Dust Extractor Tripping the House RCD?

[Myfordman]

How can there be any possible imbalance during starting unless there is a leakage path to earth?

In two ways.
Firstly due to the capacitor. The small time the cap takes to charge can be enough time of power in with no power out to trip the rcd.
Secondly if the motor uses a centrifugal switch with a seperate line & nuetral contracts then both contacts must make at the same time, even a delay of mili secods can cause enough of an imbalance to trip.

There are other reasons too but usually they are on used motirs not new.

It doesn't need to be a leakage to earth just an imbalance between line & neutral.

You really don't understand this sort of thing do you?

 

[Monkey Mark]

How can there be any possible imbalance during starting unless there is a leakage path to earth?

In two ways.
Firstly due to the capacitor. The small time the cap takes to charge can be enough time of power in with no power out to trip the rcd.
Secondly if the motor uses a centrifugal switch with a seperate line & nuetral contracts then both contacts must make at the same time, even a delay of mili secods can cause enough of an imbalance to trip.

There are other reasons too but usually they are on used motirs not new.

It doesn't need to be a leakage to earth just an imbalance between line & neutral.

You really don't understand this sort of thing do you?

Actually, yes i do. Otherwise I'd have kept my mouth shut. But in the future I'll not bother and stick to lurking.

 

[Eric The Viking]

Sigh.

To get back to the original issue (he said, trying to be tactful), this has NOTHING to do with the type of MCB fitted to either board. I'll come back to that, but don't get distracted by it at the moment.

* You tried the extractor in the house. The fault moved with it.
* You tried other items in the shed. No fault occured.

That is pretty conclusive. The extractor has some sort of problem, causing the RCD to trip. This is beyond your ability or obligation to sort out (assuming the extractor is new and under warranty).

It shouldn't do that, and the fact the fault occurs some time after startup indicates it has nothing to do with inrush current, nor the centrifugally switched startup circuit (which disengages much earlier than 30s, anyway, or should). There are any number of possible faults causing these symptoms - swarf trapped in the motor from manufacture; a damaged coil (varnish scratch) that occasionally shorts to ground; a loose earth connection (with a constant fault), so it only occasionally shorts with enough leakage current to trip the RCD.

But all this is moot - all these faults would lie INSIDE the machine, and thus they're legally beyond your control (if you want to claim on the warranty). One thing: I expect it's moulded on, BUT if you fitted the plug yourself, do check that for loose connections or stray wire whiskers. And then...

... Ask Axminster politely but firmly to replace it with a known good one (that they've tested). They're not obligated to give you a brand new one, incidentally, but that's probably a good thing in this case. You want a known-good one.

There, I expect, all will end well. If it doesn't, then something seriously weird will be going on, that doesn't have anything to do with the extractor. And I have NO IDEA what that might be, as (superficially( it denies the laws of Physics.

If it turns out to be cold fusion, patent it quickly.

. . .

Back at your miniature circuit breakers (MCBs): The house stuff and everything not motor-ish should be type B (trips quickly). The motor circuit, right back to the main board, should be type C (allows motor inrush current spikes to pass). That means type C on the sockets in the shed, and, at the main board in the house, ONLY ON THE ONE MCB that feeds the shed (NOT every breaker in the box!).

Ideally, you ought to split the shed wiring, so that the extractor and any other big motors are on a type C breaker, whereas normal "domestic" 13A outlets are on type B, for maximum safety. But even if you don't, you should be well protected by the RCDs across the circuit - most life-threatening incidents involve live-to-ground issues and will cause the RCD to trip anyway.

Hope that helps.

E.

 

[Copes]

Thanks everyone for the sound advice, I'm going to give the "unplug everything" and work back from there ago, as that's something I can do without too much trouble but yes beyond that unless something conclusive comes from it I'm going back to axi.

I'll talk to the sparky about the type C mcbs for those two.

If I could actually manage to flip my AW10 the right way up I could use that to test everything as well.

While I've got the sparky out is it worth actually getting a 16amp mcb/plug wired for that? Most of the cost is getting the chap out in the first place.

Will keep you informed

Thanks again

 

[Copes]

Right well i unplugged everything and turned off all the MCB's except the sheds...

I did 7 test runs, ran it for 60 seconds, powered it off and waited until the machine was completely stopped then started again.

The first 6 test were fine, on the 7th test it tripped the RCD again after only maybe 4-5 seconds of it being switched on... is that a suitable test that it isnt just tipping the house leakage over the edge?

Should i phone Axi now and suggest it probably is the machine at fault?

Cheers
Mark

 

[Terry - Somerset]

I think you have been far too tolerant. Eric the Viking seems to have a very sensible view of the world - the fault moves with the extractor. The power requirement - 1.5kw - is definitely 13A domestic hobby territory, not a a high marginal load. You may well have other machines in your workshop drawing similar currents!!

Axminster are usually good on problems - they should really just replace.

Terry

 

[Copes]

Well phone again this morning and they've agreed to replace it, but not without a bit of ball ache for me.

They want it all disasembled and reboxing. Dispite it being delivered on a saturday, they can't possibly come and pick it back up on a weekend so i'm going to have to take a whole day off because they also can't tell me if it would be morning or evening.

I'll admit i'm new to buying machinery, but it seems like i'm being a bit put out having to sort out a problem from their side.

Its a big difference between the delivery from the high wycomb store which were absolutely marvelous. Couldn't have asked for anything better.

 

[Eric The Viking]

They replaced one of their mortisers for me several years back. Similarly annoying, having to box it up, etc., so I do understand. All the parts on that are cast steel (or iron) and heavy, and the polystyrene packing had got a bit broken up by the time it first arrived. This I explained to them, and they weren't fussed about it - something along the lines of "just do the best you can".

But I also remember they were very keen to find out exactly what the fault was (they do test their returns carefully). They have a buying team permanently based in China, and I think one of their remits is quality issues and similar feedback. IIRC mine had a motor issue, and I'm guessing it's what's wrong with your extractor too - Axy were dead keen to get a solid root cause analysis, because these things have the potential to be expensive, as issues like varnish failures tend to go with production batches. For an importer that can be really expensive, never mind loss of customer satisfaction.

That's one reason they want it back as originally packed (or as near as possible) - it won't or shouldn't get further damaged coming back to them, and the return trip shouldn't introduce new faults to complicate the analysis (and if it actually got damaged during the original delivery process, that too can be identified - the broken polystyrene is itself informative*).

You mentioned their High Wycombe store - can you get to that easily? They might accept it there instead - worth a phone call, perhaps?

E.

*Years ago I helped nail a slapdash shipping agent in California who was costing my company (in the UK) tens of thousands of dollars monthly. It turned out they had very lazy forklift operators at their warehouse, who couldn't be bothered to pick up palletized product correctly. It was for airfreight and vulnerable to vibration, so was packed in large boxes with shock absorbing materials round the equipment in the middle. They thought it was cool to spear this with a fork, with obvious consequences and really angry customers (the things cost a lot more than a dust extractor!). Incredible, literally, until by chance I was in the right place at the right moment (with a camera) and brought back photographs, and our purchasing and legal teams had the evidence they needed. I think it was settled out of court

So even damaged packaging can be helpful!

 

[HappyHacker]

If you are getting your electrician out again ask about taking the garage supply off the RCD and putting an RCD or two at the garage end. Then if you do have an RCD trip it will be local to the garage and not take the house out. Probably no reason to put it on a 16A circuit as the MCB is not tripping but if you are having some work done a 16A socket is often useful.

Good luck with the replacement, from the test you have done it definitely sounds like the first one was a faulty unit.