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Amperage for 5HP table saw?
What amperage breaker does one need for a 5HP table saw on a 240V
single phase circuit? My logic: Typically, single phase 5HP 240V (or 230V) motors are rated at 19.8 or 20 A. Given that a circuit is supposed to be loaded 80% (look it up in the NEC sometime), this means a 25 A breaker would be borderline sufficient, and that a 30A breaker should be generous. With a slow breaker (not a fuse), there should be no problems with the startup surge of the motor tripping the breaker. The reason I'm asking is that I've recently read a few posts claiming that a 5HP tool needs a 40A or even 50A breaker. There are a few reasons not to do that. First, it requires 8 gauge wire (for 40A) or 6 gauge wire (for 50A), which is considerably harder to work with. Second, it requires a different connector, which means less flexibility in moving tools around. For this reason, I had been planning to make all the 240 V outlets be twist-look 30A outlets in my soon-to-be-built shop. Third, it is unsafe to use too large a breaker: If something goes wrong, there is more current around to fry things or start a fire. While we are it it. I have converted on of our waterpumps (a 1.5HP pump) from single-phase to three-phase motor, with a VFD (or inverter) driving it. This gives me a really nice slow start, with no current surges (which is vital when running on a generator). I'm planning to convert my drill press similarly, one of these days. This would give me the ability to run at variable speed (within a range of maybe a factor of two), without having to change belts, and it would again remove the startup surge and the mechanical stress associated with it. This brings up the following question: Is there a point using a 3-phase tablesaw motor on an inverter? There is no point running a tablesaw at reduced speed, is there? So the only point would be slow start (which is not worth the extra couple hundred $$$ for the inverter). Also, in principle, one can buy 3 HP inverters that run on single-phase 240V, but if the single-phase motor on the table saw has a service factor 1, a nominal 3 HP inverter will not be quite sufficient. Does anyone know whether electronic VFD inverters with single-phase input and 5HP capacity even exist? I haven't seen one yet. -- The address in the header is invalid for obvious reasons. Please reconstruct the address from the information below (look for _). Ralph Becker-Szendy _firstname_@lr _dot_ los-gatos _dot_ ca.us |
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