Hi. I live in NZ and here we have entirely different plugs for 10A and 15A circuits, so if you dont have a dedicated 15A circuit, you have to get one specifically wired in for anything that requires one. Ive noticed a lot of new 3hp machines (eg):

W450 | ST-250 Table Saw | machineryhouse.co.nz

require 15A circuits, despite having current draw which could theoretically be managed on a 10A (2200W, on a 240v circuit). i realise i couldnt run anything else on a 10A circuit with this machine on, but since i only ever have one machine running at a time, why not?!

Anyone know why manufacturers are limiting the use of their products in this way, when it seems more ideal than absolutely necessary?

Or am i missing something here?

 

Welcome to the forums! Please remember this is primarily a North American forum so we aren't as savvy on your 240 volt systems. With that said, however, you have to consider spool up amperage draw, and not just running amperage. That is why many manufacturers require a little higher over current protection for their machinery. Here, too, we isolate 240 volts for use on machinery, and 120 volts for lighting and general receptacles such as small equipment. I have my shop's 240 volt supply split over two circuits, and as you say, although machinery is connected to the same circuit, it is impossible to run both pieces of equipment at the same time. Those that can be run simultaneously will, of course, be relegated to separate circuits.

 

Thanks chandler. So is there any way to calculate spool up (ie, maximum) current draw, if P=IV doesnt cut it? Im also wondering now, when a motor is quoted at 3hp, or 2250W, or whatever, are these not the maximum figures for the power that it consumes? If so, then spool up current draw couldnt exceed 10A for a 2200W motor on a 240V supply, no? Sorry for being an idiot if this is obvious to everyone except me....

 

G'day Yourmomm.
Mate its all to do with inrush current.Depending on the design of the motor you have, inrush current can be anywhere from 4 to 10 times the nameplate current.Its a fairly common thing here on the west island..

 

I'm only a 2nd year and haven't been schooled on motors yet, but do you not take the motor's draw at 125% to compensate for startup?

 

G'day Mr.Awesome.....mate you will find single phase motors(still dependant on design) will draw anywhere from 250% to 1000% of nameplate current.This normally applies to split phase/cap start cap run motors...not so much for shaded pole motors..

 

@ Mr Awesome, Look in the motor section of the code. The NEC it is 440 particularity, 440.52 table. It can be anywhere between 150 - 800%. Again, this is the NEC. The CEC may be different.