Siemens RCCB trips even while inductive motor is off

[NicElectrician]

PS: Second thoughts on my initial thoughts OP said DOL remains closed when RCCD trips...

As shown in the electric diagram, first comes and MCB of 25A, then the RCCB also of 25A. The only thing that trips is the RCCB. The equipment detects the trip and stops the process. As I previously said It also tripped when the motor was not ON.

My current thought following marconi ideas is to constantly measure earth line from the motor to check if I actually have a leak, if not leak I'll try just to change the RCCB for a new one.

 

[marconi]

Thank you Nicelectrician. Do work safely at all times.

Your measurement readings are very useful to us in helping you. Please be careful to describe the measurement you are taking and the circumstances of it (ie what is or is not on/off, running/stopped). Those voltage and IR measurements I mentioned are typical standard first checks to do so if you can safely do them that would be great.

What is definitely wrong is that the RCCB does not trip when the test button is pressed.

What is the temperature in the electrical cabinet?

There is no harm in doing low voltage insulation resistance(IR) checks using a multimeter set to Ohms of motor winding or heating element to earth and between windings of the motor, but the proper way would be using a proper 250/500V IR tester such as a Megger if you can get or borrow one. Please report any measurements you take. Remember safe isolation before you do any testing and have someone standing by you. Wear electricians rubber gloves near exposed live equipment and remove watches, bracelets, rings, etcetera.

 

[marconi]

I have read again what you said in your #8. You wrote:

This is the electrical diagram the currents displayed are not correct. The OLR1 (The RCCB) is as specified in the picture before and that is what goes open.

I need to check what you mean to say. In #8 you say that the motor's protection Overload Relay OLR1 trips but then you mention and have shown a picture of a different electrical device - a Residual Current Circuit Breaker(RCCB): They are not one and the same device. The RCCB will be before the Miniature Curcuit Breaker MCB1.

If OLR1 trips then the motor has drawn a sustained over current in one or more lines (L1, L2, L3). If the RCCB trips then there is overall an unbalanced/residual current flowing (to earth) across L1, L2, L3 and N through the RCCB. Could you confirm OLR1 trips as well? If it does then there are a number of reasons why this could be happening.

 

[marconi]

Could try to find out and provide a circuit diagram for how the autoclave's computer/controller monitors the incoming power supply to detect a power failure?

 

[Bobster]

Could try to find out and provide a circuit diagram for how the autoclave's computer/controller monitors the incoming power supply to detect a power failure?

Most common way of monitoring a tripped device in these situations is to include an auxiliary volt free contact onto the motor protection circuit breaker, or in this case RCCB.

I'm still trying to understand, which device is actually tripping.

An if the contactor is closed when it does. One post suggests when the motor is running, the other suggests that the contactor is closed even when there isn't power?

He also suggests that OLR1 is an RCCB, if this is the case, it is not offering correct protection to the motor.

I imagine this problem would be rather quickly fixed with a few tests using an insulation tester. OP says there is no funding for this, ask your boss/manager, how much is downtime costing him?

A decent top end insulation tested will be around £400 but can be gotten for <£100. Take a look here, also I believe a forum member discount can be gotten:

Insulation Testers from Megger, Metrel, Kewtech and Martindale

Suppliers of insulation testers from leading manufacturers including Megger, Kewtech, Metrel and Martindale. Our analogue, digital insulation testers and Megohmmeters are great for electricians.

www.test-meter.co.uk

 

[Spoon]

There is a thermal overload shown in the schematic. How come this is not fitted?

 

[marconi]

Nicelectrician: You wrote in your first post:

We use a normal 4x1.5mm cablet (3power 1ground).

by which I understand you provide L1, L2 and L3 and an earth/cpc to the autoclave.

But the image you show of the RCCB shows L1, L2, L3 and a neutral - to the far right of the four terminals top and bottom - there is a black conductor going in and not out. This indicates to me that the autoclave requires a four wire 3 phase supply - L1, L2, L3 and N plus an earth/cpc.

The fact that the RCCB trip test button does not work also indicates the N is absent.

I think then that you should check the installation instructions to confirm whether a Neutral is required - because I reckon it most certainly is.

At the stage of the autoclave process, the sterilisation has been completed and the chamber and its contents are now being rapidly cooled by a number of cycles of vacuum pump on, vacuum pump off(hold), vacuum pump on, VP off(hold)... see:

Steam Sterilization Cycles, Part 4: Rapid Cool Cycles

Every research facility is interested in improving their overall autoclave efficiencies. Here, we explore the steam sterilization cycles: Rapid Cool Cycles.

consteril.com

If the autoclave uses a water cooled cooled jacket system to reduce the the chamber temperature, there is either a small water pump being turned on/off to circulate cold water or an electrically operated solenoid valve is opening/closed to do it. The pump or valve may be the only electrical part of the autoclave which require a Neutral. The absence of the supply neutral only becomes a problem then the first time they are energised by the autoclave's computer/controller.

(For my EF colleagues, I suspect there are other light current loads using a neutral, the net effect being a virtual neutral is produced which is good enough for them until the higher current required by the pump/solenoid I mentioned in the previous paragraph disturbs its potential wrt the lines and earth and then transient leakage currents trip the RCCB or the residual current over the 3Ls and N through the RCCB sense coil - the virtual N being on the load side of the RCCB -or something along these lines.)

 

[NicElectrician]

Hello All

Thank you for your quick response. First I need to apologize, I did not check in person the electric cabinet until now. I will have to fire my "electrician" or re-evaluate him. He told me incorrect information which I provided to you EF. I have attched the whole manual, from page 178-196 are the electric diagrams.

Also the RCCB does indeed feed not just the motor but other components, L1 and L3 goes to other components. I will check them personally later. I tested the motor the insulation is ok and the loads are balanced when I tested the motor outside the machine.



So from now on, I will provide tested information by me.

Again huge thanks to Marconi and everyone who are at this moment teaching me with just comments on the problem.

Best regards to you all

 

[NicElectrician]

Ahh one more thing this is an Indian low-cost machine, I already told management that this machine is not new but used or it got wet during shipment, the motor is not by close new, not even second hand, super used. They told me to just keep repairing it to make it operative.

Thanks again

 

[marconi]

Page 179/196 details how the 'Power Fail' signal is produced. Monitor its state at the relay and also at the input to the PLC.

The Autoclave does require a Neutral so a 5 wire cable to it.

Have you really connected N to ground at the output of the RCCB? That would not be right to do.

There is a power supply filter which may have failed/is failing - has the problem only just started after a period of trouble-free operation? (see the page with the wiring diagram which shows the RCCB).

Do the checks suggested and of all other power supplies eg: 24V ac and 24 dc. Pay particular attention to check and test components I suggested and others which only come into use after the Sterilise phase has ended and the cool down starts eg: vacuum exhaust valve.

I am off to bed now.