Please help if you can

[devonwoody]

I was working at the tablesaw this morning.

Tablesaw was switched off at the wall switch.

Dust extractor pictured above was switched off at wall also.

wall switch was switched on (the dust extractor switch is permanently switched on)

There was a loud bang and a flash of electricity that came up the dust tube and exited at the tablesaw blade aperture, the tablesaw was not switched on at any point during this time.

The wiring of the dust extractor although touches the TS is not damaged at any point.

No fuses or RCD blew..

The dust extractor switched on later without any explosion.

Then after around another five switches it did it again. Now permanently switched off.

What is my problem do you think?

 

[RogerP]

Dust itself can explode sometimes caused by a static electric spark. It specifically mentions sawdust in this article http://en.wikipedia.org/wiki/Dust_explosion

 

[devonwoody]

Help!!!!!!!!!!!

It is a bit thundery as well today.

Anyway of proving the electrics are actually OK?

(The Record container for dust does specifically have a notice stating not to do a flash test)

 

[Racers]

Hi,

I think it might be a problem with either your dust extractor motor a faulty cap or wiring causing the arking.

Pete

 

[devonwoody]

Its odd that no fuses or RCD have blown?

 

[Racers]

Hi,

Yes and no, if it was a short to earth then the RCD would have gone and if the short was bad enough then the fuse would have gone.
I suspect cap or frayed wires.

Pete

 

[thick_mike]

I should start by saying that i'm not an electrician or experienced in electrical installation in any way. I am a chemistry and physics teacher.

Sounds like it could be a dust explosion as it sounds as though the spark and explosion was all within the ducting. Static can build up in dry insulated powders (e.g. Grain silos). Dusty atmospheres can be ignited by the spark produced (there's a classic school demo using lycopodium powder). If it was a dust explosion it would explain why the RCDs hadn't tripped. Is your dust extractor container and ducting earthed in any way? This would help to stop static discharge. Do you have a lot of very dry fine dust in your container?

 

[devonwoody]

Just taken off the casing of extractor and there is a black exhaust on casing at side of capacitor, so order a new one?

Why does the machine run tho?

Edit, just seen reply from thick M (!) yes there is a lot of very fine dust around.

 

[devonwoody]

No earth to container; Motor holder is plastic and plastic to metal container.

 

[Racers]

Hi,

The cap might have blown away the area where the orignal short was, but it won't last long, so don't use it untill you have replaced it.

Pete

 

[thick_mike]

Does the cap look damaged?

 

[Racers]

He did say "Just taken off the casing of extractor and there is a black exhaust on casing at side of capacitor"

Pete

 

[Blister]

Does you extractor hose have a wire spiral running through it ?
I am sure this is for earth use to overcome static

 

[thick_mike]

He did say "Just taken off the casing of extractor and there is a black exhaust on casing at side of capacitor"

Pete

Couldn't work out if he meant next to the cap, or on the side of the cap. If it's next to the cap it could be a coincidence. It's just odd that the RCDs didn't trip. Anyway, plenty of people better qualified than me to help I'm sure.

 

[DIY Stew]

I should start by saying that i'm not an electrician or experienced in electrical installation in any way. I am a chemistry and physics teacher.

Sounds like it could be a dust explosion as it sounds as though the spark and explosion was all within the ducting. Static can build up in dry insulated powders (e.g. Grain silos). Dusty atmospheres can be ignited by the spark produced (there's a classic school demo using lycopodium powder). If it was a dust explosion it would explain why the RCDs hadn't tripped. Is your dust extractor container and ducting earthed in any way? This would help to stop static discharge. Do you have a lot of very dry fine dust in your container?

I agree this is possible reason for the explosion, I would clean all ducting thoroughly and get extractor checked by an electrician, get him to check earths as well. Good thing you were there when it happened and no further damage was done.

Stew

 

[9fingers]

I strongly suspect that a suppression capacitor has failed. They do that. It will have no bearing on the running of the machine and is fairly pointless replacing it unless you are getting radio interference when you run the extractor (which is so loud that you won't be able to hear the radio.
Whilst being dramatic and possibly alarming - it is nothing really to worry about.

Can we have a picture of the blackened component just to check please John

Bob

 

[devonwoody]

Sorry I have been absent a few hours, routine hospital appointment.

This appears to be the scorch mark at site of capacitor.

The capacitor appears undamaged.

The capacitor put back in its fixed position.

The dust in the container does not look if there is any burn around.

The dust tube does have a metal spiral but unlikely to have and connection to an earthed surface, its covered in plastic.

So will order a cap next week, but use my alternative blower (lung pressure) for any build up in saw box.

Quite frightening if it is a static blow out because I have a lot of dust around under that table.

 

[9fingers]

Yes that is a suppression capacitor and does not affect the running of the motor.
You don't need to replace it.
It is only there so the machine meets the emc directive at the time of sale.
Bob

 

[devonwoody]

I have had another peek at the motor this morning and cannot see any other caps. so this afternoon I will empty the container and tube of dust and do some test runs out in the garden.

If no further discharges perhaps it is static ( and that humidty yesterday) that was causing the explosions.

The system isolates the electrics from the metal container and the motor is in an insulated area at the top as well.

 

[thick_mike]

I have had another peek at the motor this morning and cannot see any other caps. so this afternoon I will empty the container and tube of dust and do some test runs out in the garden.

If no further discharges perhaps it is static ( and that humidty yesterday) that was causing the explosions.

The system isolates the electrics from the metal container and the motor is in an insulated area at the top as well.

Usually there is less static build up on humid days. The charge is dissipated through the moisture in the air.

I would certainly follow Bob's advice rather than mine! From your photo it looks like the suppressor has blown.