Compressor Tripping RCD

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TLD

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#290683 27-Nov-2021 20:53

A while back I asked here about my compressor that was tripping breakers in the consumer unit. At that time it was powered off the ring main, so it was assumed that it needed it's own 15A supply. The new circuit was installed a few weeks ago so the compressor now has its own supply back to an RCD, but it is still tripping it. (I'm saying it is an RCD because it is in the RCD box. Google tells me the AD63 is an Earth Leakage Circuit Breaker — is that the same thing as an RCD?)

It's difficult to say how often. I haven't done any spraying since the circuit was installed, but at a guess, I'd say every 20 to 30 minutes when using a 150mm air sander that is spec'd at 120LPM. You can see it was tripped when I took the picture. Incidentally, it cost more to have the new circuit installed than it did to buy the compressor. We had three double wall sockets with a single USB charging socket fitted at the same time, and the total came to a fraction under $1000. The USB sockets cost $132.20 each (without the labour)!

The compressor is the Remington RA3000-50 from Mitre 10

I've noticed a flash from the compressor, but I am not sure if it came from the switch box, or somewhere from the motor. I might have had the covers off at the time, so it might have been the motor — I just can't remember. Would this motor have brushes, or what is likely to making this happen? The product blurb says it has a 3HP induction motor.

Trevor Dennis
Rapaura (near Blenheim)

compound

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#2820357 27-Nov-2021 22:10

At 20-30 minutes to trip the first thing I would be suspect of is high current. Ideal way to check this is get a voltage and current reading at the compressor when it is running under load. It could be a RCD trip but normally that would be instant at turn on rather than after a long period of time because it is looking for immediate minute leakage to earth.

it is not uncommon to see a short flash from switch contacts opening or closing so you could see that from the pressure switch but not from the motor directly as it is induction so no brushes (carbon brushes switching across the commutator segments creates flash).

TLD

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#2820382 27-Nov-2021 23:54

In the example I gave using a large sander, the compressor would kick in at least once every minute, so I think it is when it starts that it trips out, rather than while running. I can measure the voltage, but I don't have the means to measure that sort of AC current. I do have a couple of shunts come to think of it, but I think I'd rather get myself an AC clamp meter than get into the math with the shunt. What would I be proving with that information? I have found a chart that says 3HP on 240V = 17amps, so is that AD63K sufficient, or is the max allowed under code?

Is that AD63K suitable for a 3HP motor? Is there such a thing as a slow blowing trip that handles the start up current?

[EDIT] I could just get the electrician who installed the circuit back and ask him I suppose.

Trevor Dennis
Rapaura (near Blenheim)

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#2820394 28-Nov-2021 06:50

The motor might claim 3hp but what does the info plate on the compressor say for power requirement? That seems to be missing from any sales blurb for it.

gregmcc

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#2820396 28-Nov-2021 07:05

Big problem here is the trip curve of the circuit breaker. I doubt it's and earth leakage fault.

With motors the inrush current when they start is 6-10 times the full load current for a few second when it starts up, this over and over causes the bi-metal strip in the circuit breaker to stay hot and eventually it will get hot enough to trip the circuit breaker.

So you have a "C" curve circuit breaker, that is the standard type, for motors a "D" curve would be ideal as these are suitable for motors.

Next problem is that RCD circuit breakers only come in "C" curve, and been a domestic installation all sockets must be RCD protected.

So the solution? - Get your electrician to install a new circuit just for the compressor with a "D" curve MCB (this may also require that the cable size be up rated depending on length and the different trip curve for a "D" breaker), and have it hard wired to the compressor - now there is no socket so no RCD protection required.

Alternatively if you want to keep it on a socket, have the electrician put in a RCCB (RCD without circuit breaker protection) and then the "D" curve circuit breaker.

andrewNZ

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#2820398 28-Nov-2021 07:39

What Greg said.

Alternatively, consider a different compressor, or maybe altering yours.
Big compressors unload (stop making pressure) instead of turning off, partly to avoid this exact situation. I seem to remember seeing a smaller compressor using some kind of popoff valve to avoid constant starting.

Edit. It looks like the valve required is a Piloted Unloader Valve.

