First, the power displayed on the dashboard is the power going to the pump itself. The power on the kill-a-watt is the power being drawn from the wall which includes the pump plus the controller plus the power supply.
There are several
potential issues with water back-siphoning into the sump when the pump is turned off:
- If the pump is restarted while water continues to flow backwards, it will generally cause an error and failure to restart
- back siphoned water can cause the sump to overflow (If this is actually an issue then you probably have a poorly/improperly designed system, but that's another discussion)
- dropping water level in the display tank may cause power heads to entertain air
- High water levels in the sump can cover float switches intended to be emergency backups and get debris on them (normally you should check and clean these as part of routine sump maintenance, so this shouldn't be an issue, but I'm listing it as at least a theoretical one)
- Restarting of the return pump after the water has siphoned back to the sump makes a lot of splashing, bubbles and noise. Having the pump at a 'static' flow speed means the system starts up more quickly, quietly, with less splashing and achieves steady state faster.
The last reason is the real reason most people do it. If none of these matter to you, there's nothing particularly wrong with having the low threshold set to 0.
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