120v/208v 3 phase residential service

[2tallpaulnaz]

Here is one, even 30 years of experience can't explain. Oh yeah, and it cost me my job. 208v 3 phase, the one with the wild-leg.


Question #1: The utility wanted the wild-leg to be on "B" phase. The city inspector wanted it to be on "C" phase. I made the switch between the meter socket and main breaker, was this wrong and if so how should it be done?


Question #2 Voltage readings from phase to phase was 238v. (A-B, B-C, A-C) The customer complained that his 240v range top was getting too hot. If the voltage is the same, and range elements have not changed their resistance, how can this be possible? After all there's Ohm's Law right?

 

[ActionDave]

Here is one, even 30 years of experience can't explain. Oh yeah, and it cost me my job. 208v 3 phase, the one with the wild-leg.

You don't have a 208V three phase, you have a 240V Delta three phase. If this is on a residence you have a one in a million service.

Question #1: The utility wanted the wild-leg to be on "B" phase. The city inspector wanted it to be on "C" phase. I made the switch between the meter socket and main breaker, was this wrong and if so how should it be done?

NEC requires the high leg to be on B phase. Here again you have an odd situation.

Question #2 Voltage readings from phase to phase was 238v. (A-B, B-C, A-C) The customer complained that his 240v range top was getting too hot. If the voltage is the same, and range elements have not changed their resistance, how can this be possible? After all there's Ohm's Law right?

How did the customer decide the elements were getting too hot? Were they more red than normal?....placing a bare hand on them?

 

[Smart $]

Here is one, even 30 years of experience can't explain. Oh yeah, and it cost me my job. 208v 3 phase, the one with the wild-leg.


Question #1: The utility wanted the wild-leg to be on "B" phase. The city inspector wanted it to be on "C" phase. I made the switch between the meter socket and main breaker, was this wrong and if so how should it be done?


Question #2 Voltage readings from phase to phase was 238v. (A-B, B-C, A-C) The customer complained that his 240v range top was getting too hot. If the voltage is the same, and range elements have not changed their resistance, how can this be possible? After all there's Ohm's Law right?

Sounds like 240/120V 3? 4W... not 208V 3 phase... but the "wild leg" will measure ~208V to neutral and ground. The others, 120V... but all 240V line-to-line.

The NEC requires the wild leg to be connected ?B in switchboards and panelboards [408.3(E)]. In many cases, the utility wants the high leg connected to C, as that's the only way the meter will measure accurately.

110.15 requires the wild leg to be marked orange or other effective means. Additional marking is required on switchboards and panel boards [408.3(F)(1)].

A range that's rated for 240V will get as hot as the manufacturer intended on this system... but there is a possibility the range is rated 208V... so it would get overly hot connected to a 240V system.

 

[Little Bill]

Here is one, even 30 years of experience can't explain. Oh yeah, and it cost me my job. 208v 3 phase, the one with the wild-leg.


Question #1: The utility wanted the wild-leg to be on "B" phase. The city inspector wanted it to be on "C" phase. I made the switch between the meter socket and main breaker, was this wrong and if so how should it be done?


Question #2 Voltage readings from phase to phase was 238v. (A-B, B-C, A-C) The customer complained that his 240v range top was getting too hot. If the voltage is the same, and range elements have not changed their resistance, how can this be possible? After all there's Ohm's Law right?

I would bet the voltage is 240/120 with a high leg. That is a Delta set up and I've never seen 208/120V with a high leg.

Sounds like the customer's range is 208V, but some are rated for either voltage.
The high leg would not matter on 240V. They could also have moved from somewhere that had 208V and the 240v would make it hotter. Or they're imagining things!
You can see by your voltage readings that you have 240V. Now any 120V loads the range might have would be affected if you used the high leg when feeding the 240V to it.

Also, it's common for the POCO to require phasing one way and NEC another way. But the NEC requires that "B" phase is the high phase. Unless the exception to 408.3(E) is met, the inspector is wrong by NEC standards. Also, unless you got it backwards and the POCO wanted "C" phase as the high leg and inspector wanted "B", which would be correct for the NEC.
What you did was correct as far as how you change the phasing if required to.

