Figure 6 Figure 7 circulators = 2.25 amps. Then, the relays; 0.40 amps per relay X three relays = 1.20 amps. So, our amperage draw would go like this; one oilburner + three circulators and relays =? 2.62 amps + 1.62 amps = 4.24 amps. For an older installation, 5.5 amps + 3.45 amps = 8.95 amps.

That 4.24 amps is the amount of amperage that the circuit would draw when on, but what does it draw on start?

Well, a lot of that depends on motor types and other factors. For now, let’ s just say that a good‘ rule of thumb’ is that‘ the start amperage is three to four times the run amperage’.

So, in this example the potential start amperage could be between 26 and 36 amps. The wire could handle that quick surge but now do you see why we tended to use‘ slow-blow’ or delay-type fuses and eventually moved 100 % to circuit breakers? But it should be noted that with the newer motors( PSC and ECM) the rule of thumb is now two to three times the run and that brings your starting amperage down to between 9 and 13 amps.

Now, what else could we calculate using Ohm’ s

Law? The resistance of the circuit, right? 115 volts % 4.24 amps = 27.12 ohms That will give you a basic understanding of how Ohm’ s Law works in the field, and as you can see, it really does matter, and it even works! Using formulas and rules is what separates servicemen from technicians.

See ya! l FON

George Lanthier is the owner of Firedragon Academy( www. FiredragonEnt. com), a 35-year-old Massachusetts Certified School teaching gas and oil and other heating subjects. Firedragon Academy’ s training facility is in Webster, Massachusetts. Firedragon also publishes Lanthier’ s more than 60 books and manuals on HVAC subjects. He is a CETP, ESCO, NATE, NORA, PMAA and PMEF Proctor and has been a Massachusetts Certified Instructor since 1975.

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