Problems with my table saw tripping out

[Iwf]

Forgive me if I've posted in the wrong place or even the wrong forum.

I'm a newbie to the forum that has just set up a small workshop including a table saw. For one reason or another I bought a Makita 315 mm site saw and then build a saw table around it. All good except occasionally when I start the saw up with the blade raised and with the sled in place, it trips a fuse. Starting it with the blade down isn't a problem, but I don't like taking my eye off the table when raising the blade up. Now I'm fine with it tripping out if it finds some resistance, seems like a good safety feature to me but I need to find a way of resetting it without having to put a new fuse in every time.

Would putting an RCD socket in line help, or am I on the wrong track altogether.

Cheers and thanks in advance

 

[Myfordman]

I suspect an internal wiring problem. Maybe chafed wires. This could give problems depending on angular position. Simply changing the protection method is definitely the wrong approach. Find out and fix the problem you know it makes sense!

 

[Fitzroy]

I'm no expert but you are talking about two different types of trip. If you are blowing the fuse then you are getting too great a current for too long a time, the highest current the machine will normally pull will be on start-up but it is normally very short lived. It will be greater than the 13A fuse you have but the fuse does not have time to blow.

An RCD works on a completely different principal, it is a 'residual current device' that basically detects the flow of electricity to the wrong place, ie to you if you touch the live wire, or to earth if there is a short circuit in the machine, etc etc.

You may have a fault that an RCD would detect and would also blow the fuse, so adding an RCD would prevent the fuse blowing. However it means you have a wiring fault that you should really correct, rather than rely on a trip device to prevent the fault reaching you.

 

[pcb1962]

You don't say whether it's the fuse in the mains plug that's blowing or a secondary fuse in the saw itself. If the latter it may be possible to replace it with a 'slow blow' fuse which will be more tolerant of the startup current.

 

[CHJ]

As the fault is blade position dependant I suspect that start up current is near the fuse limit and for some reason there is more mechanical load to start-up when the blade is raised.

With saw disconnected from power, spin the blade by hand at a lower level and judge the resistance, now do this in stages as you raise it and see if you can detect when/if the resistance increases.

If it does then find what is binding, shafts, support mechanism twisting etc.

Does the blade securing nut or other shaft parts come into contact with the table when raised to its maximum?
(I don't know the construction details)

Is your sledge close to Zero Clearance and binding on the blade at times?

You need to find what's causing the occasional fuse blow, regular prolonging high current flow on startup is not good for motor and its associated capacitor or the switch gear.

 

[Homerjh]

if a fuse is blowing then check that the fuse is correct, is there a 10amp in there when it should be a 13?

and with it unplugged see if you can feel the resistance, take a good look around if there is anything that may get in the way, so any fittings/etc.

you also say when the sled is in place, does it do it with the blade raised and no sled? if so then the sled is the issue.

 

[Iwf]

Thanks everyone for the speedy replies.

There's no issue when the sled is not in place, so it's the problem. I'll run it through a few time with the blade raised and see if I can clear the obstruction on the sled. I'll also have good look at the saw teeth. Maybe one's out of alignment. It's an Axminster 70 tooth cross cut blade. All I can afford for the moment.

I was just a bit surprised that a single tooth catching on the sled could trip the fuse. Thanks for the confirmation of the RDA business too. I'll also look to extending the rise handle. That'll allow me to raise and lower it without taking my eye off things. It's a great motor all the same.

My workshop is actually in my loft. Hence I couldn't get a proper saw up there. It's an induction motor which is what drew me to it.

Cheers

 

[OLD]

motors present a very low resistance at the point of start up and as they get turning produce back emf which reduces there current requirement if the motor struggles to turn the high current blows its protection, fuse or miniature circuit breaker which has to be correctly rated probably 13 amp in this case so start it up with no load and you should be all good .If you still have problems get the dust blown out of the motor and the starter switch, if still no good have the machine tested with a megger insulation tester (pat tester).
I am assuming you have a proper ring main connection in the loft.

