Thread: Table Saw Maximum Power Question

They will pull more when they start up, so first you have to avoid starting both at once. You might squeeze in 2 hp but 1.5 would be safer.

It's a simple calculation. P=V*I so power in watts = volts (240) * current. 1 hp is about 750 watts, or 0.75 kilowatts (a kilowatt is 1000 watts), so 2 hp is 1.5 kilowatts, divided by 240 is about 6 amps or so. The you have inefficiency so the current draw will be a tad higher, as per the 7.7 of your blower.

So hanging 2 + 2 hp off 1 16 amp circuit is pushing it.

Anyway another way of looking at it is 16 amps at 240 volts is 3840 watts, or 5.1 HP. Remember nothing is 100% efficient (except possibly stupidity) so you can't actually get 5.1 hp out of that circuit. I reckon you'll squeeze in 4 if you don't start both at once, but I wouldn't go more than that.

That 15 amps on the 3 horse might be peak current draw ?

Thanks for that Damian
It is a long time since I did those calculations in physics at secondary school.
I always switch on DC first anyway and after posting I checked the bandsaw. It is 2HP and have used both together without a problem.

ONe 16A circuit? I would check that. There are a lot of dodgy, not up to current code electrical installations out there. 16A is the rating of the circuit breaker. This is sometimes a misnoma, as there are many things that can influence the current carrying capacity of the cable, the stuff the breaker is trying to protect. What needs to be considered is how the cable is installed- basically cable can only carry enough current as the amount of heat it can dissipate, and keep it below the 75deg rating of the insulation. An aerial cable (spaced from a wall or suspended), 2.5mm2 can carry something like 23A. This is for your standard domestic 'twin and earth' cable- active, neutral and earth.
However, the same cable, completely surrounded by thermal or similar insulation can only carry 11A!
The old 'standard' cabling (not to standard, but how it used to be done) was to run 1 or 1.5mm cable for lighting, and 2.5mm for power. This 'standard' comes from back in the days when cabling was run in timber or brick wall/ceiling cavities, houses were 200 odd m2 and you had one light and one power point in each room.

Hopefully this goes some way to explaining why a 16A circuit may not actually be good for 16A, particularly if the installation has been modified- ever put insulation in your ceiling??

Another thing to consider is what is called a duty cycle- typically this is only used in machines like welders, which are not running constantly. From memory, a 40% duty cycle is equivalent to 70% or thereabouts of full load current. Again, this is related to heat dissipation of the cable- dont run it all the time, and it has a chance to cool off, and not melt the insulation.

Regarding starting current, you can practically ignore it- it only lasts a few cycles, in which time a circuit breaker shouldn't trip- you can get specific breakers for this purpose- D curve i seem to recall (normal ones are C curve).

Sorry if i am a bit vague, its been a few years since i studied all this stuff. I now work on transmission and supply, giving Brisbanes city all the power it needs.

If you need any clarification of further info, just post a reply, and i will look into it.
Cheers

Thanks for that info Benja
The wiring for my garage runs under the house which is elevated at the rear and therefore well ventilated and then underground to the garage so no insulation around it.

Originally Posted by Chesand

Thanks for that info Benja
The wiring for my garage runs under the house which is elevated at the rear and therefore well ventilated and then underground to the garage so no insulation around it.

So you dont think dirt will keep the heat in?? And wiring underneath something needs derating too- remember heat rises!!

'if' your house/shed are relatively modern & 'if' the wiring was done to Australian standards then u will prob find that the actual wiring is in fact 25amp rated even tho it only has a 16a breaker on it. I'm not an electrician but a electronics technician & i am in the same boat, a power line buried & cemented in conduit out to my shed. A good friend of mine is a sparky & had me check the actual cable size & told me that i could easily & safely slap a 20amp breaker on the shed line because the correct cable was used & its actually rated at 25amp.
If u can get access to any part of the power cable, after first turning off the power naturally, check for a rating figure written on the outer cable casing or if u can't find writing then grab some calipars & measure the actual thickness of the copper cores. A sparky should easily be able to tell u the actual current ratting of the line from the core diamater - that is provided the job wasn't 'doggy' right from the start.
As Benja mentioned, there are a lot of 'doggy' installations out there especally where shed connections are concerned so it would be a good idea to look into it closely.

Originally Posted by damian

They will pull more when they start up, so first you have to avoid starting both at once. You might squeeze in 2 hp but 1.5 would be safer.

That 15 amps on the 3 horse might be peak current draw ?

The current/power rating on machinery actually means very little. It's a nominal number within reason made up by the motor supplier to suit what the machinery supplier wants. In practice its an average working current or power rating. A 3HP 220V motor should draw 10.3 A but I have measured the motor on my TS drawing around
- 30 - 40A momentarily when it first starts,
- 3 A when free running
- 5 A under moderate load
- up to 12A on a heavy load
- as much as 18A contbefore it stalls.

To read more check out this thread.

Sorry rattrap, you will NEVER find a rating on cable, except for the insulation breakdown voltage- 600/1000V nominally. Like i have said, the rating depends on the installation, more specifically how effectively the cable dissipates heat.
I think your so called sparky mate needs a refresher in AS 3000/2007 (wiring rules), and AS 3008.1.1(cable selection).
There is no single cable able to give 20A, it depends on installation, location, proximity to other cables, cable length etc.
As i said above, 2.5mm cable may withstand 23A, but it could be as low or lower than 11A, depending on the installation. I have seen installations which require 4mm or even 6mm (longer distance) cable for standard, 10A outlets. Length is important- the longer the run, the greater the voltage drop, which actually means you will be pulling MORE current, creating more heat etc etc.

I agree with most of what has been said above, but the bottom line is that at some point you are going to have to assume that the installation was done legally and is up to standard (unless you are aware that it is not legal and/or up to standard)

or

you need to get someone in to inspect and "certify" the installation.

If the install is ok then you can draw up to around 16 amps on the circuit before the breaker will trip. As mentioned, startup current shouldn't be an issue, but if it is change the breaker for a d-curve

Thanks everyone.
The installation was certainly done legally although some time ago before the addiction to woodworking and necessary tools set in.