing basis. It would also have an effect if you decided to install solar.

 

[Sophias_dad]

I'd get the new panel/meter in the garage. Its only a matter of time before you want more electric cars....(I'm not kidding here)

Of course, you need to check the cost for the extra meter/service. I could imagine a second meter/service for the same house being discounted somewhat.

 

[darth_vad3r]

I'd get the new panel/meter in the garage. Its only a matter of time before you want more electric cars....(I'm not kidding here)

Of course, you need to check the cost for the extra meter/service. I could imagine a second meter/service for the same house being discounted somewhat.

Except for the point @davewill made about going solar ... how is that complicated by having 2 service drops ... you'd want solar to be able to power your house or the car or feed back to the grid ... but can you connect the same solar installation across two separate services?

 

[mongo]

I could imagine a second meter/service for the same house being discounted somewhat.

It can be the opposite. A garage doesn't have the guaranteed load a house does, so some pocos won't install one, or will charge extra to do so.

 

[Sophias_dad]

Except for the point @davewill made about going solar ... how is that complicated by having 2 service drops ... you'd want solar to be able to power your house or the car or feed back to the grid ... but can you connect the same solar installation across two separate services?

No, you couldn't connect that same solar installation to two services at once, but unless that 5000 sq ft home is a single level, its unlikely the panels would generate enough to exceed the power draw of the main home. If you REALLY wanted, you could partition the panel-space so some is fed to the second meter, but then you need some really long wires(again!)... or just put some panels on the garage...

 

[233.3]

Looks to me like 4 wires are entering from the rear of the panel, two black (hots), one white (neutral), and one green (ground). Could be 8AWG or 6AWG, which would be consistent with 240v 40a feeding the panel and the four 20a breakers, but I'm finding it really hard to tell. Does anybody else see it differently? The pics are not all that clear.

If you zoom in on IMG_0096 it is clear that the feeder going to the left lug is 12 AWG THHN.

 

[user212_nr]

@233.3 thanks. I was going to say your comment wasn't useful as I got things sorted out, but I was perplexed why the overhead cable was 10 AWG UF and this entrance cable 12 AWG - being THHN that makes them similar. It looks like it could support 30A, but it is clearly designed 240v 20A (either as a safety margin or just that the garage door and lights would never need more than 20A).

thanks @davewill and others who mentioned about the ground rod. I did have one installed. Also cleaned off the dust and it doesn't look that bad. The panel itself is is fairly new, still for sale. Mainly, I had needed to figure out about the 240V and how that worked in the U.S.

 

[mongo]

233.3 thanks. I was going to say your comment wasn't useful as I got things sorted out, but I was perplexed why the overhead cable was 10 AWG UF and this entrance cable 12 AWG - being THHN that makes them similar. It looks like it could support 30A, but it is clearly designed 240v 20A (either as a safety margin or just that the garage door and lights would never need more than 20A).

12 AWG THHN is only 30A if both ends are terminated on 90C rated terminals. This is not equivalent to 10AWG which is rated at 30A with 60C terminals.
Wire Current Ampacities NEC Table 310-16
https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm
Since your equipment (the panel) is 100A or less, you must use the 60C rating:
When Can I Use 90°C Conductor Ampacity for Feeders?

 

[user212_nr]

Makes sense. Wasn't going to go over the 20A.

 

[233.3]

12 AWG THHN is only 30A if both ends are terminated on 90C rated terminals. This is not equivalent to 10AWG which is rated at 30A with 60C terminals.
Wire Current Ampacities NEC Table 310-16
Since your equipment (the panel) is 100A or less, you must use the 60C rating:
When Can I Use 90°C Conductor Ampacity for Feeders?

In the link (a)(1) and (a)(3) seem to be in conflict with one and other. What am I missing?

(a) Equipment Rated 100A and Less.

(1) Conductor sizing for equipment rated 100A or less must be sized using the 60°*C temperature column of Table 310.16. Figure 110-14C1a1 01 NEW

(3) If the terminals are listed and identified as suitable for 75°*C, then conductors rated not less than 75°*C can be sized to the 75°*C temperature column of Table 310.16. See Figure 110-25​

 

[mongo]

In the link (a)(1) and (a)(3) seem to be in conflict with one and other. What am I missing?

(a) Equipment Rated 100A and Less.

(1) Conductor sizing for equipment rated 100A or less must be sized using the 60°*C temperature column of Table 310.16. Figure 110-14C1a1 01 NEW

(3) If the terminals are listed and identified as suitable for 75°*C, then conductors rated not less than 75°*C can be sized to the 75°*C temperature column of Table 310.16. See Figure 110-25​

Good catch, 3 overrides 1. Wording could be better.

