Circuit Breaker Size
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How to Calculate How What Size Circuit Breaker a Machine will Need:

Are you buying a new machine and need to know what size Circuit Breaker to use? Calculating the correct size Circuit Breaker to attach your wiring to is easy if you follow our guidelines shown in the chart below. Circuit Breakers are rated by Amps. The Amperage needed when the machine is idling will roughly correspond to the horsePower of the main motor on the machine. For startup and other peak performance uses of a machine you should size the circuit breaker to DOUBLE the Amps show for machine when idling. Slow Blow style circuit breakers are less likely to flip during a brief heavy load. The Amp Ratings we show are approximate and should only be a guideline. You should have your electrical connections done by an electrician. Machines driven by a simple electrical motor will use different levels of power than machines that are hydraulically driven. Machines driven by good quality American, Canadian, Japanese or European electric motors will use lower levels of power than electric motors made in China or India. Electric motors made in Taiwan will be somewhere in between. Locate the machine close to the circuit breaker to avoid a build-up of resistance and heat in the wiring between the circuit breaker and the machine. REMEMBER (for most machines) USE A CIRCUIT BREAKER APPROXIMATELY DOUBLE THE AMPS THAT CORESPOND TO THE HP OF YOUR MOTOR SO IT WILL HANDLE STARTUP AND PEAK LOADS.

HorsePower of Main Motor
220 Volts, 1 phase
220 Volts, 3 phase
440 Volts, 3 phase
1 Hp
5.6 Amps
2.8
1.4
2
11.2
5.6
2.8
3
16.8
8.4
4.2
4
22.4
11.2
5.6
5
28
14
7
6
33.6
16.8
8.4
7
39.2
19.6
9.8
8
44.8
22.4
11.2
10
56
28
14
15
84
42
21
20
112
56
28
25
140
70
35
30
168
84
42
40
224
112
56
50
280
140
70

The Amperage Ratings shown are while the machine is idling, not being used to perform heavy work. If in doubt, please ask your American Machine Tools Company representative for guidance when purchasing a machine from us. This information is offered for reference only and should be confirmed by an electrician before you install circuit breakers.

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American Machine Tools Corp.
5864 Northwest Hwy
Chicago IL 60631 USA

Phone: 773-334-5000
Fax: 773-442-0314

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