Sred

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#2820407 28-Nov-2021 07:52

Get your compressor start capacitor or pressure drop valve checked, they usually have one fitted. as to get the compressor running takes a short high current draw so some have a capacitor to aid the start up and some have a valve. My 3hp compressor at home runs ok off a 10a circuit no problem

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andrewNZ

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#2820408 28-Nov-2021 07:56

Sred:
Get your compressor start capacitor or pressure drop valve checked, they usually have one fitted. as to get the compressor running takes a short high current draw so some have a capacitor to aid the start up and some have a valve. My 3hp compressor at home runs ok off a 10a circuit no problem

In this case, the Issue is very likely caused by excessive starting as Greg has already stated. A start every minute is quite a lot.

Sred

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#2820414 28-Nov-2021 08:18

Starting every minute, says the tank isnt big enough for the job and having to start 2 often and maybe start capacitor not keeping up or pressure drop valve sticking

Sred

TLD

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#2820418 28-Nov-2021 09:08

Sred:

Starting every minute, says the tank isnt big enough for the job and having to start 2 often and maybe start capacitor not keeping up or pressure drop valve sticking

I was only guessing with that and have not actually tested it. It's a 50 litre tank, and the compressor is rated 360L/M. The sander I used as an example requires 120L/M. When the compressor came on while using the sander it would run for maybe 15 seconds (still completely guessing). The most work the compressor has done was spray painting several trellis panels which was taking hours. I made a stupid mistake doing that job — I left the compressor inside its sound reducing box and it over heated to the extent that the plastic air filters melted and it stopped running. That's why I had the outer airflow covers off the motor, and that's when I noticed the flash I mentioned because I was right in front of it. I've not put the sound proofing back since, but my use is not so great that the noise is a real problem. Plus I have a jobsite saw and router, and thankfully, tolerant neighbours. I've drawn the line at having a thicknesser in my home shop because they are a whole other level of loud. Incidentally, we recently replaced the thicknesser at the Blenheim Menz Shed with this Macma with a helical head, and it is probably no louder than a table saw.

There are some interesting thoughts in this thread, and especially Greg's post. I'll read through it all again, and feel better equipped to talk to the electrician. I'll also try contacting Remington — if anyone would know the best way to power their compressors it would surely be them.

Thanks for the suggestions and ideas guys. This forum has never let me down.

Trevor Dennis
Rapaura (near Blenheim)

TLD

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#2825525 7-Dec-2021 10:02

I finally got round to emailing support at Remington who replied:

Thanks for your enquiry.

The AD63K appears to be a 6a breaker – so that would trip from time to time.

If you have wiring that can support a 15amp breaker, then this should solve your problem.

I hope this helps!

I need the electrician back anyway because a power point needs changing in the kitchen, so I'll see if he can change out the AD63K.

Trevor Dennis
Rapaura (near Blenheim)

andrewNZ

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#2825556 7-Dec-2021 11:00

That breaker is clearly not 6 Amp. It is a 20 Amp C curve as per the "C20" on the front.

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#2825559 7-Dec-2021 11:05

The solution to your issue is what gregmcc stated in his earlier post. Get the appropriate D curve breaker & circuit installed by your sparky.

andrewNZ is also correct, your current breaker is clearly a 20A C curve unit.

TLD

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#2825834 7-Dec-2021 14:18

Thanks guys. It's good to know that Remington support know what they are talking about. I'll get back to the electrician and ask about a D curve breaker.

Trevor Dennis
Rapaura (near Blenheim)

Froglotion

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#2826392 8-Dec-2021 00:47

Compressor won't like starting every minute either. That's why the big boy units have continuous run as an option. Someone mentioned a valve above, it could be worth looking into that before spending more on the sparky. I have one of the largest compressors you can run on 240v and i've never had an issue with circuits blowing. It has continuous run option which helps on the big jobs. You'll probably find the motor is half cooking itself to start up so frequently.

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#2826393 8-Dec-2021 00:55

I doubt it's a magnetic trip issue. That would trip on every start, or at least e.g. 1 in 10 at random. It has no memory so would be unlikely to only trip after the compressor had been running for a while.

The C & D curves are identical in the thermal (bimetallic) element.

See if you can adjust the pressure switch to give a greater differential between cut-in and cut-out. Alternatively, get an extra tank and pipe it in parallel.