How can I feed 240 service from 208?
- Thread starter sketchy
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Yes there are transformer that step down or up for voltage. Is the the service 3 Phase? or do you need to go from single phase to 3 phase also?
masterinbama
Senior Member
- Location
- Huntsville Alabama
- Location
- Massachusetts
There should be no need for any transformer, just refeed the old service with 208.
If there is a particular piece of equipment that cannot run on 208 I would deal with that separately
If there is a particular piece of equipment that cannot run on 208 I would deal with that separately
agree
I'm curious as to the reason for the change to 208/120V 3? 4W rather than 240/120V 3? 4w? Adding 3? equipment? Or simply needing more power? Was the POCO asked to furnish more compatible voltage, i.e. higher rated 120/240 1? (if no need for 3?), or a 240/120 3? system?
Bob (iwire) mentioned just refeeding the existing 120/240 with 120/208... but that would be 120/208 1? 3W. You'd have no existing loads on the third leg. To balance out the system, you'll have to change panels (at least the MDP) to 3? and reconfigure the load distributon.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I am still sketchy about Sketchy's info. Is the new service there or is that what is needed. Each post gets me asking other questions-- could you lay it out more clearly.
kwired
Electron manager
- Location
- NE Nebraska
Being someone that has worked on a lot of farms, I would guess that load is being added, and there may be need for three phase loads.
Most farm places around here that still have a lot of 120/240 single phase load but need additional three phase loads it is common to change to 120/240 delta (with high leg) that way the existing single phase loads remain pretty much unchanged.
Unless there is larger motors involved it is still more common to just go with 400 amp single phase instead of three phase on that small of a system (OP mentioned 75kVA)
But farms are changing, livestock operations are no longer 50 - 100 head they are 1000+ head in one location big difference in power needed to operate a dairy farm that milks 4-8 cows at a time vs one that milks 25-50 at a time.
Grain farming is same way. Not many farmers left only farming 160 acres or so, many are farming well over 1000 acres anymore, this means storage and handling equipment is much larger than it used to be and needs much more power than a generation ago. Those livestock producers need to supply a lot more feeding operation equipment than they used to also.
Many farms electrical systems are just as complicated or even more so than a small industrial plant.
Most farm places around here that still have a lot of 120/240 single phase load but need additional three phase loads it is common to change to 120/240 delta (with high leg) that way the existing single phase loads remain pretty much unchanged.
Unless there is larger motors involved it is still more common to just go with 400 amp single phase instead of three phase on that small of a system (OP mentioned 75kVA)
But farms are changing, livestock operations are no longer 50 - 100 head they are 1000+ head in one location big difference in power needed to operate a dairy farm that milks 4-8 cows at a time vs one that milks 25-50 at a time.
Grain farming is same way. Not many farmers left only farming 160 acres or so, many are farming well over 1000 acres anymore, this means storage and handling equipment is much larger than it used to be and needs much more power than a generation ago. Those livestock producers need to supply a lot more feeding operation equipment than they used to also.
Many farms electrical systems are just as complicated or even more so than a small industrial plant.
The farm is getting a new wind turbine. The turbine puts out 3 phase 480. We step it down to whatever the existing service is. Why the customer changed to 3 phase I don't know as I just started at the company a month ago. The previous electrician did the initial survey 2 years ago and I have to put together the pieces. The plan is to refeed the existing 200 amp service with 208, nothing existing will be severely affected. I was asking the question because of the unbalanced leg issue. The cost of such a transformer is a lot so I'll deal with an unbalanced load.
Hmm... I'm at a loss now. Wind turbines are not on-demand power sources. And if you are going to be grid-tied (necessary to utilize both simultaneously on the same system), you can't tie in turbine supplied 120/208 with POCO furnished 120/240. Is the service getting changed to 208/120 3?, or 120/208 1????
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Your existing neutral could now be loaded effectively equal to a line conductor. This was a big issue in the days of reduced size neutrals.
Will your generator like being so severely unbalanced?
Why not try to do a little bit of balancing !-pole circuits across all three phases?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
I understand turbines.
How much of the existing 120/240V infrastructure are you changing?
In a grid tied system, wouldn't the extra go to the grid, thus balancing the generator output
That's why I suggested at least changing out the MDP to 3?... and that's before I knew there was a wind turbine in the picture.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Yes, it would, though I am not sure that the utility is suppling the farm with 3-phase.
None. This is my first time doing this and won't be the last. I want to make sure everything works and based on some people I've talked to there won't be an issue re-feeding everything 208. The oven my take a little longer to warm up, motors may run a little slower but there shouldn't be anything severe.
Sketchy said yes back in post#12...
kwired
Electron manager
- Location
- NE Nebraska
Motors will not run slower - they will draw more current than they did @ 240. Probably about 10% more. If you have motors that were loaded near full load before you may have overloading issues with them after changing to 208 volts.
Heating loads will have less capacity - by about 25%.
If your generator is 480 volts and you need a transformer anyway why not a 120/240 three phase and get POCO to do the same?? (I know some of these decisions were made before you were involved, but not sure why they decided to do what they did.) If you are not really increasing the load POCO could have easily just installed a second transformer (and likely a smaller one if the load is not there) and supplied this with an open delta system, instead they built an entire new transformer bank that apparently will not even have much of a balanced load on it
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