OK, I've posted enough responses, now I'm posting a question. In 1960, when my building was built, the heating system (boiler transformer, and water circulating pump) were on a 15 amp screw-in fuse in a fuse box in my electrical service room. Since then, we've added an circuit breaker panel for the parking lot plugs in that same electrical service room that neighbors the boiler room. In August of 2006, we replaced the old boiler with two new high efficiency boilers and an indirect fired water heater. Each boiler has it's own circulating pump, there's a pump to pump hot boiler water through the heat exchanger coil inside the water heater, and there's still the main circulating pump for heating the building in winter. So, there's a lot more load on that one screw in fuse. Now, it seems that there's a problem with the undirect fired water heater that can only be corrected by replacing the water pump for the water heater with a larger one. The existing pump draws 2.5 amps, and the proposed pump will draw 4.5 amps. There is concern that replacing the pump is going to result in the new heating system blowing 15 amp screw-in fuses, so we've run another circuit into the boiler room from the circuit breaker panel. I know how to free up the power going to the existing water pump on the original circuit. Also, I know how to wire the new power source to the boiler control so that the new pump runs off the power from the new circuit instead of the old one. The white neutral wire from the existing pump joins all the other white wires from all the other 120 volt pumps and controls and connects to the white bus bar in the original fuse box. My question is this: Will it be necessary to ALSO trace back the white wire from the pump location, disconnect it from all the other white wires and connect it to the new white wire from the circuit breaker? Or, is it appropriate to leave it connected as is. I'm thinking the white return lines from both voltage sources all get connected together inside the circuit breaker panel, and in the fuse box, so sharing white wires that way isn't a problem. However, in this case, I'm sharing white neutral wires BETWEEN electrical panels. That is, the power going from the new circuit breaker panel will go through the new pump and end up going back to the original fuse box for the building, which is a different electrical "panel". Obviously, the most rigorous way to do this would be to trace the white wire to the pump back, disconnect it from all the rest of the white wires it's pigtailed to, and connect it to the white wire from the circuit breaker panel. But, is it actually necessary to do that?