Working Out Current and MCB Size for Machines

[fergusmacdonald]

Hello
I have 3 new machines and I'm wondering if there are any rules of thumb to follow for what the maximum current a motor will draw?
For example I have:

Axminster T-2000CK-200H dust extractor
Motor 1.5kW
Running load 6.5A
Came with a 16A plug and is on a 16A MCB. However the running load is 6.5A so could this work on a 13A plug?

Hammer HS950
Motor 2.2kW
Running load 9.5A
Plug/MCB 16A
Could this run on 13A?

Hammer N4400
Motor 2.5kW
Running load 10.9A
I was putting this on a 16A and I guess it needs it?

Hammer A3-41
Motor 3kW
Running load 13.05A
MCB 16A

I'm slightly confused as to how I should know whether it needs a 13A or 16A? For example the Axminster dust extractor is approx half of the 13A but came with a 16A but the A3-41 has double the power but still also only needs a 16A? Is the only way to ask the manufacturer or could some of the smaller machines be on 13A plugs?

Thanks in advance.

 

[Alli]

As I understand it, its not the running load that is a problem but the starting current of the motor which can be sometimes 5 times the running load. A 13amp plug and fuse may blow because of the start up currents. If these where my machines I would look to have them on a dedicated 16amp supply fed by a 16A MCB with a 'C' curve . The C curve allows for a very small amount of time more than 16 amps to flow which stops nuisance tripping due to the motor start up.

 

[Spectric]

The maximum current a motor can draw will be the stall current which should trip the overload device. Then there is the startup current which will depend on the initial load the motor is going to power and the size of the motor and last you have the running current, this is the current the machine will draw in normal operation. For me the only machine I have that needed a dedicated 16 amp supply was my planer thicknesser due to startup current, everything else works fine on a 13 amp socket like my BS400 bandsaw at 2.2 Kw and my tablesaw also at 2.2 Kw. I would suggest the dust extractor at just 1.5Kw would be fine on a 13 amp but your electrical distribution system will also have an effect in that cable sizes and run lengths will all have an input to the calcs so giving hard and fast rules is not feasable.

 

[Spectric]

The C curve allows for a very small amount of time more than 16 amps to flow which stops nuisance tripping due to the motor start up.

Again if you look on these forums you will find more information and changing a type B protective device for a type C without the right test equipment and knowledge is a do not do, it is also a change in design which needs an electrician to certify otherwise you could end up with a thermal event during a fault condition. This is because if your circuit impedance is to high then the fault current might be to low to trip a type C and things can only get hot, I have seen good examples of wiring that has caused extensive damage to property all because someone has made something work without investigating what happens during a fault.

 

[Alli]

Again if you look on these forums you will find more information and changing a type B protective device for a type C without the right test equipment and knowledge is a do not do, it is also a change in design which needs an electrician to certify otherwise you could end up with a thermal event during a fault condition. This is because if your circuit impedance is to high then the fault current might be to low to trip a type C and things can only get hot, I have seen good examples of wiring that has caused extensive damage to property all because someone has made something work without investigating what happens during a fault.

@Spectric - I couldn't agree more, as you need to open and swap the mcb's this is very much leave it to an electrician, as they should design, test and sign it off properly.

I was trying to give advise that if you ask an electrician to carry out the work, my preference would be for a type C curve to avoid any nuisance tripping.

 

[Inspector]

Can't say because your wiring etc is very much different than ours. You can reduce the startup draw on the dust collector by closing all the blast gates. The impeller isn't moving air so it draws less current.

Pete

 

[Sideways]

I would expect your dust extractor to work off a 13A 3 pin plug. 1.5kW motors usually do.
The 2.2kW machines are too big for 13A and need their 16A circuits. The motor rating plates should show a full load current and the supply should be designed for that.
3kW motor may well have a Full Load Current as much as 24A and in that case you will need a 32A outlet or a hardwired connection with an isolator switch and a suitably sized breaker.