Why did you lose your job?

Edit: Sorry guys, I type slow and was typing away while you both posted!

 

[kwired]

Whoever decided a high leg delta service was what is needed here is the one that should have lost their job:happysad:

Unless there is a pretty significant straight 240 volt load this service type is not very practical for dwelling units.

I wouldn't want the high leg supplying cord connected ranges or dryers either, the chance of getting the 120 volt portions of those appliances on the wrong side are too great.

 

[augie47]

Curious: Was this a multi-unit building and was there any 3 phase load ?

 

[zbang]

Whoever decided a high leg delta service was what is needed here is the one that should have lost their job

This type of service was used in that area 40-50 years ago to supply central A/C compressors. The entire house was wired as if single phase, only the a/c got 3.

Residential Electrical Service Replacement/Relocation Checklist for Services of 200 amps or less mentions it
http://www.tempe.gov/modules/showdocument.aspx?documentid=5312:

"For a 3? 4 wire Delta service, the power phase (high leg) must be installed in the right hand (C?)
test block and meter socket position and identified by an outer finish that is orange in color. See
Section 300, Paragraph 303.7."

I also found http://www.diychatroom.com/f18/3-phase-residential-garage-phoenix-160336/

I just bought a house in Phoenix, and it's in an old neighborhood where some homes have high-leg open delta services for 3-phase air conditioners. The overhead utility easement is on the alley along my back property line, and there is an open delta transformer bank on the pole next to my property. 3-phase secondary runs past my lot, but my mid-span drop is only single phase. It's nominally a 200A service but the POCO conductors are way undersized for that.

 

[mivey]

If this is on a residence you have a one in a million service.

Not that rare around here. Maybe several in thousands. A pretty easy way to provide three-phase to residential loads with 3-phase A/C units.

Whoever decided a high leg delta service was what is needed here is the one that should have lost their job

Maybe the A/C salesman who convinced them they needed a 3-phase A/C unit should get the axe.

This type of service was used in that area 40-50 years ago to supply central A/C compressors. The entire house was wired as if single phase, only the a/c got 3.

That is what I usually see, and not necessarily on mansions but usually larger homes.

 

[suemarkp]

At the range, measure the voltage from each phase to neutral (or whoever replaced you can measure...). If you're getting 208V instead of 120V, then you've got the wild leg going to the range. Can't do that with a 120/240V load such as clothes dryers and ranges -- must be phases AC and neutral. That is assuming the wild leg is on phase B (in the panel) like its supposed to be. I don't see a reason why the wild leg can't be on leg C of the meter and leg B of the panel. That should make the POCO and inspector happy. But that orange tape or wire is a critical red flag to have installed.

In 240/120 delta, you get 240V phase to phase, 120V from phases A and C to neutral, and 208V from phase B to neutral.

 

[jumper]

At the range, measure the voltage from each phase to neutral (or whoever replaced you can measure...). If you're getting 208V instead of 120V, then you've got the wild leg going to the range. Can't do that with a 120/240V load such as clothes dryers and ranges -- must be phases AC and neutral. That is assuming the wild leg is on phase B (in the panel) like its supposed to be. I don't see a reason why the wild leg can't be on leg C of the meter and leg B of the panel. That should make the POCO and inspector happy. But that orange tape or wire is a critical red flag to have installed.

In 240/120 delta, you get 240V phase to phase, 120V from phases A and C to neutral, and 208V from phase B to neutral.

There is no reason that the high leg/B phase cannot not serve 120/240V loads as long as the 120V portion of the the load is on either A or C phase.

Not the best design choice IMO, but legal.

 

[iwire]

Here is my guess.

The range was getting 208, after you changed things it was getting 240. This would certainly seem much hotter, in my experience at 208 my stove top burners would not really glow, at 240 they will be bright red.

If this is too hot can be determined by looking at the units labeling, is it rated for 208 or is it rated for 240.

 

[kwired]

This type of service was used in that area 40-50 years ago to supply central A/C compressors. The entire house was wired as if single phase, only the a/c got 3.