 

[Iwf]

I think I got it sorted now, I just hadn't realised how sensitive it was at startup.the motor and starter actually sit out side the blade assembly, and I've got dust extraction working reasonly well. More yo do with that though, much more to do.

It's running off a spur at the moment, but it's the only thing at is. a proper extension to the ring main is now on my to do list. Luckily it's not too difficult. I like the idea of a small circuit breaker in the loft itself. Will investigate.

Again thanks for all the contributions

 

[Iwf]

So, after a couple of months of infrequent use and after a couple of weeks of cold weather and no use I came back to tripping problems again.

5 blown 13 amp fuses later I've concluded/noticed.

1. the zero clearance MDF table insert didn't help.
2. I've tripped two fuses with the original plastic insert and under no load.
3. the Axminster replacement saw blade is heavier than the blade supplied with the saw and there's actually a slight shimmy on the blade at start up
4. the motor, perhaps when cold is drawing near to 13amps on start up.

My solution is to bypass the 13amp plug and use an industrial plug and socket into a spur off the ring main protected by a 16 amp MCB

Any views about this ?

 

[RobinBHM]

Where are you using the saw?

If its in a workshop some distance from the consumer unit, maybe the voltage drop is causing too high a start up current.

 

[richy3333]

Hi.
I'd like to try and help if I can. But to do so can you describe the set up of the fixed wiring in the property? Is it a ring final circuit that had had a spur taken from off into the attic? Is it 2.5mm cable and a 32A MCB? Is the attic spur fused?

It sounds like the saw is fitted with a three pin plug top fused to 13A? Do not cut this off and fit a commando plug arrangement. The fuse in that plug top is protecting the saws flexible supply cable. Doing as you suggest at best will damage the cable and/or saw and at worst cause a house fire.

Is the saw blade designed to run with that saw? The plug top fuse protects against short circuit and overload faults. As the issue only appears to occur when you run the blade with the sled it does suggest an overload. Can you get the saw nspected and tested? PAT tested to rule out any faults with the unit?

Hope that helps.

R

 

[Iwf]

My setup is probably one of the oddest you could come across. My shop is actually in my attic ( I only tackle small scale stuff)

From a power perspective there's a single 30amp ring main, lighting and kitchen being off separate circuits. Currently I'm running essentially extension cords perhaps 10m from the ring main , with the extension cable made up of 2.5mm mains cable with a 13amp plug on the end. I could extend the ring main, or simply add a spur. In the shop I have table saw , router table, band saw , drill press and various mains power held held. I have a dust collection system, with an old Axminster vacuum extractor. I'd only ever use the extractor and one other power tool at the same time. The kids have all grown up so little other power usage when I'm in the shop.

Interestingly I put the Makita saw blade back in this afternoon and had no trouble. The Axminster blade weighs around 150 g more then the Makita, but then it's a 40t whereas the Axminster is 72t. The only reason I bought the Makita , apart being able to get into the loft in the first place, is that it boasts an induction motor, if that makes any difference.

When the fuse pops it can either be at the saw plug itself or the one on the end of the extension cable.

Clearly the on start up load is too much for the fuse hence my thoughts of bypassing it. But perhaps I need to be more careful in my blade selection.

Thanks for all the help.

 

[Iwf]

Even with the standard Makita blade, no load, no sled the saw tripped out first time on Sunday.

So I bought a measurement tool, the sort that measures power from a single device. Tested a few things around the house (Kettle 7 amps), before taking in the shop.

Imagine my surprise when hooked up to the saw to see 26amps on startup, quickly settling to around 6. This was repeatable, but didn't blow the fuse. I'm now suspecting poor quality fuses as being my main problem. I bought cheap ones from screwfix in tens.

Maybe I just need some decent , say MK fuses. Even so 26 amps !

 

[skipdiver]

I plugged my planer into a lead the other day, which i don't normally do because i couldn't be bothered to wheel it to it's usual spot for a couple of quick passes on a piece of timber. Blew the plug fuse in the lead as soon as i turned it on. Wheeled it out to where i normally use it and plugged it into the socket and it started up no problem, so it could be your fuses.

