Common Failure Mechanisms for Submersible Pumps & RCDs

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In summary: Then measure the resistance from the active lead to Earth. If it is low (below 10 Ω), the motor might have water in it. If it is high (>100 Ω), the filter capacitors might be the issue.In summary, the pumps failed because they were inductive loads and the induction of the motor starting is probably causing the inbalance between the line and neutral.
  • #1
matheinste
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Hello all.

Does anyone know of a common failure mechanism for submersible pumps whereby they trip household Residual Current Devices. I have had the same problem with three such pumps. I assume the problem is not the fact that they are inductive loads (I assume that they are inductive loads) because they all worked for some time before failing.

They work(ed) on a 240V 50Hz supply and are rated at 300-400W and are fitted with a domestic, pre-wired three pin plug. I do not know the setting of the RCD but the whole supply for the house runs through it.

Thanks for any replies.

Matheinste
 
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  • #2
...because they all worked for some time before failing.
Do you mean that the pump failed or that it tripped the RCD?
A residual current device (RCD), similar to a residual current circuit breaker (RCCB), is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor.
http://en.wikipedia.org/wiki/Residual-current_device"
The induction of the motor starting is probably causing the inbalance between the line and neutral.
 
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  • #3
dlgoff said:
Do you mean that the pump failed or that it tripped the RCD?
http://en.wikipedia.org/wiki/Residual-current_device"
The induction of the motor starting is probably causing the inbalance between the line and neutral.

Thanks for your reply.

By failing I mean that the pump caused the RCD to trip and does so immediately it is switched on again. I understand that an inductive load puts current and voltage out of phase and can cause problems with trips but I assumed that as the pumps were fitted with plugs for household use (as cellar sump pumps)that they would be OK in that respect.

Matheinste
 
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  • #4
My suggestion would be to get an electrician to take a look at the wiring/circuit that the pump is on to see if all the connections are good. As you say, "the pumps were fitted with plugs for household use (as cellar sump pumps)that they would be OK".
 
  • #5
Do they only fail when they are submerged?

Maybe they are getting water in them?
 
  • #6
vk6kro said:
Do they only fail when they are submerged?

Maybe they are getting water in them?

That is of course a possibility but with such a failure rate any such fault would surely be a design failure and have been flagged up before now. They were being used well above their maximum depth specification and were not running dry.

Although the pumps were wired for household supply, my RCD may not be normal. Perhaps the motor characteristics change with age. I will get more info on the RCD, such as its trip current magnitude and duration. I suppose it may be faulty.

Thanks for your replies.

Matheinste.
 
  • #7
Hi,

If you can, get hold of a high voltage insulation tester and measure the resistance to the casing from the active lead of your motor.
If it is anything but an open circuit, the motor might have water in it.
Even a multimeter on the high ohms scale might give you a reading.

The other thing that can trip an RCD is if the motor has large filter capacitors across the input.
These carry AC current to Earth and can trip an RCD if they are big enough.
 
  • #8
vk6kro said:
Hi,

If you can, get hold of a high voltage insulation tester and measure the resistance to the casing from the active lead of your motor.
If it is anything but an open circuit, the motor might have water in it.
Even a multimeter on the high ohms scale might give you a reading.

The other thing that can trip an RCD is if the motor has large filter capacitors across the input.
These carry AC current to Earth and can trip an RCD if they are big enough.

Yes I have access to a Megger and will do a check to the exposed screw heads in the otherwisw plastic casing. I am an electronics technician by trade and so understand low voltage circuitry but am wary of anything domestic. These things, I know, can have hidden technicalities not always known to an unqualified electrician and this is why, for safety reasons, I asked for help.

I think for now this has gone as far as it can. Thanks for your replies and if I find an answer I will post it.

Matheinste
 
  • #9
The pumps have 3 pin plugs, so just measure from active to Earth on the plug.
Glad you have a megger. Set it on minimum voltage (250 V ?) so you don't generate any new faults.
 

1. What are the common failure mechanisms for submersible pumps and RCDs?

The most common failure mechanisms for submersible pumps and RCDs include electrical failure, mechanical failure, corrosion, and wear and tear. Electrical failure can occur due to issues with the power supply or wiring, while mechanical failure can be caused by wear and tear on moving parts or issues with the motor. Corrosion can also be a major factor, especially in submersible pumps that are constantly exposed to water. Finally, wear and tear from regular use can also lead to failure over time.

2. How can electrical failure in submersible pumps and RCDs be prevented?

To prevent electrical failure in submersible pumps and RCDs, it is important to regularly inspect and maintain the power supply and wiring. This includes checking for any loose connections, damaged wires, or issues with the power source. It is also recommended to install surge protectors and ground fault circuit interrupters (GFCIs) to prevent electrical surges or short circuits.

3. What are some common signs of mechanical failure in submersible pumps and RCDs?

Some common signs of mechanical failure in submersible pumps and RCDs include strange noises, decreased performance, and leaks. If you hear grinding or squeaking noises coming from the pump, or if it is not pumping as efficiently as it used to, these could be signs of mechanical failure. Additionally, any leaks or visible damage to the pump or motor should be addressed immediately to prevent further damage.

4. How can corrosion be prevented in submersible pumps and RCDs?

Corrosion in submersible pumps and RCDs can be prevented by using materials that are resistant to corrosion, such as stainless steel or corrosion-resistant coatings. Regular maintenance and cleaning can also help prevent buildup of corrosive substances and prolong the lifespan of the equipment. Additionally, installing sacrificial anodes or using corrosion inhibitors can also help prevent corrosion.

5. What is the recommended maintenance schedule for submersible pumps and RCDs?

The recommended maintenance schedule for submersible pumps and RCDs varies depending on the manufacturer and the specific equipment, but generally it is recommended to have them inspected and serviced at least once a year. This includes checking for any signs of wear and tear, cleaning and lubricating moving parts, and testing the electrical components. Regular maintenance can help prevent failures and extend the lifespan of the equipment.

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