Economical wires to subpanel, running inside??

[cdherman]

My attached garage was built in the 70's and the orignal owner put a subpanel that he had salvaged from some earlier installation. As you might imagine, time has come to upgrade.

I have an electric car (Leaf), and the current 6-3 copper to the subpanel is fine. The breaker at the main panel is a 50A

But I need some new circuits and envision putting a 100A panel in the garage. I know I *could* just keep the old 50A breaker at the main and 6-3 copper romax (NM), but like an idiot, I went and bought 60A EVSE (electric vehicle service equipement), so that I would be all set for my next, bigger, better electric car. (Leaf can drink only 14A at 220V)

The hitch with code is that EVSE stuff is continuous duty and that requires derating. So even though the 60A EVSE really never will pull over 48A, it takes a 60A breaker.

I need to decide if the existing 6-3 Cu NM running through the basement and attick, NOT in conduit, is suficient to handle a continuous 48A load? And if so, dare I put a 60A breaker at the main, once I have upgraded the subpanel?

I know it would be cutting it close, additional loads occur while charging this theoretical future electric Hummer, I am nearly certain to pop the breaker at the main.

Or do I need new wire (about 125 ft) and if so, what is cheapest for interior work, not in a conduit...

Tried to find answer, but came up empty so far....

thanks in advance....

 

[wyliesdiesels]

And even if he could do 60a on 6-3NM, voltage drop will be his enemy @ that distance!

 

[pattenp]

He can do 60A breaker on #6 NM. Since #6 is 55A NEC allows you to go the next common breaker size which is 60A. Also at 125' at 60A the VD should be less than 3%.

 

[sparky36000]

He can do 60A breaker on #6 NM. Since #6 is 55A NEC allows you to go the next common breaker size which is 60A. Also at 125' at 60A the VD should be less than 3%.

Yup, he is correct. 55amp isn't a standard size(maybe that's why I've never seen one )My mistake.

 

[cdherman]

Looks like your going to be too small to go to 60amp. #6 NM is only good for 55amps. The cheapest route I can think of to get a 100amp sub panel would be going to a 1/0 type SE aluminum service entrance cable. Maybe a few other guys can chime in with some other ideas.

He can do 60A breaker on #6 NM. Since #6 is 55A NEC allows you to go the next common breaker size which is 60A. Also at 125' at 60A the VD should be less than 3%.

Well, that's the problem -- I keep on finding two different answers. Probably both being correct...

Now, a 100A subpanel does NOT have to be fed with 100A. When you put one in, what the panel is spec'ed out as 100 is simply to say that it will handle 100A (non-continuous) loads, and has a bus capable of that. That's why, BTW, you see some 125A subpanels -- those can be used at 100A continuous loads after derating. (I think)

I want to go with a 100A subpanel due to the number of curcuits that I have to deal with, even though a whole lot of them have little or no draw most or all of the time. Its a modern convenience to have lots of circuits rather than a rats nest somewhere else in the building. I really need about 70A, and probably will be fine with 60A 364 days a year....

I may be making this too complicated:

-- For a 60A subpanel (nevermind that I am putting a 100A bus panel in there and then downgrading with a 60A breaker at the main), will 125 ft of 6 cu be OK, in a continuous duty situation?
-- And will the 60A breaker at the main be adaquate protection?
-- Are there codes that prevent a 60A circuit out of a 60A subpanel?

Well, thanks for the stimulating advice thus far....

 

[pattenp]

... will 125 ft of 6 cu be OK, in a continuous duty situation?....

For the 48 amps , yes. But that's really the max continuous load you should put on a 60A circuit (48A X 125% = 60A).

-- And will the 60A breaker at the main be adaquate protection?....

Yes

-- Are there codes that prevent a 60A circuit out of a 60A subpanel?....

No



***

 

[wyliesdiesels]

He can do 60A breaker on #6 NM. Since #6 is 55A NEC allows you to go the next common breaker size which is 60A. Also at 125' at 60A the VD should be less than 3%.

I forgot about that rule! However, he can only go to the next standard size if the calculated load is less than 55a, IIRCC. It sounds like he wants to run the service at full load continuously which wont work!

And when i did voltage drop calcs, i got just over 3%- 12.9*2*60*125/7.2=26,875CirMils, which is just over the size of #6!

 

[aandpdan]

This 6-3 NM you have, does it have a ground? I'm just trying to clarify.