Residential Electrical Service Replacement/Relocation Checklist for Services of 200 amps or less mentions it
http://www.tempe.gov/modules/showdocument.aspx?documentid=5312:



I also found http://www.diychatroom.com/f18/3-phase-residential-garage-phoenix-160336/

I have run into commercial buildings that have three phase high leg systems but the high leg only supplies an air conditioner unit. Usually older installs. I can't ever recall seeing a dwelling this way.

Sounds like a good possible place to run into the old "delta breakers" if the AC is the only three phase load.

 

[jumper]

I have run into commercial buildings that have three phase high leg systems but the high leg only supplies an air conditioner unit. Usually older installs. I can't ever recall seeing a dwelling this way.

Sounds like a good possible place to run into the old "delta breakers" if the AC is the only three phase load.

Actually quite common over here on the East coast for older resi installs also, neighbor had one.

 

[kwired]

Actually quite common over here on the East coast for older resi installs also, neighbor had one.

Was it common to see delta breakers on these installs since there likely was only one three phase load?

If you used a three phase loadcenter you would only have 2/3 of the spaces usable for 120 volts and would likely have the occasional HO or handyman not knowing any better connect a 120 volt circuit to the wild leg.

 

[texie]

At the range, measure the voltage from each phase to neutral (or whoever replaced you can measure...). If you're getting 208V instead of 120V, then you've got the wild leg going to the range. Can't do that with a 120/240V load such as clothes dryers and ranges -- must be phases AC and neutral. That is assuming the wild leg is on phase B (in the panel) like its supposed to be. I don't see a reason why the wild leg can't be on leg C of the meter and leg B of the panel. That should make the POCO and inspector happy. But that orange tape or wire is a critical red flag to have installed.

In 240/120 delta, you get 240V phase to phase, 120V from phases A and C to neutral, and 208V from phase B to neutral.

Bingo! Correct on all counts.

 

[texie]

Was it common to see delta breakers on these installs since there likely was only one three phase load?

If you used a three phase loadcenter you would only have 2/3 of the spaces usable for 120 volts and would likely have the occasional HO or handyman not knowing any better connect a 120 volt circuit to the wild leg.

Typical for these set ups in the early days of A/C for large homes was a single phase panel for all loads except the A/C. The A/C was usually fed from a second fusible safety switch from the meter. Usually the service conductor for the high leg was reduced to the minimum. Rarely ever saw a delta breaker used for this these. These residential high leg services were actually pretty common back in the day in some hot areas of the US.

 

[suemarkp]

There is no reason that the high leg/B phase cannot not serve 120/240V loads as long as the 120V portion of the the load is on either A or C phase.

Not the best design choice IMO, but legal.

And how are you supposed to know which leg of a range or dryer will be pulling from for its 120V items (it may even try to get 120V from each leg)? If you've got phase B on one of those two lines, you're just asking for trouble. Cord and plug appliances get changed out all the time, so how it works today may not be the same tomorrow.

I'd argue that a 120/240V receptacle that has 208V from one phase to neutral is not code legal. You're exceeding the voltage rating between pins from one of the two phases if it has B phase on that receptacle.

 

[texie]

And how are you supposed to know which leg of a range or dryer will be pulling from for its 120V items (it may even try to get 120V from each leg)? If you've got phase B on one of those two lines, you're just asking for trouble. Cord and plug appliances get changed out all the time, so how it works today may not be the same tomorrow.

I'd argue that a 120/240V receptacle that has 208V from one phase to neutral is not code legal. You're exceeding the voltage rating between pins from one of the two phases if it has B phase on that receptacle.

Agree on all counts.

 

[ActionDave]

Not that rare around here. Maybe several in thousands. A pretty easy way to provide three-phase to residential loads with 3-phase A/C units.....

Actually quite common over here on the East coast for older resi installs also, neighbor had one.

It's a new one for me.

 

[texie]

It's a new one for me.

Dave, us Coloradoan's didn't have A/C back in the early days. I grew up in a house in the deep south, built in '49 or '50, with such a service for A/C. Also I should have mentioned in my previous post that all these services were CT metered as self contained metering above about 100 amps of calculated load were not yet made. All 3 phase was CT in those days. I'm dating myself. PS:you getting any smoke over there from the fires? The wind has been in our favor and we have none.