# Lift station pump electrical questions



## rocksteady (Oct 8, 2008)

I went to look at a burnt out Zoeller high head effluent pump today and when testing for voltage I got a little confused. It's a 230v, single phase pump fed with a 3 conductor wire (hot, hot, ground) so I'm expecting 110-120 volts at each leg. I test one leg and see 120v, everything's good. I test the other leg and see 208v. In my mind this means the pump sees 328v AC and can't be good for the pump. The maintenance guy calls his electrician and is told that this is normal and won't hurt the pump. Something about a "stinger" leg of a 3 phase system? At the panel is a regular looking (to my eyes) 30 amp double pole breaker. 

My question is about the voltage. Is 120/208 going to damage the new pump? If not, how does 120 on one leg and 208 on the other not add up to 328 volts?






Paul


----------



## Mississippiplum (Sep 30, 2011)

Yep it's the high leg of a 240 volt 3 phase delta config. And it won't hurt the pump cause the pump is actually getting 240 volts. Phase to phase.

Phase to phase is all that matters in this situation, as long as you are getting 240 phase to phase it's not a problem. The problems arise when someone decides to feed a single phase 120v appliance with the "high leg" that's when the sparks fly literally. Because then you are getting 208 volts to ground.


----------



## rocksteady (Oct 8, 2008)

So, explain to me how this works. Where do the extra volts go? How does 208v on one leg and 120v on the other add up to 240v at the pump? I'm not saying your wrong but when it comes to electrical I like to know why something is the way it is. I'm going to put a new $1500 pump in and I have to KNOW that the way things are currently won't damage the new pump.






Paul


----------



## Mississippiplum (Sep 30, 2011)

The reason why is because of how the transformer bank creates 240 high leg. I can't really offer you a scientific explanation, but I do know how these 3 phase configs. Work.


----------



## Mississippiplum (Sep 30, 2011)

The main thing is- make sure that you are getting 240v from phase to phase. Split phase and 3 phase motors, don't use a neutral conductor, so current is not going from phase to neutral. that's why the 208v won't hurt the pump.


----------



## rocksteady (Oct 8, 2008)

So, is this a 3 phase or single phase circuit? The pump that's in there is a 230v single phase unit.






Paul


----------



## Mississippiplum (Sep 30, 2011)

rocksteady said:


> So, is this a 3 phase or single phase circuit? The pump that's in there is a 230v single phase unit.
> 
> Paul


You got a single phase circuit


----------



## TPWinc (May 30, 2011)

Like Mississippiplum said check "phase to phase" or leg to leg, not leg to ground. If you have 230/240 you're good. Explaining 3 phase is kinda hard but basically your 120 leg is phased so the extra voltage on the other leg is cancelled out. Remember AC voltage has no + or - wire. Each hot wire is both + and -.


----------



## TPWinc (May 30, 2011)

My attemp at further explanation... the 120 phase cycle is half of a 240 single phase. The 208 phase cycle is part of a 3 phase. But when the 208 phase is at it's peak the 120 phase is not or vice versa. So when measured between the two you will not get 328 you should get 240 just like you would using both sides of the single phase. Hope that helps.


----------



## user7551 (Oct 21, 2011)

So basically as long as you are getting no more than 240 volts when testing hot to hot you should be fine ?


----------



## TPWinc (May 30, 2011)

playme1979 said:


> So basically as long as you are getting no more than 240 volts when testing hot to hot you should be fine ?


Yes.


----------



## rocksteady (Oct 8, 2008)

Thank you for the info. I'm never going to be an electrician but I'd like to learn all I can so I can safely diagnose and work on the larger pumps. Anyone can disconnect and reconnect a couple of wires but I want to be able to understand what's going on in the control boxes better. Residential is no big deal but I'm getting more involved in commercial/industrial work and that's a different ball game.






Paul


----------



## ZL700 (Dec 8, 2009)

It usually older 3-phase systems that served both lighting and motors in mostly commercial applications. The higher voltage to neutral/ground is most commonly called the "wild leg"
Try googling "wild leg delta" I'm sure someone will explain it well.

FYI, have to watch circuit breaker placement for 120v single ph lights and appliances. Common mistake for amateurs when adding a circuit to a wild leg panel. Motor runs real fast or bulb is real bright for just a little while.


----------



## Redwood (Sep 8, 2008)

Paul, The 208/120 volt 3 phase supply is slightly different from what you see in residential. The transformer is essentially 3 transformers either separate or all in one box that uses 3 phases off the pole as shown in the diagram below. The voltages can be 480/277 or 208/120 depending on the transformer used.











In a residence only a single phase is used then stepped down via a center tapped transformer as shown below and you'll get 240/120.










Up to a 10% variation in voltage is acceptable in most cases.
Digest that and if you have any questions I'd be happy to answer them for you.


----------