 

[user212_nr]

"terminals are listed and identified as suitable for 75°*C" is the case. Still don't need more than 20A.

 

[user212_nr]

So I have one more idea I have been thinking about, though I don't necessarily want to do it.

The garage is served with 2 overhead wires, each with 2 wires and a ground. When charging the Tesla at 240v the two black wires (phase 1, phase 2) are used, one from each overhead and the two white wires are unused. When running an outlet, one black wire (phase 1) and one neutral are used. They can't both be used as there is only 20A and the Tesla uses 16A continuous, but with that strategy, at any given time, there are 2 unused wires.

Would it be better to put another 20A phase over one of the white wires, and then wire directly 2 outlets (240v 20A, 120v 20A), then I could charge the Tesla, and a 16A continuous load (ex. 12V battery charger could be put on the 120v outlet)?

I theory it should work, assuming that both the white and black wires are expected to carry the same current in the wire design, but disadvantages are (I think):
a) using a white wire to carry current might confuse someone
b) possibly pushing the system closer to its max

This is not really a problem, as now the 120v outlet is rarely used, and I'd rather not do more work, but still thinking about it.

 

[mongo]

So I have one more idea I have been thinking about, though I don't necessarily want to do it.

The garage is served with 2 overhead wires, each with 2 wires and a ground. When charging the Tesla at 240v the two black wires (phase 1, phase 2) are used, one from each overhead and the two white wires are unused. When running an outlet, one black wire (phase 1) and one neutral are used. They can't both be used as there is only 20A and the Tesla uses 16A continuous, but with that strategy, at any given time, there are 2 unused wires.

Would it be better to put another 20A phase over one of the white wires, and then wire directly 2 outlets (240v 20A, 120v 20A), then I could charge the Tesla, and a 16A continuous load (ex. 12V battery charger could be put on the 120v outlet)?

I theory it should work, assuming that both the white and black wires are expected to carry the same current in the wire design, but disadvantages are (I think):
a) using a white wire to carry current might confuse someone
b) possibly pushing the system closer to its max

This is not really a problem, as now the 120v outlet is rarely used, and I'd rather not do more work, but still thinking about it.

It is possible electrically (4 insulated wires), but not allowed under NEC (white as power only for switches). (neither is the current setup (non-grouped wires feeding a circuit))

 

[Bill25cycle]

So I took another look at the sub-panel box, and there are 5 wires coming from the outside - 2 black wires, 2 white wires, and a red wire. One of the white wires has black tape on it towards the end, and the red wire is mostly covered in green tape (in the photo, you can see a very small bit of red where it enters the box). The two white wires are basically connected to the same place, and the red wire is close by (not clear if it is connected to the white wires).

I'm a bit confused as to what these wires are, especially as there are two identically looking overhead wires coming from the house, and an odd number of wires. The wires all say "12 AWG"

Some posters have stated that it is missing a ground wire - so maybe there are 2 black and 2 white both live that could be used to make 240v, and then the 12 gauge copper wire, when they are duplicates, could get 70 amps? That doesn't account for the red/green wire of course.

User212_Elijah I'm curious: What is the feed inside the house for your garage, is it a single 30 ampere fuse or circuit breaker? If you measure between the LEFT SIDE Big Lug and the LOWER of the 2 Big lugs on the right side, I'd assume on both you would see 120 volts to the BIG lug on the Top RIGHT side.... Do you get 0 volts or 240 volts from the left big lug to the right lower big lug?

I hope this plumber is better with water than he is with electric juice... I don't see any box fitting on the entrance wires nor is there any rubber or friction tape around the hole, so eventually this could cut through the wire's insulation and energize the garage breaker box.

If you are sure there are only 2 overhead wires to the garage, and he has 5 wires tied to the 2 at the garage - then it sounds like you only have 120 volts there.
What size is the feed breaker for this inside your home? Is it a single breaker or does it look like 2 breakers wide (double pole)? Hopefully, they didn't run 2 leg wires overhead and buried the neutral in the ground so that what APPEARS to be a 2 wire feed to the garage is actually 3 or more.

But it looks like, if you only have 120 volts to the garage, you may want something a bit better for your Model 3 - unless you are satisfied with the way it is currently working.

*******OH my mistake -just reread. Your plumber friend ran 2- 20 amp flying romexs to the garage and that's how you get the 20 amps at 240.....

