I was hoping someone could help me out. I am being asked to install a 100 amp, 240 volt control panel on a 120/208 volt 3 phase system. Am I right in thinking I could just install a buck/boost transformer and be done? The thing is this is a control panel that cost around 10k and has a lot of sensitive electronics onboard. Should I consider a phase converter too? I’m worried about the phases being out of sync since I’ll only be using 2 out of the 3 phases. Does anyone have any feedback? Thank you for your time.
Running a single phase 100 amp, 240 volt control panel on a 3 phase 120/208 system
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LarryFine
Master Electrician Electric Contractor Richmond VA
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- Henrico County, VA
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- Electrical Contractor
The "phases out of sync" is why the line-to-line voltage is 208 instead of 240. If you need 120/240v, a single buck-boost won't do it. You'd need a 208v-to-240v transformer with a center tap, which you'll have to bond as an SDS, to get 120/240v. If you only need 240v, a buck-boost will work, but you'll end up with two different voltages to the neutral. If your control center doesn't have a problem with that, you should be okay.
Thanks Larry
Thanks Larry
Larry,
Thank you for the reply. This control panel is just 240 so the buck/boost will work in that respect. The "2 different voltages to the neutral" is the thing that concerns me. This friggin thing has more electronics than the starship enterprise and I don't want to be the guy who fries it. I'm not an electrical engineer but here's the feedback I'm getting.
1) Oronco - These guys built the control panel - They say it's not a good idea to try what I'm suggesting
2) Septic Company that supplied this board - They say they've had to do this before (buck/boost) and have not had any issues
3) Septic Design Engineer - non-committal
Thanks again for your help. This board was custom built on the assumption it was going to be fed with single phase. Nobody did a site visit to confirm. I'm just trying to keep rolling. :blink:
Thanks Larry
Larry,
Thank you for the reply. This control panel is just 240 so the buck/boost will work in that respect. The "2 different voltages to the neutral" is the thing that concerns me. This friggin thing has more electronics than the starship enterprise and I don't want to be the guy who fries it. I'm not an electrical engineer but here's the feedback I'm getting.
1) Oronco - These guys built the control panel - They say it's not a good idea to try what I'm suggesting
2) Septic Company that supplied this board - They say they've had to do this before (buck/boost) and have not had any issues
3) Septic Design Engineer - non-committal
Thanks again for your help. This board was custom built on the assumption it was going to be fed with single phase. Nobody did a site visit to confirm. I'm just trying to keep rolling. :blink:
kwired
Electron manager
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- NE Nebraska
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- EC
What exactly is the load, is there a control transformer already supplying the control circuit?
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
Orenco makes small sewage lift pump panels, for what's called a "force main" system where a lot of small individual pump stations at each house (or maybe pair of houses) collectively feed into a pressurized sewer main to force the flow up hill toward a treatment plant, rather than have to use gravity feed down into bigger lift stations. I did a project about 25 years ago with 123 Oronco panels in a housing tract around a lake, all of them "rated" for 240V single phase, all of them fed with 208V. No issues whatsoever. The sewage pumps on my project were all 3HP or less and rated for 208/240V single phase. The FLA at 208V was a little higher, but these submersible pumps were self protected and only ran for a few minutes at a time at worst. So I didn't even have OL relays that had to be adjusted.
The more important people to check with though are the pump suppliers, the Orenco panels themselves couldn't care less. The controls and electronic power supplies are all tapped off of 120V taken from Line to Neutral, and that will be the same no matter what. The 208 or 240V is just passed through to the pumps.
The more important people to check with though are the pump suppliers, the Orenco panels themselves couldn't care less. The controls and electronic power supplies are all tapped off of 120V taken from Line to Neutral, and that will be the same no matter what. The 208 or 240V is just passed through to the pumps.
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
petersonra
Senior Member
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- Northern illinois
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- Semi-retired engineer
I don't understand the phases out of sync thing. they can't be out of synch. they are in perfect synch for a 3 phase system.
If you want to you can buy a single phase xfmr, 208V primary and 120/240 secondary and ground the center point. then you would have exactly the same thing as in most residences.
petersonra
Senior Member
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- Northern illinois
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- Semi-retired engineer
did you notice the brand of the PLU in the pictures?
and that it claimed to be listed to UL508? I wonder if it is really UL508a? Marketing guys probably don't know the difference.
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
Yes I did notice and I think you're right. Marketing people rarely care about details... Putting that "a" on the end meant one more keystroke, but that wasn't in the marketing budget.
Back to the "PLU" though, they used their own green-board unit on the ones I did so long ago, but even back then they were already talking about going to a "PLC" to be able to get out of having to manufacture their own electronics. As funky as the programming is for those things, it's still a decent little "smart relay", plus they have an "Extended Environment version" that can be used at up to 70 deg. C, which is a good thing for little enclosed pump panels like that. There are better ones on the market now, but not likely cheaper for them because they don't have to re-engineer anything, so long as Siemens keeps making and selling them Orenco will probably keep using them. That product is now 22 years old, which is an eternity in the electronics world...
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The electronics don't care about phase angle or whatever, it's all A.C. power.
Count me on the side of those who don't think a buck/boost is needed.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
He's referring to two lines not being 180 degrees apart relative to the neutral.
Didn't I say that?
If it were me I would install a single phase 208V to 120/240V isolation transformer and wire the secondary as an SDS. Basically you will have a 240V line-to-line and 120V line to ground Technical Power Balanced Power System.
drcampbell
Senior Member
- Location
- The Motor City, Michigan USA
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- Registered Professional Engineer
I would want to know exactly what's consuming 100 amps. I'm guessing it's not the controls themselves.
If the panel just passes 240 volts through to the motor(s), the controls themselves run on 120 volts (quite likely) and there's 3-phase power available, the best answer might be to separate control power from motor power and use 3-phase motors.
It's time for a a conference between the customer, manufacturer and electrician. The safe route, a separately-derived system with a 208-120/240 transformer big enough to carry the whole load, is going to be expensive. Maybe they'll decide to go with a different controller after learning what it'll cost to install.
kwired
Electron manager
- Location
- NE Nebraska
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- EC
Actually from post 3 "This board was custom built on the assumption it was going to be fed with single phase. Nobody did a site visit to confirm."
It is time to talk to whoever was responsible for specifying what was built, or if the specs were correct then the manufacturer didn't build what was spec'd.
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