How about running 2-2-2-4 AL SER cable. It's good for 90 amps, your inspector may even allow you to use it at 100 amp. There's nothing wrong with aluminum for a feeder, it gives you some margin to work with AND it will reduce voltage drop. Repurpose the existing #6 for your car.

 

[pattenp]

I forgot about that rule! However, he can only go to the next standard size if the calculated load is less than 55a, IIRCC. It sounds like he wants to run the service at full load continuously which wont work!

And when i did voltage drop calcs, i got just over 3%- 12.9*2*60*125/7.2=26,875CirMils, which is just over the size of #6!

Yeah, can't disagree with you. I don't do the manual calculation. I use Wireguide software from the Mike Holt site and it comes up with 2.914% @ 240V, but if I use 230V it comes up with 3.04%. The #6 would be at it's continuous load limit with just the car charging so it would be best to up size the wire.

 

[Aceman]

What are the actual nameplate amps on the charger? Not the required breaker size, but the running amps.

What other kind of loads do you have in the garage? Compressor, heater, big table saw, etc?

 

[wyliesdiesels]

This 6-3 NM you have, does it have a ground? I'm just trying to clarify.

How about running 2-2-2-4 AL SER cable. It's good for 90 amps, your inspector may even allow you to use it at 100 amp. There's nothing wrong with aluminum for a feeder, it gives you some margin to work with AND it will reduce voltage drop. Repurpose the existing #6 for your car.

You cant have 2 separate feeds to the same building!

 

[jrsulo]

You cant have 2 separate feeds to the same building!

He said its attached !

 

[wyliesdiesels]

He said its attached !

Whoops, i missed that!

 

[cdherman]

This 6-3 NM you have, does it have a ground? I'm just trying to clarify.

Yes, has ground.

What are the actual nameplate amps on the charger? Not the required breaker size, but the running amps.

What other kind of loads do you have in the garage? Compressor, heater, big table saw, etc?

The 60A EVSE (commonly called charger) can deliver up to 48A, depending on the car. But I am not sure that even a Tesla can take in juice that fast. Most cars are at 32A currently, and my first generation Leaf is at 16A.

So with *this* car, there is no problem at all with the existing wiring. But someday down the road, someone might plug in an EV that can take the full 48A

Then, there *could* be a problem if there are many additional loads. I have a number of power tools, but none that are continuous duty (like a dust collector). And I personally would not be foolish enough to plug in a 48A load and then start my planner and table saw at the same time....

If someone plugged in some additional loads down the road, and started pulling say a full 60A continuously, that would result in the breaker throwing before the 6-3 wire fails, right?

What really matters is the safety of the installation. I don't care if someone down the road throws a breaker a couple times learning that the garage circuits have limitations. But I'd hate to burn the house down....

 

[timewarp]

Since it's an attached garage you could have 2 feeds to it, instead of going to a larger feed and throwing out the existing #6 wires, leave the existing the way it is and just run another #6 run from the main panel to the garage for the car charger, and feed it from another 60 amp breaker in the main panel if there is room. Should be much cheaper than replacing with a larger feed and subpanel.

 

[Aceman]

Yes, has ground.



The 60A EVSE (commonly called charger) can deliver up to 48A, depending on the car. But I am not sure that even a Tesla can take in juice that fast. Most cars are at 32A currently, and my first generation Leaf is at 16A.

So with *this* car, there is no problem at all with the existing wiring. But someday down the road, someone might plug in an EV that can take the full 48A

Then, there *could* be a problem if there are many additional loads. I have a number of power tools, but none that are continuous duty (like a dust collector). And I personally would not be foolish enough to plug in a 48A load and then start my planner and table saw at the same time....

If someone plugged in some additional loads down the road, and started pulling say a full 60A continuously, that would result in the breaker throwing before the 6-3 wire fails, right?

What really matters is the safety of the installation. I don't care if someone down the road throws a breaker a couple times learning that the garage circuits have limitations. But I'd hate to burn the house down....

48A x 125%=60 amp wire.

That means you need either:

#4 Copper NM or SE
#3(or #2) AL SE
#6 Copper THHN in pipe

This wire size is just to feed the charger. Nothing else.

 

[wyliesdiesels]

....If someone plugged in some additional loads down the road, and started pulling say a full 60A continuously, that would result in the breaker throwing before the 6-3 wire fails, right?....