Well, in a pinch it sounds like you could charge your tesla at either 12 or 16 amps 240 if you have nothing else on - but the whole installation seems a bit ricketty. If the layout of your property prevents going underground, I'd try getting some quadplex cable between the house and garage for the overhead span. Since this cable cannot be used for anything else, you'd have to splice it at each end and have a weatherhead at each end to keep the elements out of the main garage and house cables. Otherwise 6-3 UF with ground (underground feeder) is good for 55 amperes and would handle at least 1 Tesla charging along with other stuff in the garage, fed from a 60 ampere double pole breaker in your main panel.

So, basically you can do anything you want, but your plumber would not be my first choice to install the stuff.

 

[Bill25cycle]

I'm in similiar situation, and could use some help:

Home built in the 1920s, but after major renovation I built a brand new detached garage recently. My electrician said there are two options:

1) dig a line from panel in basement to the garage to get a 240V out there....Garage is probably 60-75' from panel
2) install a brand new service for the garage only

He said the cost would be about the same, $2-3k, which I can't figure out. Option 2 entails a whole new panel, new service, etc. While option 1 is dropping wiring in the dirt (I would be responsible for the trench).

Can someone clarify what other expenses are involved with option 1? We have a 200A main panel, a sub panel, and house is 5k sq ft, two AC/furnaces, etc., so I imagine I'm using a lot of our capacity during peak times. This is why he suggested option 2, which would allow a dedicated 100-200 amp panel just for cars...

Mod220 the one thing you never mentioned is how many ev's do you have, how many can the garage hold, and how fast do you insist on charging them?

200 amps is usually a lot,unless you have electric heat, hot tubs, saunas, electric cooking in 2 kitchens, multiple laundry rooms, big hot tub, etc.

IN my area a separate service would be billed at commercial rates since a residential premises can only have one meter by my utility's rules. But every company is different so you might want to check on that. I would think it would be cheaper to enlarge the house service to 300 amperes with 100-150 going to the garage and the existing 200 amp main breaker panel for the house. IN this case you would have 2 mains subtending from the new 300 ampere meter socket, and if load calculations allow, it doesn't matter that both 'main breakers' add up to more than the service rating..

 

[user212_nr]

User212_Elijah I'm curious: What is the feed inside the house for your garage, is it a single 30 ampere fuse or circuit breaker? If you measure between the LEFT SIDE Big Lug and the LOWER of the 2 Big lugs on the right side, I'd assume on both you would see 120 volts to the BIG lug on the Top RIGHT side.... Do you get 0 volts or 240 volts from the left big lug to the right lower big lug?

I hope this plumber is better with water than he is with electric juice... I don't see any box fitting on the entrance wires nor is there any rubber or friction tape around the hole, so eventually this could cut through the wire's insulation and energize the garage breaker box.

If you are sure there are only 2 overhead wires to the garage, and he has 5 wires tied to the 2 at the garage - then it sounds like you only have 120 volts there.
What size is the feed breaker for this inside your home? Is it a single breaker or does it look like 2 breakers wide (double pole)? Hopefully, they didn't run 2 leg wires overhead and buried the neutral in the ground so that what APPEARS to be a 2 wire feed to the garage is actually 3 or more.

But it looks like, if you only have 120 volts to the garage, you may want something a bit better for your Model 3 - unless you are satisfied with the way it is currently working.

*******OH my mistake -just reread. Your plumber friend ran 2- 20 amp flying romexs to the garage and that's how you get the 20 amps at 240.....

Well, in a pinch it sounds like you could charge your tesla at either 12 or 16 amps 240 if you have nothing else on - but the whole installation seems a bit ricketty. If the layout of your property prevents going underground, I'd try getting some quadplex cable between the house and garage for the overhead span. Since this cable cannot be used for anything else, you'd have to splice it at each end and have a weatherhead at each end to keep the elements out of the main garage and house cables. Otherwise 6-3 UF with ground (underground feeder) is good for 55 amperes and would handle at least 1 Tesla charging along with other stuff in the garage, fed from a 60 ampere double pole breaker in your main panel.

So, basically you can do anything you want, but your plumber would not be my first choice to install the stuff.

I think the two overhead wires came with the house. I've got the charging done at 240v 16A, but that leaves no current for the garage that no one uses. There's no problem left to solve, really, just was curious about the extra wire.

I'm leaning more towards the idea of moving, so investing a big project doesn't make sense. I don't mind the electrical stuff, or buying the wire, but re-doing the service entrance would be a big undertaking.