If the motor doesn't show the full load current and you have to calculate it from the rated power, you need to allow for motor efficiency which will be 80 something percent and for Cos phi because it's an inductive load. It's NOT 3kW / 240V = 12.5A

Simplifying: your electrician will design according to the motor Full Load Current, select a B or C type breaker according to the inrush, and finally size the wiring according to the breaker and all the installation details.

In my own experience, planer thicknessers (the 3kW in your case) have some of the highest inrush currents among woodworking machines because they have a lot of mass to accelerate in the cutter block. Old school bandsaws with heavy cast iron wheels have a high inrush multiple too but not the absolute biggest motors. Table saws, lightweight bandsaws not so much inrush and smaller extractors with lightweight impellers least of all.

 

[fergusmacdonald]

Thank you for all the information. I had thought it was to do with startup inrush but wasn't sure if current under load would be higher also.

As I understand it, there's no way of knowing just from the motor power rating but one can make an estimation based on a formula that takes a few different characteristics into account. However, the motor rating plate should show this information, though sadly it doesn't seem to on some of them.

Plate info (would've been handy to include this in the first post!)

Axminster T-2000CK-200H
Power 1.5kW (230V, 1ph)

Axminster PS315
Power 2.2kw output 230V 1ph, 2.8kW (max input)

Hammer HS950
V: 230, PH: 1, KW: 2.2, HZ: 50, RPM: 2800
A: 12.2 - because of this, I put a 13A plug on it and have used it a couple of times with that.

Hammer N4400
V: 230.0, PH: 1, HZ: 50, KW: 2.5
A:15.0

Hammer A3 41
V: 230.0, PH: 1, HZ: 50, KW: 3.0
A: 19.8 - from this I would assume 20A circuit but apparently it needs 16A - according to an electrician that came out yesterday and the Felder sales rep. I don't have a 20A circuit so have tested starting it on a 16A with C curve MCB and started fine (I assume - first time I've started it).

I think what I find confusing is that if the 'A' is the maximum draw on the Hammer machines then seems strange that the A3 can run on a 16A yet I'm pretty sure when I bought the dust collector the product page specified that it needed a 16A supply. Also the table saw even 'max input' is still under 13A.

At the moment they're all connected to individual 16A supplies with C curve breakers and I'm happy to leave them that way, I just started getting confused when I realised the most powerful machine only needs a 16A so wondered whether some of the smaller ones could be moved to 13A for more flexibility with power.

PS as far as I can see none of the manuals mention anything about electrical connection other than get an electrician to do it.

 

[fergusmacdonald]

To make things more complicated, just spoke with Felder support and was told:

HS950 - 16A MCB
N4400 - 16A or 20A MCB
A3 41 - 20A MCB - will run on 16A but 20A will be more reliable.

Sales rep sent over this screenshot for the A3 41. I noticed the supplied power cable is 4mm2.

 

[Sideways]

Your salesman and your electrician are both cutting corners, but there will be logic behind that.
A machine isn't often operated at full load for a sustained period. If you were planing planks in an industrial setting, you'd have someone constantly feeding planks into the planer for 4 hours straight and taking maximum cuts. That won't be you.
So you won't be maintaining the motors at full load current for long.
16A breaker is there to protect the fixed wiring. It will trip before that overheats so no hazard.
The planer isn't at risk if it can't get the power it needs. It'll just stop when the breaker trips, so they are both gambling on experience that you won't work the machine hard enough to have problems.

Of course thicker wire is harder to bend as well as more expensive so your sparky would rather install a 16 than a 32A if they can.

The Felder tech info is minimally useful. It confirms they think you need C type breakers and 2.5mm sq wiring is safe for 20A depending on the installation.
The 4mm power cable supplied is good for 30A. Probably cheaper to stock just a couple of sizes of cable and use them on everything rather than tailoring the flex to every machine.

 

[fergusmacdonald]

I think you could well be right. To be fair to the electrician he said could be either 16A or 20A but I was keen for 16A so I could use the same plug for another machine if I move things around. However, it's not that hard to move a socket so I'll go with 20A for the A3 41 and 16A for all the others - including the sander which I currently have at 13A.