Line to Line Voltage vs Line to Neutral Voltage

[Misoc]

Hi,

I measured the voltage on the main service panel on a 240v nominal singe phase service. The line to neutral voltage on each phase is 130v and the line to line voltage is 227v. What would cause the line to line voltage to read lower then the sum of both phases in this case 227v vs 260v?

Thanks in advance

 

[synchro]

Very likely the two L-N phases are 120 degrees apart instead of 180.
So the the L-L voltage would be √3 ≊ 1.732 times the L-N voltage, and not 2 times.
1.732 x 130V = 225V which is close to your measured 227V.

 

[Misoc]

Very likely the two L-N phases are 120 degrees apart instead of 180.
So the the line-to-line voltage would be √3 ≊ 1.732 times the line-to-neutral voltage, and not 2 times.
1.732 x 130V = 225V which is close to your measured 227V.

Thanks Synchro. So this is an utility issue? Is this common?

 

[Misoc]

Very likely the two L-N phases are 120 degrees apart instead of 180.
So the the L-L voltage would be √3 ≊ 1.732 times the L-N voltage, and not 2 times.
1.732 x 130V = 225V which is close to your measured 227V.

Or maybe 2 legs of a three phase service is entering this house?

 

[infinity]

Something is wrong if your seeing 130 volts to the neutral.

 

[Misoc]

Something is wrong if your seeing 130 volts to the neutral.

Thanks Infinity. The house is connected to a community meter enclosure. There is also a three phase meter. If Synchro is right, I am thinking that the utlity transformer might be a 3 phase 240/120 4 wire high leg and whoever installed the service brought the A & C phases to the house to get a 240/120 service.

FYI - This house is in Baja CA Mexico and although Mexico accepts the NEC there are no building inspectors so anything is possible.

 

[synchro]

Apparently in Mexico 220/127 4-wire three phase is common. Also 3-wire (2 legs) or 2-wire (1 leg) of the 220/127 wye. So your measured 227/130 is about 2 to 3 percent higher than nominal.

Electric Current Abroad

Lists the characteristics of electric current available and the type of attachment plugs used in principal cities in over 180 countries. Details include: type of current (AC or DC), number of phases, frequency (hertz), voltage, stability of frequency and the number of wires to a commercial or...

books.google.com

 

[Misoc]

Thanks a bunch. Really appreciated.

 

[paulengr]

Not high leg delta. That would be indeed 240/120 or whatever it is, the two legs add up to the third.

Other than being tapped up it’s 208/120 which is a wye transformer not delta.

In terms of standards IEC/IEEE specifies that the distribution voltage would be 208/120. The corresponding utilization voltages are 110/191 V. NEMA among others requires loads to tolerate +/-15% so that’s 94 to 127 V. So there is just barely coverage for a “hot” supply but this is truly out of tolerance for a lot of equipment.

Usually you have 5 taps on a transformer at -5, -2.5, 0, 2.5, and 5% below and above nominal. Occasionally you might see a 9 tap transformer (extended range). The IEEE chart doesn’t have 140 V anywhere on it. Sounds like a soft bus and they are compensating by trying to jack up the taps but overdoing it.

On the 200-ish side we have a little u usual situation. 220/240 V is pretty common but so is 208 V AND in some European countries 200 V is also fairly common. So a lot of equipment is built to accept anything from around 190 V to 250 V to avoid having two very similar models.

This web site covers voltage tolerance:

Voltage Tolerance Standard – ANSI C84.1 – Voltage Disturbance

 

[LarryFine]

I measured the voltage on the main service panel on a 240v nominal singe phase service. The line to neutral voltage on each phase is 130v and the line to line voltage is 227v. What would cause the line to line voltage to read lower then the sum of both phases in this case 227v vs 260v?

What we're saying is that you're reading voltages proportional to a 208Y/120v 3-phase service, but the voltages (or your meter) are reading higher than "nominal" voltages. So, instead of seeing 120v L-N and 208v L-L, your seeing 130v L-N and 227v L-L.

It's common for apartment and condominium buildings to be supplied with 3-wire services just like in a home, except the line-to-line voltage is lower, resulting in L-L heating appliances achieving 75% of heating power, but otherwise function normally.

 

[Misoc]

What we're saying is that you're reading voltages proportional to a 208Y/120v 3-phase service, but the voltages (or your meter) are reading higher than "nominal" voltages. So, instead of seeing 120v L-N and 208v L-L, your seeing 130v L-N and 227v L-L.

It's common for apartment and condominium buildings to be supplied with 3-wire services just like in a home, except the line-to-line voltage is lower, resulting in L-L heating appliances achieving 75% of heating power, but otherwise function normally.

I think I understand. The book that Synchro linked to states that in Tijuana, BC they use 220/127. Are you saying that 220/127 is actually a 208y/120 that is "tapped up"?

Paulengr - What is a soft bus?

 

[jaggedben]

I think I understand. The book that Synchro linked to states that in Tijuana, BC they use 220/127. Are you saying that 220/127 is actually a 208y/120 that is "tapped up"?

If it's actually 220/127 nominal, then they are within acceptable range. Pretty weird if you ask me, particularly since I'm sure folks there just plug in lots of things made for 115-120v. (Most of those items probably aren't harmed, but I imagine some are.) But if that's what they say it is, they are making it so.

Whatever the voltage is, it is two legs of a three-phase wye.

 

[LarryFine]

Are you saying that 220/127 is actually a 208y/120 that is "tapped up"?

I am. Same ratio: 1.73

Whatever the voltage is, it is two legs of a three-phase wye.

That's what the numbers say.

 

[Misoc]

Thanks for your time guys. Super Kind.

 

[LarryFine]

I am. Same ratio: 1.73

Excuse me; that's not a ratio. I meant 1.73:1.