Hi all, I just got around to install my 14-50 outlet in my garage. When I finished installing the outlet, I used my multimeter to test the voltages. I tested from hot1 to ground and hot2 to ground both measured at exactly 120v. However, when I measured across hot1 and hot2, I get 208v. I thought that was weird, so I tested the voltages at the breaker with the same result. I measured my other 240v circuits and also got 208v. I then measured at the thick cables coming into the breaker (mains) and it also measured at 208v. Why am I getting 208v instead of 240v? Would this affect charging? Any issues I should be concerned with?
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Home circuit breaker 208 volts?
- Thread starter kevinf1990
- Start date
DerbyCityY
Member
Hey, I googled your exact problem and this is what it came up...It's some electricians forum where the discuss what you're talking about.
Hope it helps.
Hope it helps.
How common is 120/208 for residential?
In class last night I mentioned that I had 208v in my house and the instructor was certain that I was mistaken. I just checked and it's dead on 208. Looks like my two ungrounded legs come off of one of 3 transformers set on the pole in the alley and the grounded conductor comes off that...
forums.mikeholt.com
you're neighborhood is on three-phase power. you've got two of three legs, your neighbor has a different pair. no big deal. most wall connectors (tesla's included) work fine on 208, just output a bit less wattage. three phase power is more efficient for transmission and can run better AC motors, so many large businesses prefer it.
While 208 would be normal for one of three phases, it is out of spec for a nominal 240V circuit-- most POCOs shoot for +/- 5% of the nominal voltage. For most things it doesn't make a difference, but some motors and such will run hot at the lower voltage. If it is a nominal 208 circuit it could be allowed sag another 5-10% in heavy demand, which will begin to really tax some 240V motors. I'm pretty sure that voltage will be fine for the car.
I would call your power company and ask them to check it out though. Other things in your house may not be so happy with it.
I would call your power company and ask them to check it out though. Other things in your house may not be so happy with it.
For some reason you have 3 phase power (well, two of the three phases are connected to your house). It's odd that they would put a residential neighborhood on 3 phase power. Do you live in a condo or other multiunit building? Generally larger buildings (say, anything bigger than a 4-flat and all but the smallest commercial buildings) receive 3 phase power. Nothing bad about it, just that the charging circuit will output 13% less power, all else equal.
the tesla mobile connector works fine at 208v, check the manual. youll also notice many/most commercial j1772 chargers are 208v.
This is a new construction and it is a condo/multi-occupancy unit (one building has 4 units). So that would explain why we are on 3 phase power. But it sounds like I shouldn't run into any issues with charging. I do see other neighbors charging their Teslas too and they pre-wired a EV box in the garage.
You won't encounter any issue when charging using Level 2 charging at 208V. Available power will be ~13% less; charging will take 13% longer to complete than if you were charging at 240V. In my home Level 2 charging happens at 230V to 236V. Compared to 230V, charging at 208V would take almost 10% longer to charge to a specific level.
ucmndd
Well-Known Member
To be clear, we do know based on the voltage measurements provided by OP in the original post. If the observed 208v was due to a sagging / high resistance connection, the individual legs to ground would be low by the same amount. They aren’t.
It’s free to verify the information with the power company and since OP is not an electrician, that is what I would recommend.
ucmndd
Well-Known Member
There is no need to verify with customer service what one can measure directly. But hey, you do you.
The question to the POCO is to ask what nominal voltage they are intending to provide (240 vs 208) and does the actual voltage provided meet their specification.
Having once burned up two $12,000 -80 freezers that were spec'd for 230-240V operation but were on one leg of a three phase circuit that sagged to 198-200 in the summertime I'm acutely aware of the possible issues of insufficient voltage. It was a hard lesson. The power to the building couldn't be changed, we had to add buck/boost transformers for each freezer outlet.
Having once burned up two $12,000 -80 freezers that were spec'd for 230-240V operation but were on one leg of a three phase circuit that sagged to 198-200 in the summertime I'm acutely aware of the possible issues of insufficient voltage. It was a hard lesson. The power to the building couldn't be changed, we had to add buck/boost transformers for each freezer outlet.
There is no way of verifying how he measured the voltage, or if he did the measurements correctly, or what the meter actually read. He isn’t an electrician, and since splitting a three phase services up like that is rare, I would suggest double checking the measurements by a professional.
My newbie electricians sometimes would read a meter and tell me they had 120v but had nothing, because on auto ranging meters they actually read 120mV.
UncleCreepy
Member
I fail to see what he could have done wrong. He clearly stated that the voltages between hot1 and ground as well as between hot2 and ground were 120 V, while the voltage between hot1 and hot2 was 208 V.
Those voltages are 120° out of phase (as opposed to 180° for 240 V). Obviously those voltages come from a 3-phase transformer.
If OP had an oscilloscope, he could just check the phase angle between the two voltages. I personally wouldn't worry about it. It can't be more obvious that he's on two legs of a three-phase system.
People, there is no problem here. Vast majority of residential, hotel and condos are 208 volt grounded WYE to each apartment/condo. 120V from each phase to ground and 208 between the phases. Each resident gets 2 of the three phases. This is completely normal and is perfectly acceptable. It is how the design engineer intended. The slight negative to this power distribution configuration, is that electric water heaters take longer to heat water, electric cars take longer to charge, and your electric range takes longer to get to temperature.
I explained what he could have done wrong in my post in the part you edited out. Obviously it’s free to double check so that’s what I recommend.
ucmndd
Well-Known Member
If by “rare” you mean nearly every commercial / multi-tenant residential building in the United States, then, sure. I guess it’s rare.
Like I said, if confirming with Janice in customer service what you can measure directly yourself is the sort of extra assurance that makes you sleep well at night, give Janice a buzz.
Again, I maintain that your original assertion that we “do not know” what’s happening is wrong. There is no other way for OP to observe the voltages they did that doesn’t involve 3-phase power. OP confirmed he lives in a multi-tenant building in the US where this sort of power distribution is the norm/expectation. Not only does it look like a duck and quack like a duck, we tested its DNA and confirmed a duck.
Mystery solved.
It’s not too common in residential. It’s free to check. I would suggest he check. We don’t know. We are guessing. Get someone who knows what they are doing to check it out. Isn’t that hard.
ucmndd
Well-Known Member
Measuring with a multimeter isn’t guessing. It’s measuring.
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