Wall Connector vs Mobile charger

[ajdelange]

To be clear, it's not simply a matter of enough physical space in the panel, nor totalling the ratings of all the branch breakers.

There is one limitation which must be honored in newer panels and that is the Maximum per Stab rating of the labeling in the panel indicates that limit. Even my electrician didn't know what that meant. If you look in the panel you will see a larger breaker at the top (for some reason in Canada they put it at the bottom) and coming down from it on are two parallel bus bars. These bars have tabs attached to then which run horizontally spanning both bus bars. These are the stabs. The breakers have fingers that plug onto them when the breaker is pushed into place. Each stab will take two thick breakers - one on either side of the panel - or 4 on the slim style ones. The usual limitation is 200 A per stab. This means you can't put a 120A two pole (for a sub panel) on the left side of the panel and a 90 Amp 2 pole breaker for a HPWC on the right on the same stab. This should not be at issue in the vast majority of installations.

You're supposed to do a load calculation, which includes a certain amount for lighting per square foot, derating factors for appliances, etc. A modest sized new home with 200A service and gas heat, hot water, dryer, and range could easily have headroom for a 100A HPWC.

A sort of general rule of thumb seems to be that the breakers in a panel are about 2.2 times the main breaker size. Thus a 200 amp panel would typically have 440 amps worth of breakers plugged into it. But that's for a typical home. A home with a 90A circuit for charging a Tesla is not, as yet, typical. In my case the panel to which I am adding the wall charger is a 200 A panel. It already has about 1200 amps worth of breakers in it and my electrician says no problem adding a 90 Amp circuit to that. Why? Because I can document that the maximum current I have ever drawn from that panel is 122 amps. This includes times when the car is charging at 40 amps. Putting in another 90 Amp breaker will bring the total breakers in that panel to 1290 amps but as I will never charge from the 50 amp circuit (14-50R) at the same time as I am charging from the HPWC I know that it is very unlikely I'll ever see a load greater than 122 - 40 + 72 = 154 A. So I'm leaving the 14-50R in as backup as many of you here have done or are planning to do.

You need to get an electrician in to be sure.

And be sure that you get a good one who has been at it for a long time and really knows the inspectors and the local as well as the NEC codes because what we are planning to do here might be in violation of some local code where you are. I was, for example, forced, in another jurisdiction (Quebec), to put in 600A service for a house at which I have never drawn more than 180 A.

 

[tga]

There is one limitation which must be honored in newer panels and that is the Maximum per Stab rating of the labeling in the panel indicates that limit. Even my electrician didn't know what that meant. If you look in the panel you will see a larger breaker at the top (for some reason in Canada they put it at the bottom) and coming down from it on are two parallel bus bars. These bars have tabs attached to then which run horizontally spanning both bus bars. These are the stabs. The breakers have fingers that plug onto them when the breaker is pushed into place. Each stab will take two thick breakers - one on either side of the panel - or 4 on the slim style ones. The usual limitation is 200 A per stab. This means you can't put a 120A two pole (for a sub panel) on the left side of the panel and a 90 Amp 2 pole breaker for a HPWC on the right on the same stab. This should not be at issue in the vast majority of installations.

I was having 2 100A subpanels installed at my prior house (one in the garage, one next to the main panel to handle overflow, since there was no more room to add the 100A breaker for the first one), and the electrician re-arranged a bunch of breakers for this very reason.

There's also a max number of circuits rating that is sometimes overlooked, as twin/quad breakers get added to add more circuits.

And be sure that you get a good one who has been at it for a long time and really knows the inspectors and the local as well as the NEC codes because what we are planning to do here might be in violation of some local code where you are. I was, for example, forced, in another jurisdiction (Quebec), to put in 600A service for a house at which I have never drawn more than 180 A.

Another one I've seen is using 2ga AL SER to feed a 100A sub, even though its limit is 90A @ 75C. The NEC allows 2ga AL to feed a main breaker, but was changed to disallow it for subs (maybe 2008 or 2011, I forget which). A lot of electricians (and inspectors) miss that one.

 

[ajdelange]

The HPWC is in and charging at 72 A giving me up to 46 mi/hr but what a nightmare. The only way to get a 90A breaker into my existing panels was to swap out the existing GE subpanel and replace it (and all its breakers) with Square D. That Square D stuff is awful. This is, I believe, the first time I have installed circuit breakers with a hammer - albeit a rubber one. That's the only way to get the breakers to engage the stabs.

No. 4 would carry the current but because mine is a long run the code requires (and I would have asked for it anyway) going up one size but when they got to the wholesaler all he had was No. 1 so rather than wait for an order to come in or run all over Northern VA looking for No. 3 we just went with the No. 1. I haven't seen the bill yet (and I don't want to).

So I've got 1/3 Copper SE run on Unistrut hanging from my garage ceiling coming down to the requisite disconnect and 1" EMT from the disconnect to the HPWC with No. 3 in it. The SE is cool as a cucumber at full charging load but the hose from the HPWC to the car is plainly warm to the touch.

It took two guys two days to pull that cable and change out the panel and breakers so, with about 100' of copper No. 1 you can imagine that my bill is not going to be the $500 that is often bandied about as the approximate cost of installing one of these things. If you have a tricky installation like mine be prepared to pay or to be content with 14-50R charging.

 

[Rocky_H]

No. 4 would carry the current but because mine is a long run the code requires (and I would have asked for it anyway) going up one size but when they got to the wholesaler all he had was No. 1 so rather than wait for an order to come in or run all over Northern VA looking for No. 3 we just went with the No. 1. I haven't seen the bill yet (and I don't want to).

I've heard that 3 gauge is hard to find, but I thought 2 gauge was really common. I'm surprised you had to go up to 1.

 

[ajdelange]

I don't think that it was a matter of it being hard to find but rather that the convenient distributor was out of stock - perhaps because it is so commonly used.

 

[BuyA2ndUMC]

Why not buy a 2nd UMC and leave it plugged into your Nema 14-50? For most people, this is the best option.

UMC is cheaper than the HPWC, and 14-50 installation is cheaper than HPWC installation.

Gen 2 mobile connector bundle. $275
Gen 2 Mobile Connector Bundle

Gen 2 adapter to whatever you're gonna plug into. $35
Gen 2 NEMA Adapters

(optional). plastic thingy to make it look cool, store cable and plug in like the HPWC $25
Cable Organizer

Total cost $335

And you have the option of taking it with you and buying a different adapter if your situation changes and maybe now you want to plug it into a dryer outlet or some such.

HPWC
$500
Gloss Black Wall Connector

HPWC is fixed in place, very difficult to move with you, costs more, costs more to install.

I don't know the difference in installation costs, but I imagine its several hundred dollars more, just because they know you can afford it.

 

[tga]

14-50 installation is cheaper than HPWC installation.

Doubtful. Assuming a 50A circuit, 6/3 for the 14-50 will cost more than 6/2 for the HPWC. Plus, depending on which version of the NEC your jurisdiction uses, you could be forced to buy a GFCI breaker for the 14-50, which could add another $75 or so over the cost of a HPWC installation.