Newbie + a question

[Myfordman]

I'm going to do both. 16a socket and a soft start.

Absolutely fit a 16amp outlet with a c type breaker but I’m really not sure a soft start is the correct thing to use with an induction motor. This type of motor needs a high current kick to get it going and it’s starting winding is only intended to be powered up for a few seconds. A soft start module will extend the time before the motor gets up to it running speed thus extending the time that the start winding is powered up and risks it over heating.
Brush motors such as on most mitre saws and small table saws are quite different in operation and usually benefit from a soft starter as several members here have found. HTH

 

[Stevekane]

Absolutely fit a 16amp outlet with a c type breaker but I’m really not sure a soft start is the correct thing to use with an induction motor. This type of motor needs a high current kick to get it going and it’s starting winding is only intended to be powered up for a few seconds. A soft start module will extend the time before the motor gets up to it running speed thus extending the time that the start winding is powered up and risks it over heating.
Brush motors such as on most mitre saws and small table saws are quite different in operation and usually benefit from a soft starter as several members here have found. HTH

Thats very intresting and somthing I hadnt thought about, a quick look on the internet seems to show “soft start” for induction motors being beneficial and mentions high initial current problems, but of course these are commercial motors and would perhaps be using somthing more sophisticated that the ebay modules,,I wonder if anyone knows for sure?
Steve

 

[Myfordman]

Those who know my work will realise that I do a lot of work with motors. I’ve never noticed induction motors delivering the same sort of semi dangerous kick that big brush motors do. In theory I could experiment with the many induction motors that lurk under the bench but I’ve only got one of the ali express soft start modules and don’t want the risk pranging that given it took weeks to arrive.
It has occurred to me to suggest to big Clive of YouTube fame to see if he fancies playing with a soft starter and various motor types.
My advice fwiw would be not to use a ss module with an induction motor.

 

[Stevekane]

Seems like sound advice and just as a matter of intrest, why is it that machines like mitre saws and smaller saw benchs would seem to use Brushed motors whereas a Saw like our OP has would have an induction motor even though its still only rated at 1500w, is it perhaps to do with long term reliability, are they more powerful or is it simply cost?
Steve.

 

[Myfordman]

Seems like sound advice and just as a matter of intrest, why is it that machines like mitre saws and smaller saw benchs would seem to use Brushed motors whereas a Saw like our OP has would have an induction motor even though its still only rated at 1500w, is it perhaps to do with long term reliability, are they more powerful or is it simply cost?
Steve.

It’s a mix of power to weight ratio - important for hand tools and cost when it comes to bottom end bench tools. Induction motor powered equipment is much quieter so more suited to longer run times.
Brush motors can be tamed with suitable electronics especially in washing machines where users would not tolerate the noise. Hth

 

[sometimewoodworker]

The beauty of changing from B to C is that it would still trip with continues current exceeding rated current 13A or 16A, but will allow for short spike of current that is too short to damage the wires it protects.

while your description of a type C MCB as having a much higher inrush limit is correct, it’s between 5 & 10 times, your statement that a 13A MCB will trip with sustained current over 13A is wrong, the minimum would be a load exceeding 14A and that would probably take quite a long time to trip depending on how much over 14A it was at 14A it might not trip or take half an hour or more. The design spec it that the load must be at or slightly in excess of 1.075 of the rated load for a long trip.

it is possible that you might need a type D though a type C is probably enough.
”MCB with class D trip characteristics trips instantaneously when the current flowing through it reaches between Above 10(excluding 10) to 20 times the rated current. Suitable for inductive and motor loads with high starting currents.”

 

[Myfordman]

Type D breakers need to be installed with care to ensure the earth loop impedance is low enough to ensure they do trip when needed. An electrician will have the correct gear to make the measurements to check this.

 

[ajs]

One other thought occurs to me, make sure you go through this thoroughly with your landlord - it's more than a courtesy clearance. Building regs Part P would apply and it is the landlord's responsibility to ensure compliance. If you have a professional or council/HA landlord (not someone with a couple of properties as a retirement plan) they'll almost certainly want their own contractors to do it.

 

[sometimewoodworker]

Type D breakers need to be installed with care to ensure the earth loop impedance is low enough to ensure they do trip when needed. An electrician will have the correct gear to make the measurements to check this.

True. But then so do type C.
With all breakers you need to check that the wiring is suitable for the breaker that is going to be fitted. If you just swap in a different class of breaker in the CU there is a very good chance that it will not provide the designed protection. I was assuming that an electrician was going to be brought in.

 

[Stevekane]

Ive just looked at the Soft Start Module that the OP found and posted a link to earlier in this thread, that one is a much more sophisticated unit and cost around £65, however it says that its suitable for both resistive and inductive loads and again lists Inrush Current control as one of its features.
Worth investigating further if your landlord doesn't allow alterations to your electrics.
Steve.

 

[Norton]

Hi all,

Thank you all for the advice. A local electrician has quoted £100-150 for the socket and I've just emailed the LL for permission. Be a shame if they say no as I'll then likely have to sell the saw on. I am going to try the soft start as well though. It's not cheapy brushed table saw that goes nuts when you first start it but maybe it'll refine it a bit further or fix my problem on it's own.

Still baffled though as to why my 3hp ABAC compressor runs perfectly but this saw...

 

[Stevekane]

Hello Norton, I asked the chap who I bought my Soft Start module from and he has just come back to me saying that they are only suitable for Brushed Motors, so I dont think it would be wise to try it, however as I said above, it would be fine to fit the module you initially found as its stated to be suitable for induction motors, and you could hold that in reserve in case your landlord doesnt play ball,
Good luck.
Steve.

 

[Norton]

Hi, don't worry, the one I linked is the one I bought. I'm going to fit it tomorrow. I'll report back after!

 

[Myfordman]

Hi all,

Thank you all for the advice. A local electrician has quoted £100-150 for the socket and I've just emailed the LL for permission. Be a shame if they say no as I'll then likely have to sell the saw on. I am going to try the soft start as well though. It's not cheapy brushed table saw that goes nuts when you first start it but maybe it'll refine it a bit further or fix my problem on it's own.

Still baffled though as to why my 3hp ABAC compressor runs perfectly but this saw...

Think about the load on the motors when starting. The compressor has no real load as the compressor has atmospheric pressure on the input and output at start up and the dump valve only closes once it is up to speed. The saw motor is having to accelerate the belts and blade up to say 4000 rp from cold. It is possibly a 2 pole motor which is harder to start in any case as the rotor has to get up to nearly 3000 rpm.

 

[Norton]

Ah yes I get what you're saying but the other day, a chunk of gunk kept that valve open after the tank was pressurised meaning the compressor later kicked in shortly after with tank pressure above the piston. It stalled and the motor WAS NOT happy! Fuse didn't blow though.

 

[Norton]

It's helped me appreciate what I thought was a gentle load actually isn't. Zero to 4k rpm in less than two seconds is quite a thing.