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Difficult situation with a Condo, advice appreciated...

mtndrew1

Active Member
May 12, 2015
1,318
3,695
Gardena, CA
It’s not L2 but consider a 120V 5-20 outlet. This will allow you to draw 16A continuous over L1 with the $35 pigtail for something like 7 MPH of charging. It might sidestep the expensive electrical work while satisfying the bulk of your charging needs. I’ve used this adapter extensively when traveling or camping and it’s surprisingly useful.
 

Tam

Well-Known Member
Nov 25, 2012
8,432
7,272
Visalia, CA
It’s not L2 but consider a 120V 5-20 outlet. This will allow you to draw 16A continuous over L1 with the $35 pigtail for something like 7 MPH of charging. It might sidestep the expensive electrical work while satisfying the bulk of your charging needs. I’ve used this adapter extensively when traveling or camping and it’s surprisingly useful.

Since an electrician will be needed to run from the home panel 80 feet to the car, 120V run is a waste of talent.

If you have an electrician, I would recommend 240V at least!
 
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MetricExpanse

Member
Mar 23, 2021
64
15
Los Angeles
Since an electrician will be needed to run from the home panel 40 feet to the garage, 120V run is a waste of talent.

If you have an electrician, I would recommend 240V at least!

Yeah, that's how I look at it. Even a crappy 240V would be better than a 120V, since either way I have to pay to make a run there. AFAIK, I think the actual voltage is less important than the amperage. For example, 20A at 120V would be the same load on my circuits as 20A at 240V, right?
 

Tam

Well-Known Member
Nov 25, 2012
8,432
7,272
Visalia, CA
....would allow me to have 50A (!!)....

I think the rule is 80% of what your rated breaker is:

If it's 120V 15A, then the maximum is 80% of that which is 12A

If the circuit is 100A, the highest HPWC will get is 80% of that or 80A for older Model S with dual onboard chargers.

And so on.

Now, since your home panel is rated for 70A, 80% of that is 56A for your whole home-usage.

Of that 30A is for Air Conditioner, then you got 56-30 = 26A for the rest of your home.

Your electrician is too enthusiastic to think that you can use 50A for your EV out of what left of 26A!!!

Do you have any other high power consumption devices besides the Air Conditioner?
 
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Tam

Well-Known Member
Nov 25, 2012
8,432
7,272
Visalia, CA
Yeah, that's how I look at it. Even a crappy 240V would be better than a 120V, since either way I have to pay to make a run there. AFAIK, I think the actual voltage is less important than the amperage. For example, 20A at 120V would be the same load on my circuits as 20A at 240V, right?

Big difference. Ohm's law V=IR (Voltage=Current x Resistance)
P=V x I (Power=Voltage x Current)

120V=18A x 6.667 Ohms = 2,160 Watts

240V=18A x 13.333 Ohms = 4,320 Watts

You double the power of charging from 2,160 Watts to 4,320 Watts.

(If the circuit is 20A, you can only draw 80% of that which is 18A).

It's important to liberally supply a thick wire (AWG--American Wire Gauge: the smaller in number means thicker in diameter of the wire) for your 80' length to prevent a drop in voltage. The longer the distance, the thicker the wire is needed (the smaller number in AWG) to prevent a drop in voltage. Voltage is very important.
 
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MetricExpanse

Member
Mar 23, 2021
64
15
Los Angeles
I think the rule is 80% of what your rated breaker is:

If it's 120V 15A, then the maximum is 80% of that which is 12A

If the circuit is 100A, the highest HPWC will get is 80% of that or 80A for older Model S with dual onboard chargers.

And so on.

Now, since your home panel is rated for 70A, 80% of that is 56A for your whole home-usage.

Of that 30A is for Air Conditioner, then you got 56-30 = 26A for the rest of your home.

Your electrician is too enthusiastic to think that you can use 50A for your EV out of what left of 26A!!!

Do you have any other high power consumption devices besides the Air Conditioner?

Well, if you look at the breaker panel, you'll see a 15A breaker for the AC fan. So I assume whenever the AC is running, the fan is as well. Seems crazy to me that a fan has its own circuit... even my electrician was surprised.

Besides that, I have a fridge, washing machine and dryer (gas), dishwasher, OLED TV, an air fryer, microwave, and a gaming PC.

I'm not sure how their calculation got 50A, but he quickly downrated me to 20A and maybe 30A if I'm lucky.