 

[sunnybob]

This appears to be your problem...

https://en.wikipedia.org/wiki/Inrush_current

and this points to your solution...
https://en.wikipedia.org/wiki/Inrush_current_limiter

 

[richy3333]

Even with the standard Makita blade, no load, no sled the saw tripped out first time on Sunday.

So I bought a measurement tool, the sort that measures power from a single device. Tested a few things around the house (Kettle 7 amps), before taking in the shop.

Imagine my surprise when hooked up to the saw to see 26amps on startup, quickly settling to around 6. This was repeatable, but didn't blow the fuse. I'm now suspecting poor quality fuses as being my main problem. I bought cheap ones from screwfix in tens.

Maybe I just need some decent , say MK fuses. Even so 26 amps !

It would appear from your last 2 posts that the problem is mainly running a saw blade not desinged to be used in that saw. You have witnessed the in rush currentnof the saw at start up and it is blowing a fuse. The fuses are doing what they should do. Because there is no discrimination between the plug top fuse in the saw and at the end of the extension lead one or other will blow. Replacing plugs tops, removing them for a commando socket etc is just bypassing the cause of the problem, not fixing it. It's also poor electrical design to run the extension off the ring final circuit too. Can you not get a new circuit run to the attic?

BTW a plug top fuse is a plug top fuse. So long as it has a BS number you're ok. MK long since stopped making anything of any quality!

 

[Iwf]

Extending the ring main to the shop, isn't practical just yet, but I've moved forward a little.

I've run a 2.5mm spur from the ring main into a comsumer unit in the shop. That's given me both an RCP and 30, 16 and 6 amp MCBs. Kevin Boon's great article suggest I can run 30amps through the cable, and I plan a couple of switched sockets off the 30 and 16 amp MCB. I am surely tempted to get a 13amp MCB then live with the occasional tripping.

I fully agree and comprehend the inrush current business even if I don't understand the maths. I've also gone back to the original Makita blade. That will still trip out with the zero clearance insert in place but not with the original Makita insert.

 

[n0legs]

Extending the ring main to the shop, isn't practical just yet, but I've moved forward a little.

I've run a 2.5mm spur from the ring main into a comsumer unit in the shop. That's given me both an RCP and 30, 16 and 6 amp MCBs. Kevin Boon's great article suggest I can run 30amps through the cable, and I plan a couple of switched sockets off the 30 and 16 amp MCB. I am surely tempted to get a 13amp MCB then live with the occasional tripping.

I fully agree and comprehend the inrush current business even if I don't understand the maths. I've also gone back to the original Makita blade. That will still trip out with the zero clearance insert in place but not with the original Makita insert.

2.5mm twin and earth has a rating of 24-27 amps.
You need an electrician.
Do you live alone? Suicide isn't illegal, but manslaughter is.


Edit to add,

I had to find out who Mr Boone was/is. His article is explaining a RING circuit which can run at 30 amps.
IWF you have installed a spur from a ring, this should go to maximum of 1 double socket so the maximum load is less than the cables rating.
Please get an electrician.

 

[Iwf]

True,

But that would assume I was going to run 30amp worth of kit. The amp reference is the loading the cable can take, when not embedded in plaster. The point being that it's better than a long extension lead with a 13 amp plug on the end.

At most I'm likely to run an dust extractor and the saw, or the extractor and the router. Not heaters, no lighting. Shouldn't be using more than 16 amps at any one time. The other MCBs came with the consumer unit and haven't been wired in. And I only have 3 double sockets. The benifit of the consumer unit is that I can isolate the shop when not in use and of course the benefits of a RCB.

Interestingly when starting up the saw in the same circuit as the extractor you could hear the voltage drop on the extractor until the saw got up to speed. This to my mind confirms the view that the saw needs more juice on start up. I suspect this saw is seldom sold in the 230 version. I can find few reviews or mentions on the web.

However I will get the thing pat tested. What to do if passes, who knows !