Question about Voltage Drop on UMC Charging

[Auriga]

Hello guys, I have a question that bother me a long time ago.
I was having this UMC came with the vehicle to charge my car on a NEMA 14-50 for years. Previously I didn't noticed my charging voltage which shows on my car is about 205-210 V. I recently went to my friends home and saw his MS is charging at 239 V constant, it brings me the question, why my UMC can only deliever 208 V to my vehicle.
I tried to use meter to measure the voltage from the hot to neutral on my nema 14-50 outlet, the number is about 121 V for both of them, which make me confused more. Previously, my guess was because my house is may be on the end of the power lane which the main cable have a lower voltage than others, but it shows me the voltage on my end is pretty solid and good which is above 120V. So in my mind, 120+120 should at least have 230 V or more.
However, I found something fun, if I turn the current down to about 5 A. the voltage will increase to about 215V-218V.
Please help me, is there possible something wrong with my UMC, are the input voltage which 121V is low. Thank you for any response!

 

[gavine]

You should try your UMC at your friend's house. If you have the same problem there, then it's the UMC. If you get 240V, then the problem is with your house, your wiring or your receptacle. Also, try charging your car on his UMC to see if the problem is with your car's charger or charge port.

 

[TexasEV]

It’s your power, not your UMC.

 

[Lloyd]

I suspect that you probably have substandard wire or a very long run to your plug. Check that you have min. #8 wire for < 20 feet run or #6 for longer. Check that the terminations are properly torqued. Check for heat at the plug and at the fuse panel after charging for awhile.

 

[Auriga]

I found the reason, as I measer from the panel box, from each bus, the reading is 212V. Which means I am having a 120/208V service. Anybody have any idea why it is a 208V service but not a 240V service, and if I can changed to 240V service? I am in NJ with PSEG.

 

[Cosmacelf]

I’d try calling your power company. I do think they should be able to help you. I haven’t heard of that thing myself, but then I’m not an electrician. Maybe someone else mow knowledgeable here can chime in. @RandyS maybe?

 

[gregd]

Never heard of 120 / 208 residential power in the USA. Is your power commercial (3-phase) for some reason? That's the only place I've seen 208 volts...

That your voltage stays constant even if the current is dropped to almost nothing tells me that it's not a wiring problem, and there is no way the UMC can "transform" the voltage. Normally a low voltage would be indicative of a bad connection, but it would depend on the current, and you've proved that's not the case. So, as odd as it seems to be, it might actually be "normal" for your house.

You might check the name plate on some of your other appliances such as the AC/furnace, electric oven, or hot water heater, if they are electric. They should indicate the voltage they are designed for (and presuming they are operating properly).

Can you post a picture of your main panel?

 

[Auriga]

Never heard of 120 / 208 residential power in the USA. Is your power commercial (3-phase) for some reason? That's the only place I've seen 208 volts...

That your voltage stays constant even if the current is dropped to almost nothing tells me that it's not a wiring problem, and there is no way the UMC can "transform" the voltage. Normally a low voltage would be indicative of a bad connection, but it would depend on the current, and you've proved that's not the case. So, as odd as it seems to be, it might actually be "normal" for your house.

You might check the name plate on some of your other appliances such as the AC/furnace, electric oven, or hot water heater, if they are electric. They should indicate the voltage they are designed for (and presuming they are operating properly).

Can you post a picture of your main panel?

I measure from the two Main power cable( the thickness one) that feed the whole panel. The reading is 210-212V, and also try on the screw on the 2 pole breaker, which are the same. This house is a apartment in a group of the same type of house together.
I dont find any other outlet in this house which supposed to be 240V. Here is the images.

 

[mongo]

Mike Holt forum via Google says 208 exists around the country. It's two legs of a three phase delta and produces 120/208. 208 is due to the 120 degree phase shift v.s. the 180 you get on a split 120/240 system.
240 heating appliances will work at a reduced heat output of around 75% of typical.

 

[gregd]

Mike Holt forum via Google says 208 exists around the country. It's two legs of a three phase delta and produces 120/208. 208 is due to the 120 degree phase shift v.s. the 180 you get on a split 120/240 system.
240 heating appliances will work at a reduced heat output of around 75% of typical.

Given that it's a multiple dwelling situation, getting commercial power like you say seems more likely. The hot water heater would definitely work on the lower voltage, but anything with a motor would need to be rewired, which I guess they can do too. Interesting... Learned something.

So, bottom line: Your charging is fine for your house. Nothing is broken, no danger. Just a bit slower than your neighbor, not enough to fuss over.

 

[Rocky_H]

I really don't get why people do this. He's carrying on the same question/discussion on both Tesla forums and giving copy/paste answers on both of them.
Question about Voltage Drop on UMC Charging | Tesla

 

[Auriga]

I really don't get why people do this. He's carrying on the same question/discussion on both Tesla forums and giving copy/paste answers on both of them.
Question about Voltage Drop on UMC Charging | Tesla

What is the problem for me to post the question to two different website? Because I want to have more answer? More helpful solutions? That is the reason. I dont understand why you are complained about it? Did my question bother you in anyways?

 

[Rocky_H]

Wasting people's time. I opened the thread to see what someone's problem was and give some answers to it, and I found that I had already answered it today on the other forum. This can be alleviated by not posting them in both places at the same time. Give it a day or two on one forum to see if you get the answers. If you want more information, then sure, check with the other forum. You're not the only one who has done this, but it always is a little irritating to open threads here that seem new, only to find that you've already read it from the other site.