Big difference. Ohm's law V=IR (Voltage=Current x Resistance)
P=V x I (Power=Voltage x Current)

120V=18A x 6.667 Ohms = 2,160 Watts

240V=18A x 13.333 Ohms = 4,320 Watts

You double the power of charging from 2,160 Watts to 4,320 Watts.

(If the circuit is 20A, you can only draw 80% of that which is 18A).

It's important to liberally supply a thick wire (AWG--American Wire Gauge: the smaller in number means thicker in diameter of the wire) for your 80' length to prevent a drop in voltage. The longer the distance, the thicker the wire is needed (the smaller number in AWG) to prevent a drop in voltage. Voltage is very important.

Right. I guess what I was saying is that it "doesn't matter" from the perspective of whether I trip my 70A main breaker or not. I assume the main breaker is rated for 70A and so 20A at either 120V or 240V will count against my 70A breaker more or less the same, right?
 

Tam

Well-Known Member
Nov 25, 2012
8,432
7,272
Visalia, CA
...calculation...

It does sound your A/C is the biggest power consumption. Another big one would electrical dryer but yours is gas so it's just like a small fan to run its motor which is not big power consumption.

Microwave, Air Fryer, hot iron... might use as much as 1,500 watts (12.5A) each.

Fridge, washing machine, gas dryer, dishwasher, OLED TV, gaming PC... each don't use as much as Microwave, Air Fryer, hot iron do.

So, in a pinch, don't iron your clothes while doing microwave, air fryer all at the same time (that's about 12.5 x 3 = 37.5A total).

I think your 70A home should be fine with sharing a 240V 20A circuit for your Tesla car.
 

Sophias_dad

Supporting Member
Jul 29, 2018
1,006
872
Massachusetts
https://iaeimagazine.org/2013/mayju...calculations-in-the-national-electrical-code/ I vaguely recall I made a spreadsheet or two to represent the two methods(for my house/installation).

And, yes, I mean remove the screws that hold the faceplate on the panel. With luck you'll be able to see the wire gauge, but I really doubt it unless the wires are arriving via conduit. I'm pretty sure if the wire arrives via NM-B that the sheath is supposed to be cut back almost to the box edge. Note that the faceplate isn't super heavy, but its not light either. Try not to let the circuit breakers take the weight of the cover, even though they can.
 

Sophias_dad

Supporting Member
Jul 29, 2018
1,006
872
Massachusetts
Right. I guess what I was saying is that it "doesn't matter" from the perspective of whether I trip my 70A main breaker or not. I assume the main breaker is rated for 70A and so 20A at either 120V or 240V will count against my 70A breaker more or less the same, right?

Yes and no. That 70A is actually divided into two 70Ax120V busses. For your case, you only have two big 240volt loads(ac and ac fan) that will use power off both busses. So lets say those are 40 amps between them(probably less than that, but whatever), you have 30 amps remaining on the two busses. Now consider your larger 120V loads, like the refrigerator and clothes washer, which probably run at 10 amps or so each. If they happen to live on the same bus, you will have 10 amps of leftover capacity on that bus but still have 30 available on the other. If you try to put in a 20 amp 240V circuit without any other rearrangement of circuits, you'll be overloading one of the 120V legs and after a while, the main will trip. Its trivial to balance loads by swapping wires in the panel in case you find a situation where two high-usage 120 volt loads are sharing.

Regarding actual power usage... You should consider checking the actual model numbers and manuals of the various loads to see what their real draw is. An electrician can also easily measure the loads with a clamp-on meter once the panel cover is off, if you don't have access to the equipment. Frequently motor-based equipment has unusually high breaker ratings for the power they actually use, but even an electric oven can have a considerably bigger breaker than it can use.
 

brulaz

Member
Feb 4, 2021
18
3
Ontario Canada
Here's an idea that might work for you...

Get a switchbox that allows either your dryer or your charger to get power, and mount it right next to your power panel. That's a 24 amp continuous 240 volt charge for $139, I assume MUCH cheaper and smaller than the DCC, albeit a little more work on a per-charge basis. I'd assume you'd keep it set to 'charger' mode unless you were actually drying clothes.


Note: I couldn't find frequency-of-switching data allowed for that switch, and I imagine you might want one with a front mounted actuator. It might be worth a chat with the electrician.
Like that.
Have also seen a smaller 30A 240V switch but it's only double pole, not triple. Can that be used by tying together the neutral?
Legrande-Pass & Seymour 1276
 

MetricExpanse

Member
Mar 23, 2021
64
15
Los Angeles
I think your 70A home should be fine with sharing a 240V 20A circuit for your Tesla car.

