[mdaigs34]

I installed a generator interlock kit on a 100AMP HO panel box. all circuits run fine using utility power. when I switch to Generator power all circuits work fine except for the sump pump. I ran 12/2 from the other end of the house where the sump pump is, to the main panel to a 20amp breaker. it works fine on utility power but not generator power. Could I be suffering from line loss and if so how do i fix it?

 

[Billy_Bob]

What is the voltage at the sump pump with regular power and the sump pump on.

What is the voltage at the sump pump with generator power and the sump pump on.

What is the distance from the breaker to the sump pump?

Are there any electronic controls which operate the sump pump? Or a simple old fashioned on/off mechanism? If electronic, some generators create "dirty electricity". Some electronic things do not run on that.

If the sump pump is easily removed, might try moving it to where the breaker is, connect a short wire, then see if it works there.

 

[J. V.]

No. You are suffering from no power at the pump when the generator is on. You say interlock kit. All the interlock does is prevent the main breaker from being turned on when the generator breaker is on.
You should have a breaker for the generator. You should have a main breaker. If you have two panels which I believe you do, you need to see which panel is off during generator usage as this is where the breaker resides for the pump.

If this pump worked before your installing of the interlock and the wiring of the pump than what I say goes.