If the water is running in from the drain tile and the pump is pumping it out, then everything is operating normally. It doesn't have to be raining for you to get water draining to the sump pump.
It's certainly not a bad idea to have a spare pump on hand just in case, but that spare pump does no good if you're not right there monitoring it to know it failed, or if the power goes out. What you really need is something with some redundancy built in.
We recently had to have our entire drainage system torn out and replaced because it wasn't installed properly and we had water coming in the basement. We had a "Triple Safe" sump pump system installed, which as the name suggests, has 3 pumps. The primary pump is a 1/3 HP Zoeller pump. The secondary pump is a 1/2 HP Zoeller pump. This takes over in the event the primary pump fails, or runs simultaneously if there's too much water volume for the primary pump to keep up. There's also a battery backup pump, which will pump over 10,000 gallons on a charge. The system also has a battery maintainer and an alarm that sounds if the water level gets within 6" of the top of the sump.

It's certainly not a bad idea to have a spare pump on hand just in case, but that spare pump does no good if you're not right there monitoring it to know it failed, or if the power goes out. What you really need is something with some redundancy built in.
We recently had to have our entire drainage system torn out and replaced because it wasn't installed properly and we had water coming in the basement. We had a "Triple Safe" sump pump system installed, which as the name suggests, has 3 pumps. The primary pump is a 1/3 HP Zoeller pump. The secondary pump is a 1/2 HP Zoeller pump. This takes over in the event the primary pump fails, or runs simultaneously if there's too much water volume for the primary pump to keep up. There's also a battery backup pump, which will pump over 10,000 gallons on a charge. The system also has a battery maintainer and an alarm that sounds if the water level gets within 6" of the top of the sump.