I really hope so! I hardly use all that stuff all the time. My washer and dryer are only run like once a week anyway. And I could also tell the car to stop charging if I think I'm going to be creating a perfect storm.

https://iaeimagazine.org/2013/mayju...calculations-in-the-national-electrical-code/ I vaguely recall I made a spreadsheet or two to represent the two methods(for my house/installation).

And, yes, I mean remove the screws that hold the faceplate on the panel. With luck you'll be able to see the wire gauge, but I really doubt it unless the wires are arriving via conduit. I'm pretty sure if the wire arrives via NM-B that the sheath is supposed to be cut back almost to the box edge. Note that the faceplate isn't super heavy, but its not light either. Try not to let the circuit breakers take the weight of the cover, even though they can.

Yeah, I think I don't really trust myself to be playing around with my load center too much. I'm too afraid I'll touch some conductor in there and zap myself. I think I'll let the electrician do it when I have him over!

Yes and no. That 70A is actually divided into two 70Ax120V busses. For your case, you only have two big 240volt loads(ac and ac fan) that will use power off both busses. So lets say those are 40 amps between them(probably less than that, but whatever), you have 30 amps remaining on the two busses. Now consider your larger 120V loads, like the refrigerator and clothes washer, which probably run at 10 amps or so each. If they happen to live on the same bus, you will have 10 amps of leftover capacity on that bus but still have 30 available on the other. If you try to put in a 20 amp 240V circuit without any other rearrangement of circuits, you'll be overloading one of the 120V legs and after a while, the main will trip. Its trivial to balance loads by swapping wires in the panel in case you find a situation where two high-usage 120 volt loads are sharing.

Regarding actual power usage... You should consider checking the actual model numbers and manuals of the various loads to see what their real draw is. An electrician can also easily measure the loads with a clamp-on meter once the panel cover is off, if you don't have access to the equipment. Frequently motor-based equipment has unusually high breaker ratings for the power they actually use, but even an electric oven can have a considerably bigger breaker than it can use.

Thanks for this. It's super insightful! I did a little bit of reading about split-phase power and I see what you mean about making sure the load is balanced.

I do have a suspicion that my AC is oversized somehow. I find it hard to believe that an AC + Fan takes nearly 45A to run, at least in steady state! I guess the startup transient is really what I should be worried about, since it does cycle several times per day. Unfortunately I don't have access to my AC unit to be able to tell what model it is. I also have a heater, but I can't tell which circuit it's on... does that just live on the AC circuit or something?

I will look around at my model numbers. On the plus side, all my appliances (except the AC) are relatively new, so I would expect them to be pretty efficient. I looked in my fridge and it says it uses 1.51 A at 120V. My microwave takes a 1550W input so I guess about 13A at 120V. Didn't see any ratings on my W/D but I can disable charging before using those. Also, my lighting here is 100% LED so I imagine it's negligible.
 
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Sophias_dad

Supporting Member
Jul 29, 2018
1,006
872
Massachusetts
I guess the startup transient is really what I should be worried about, since it does cycle several times per day. Unfortunately I don't have access to my AC unit to be able to tell what model it is. I also have a heater, but I can't tell which circuit it's on... does that just live on the AC circuit or something?

Actually, the startup transient isn't a problem for circuit breakers. They are designed to deal with short-term overloads gracefully. I don't recall the specifics, but there are at least tens of seconds of 135-150% overload before the breakers will trip.

https://download.schneider-electric...File_Name=0730CT9801.pdf&p_Doc_Ref=0730CT9801 shows on page 19 that a typical QO breaker will not trip for at least 10 seconds while carrying DOUBLE its rated current.

Your fridge is using on the order of 1.5 amps during normal operation. If its like mine, every day or two it'll do a defrost cycle that will take much more.

Yes, your AC or maybe ACfan will have electric resistance heaters in it. Make sure if the electrician is testing draw that he also tries the heat mode, which is likely to take more power than cooling mode.
 

MetricExpanse

Member
Mar 23, 2021
64
15
Los Angeles
Actually, the startup transient isn't a problem for circuit breakers. They are designed to deal with short-term overloads gracefully. I don't recall the specifics, but there are at least tens of seconds of 135-150% overload before the breakers will trip.

https://download.schneider-electric...File_Name=0730CT9801.pdf&p_Doc_Ref=0730CT9801 shows on page 19 that a typical QO breaker will not trip for at least 10 seconds while carrying DOUBLE its rated current.

