50A NEMA on 60A SubPanel

[PCARs]

Hi All, picking up my first Tesla. RWD Model 3 and getting quotes for home charger.

One of the Tesla certified installers wants to run a 50A NEMA outlet off my subpanel in the garage. The subpanel connects to my main electric panel outside the house on a 60A circuit. The installer said this was sufficient as their max estimated load on the 60A circuit, assuming 40A draw on the charger, was 59A (I know the RWD will max at 32A charge too). 59A potential draw on a 60A circuit seems really high and I'm nervous I might be routinely tripping this 60A circuit which includes almost everything in the house on it too. (A/C, Dryer and Oven are all on their own independent circuits from the main electric panel)

Another installer wanted to run an independent 50A circuit to the garage from my main electric panel outside the house, but it will be an extra $1K to do so.

Does anyone see a concern by just running the 50A NEMA outlet off the 60A subpanel in the garage?

 

[ewoodrick]

A 50A NEMA 14-50 plug will charge only at 80% of the 50A or 40A. If there is nothing else on the 60A panel, then you should be in great shape!

 

[PCARs]

A 50A NEMA 14-50 plug will charge only at 80% of the 50A or 40A. If there is nothing else on the 60A panel, then you should be in great shape!

The rest of the house (minus AC, Dryer and Oven) is on the same 60A subpanel. That's why I'm concerned I might overload it.

 

[BigNick]

The 60A circuit that feeds the subpanel should have no more than 48A continuous draw.

IMO you're better off to go with a NEMA 14-30R instead of the NEMA 14-50R if using the subpanel feed (ie, you don't want to spend the extra $1K for the 50A independent circuit.)

 

[PCARs]

The 60A circuit that feeds the subpanel should have no more than 48A continuous draw.

IMO you're better off to go with a NEMA 14-30R instead of the NEMA 14-50R if using the subpanel feed (ie, you don't want to spend the extra $1K for the 50A independent circuit.)

Thanks for the feedback. Does the 80% rule apply still to a circuit?

I wonder why this electrician is saying 59A draw on a 60A circuit is okay then?

 

[ewoodrick]

The rest of the house (minus AC, Dryer and Oven) is on the same 60A subpanel. That's why I'm concerned I might overload it.

Oh yea, it will overload it.

The "rest of the house" isn't commonly on a sub-panel. Are you sure? Do you have dozens of breaker in the panel? How many breakers are they.
The "rest of the house" is commonly in the main panel and that includes the dryer and oven, and the AC is often on a subpanel.

 

[PCARs]

Oh yea, it will overload it.

The "rest of the house" isn't commonly on a sub-panel. Are you sure? Do you have dozens of breaker in the panel? How many breakers are they.
The "rest of the house" is commonly in the main panel and that includes the dryer and oven, and the AC is often on a subpanel.

Here are pictures of the two panels. The left is the subpanel on the 60A circuit from the main panel. That's where all the breakers are.

The main panel has independent circuits for A/C, Dryer and Oven. Not sure why it was done that way.

 

[ewoodrick]

I'd say that there is absolutely no way that you could add anything to the subpanel. The main panel definitely seems to have some room though.

 

[BigNick]

That's a LOT of 15A and 20A (120V) breakers fed off a single 60A (240V) circuit.

I'd go with a dedicated 50A from your main panel, no question.

edit: The only reason I could think things were wired up this way is if there's a lot of distance between the main panel/service entry and the "rest of the house" subpanel to save on wire price. But I suspect that 60A isn't really adequate.

 

[PCARs]

Thanks all! My gut was saying to spend the extra $$ on the dedicated circuit, but wanted to make sure I wasn't completely unnecessary.

 

[terranx]

Any chance the wiring going to the subpanel is sufficient to handle a larger breaker?

 

[GSP]

That is a lot of breakers in the 60 A subpanel! I wonder what the electrician's load calculation looks like. I am not an electrician, but I would guess it is close to being overloaded already. I recommend getting an electrician that will do the load calculation and show it to you, or maybe try to do it yourself with an on-line calculator.

Based on how I expect the load calc to come out, I would run a separate circuit from your main panel. Maybe ask for quotes for a 60 A circuit and a 30 A circuit to a hard wired wall connector. If the 30 A wiring saves a significant amount, it would be sufficient for one EV. Perhaps two EVs if you don't drive much.

GSP

 

[ewoodrick]

I'd say that there is absolutely no way that you could add anything to the subpanel. The main panel definitely seems to have some room though.

@SSonnentag Would you care to explain your down vote?

 

[PCARs]

Any chance the wiring going to the subpanel is sufficient to handle a larger breaker?

That would be ideal, but I suspect the builder didn't spend extra money on higher load wiring. This is a tract home after all .

 

[GSP]

@PCARs
Since it likely is a long run from the main panel, I recommend using a hard wired EVSE, like Tesla's wall connector. That saves the cost of an unused neutral wire, needed for 14-50 and 14-30 outlets. It also saves the cost of a GFCI breaker, allowing a normal breaker to be used.

GSP

 

[SSonnentag]

As a computer scientist who does his own wiring as close to code as possible. I'd say, no way! On the other hand, it looks to me as though your main has enough overhead to run a dedicated circuit from it. I predict a lot of 60A breaker trips.

 

[PCARs]

That is a lot of breakers in the 60 A subpanel! I wonder what the electrician's load calculation looks like. I am not an electrician, but I would guess it is close to being overloaded already. I recommend getting an electrician that will do the load calculation and show it to you, or maybe try to do it yourself with an on-line calculator.

Based on how I expect the load calc to come out, I would run a separate circuit from your main panel. Maybe ask for quotes for a 60 A circuit and a 30 A circuit to a hard wired wall connector. If the 30 A wiring saves a significant amount, it would be sufficient for one EV. Perhaps two EVs if you don't drive much.

GSP

The electrician who quoted this did include an estimated load analysis of 59A on the 60A circuit. Seems very "convenient" to be right under the max load. I don't know if this is truly accurate or are just trying to show a lower price to get the job and then say they need to do an attic run on an independent circuit at 3X the cost?

 

[SSonnentag]

@SSonnentag Would you care to explain your down vote?

Sure. Mouse hovered too long before clicking like, which caused a pop-up, presenting the dislike below my mouse before I actually clicked, followed by me not noticing. I've fixed it.

 

[brkaus]

My house looks similar. I have a main panel with AC units (3), dryer, ovens (2), and then two sub panels each on 60a to run everything else (a crap ton of 15 & 20a breakers).

My electrician put the HPWC on the main panel.

I would run it back to the main or consider 30a outlet off the sub panel.

In your case, the car will not exceed 32a, but I’m worried your setting up your future you for problems if you get something that can pull more.

How much is the quote to take it from the subpanel? You said $1k more from the main.

Is it going to be inspected?

 

[Big Earl]

Your car can charge at a maximum of 32 amps. As such, I would install a 40 amp circuit breaker on that NEMA 14-50 receptacle (code allows that). Make sure it’s a Hubbell or Bryant brand (there’s a third that I don’t remember the name of) - NOT a Leviton, which are known for melting and arcing.

I would also do the extra work to power it from the main panel, not the sub panel. Your sub panel already appears to be doing most of the heavy lifting - perhaps more than it should be.

That said, if you’re going through the effort of running to the main panel, I’d do a hard wired install on a 60 amp circuit. Future proof and done correctly.