Just a few general comments on the application ...
"Septic pumps" aren't that severe of an application. Let's look at their operation.
A motor has the greatest current draw at start-up. This factor is worst where the motor starts off against a full load, as would happen with a compressor. An ordinary fan, by comparison, starts off with very little load. A septic pump usually has little load as well; it just has to pump against the "head" (which is usually well under FLA), and there's usually a 'weep hole' near the pump, and before the check valve.
The pump operates for short periods of time, so it's not continuous duty. You MIGHT have other issues if the pump is 'short cycling,' or operating more than six times an hour.
Your enemy is heat - whether from the start-up load or short cycling. With a sewage pump, this is mitigated by the cooling effect of the sewage. I am assuming these are submerged pumps - as discussed in another post. Not that it's pretty important for the pumps to shut off while still submerged; you do not want to pump that pit dry every time the pumps cycle.
At any rate, we over-size the breaker to allow for that moment of high start-up current. As others have mentioned, the "heaters" in the starter are there to shut things down if the motors are continually drawing excessive current.
You need to MEASURE the actual current drawn by the pumps. One of the best indications of what is happening in the pit is the current drawn by the pump. When the system is new and clean, measure current, write it on a piece of tape, stick it in the panel. This gives you a reference for your next visit.
One cause of high current draw is simple the accumulation of crud in the discharge line. Over time, that 2" line will be reduced to 1/2". Discharge lines need periodic cleaning. I've been down this road with reluctant customers and sceptical plumbers; in one instance the problem festered for three years, and several pump replacements, before the necessary clean-outs were added. In that case, cleaning the pipe cut the amps drawn to 1/3 of the previous level.
Last edited by renosteinke; 01/06/10 02:31 PM.
