Tripping breaker

[kwired]

I've designed more than a few sewage pump stations
elec, mech and sanitary design
in my experience they are typically over sized for peak demand and storm water infiltration

I designed for a duty cycle of 25-30% avg
10-20 low flow
60-70 peak

another consideration is retention time, in both the wet well and force main
too long = septic
you want to evacuate the fm every 4-6 hrs since no air in line
it is a balance: too big = septic, too small friction loss, wasted hp

the whole system needs reviewd
piping
well size
pump size
controls
not only elec

could be as simple as adjusting the level control

Isn't duty cycle somewhat a guesstimate?

When that new lift station goes in there are only 25 houses feeding into it. 50 years later that same station is still there, maybe a few parts have been replaced after wearing out but still mostly the same thing - but there is now 150 houses feeding into it. Thing happen over time.

 

[Ingenieur]

Isn't duty cycle somewhat a guesstimate?

When that new lift station goes in there are only 25 houses feeding into it. 50 years later that same station is still there, maybe a few parts have been replaced after wearing out but still mostly the same thing - but there is now 150 houses feeding into it. Thing happen over time.

isn't that obvious?
it is all edtimates
but you design for a service life of 10-20 years
and current edu's x the areas population growth rate
unless a new development, then for projected buildout
and hope you can get the times you need with float adjustment
some times vfd's are required
sometimes 3 pumps
it depends on the area

have you done the capacity calcs for pump stations?
we used water records

one of the larger ones

 

[kwired]

isn't that obvious?
it is all edtimates
but you design for a service life of 10-20 years
and current edu's x the areas population growth rate
unless a new development, then for projected buildout
and hope you can get the times you need with float adjustment
some times vfd's are required
it depends on the area

have you done the capacity calcs for pump stations?
we used water records

My experience is service calls on mostly 40+ year old pumping stations in small villages.

And there is almost always equipment that has been replaced or added that wasn't the original equipment either.

 

[Ingenieur]

My experience is service calls on mostly 40+ year old pumping stations in small villages.

And there is almost always equipment that has been replaced or added that wasn't the original equipment either.

there are different scenarios
extending sewers into new areas
easiest because you know counts and new building rates
although sewers will increase that some

replacement of existing
law requires hour meters, so flow can be estimated from pump down/in flow tests
if you see 1 hr/day run time you know you have too much pump
you can resize off of that data

new development
the toughest
it may be sized for 50 homes but that may take 10 years
so size for 25 and plan on upsizing in 5-10 years
3 pumps: 1 for low flow, 2 for high, the 3rd is the required back-up
vfd?

I liked it
it was challenging

 

[Djglennon62]

It is not a new installation, and one of the 2 pumps is bad. The customer was concerned about the 60A breaker tripping ahead of the 50A. The response where one pump is running while the bad pump sits idle, and then try’s to start, that breaker is cold, but the 60A breaker has been protecting the other 50A breaker and pump. Seems to make sense. If there are any theories or ideas of why the 60A breaker would trip before the 50A breaker I would be glad to hear them.

 

[ptonsparky]

It is not a new installation, and one of the 2 pumps is bad. The customer was concerned about the 60A breaker tripping ahead of the 50A. The response where one pump is running while the bad pump sits idle, and then try’s to start, that breaker is cold, but the 60A breaker has been protecting the other 50A breaker and pump. Seems to make sense. If there are any theories or ideas of why the 60A breaker would trip before the 50A breaker I would be glad to hear them.

See post 5 again. Then look at post 2. We don’t know how bad your motor is but it is not that unusual for a 100 or even a 200 to clear before the 50 does on a fault. It is not what we want to happen but it does or I should say, it can.

 

[GoldDigger]

See post 5 again. Then look at post 2. We don’t know how bad your motor is but it is not that unusual for a 100 or even a 200 to clear before the 50 does on a fault. It is not what we want to happen but it does or I should say, it can.

And one reason that it can is that the time-current trip curves of two different size breakers, even in the same line from the same manufacturer, may be shaped such that the trip current versus time curves of one breaker cross those of the other, leaving a region of time and current combinations that trip the nominally larger breaker first.
This is less likely to happen with "identical" fuses of different nominal ratings, but is still possible.

 

[kwired]

The higher the available fault current the easier it may be for this to happen also.

Since you have 50 and 60 amp breakers involved their instant trip settings are likely fairly close to one another. In the 60 is probably supposed to be higher, especially if both are same series of units, but time and deterioration can have impact plus any tolerances that were allowed in the manufacturing.

 

[Russs57]

Strikes me as strange to have a 60 amp main with two 50 amp pump breakers. That isn’t what I’m used to seeing.

Might be worth the time to find out who made pump panel and makes sure 60 was the intended size. People will use what they have in an emergency.

And for pete’s sake, if you have known bad pump remove it from service and get it replaced ASAP.

FWIW, had good service from Flyght pumps and Stacon panels. Heck if nothing else contact them with pump specs, ask for a quote, and see what they size breakers at.