RCBO 30MAmp B40, tripping

MyHouse

I have a controller box which turns on and off a 5hp Hydrolic pump. It is operated by an air pressure sensor microswitch on a PCB which when activated, engages a magnetic coil to close and open contact breaker type points to send power to a further electronic switch (magnetic coil) and this closes the circuit to start the Pump which is single phase.
The problem which has arisen lately is that the RCBO 30MAmp, B40 trips out regularly on startup. I have replaced the RCBO in case it was faulty but this seems to be primed to fail after one on/off action.
I think the spark created by the contact breaker points on the PCB is the cause. Is this possible? This whole operation worked fine for 11 months and nothing has changed and all wires have been checked out.
The fail can be overidden when main control switch is pressed and then the air operated microswitch pressed. This is why I feel the PCB action is the primary cause.
My question is, finally, can this be resolved in any way by another type of RCBO? I can supply a photo of controler when I familiarize myself with forum.
Sean

LeBash

Sounds like it could be the start up load. try using a C40 RCBO

davelerave

The start-up on the b40 could be an issue alright,or maybe the controller.
To help troubleshoot you could try a mcb/rcd combination.
The equipment may not need rcd protection.The S-type has a delayed trip but doesn't provide shock protection.

MyHouse

Thanks for both suggestions. I will proceed to remove the control unit from the RCBO circuit and go with the MCB breaker supply only which is already available and see if Controler works independently. This is easy enough to do. The reason I stuck with the two pole RCBO was that it was a requirement on the circuit scheme that came with the installation instructions and as stated, there were no issues for 11 months?:)

MyHouse

Will reveal results asap. First...........Golf>>>>>>

MyHouse

Well, I took the RCBO out of the circuit and wired live to a 32 amp MCB.
No problems. 5HP pump can be switched on/off at will with no tripping of the MCB, so clearly, I think we may have cracked this one at least to the
fact that the RCBO is too sensitive for the controler. I should, therefore look into the C rated one suggested to see if this is the answer. The 5hp pump is clearly pulling alot of current on startup and or the RCBO is detecting the spark created by the breaker points, either way, the RCBO is not good enough in this situation.
If anyone knows the exact protection I should use, please mention it.
really appreciate the input by all.

Thanks a mill. Sean.....

.G.

Is the 32 amp MCB you're using now a B type or C type?

If its a B type then overcurrent at start up is not the issue causing the RCBO to trip as it would also cause a B type 32 amp MCB to trip since its rating is lower than the 40a RCBO you were using.

If it is a C type MCB then clearly the problem does lie with overcurrent at motor start up and a 40 amp RCBO should solve the issue.

MyHouse

DSC_0203.JPG Pic. of Control box and Contactor/PCB
Right. Here's how things stand.
Seperate 3 core dbl insulated, high capacity, crush proof, cable from standard 63A breaker to auxillary, dedicated mini fuseboard. On this I had the RCBO as first contact and then ran power to control switch system and 2 other fuses which supply a 5.5kw heater(Garo G MCB B32) and 3/4 hp water pump (Garo MCB B20) none of which have ever caused a problem.
I took a supply from the RCBO out to the control box which in turn has a built-in 30Amp, Timedelay fuse, (US Type). The Positive and Negative are fed directly on to the Contactor( Line 1 and Line 2). A feed supplies a PCB with an air operated micro-switch which sends the on/off signal to the Contactor which then activates and sends the power to the load side of contactor and the 5hp Pump.
The problem occurs when the air operated switch is pressed on/off more than once( which is necessary alot). It generally turns on once and then off, but the trip of the RCBO occurs immediately and it is quite difficult to reset.
As regards the test I did yesterday. Removed RCBO out of picture and took feed from G MCB b32 onto control. Was able to switch on/off at will.?