Your fridge is using on the order of 1.5 amps during normal operation. If its like mine, every day or two it'll do a defrost cycle that will take much more.

Yes, your AC or maybe ACfan will have electric resistance heaters in it. Make sure if the electrician is testing draw that he also tries the heat mode, which is likely to take more power than cooling mode.

Good to know about the breakers being able to deal with a short term overload. I didn't know that!

I looked up my fridge online and it does say 15A on the specs. It's this one: GE® 21.8 Cu. Ft. Counter-Depth Fingerprint Resistant Side-By-Side Refrigerator|^|GZS22IYNFS

Here's a pic of what I think is my AC unit (not sure)? I guess it has both the heating and cooling. Not sure where to look to be able to find my AC Fan though. Looks like it's a pretty old unit so perhaps an upgrade is in order? I only need to cool 650 sqft and maybe a newer unit can use less current?

IMG_4152.jpeg
 

Sophias_dad

Supporting Member
Jul 29, 2018
1,006
872
Massachusetts
So, when your AC(actually heat pump) is in heater mode, it can use a 5kw heater sometimes. That's ~21 amps right there, at 240V. Add the two amps from the compressor and you are at 23 amps. If nothing else, I imagine you could disable the heater-part of the system except in the rarest of circumstances, leaving you 20 amps of unused capacity. (Note that that consideration probably isn't allowed by the NEC). Replacing the AC isn't necessarily going to help unless you go to one that doesn't require the electric resistance heaters.

The AC fan unit would be inside your condo somewhere, turn the blower on high and listen for the noisiest place, likely in a closet or just above the ceiling.
 

MetricExpanse

Member
Mar 23, 2021
64
15
Los Angeles
So, when your AC(actually heat pump) is in heater mode, it can use a 5kw heater sometimes. That's ~21 amps right there, at 240V. Add the two amps from the compressor and you are at 23 amps. If nothing else, I imagine you could disable the heater-part of the system except in the rarest of circumstances, leaving you 20 amps of unused capacity. (Note that that consideration probably isn't allowed by the NEC). Replacing the AC isn't necessarily going to help unless you go to one that doesn't require the electric resistance heaters.

The AC fan unit would be inside your condo somewhere, turn the blower on high and listen for the noisiest place, likely in a closet or just above the ceiling.

Very interesting... I live in SoCal and so almost never need to use the heater. Cooling is almost exclusively what I use. What would we guess amp draw is in cooling mode?

Also, I just found the fan, but it doesn't have a sticker on it or anything... it sort of seems like it's part of the same "unit" as the AC is? Here's a picture. The thing left is the thing that had the label I also showed (the heat pump, I guess). The right thing appears to be the fan (it spins when I turn on the fan) but it has no label.

It kind of looks like they're part of "the same" unit, but I guess they're still on separate circuits, right?

IMG_4155.jpeg
 

Sophias_dad

Supporting Member
Jul 29, 2018
1,006
872
Massachusetts
I'm not really trusting that nameplate. It looks like the fan nameplate(2.0 amps), but clearly specifies the heat strip output. The heat strips would indeed be in the fan area, so I imagine there are dual lines(indoor for heat strips and outdoor for compressor) for the 30 amp 240v circuit.

The compressor motor(in the condenser) would be outside somewhere, either hanging off the building or on the ground floor or roof.
 
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MetricExpanse

Member
Mar 23, 2021
64
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Los Angeles
I think you’re right. There is indeed a condenser on the roof, but I don’t have easy access to it. It would make sense that the condenser and heater would share the single 30A circuit. What I’m wondering is why the fan has a whole 15A circuit if it’s only 2A. Perhaps my electrician could downsize that fan breaker?
 

Sophias_dad

Supporting Member
Jul 29, 2018
1,006
872
Massachusetts
Perhaps my electrician could downsize that fan breaker?
He could, but it's not really necessary. Its the fan motor that's dictating how much current its taking, not the breaker. You could replace the breaker with a 30 amp(assuming the wires would support it, which they won't), and the fan will still only draw 2.1 amps.

That's why you should do a real load calculation, btw. Its things like this that give you unexpected headroom. You just got 5 amps at 240 volts back, since my earlier guess was 7 amps for the AC fan.

Regarding your refrigerator, find the model/serial plate(usually at the top inside the refrigerator section) and it might give you more detailed information about its power usage.
 
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