Motor running backwards? Be careful

What if you start up your heater and you see this happening:

  • The fuel pump is sucking fuel from the line, instead of pumping it from the tank.
  • You smell smoke or see smoke going into the burner housing (the sign that the burner is drawing combustion air out of the stack and into the chamber).
  • When you put your hand in front of the blower, air is not blowing out. Instead, the blower is drawing in air.

These are the signs that the motor is running backwards.

Last month we received a service call to an oilfield well site that was starting up for the season. The 4M BTU oilfield boiler had just come back from recertification and annual maintenance. The eight-member crew was standing by, waiting for heat so that they could begin working in the -2C weather.

The technician hooked up the heater, turned it on, and knew from the signs that the motor was running backwards. He went to the Internet and found instructions for reversing the rotation of a three phase motor. The instruction was simply this: switch any two wires.

This is where the problem begins.

The boiler’s motor actually has five wires:

  1. White – neutral
  2. Green – ground
  3. Red – hot lead
  4. Blue – hot lead
  5. Black – hot lead

If the technician had switched any two of the three hot leads (red, blue, black), he would have got the result he wanted. Instead, he randomly chose the white and red wires. When he started the boiler, 208 volts, instead of 120, surged through the controller.

At 9 a.m. he called for help. We talked through the problem and had him try some different things, but nothing was working. Mark grabbed some parts and drove to the wellsite. By 1 p.m. he had the boiler repaired and working again.

It was a costly mistake. The voltage had burned the ignition transformer ($800) and the flame controller ($1,400). The service call was $3,000. And these were minor costs compared to the downtime of eight-crew members for half a day.

My best advice is to have an electrician hook up your boiler or heater. Otherwise, keep in mind this lesson and remember the facts about the motor’s five wires.

In another post, I’ll tell you why motors sometimes get reversed, and what you can and cannot do about it.