2011

Just to deal with the pump in isolation:

5 hp = 3730 watts
with a power factor of about 0.85 the full load current of the motor is about 19 amps. The MCB should be matched to the full load current of the motor (or the next size above) so you should be using a 20 amp MCB. As the others have said this should be a motor rated MCB so that it does not trip due to the large start up current. This start up current is typically 4 to 6 times full load current for an instant.

From the information given I can see no reason for this motor to be protected by a RCD, as it is fixed equipment.

cornet

Agree with 2011.

RCD protection is not required and motor earth leakage current will trip it.

For guidance on RCD usage and selection see http://www.etci.ie/docs/ET214.pdf

davelerave

2011 wrote: »

Just to deal with the pump in isolation:

5 hp = 3730 watts
with a power factor of about 0.85 the full load current of the motor is about 19 amps. The MCB should be matched to the full load current of the motor (or the next size above) so you should be using a 20 amp MCB. As the others have said this should be a motor rated MCB so that it does not trip due to the large start up current. This start up current is typically 4 to 6 times full load current for an instant.

From the information given I can see no reason for this motor to be protected by a RCD, as it is fixed equipment.

Equipment shouldn't normally rcd need protection(Op said it was specified) 25amp(~125% FLC) C or D protection probably.Afaik insulation resistance resistance of this motor should be very high. and shouldn't trip an rcd

2011

1) If you conform to ET101 (4th edition) you are Ok even if the appliance says use an RCD. The only fixed appliance that requires an RCD that I can think of is an instantaneous shower. Sometimes regulations are written for other countries that don't apply here. I think you will find that this pump is not made in Ireland. Once you comply with the regs you should be ok. Having said this if you are unhappy put the RCD in, but remember it provides secondary protection only.

2) I have always matched protective devices to the full load current of the motors and so far so good!! If the motor has overload protection in addition to the MCBs/fuses then I may rate them higher as they are providing shortcircuit only. Remember a 20amp C type MCB will not trip with a sustained overload of 25 amps!!

3) Poor insulation resistance will cause an RCD to operate. Why? Because once a current >30mA flows to earth then there is a difference between the current flowing in the live than the neutral. RCDs are designed to operate under these conditions.

Curtis E Bear

On a safety note, i am not sure to operate this pump with out rcd protection! do we know what this pump is used for? it was part of the spec for a reason. i would be more inclined to find out why its tripping the rcd element.
also, as pointed out already its single phase and i dont think the ESB would be to happy with you switching on a 5hp motor DOL.

Curtis E Bear.

2011

On a safety note, i am not sure to operate this pump with out rcd protection

It is not normal to protect pumps with an RCD. The regulations are quite clear about when an RCD is required and the ETCI regulations are a higher standard that most if not all of the rest of the EU.

If you look at large projects in Ireland where engineers design the electrical installations so that they are installed to standards far higher than the ET101 regulations require it can be seen that motors (including pumps) are not protected by RCDs. This is even the case with 3 phase motors when the line voltage is increased to 400 volts. In fact you will find that very little fixed equipment is protected by RCDs.

Even in hospitals where some RCDs protecting socket circuits are designed to operate when the current differential is just 10mA (30mA is standard for domestic) the pumps and motors there are not protected by RCDs.


As I said in an earlier post

From the information given I can see no reason for this motor to be protected by a RCD

I do take your point that there may be circumstances that I am not aware of in this situation that could lead me to change my mind, but not from the information given. The pump the OP describes is hydraulic, so I would guess it pumps oil which has good insulating properties.

as pointed out already its single phase and i dont think the ESB would be to happy with you switching on a 5hp motor DOL.

A separate issue, but a good point!

davelerave

2011 wrote: »

1) If you conform to ET101 (4th edition) you are Ok even if the appliance says use an RCD. The only fixed appliance that requires an RCD that I can think of is an instantaneous shower. Sometimes regulations are written for other countries that don't apply here. I think you will find that this pump is not made in Ireland. Once you comply with the regs you should be ok. Having said this if you are unhappy put the RCD in, but remember it provides secondary protection only.