Not necessarily....depends on the breaker and its age, how many trips it has seen, brand, etc. I've seen old breakers that kept nuisance tripping, I've seen other older breakers not trip when they should have(FPE and sh*tsco(Zinsco) come to mind!) and still others trip right when they should have! Breakers are thermal devices. They work by way of heat. The breaker being rated for no more than 60a, means it will trip at >60a. If the wire has 59a or 60a running through it for an extended period of time the wire will heat up and may fail but the breaker might not trip!

And as ACEMAN has pointed out, wire for a continous load is sized @ 125% of the load because of the constant current running through the wire creating the possibility of continous heat, so that #6 NM is too small because of it's 60 deg C rating requirement!

 

[cdherman]

Not necessarily....depends on the breaker and its age, how many trips it has seen, brand, etc. I've seen old breakers that kept nuisance tripping, I've seen other older breakers not trip when they should have(FPE and sh*tsco(Zinsco) come to mind!) and still others trip right when they should have! Breakers are thermal devices. They work by way of heat. The breaker being rated for no more than 60a, means it will trip at >60a. If the wire has 59a or 60a running through it for an extended period of time the wire will heat up and may fail but the breaker might not trip!

And as ACEMAN has pointed out, wire for a continous load is sized @ 125% of the load because of the constant current running through the wire creating the possibility of continous heat, so that #6 NM is too small because of it's 60 deg C rating requirement!

OK, so back to the original question: I am going to need to run a new set of wires to said attached garage, via some non-conduit, hot locations, about 125'. Not afraid of Al wires. What's the cheapest for a 100A cont load?

 

[megalo]

As stated above, 2-2-2-4 aluminum cable (90A) can be had for quite cheap, and if it's rated properly, it can be run indoors without conduit. To get the full 100A, though, you would have to go with 3 gauge copper, I beileve - but when I priced it out, it was about triple the cost just to get those last 10A.

I actually got a Leaf a little over 2 weeks ago. I got my factory EVSE modified to run at 240V ~17A, but I'm contemplating getting or building one so I can get to the full 6.6 kW that the car is capable of. What EVSE are you putting in?

 

[pattenp]

You want to get 4 conductor SER cable. As already said, #2 aluminum you'll need a 90A feeding breaker. Or, you can use #1 aluminum with a 100A feeding breaker. Also if you are looking at 100A continuous load you need 125A. The continuous should be no more than 80% of the circuit capacity.

 

[cdherman]

As stated above, 2-2-2-4 aluminum cable (90A) can be had for quite cheap, and if it's rated properly, it can be run indoors without conduit. To get the full 100A, though, you would have to go with 3 gauge copper, I beileve - but when I priced it out, it was about triple the cost just to get those last 10A.

I actually got a Leaf a little over 2 weeks ago. I got my factory EVSE modified to run at 240V ~17A, but I'm contemplating getting or building one so I can get to the full 6.6 kW that the car is capable of. What EVSE are you putting in?

I had the factory portable EVSE modded as well. Then, since they (Washington) re-instated the tax credit for EVSE equipment, I decided that I would like a proper EVSE. And since I found a good deal for a Level III EVSE 60A (48A cont load) Clipper Creek off eBay, I bought that.

Of course, sounds like you have a 2013 Lead that can take 6.6 kw (level II). My 2012 can only handle 3.3kw (16A x 220V).

I don't need the larger charger now --- just bought it cause it was only marginally more expensive. And at the time I *thought* I had 100A service to the garage. My mistake partially.

That's the decision problem here -- I may NEVER pull 48A with this EVSE. I don't even own a vehicle that can pull 32A.

I would be upgrading the wires for a future vehicle that I or the next owner might own.....

For now, I am going to keep the 6-3, put in a 60A breaker at the service entrance, and just keep the current setup. If I buy a vehicle down the road that can take 48A, I'll deal with it then by upgrading the wires, and/or adding a second sub panel dedicated to the EVSE.

I assume some 4-4-4-6 ish AL would be good for 60A cont load, if that was the ONLY thing ever running through it.

 

[pattenp]

......
I assume some 4-4-4-6 ish AL would be good for 60A cont load, if that was the ONLY thing ever running through it.

When you start talking continuous loads your circuit needs to be sized at 125%. So for 60A continuous load you need 75A circuit, but the next standard size is 80A. If you just want a 60A circuit then the continuous load should be no more than 80% or 48A. A 60A circuit will need #4 Al.