2) I have always matched protective devices to the full load current of the motors and so far so good!! If the motor has overload protection in addition to the MCBs/fuses then I may rate them higher as they are providing shortcircuit only. Remember a 20amp C type MCB will not trip with a sustained overload of 25 amps!!

3) Poor insulation resistance will cause an RCD to operate. Why? Because once a current >30mA flows to earth then there is a difference between the current flowing in the live than the neutral. RCDs are designed to operate under these conditions.

As you say a simple 'motor rated' mcb is not designed to provide 'close' overload protection for a motor.(MPCB or thermal overload relay for this).

It may be simply that the machine came with a plug fitted.It is common for industrial workshops and items of machinery to be pre-wired with 3-phase sockets and plugs requiring rcd protection.
Small motors and pumps tripping rcds will show a low insulation-resistance when tested .I've seen it many times

MyHouse

The instructions are indeed USA with reference to UK installation, so there may be truth in what you(davelerave) say. The controler unit itself is protected by a 30amp time delay fuse (USA) type. So the fact that I took the supply away from the RCBO and took it from an available 32amp, so that should be alright.
The thought did occur to me that a single pole RCBO rather than the 2 pole, might also work if it was necessary, but I feel confident now from all the input, that if I fit a new C rated MCB say 32Amp and take power from there, that this will do the trick.
The Single Phase motor came un-wired, by the way.

davelerave

Don't remove earth-leakage protection yourself.(earthing,IR ,loop-impedance needs to be checked).You may also need to check overload protection on motor.Get a sparkie .

2011

+1 get a sparks to look at it and ensure it is safe.
RCBOs are all 2 pole. What you may think is a single pole RCBO is an MCB I would think.

32 amp MCB is too large for the pump. From the photo it looks like there is no overload protection, this is why I would go for a 20 amp MCB.

It would be good to measure the current drawn with a grip on ammeter.

davelerave

2011 wrote: »

It is not normal to protect pumps with an RCD. The regulations are quite clear about when an RCD is required and the ETCI regulations are a higher standard that most if not all of the rest of the EU.

If you look at large projects in Ireland where engineers design the electrical installations so that they are installed to standards far higher than the ET101 regulations require it can be seen that motors (including pumps) are not protected by RCDs. This is even the case with 3 phase motors when the line voltage is increased to 400 volts. In fact you will find that very little fixed equipment is protected by RCDs.

Even in hospitals where some RCDs protecting socket circuits are designed to operate when the current differential is just 10mA (30mA is standard for domestic) the pumps and motors there are not protected by RCDs.


As I said in an earlier post

I do take your point that there may be circumstances that I am not aware of in this situation that could lead me to change my mind, but not from the information given. The pump the OP describes is hydraulic, so I would guess it pumps oil which has good insulating properties.



A separate issue, but a good point!

Water pumps require 30ma rcd protection (ET 101, 555.3.2).

2011

Water pumps require 30ma rcd protection (ET 101, 555.3.2).

In some cases, yes. Not in the OP's case though.

555.3.2 is a sub-section of 555.3

555.3 titled "Water heating Appliances".
Anything within this section therefore relates to water heating.

555.3.2 relates to items such as water pumps that are part of a water heating system.

The OP has a hydraulic pump that is not part of a water heating system so 555.3 does not apply.

Furthermore the OP's pump is hydraulic i.e. it pumps oil.

davelerave

of course not in the ops case,:D i was referring to your statement regarding pumps

2011

of course not in the ops case, i was referring to your statement regarding pumps

sorry dave this was not clear to me from your post.

I guess you mean where I said that it was not normal to protect pumps with an RCD? This is the case. I gave a hospital as an example, go to any plant room and you will see all sorts of motive power including water pumps that have no RCD protection. This applies to a varity of pumps for sprinkler systems, heat exchangers etc.

In some limited situations such as the example you gave some water pumps are protected by an RCD, but this is not the norm.