Whirlpool Bath, Safe-t-cut, And Nuisance Trips

[gregb]

So, I recently installed a whirlpool bathtub, and now have a problem I wasn't expecting. Whenever I try to start the air compressor, I trip the Safe-T-Cut downstairs.

This happens every time on 5 mA, about 50% of the time on 15 mA, and about 20% of the time on 25 mA. Of course, it doesn't happen at all on the bypass setting. :-)

My question is, what can I do to solve this problem? If I set to bypass to start it, and then switch it back to 5 mA after the compressor is started, it runs just fine. This is very annoying however as the Safe-T-Cut is downstairs, and I'm usually dripping wet when I want to start the airpool.

Anyone ever dealt with an issue like this before and have an idea of how to fix it? It seems to be the surge current which causes the problem. Is there a way around it?

Disabling the GFI completely is not really a practical idea, as this is my life we are talking about, and having paid all of this money for the bathtub, I want to be around to enjoy it. On the other hand, the inconvenience of running down the stairs wet and naked in the dark everytime I blow the GFI is not particulary pleasant either.

Ideas?

Thanks for any advice.

[Crossy]

Where physically is the air compressor?

Is the air tube plastic?

How is the compressor connected to the power (plug?)?

How are you switching on the compressor, is there a control panel or is it a regular switch somewhere?

I have a couple of ideas which don't involve disabling your safety device

[gregb]

Where physically is the air compressor?

Is the air tube plastic?

How is the compressor connected to the power (plug?)?

How are you switching on the compressor, is there a control panel or is it a regular switch somewhere?

I have a couple of ideas which don't involve disabling your safety device

The compressor is physically attached to the bathtub, located directly underneath the left side against the wall.

The airtube connecting the compressor to the jets does appear to be a polymer of some kind. Probably not conductive, although the air jets are metal.

A single, grounded power plug comes out the bathtub and is plugged into the wall. This plug goes to a junction box on the bathtub, and the various components attach there. (Whirlpool pump, air compressor, stereo, lights etc.)

The compressor is switched on by pressing a button on the bathtub panel. Other buttons here switch on the lights, stereo or whirlpool pump as appropriate.

Basically, everything is self contained inside the bathtub unit. What comes out is a single, grounded plug which plugs into the wall.

Thanks.

[Crossy]

OK.

Some ideas, may work, may not.

• Check your ground is good (I'm sure you already have )
  
• Check the outlet is wired the correct way round, live should be on the left if you look at the outlet with the ground at the top (it SHOULD have no effect but as we all know TiT). Use your trusty neon screwdriver.
  
• Open all the other breakers and see if things improve, some other appliance may be drawing leakage near the tripping value, the surge on switching on the tub may be enough to pull it over the edge.
  
• Check for damp ingress on the control panel (I hope this is low voltage)
  

[david96]

RCD Fault finding

RCD trips intermittently or will not reset.

Possible faults.

1.1 Faulty equipment or appliance

1.2 RCD faulty- disconnect circuit conductors and test the RCD.

1.3 Low insulation resistance to earth, check using a 500VDC insulation tester,test the active and neutral to earth.

RCD test button inoperative.

2.1 Check that there is an A to N voltage on the line input terminals and the load terminals.

2.2 If supply voltage present disconnect active and neutral load conductors from RCD, if the RCD now trips on the test button check the insulation resistance between neutral and earth, it will be low.

2.3 A low resistance connection between the neutral and earth may occur in the wiring,or in appliances even those plugged in but not switched on. This type of fault can inhibit operation from the test button and lead to failure of the RCD to trip on test.

Neutral to earth connection.

3.1 The MEN connection must always be at the main neutral link on the line side of the RCD.

3.2 Faulty insulation between a protected circuit neutral conductor and earth is the major cause of problems in installations protected by RCDs.

3.3 Spurious tripping in the case of neutral to earth faults are caused by two different reasons.The RCD will trip when the load current drawn because the neutral conductor will divide between two parallel paths, one through the neutral pole of the RCD and one through the earth connection. The percentage which returns through the earth connection will appear in the RCD as an imbalance and cause the device to trip. Even in the case of a comparatively high resistance, tripping of the RCD may still occur during periods of high inrush current demand such as the starting of an airconditioning unit.

3.4 If there is a small neutral potential at the installation due to out of balance on the Supply Authority system, there may be sufficient current flowing in the earth connection where there is good conductivity to ground to trip the RCD.This will occur with all active circuits disconnected.

3.5 It should also be noted that, in the case of a neutral to earth fault where only a small neutral potential exists it is possible for a current less than the devices tripping current to flow in the earth connection .This current will oppose that introduced by the test circuit and can cause failure to trip on test.

3.6 A neutral to earth fault also constitutes a short ciruited turn around the RCD toroidal transformer which will have the effect of the RCD toroidal transformer which will have the effect of desensitising the device, causing it to fail on test.

4. Nuisance tripping of RCDs can be caused by the following,

1 Moisture

2 High leakage currents

3 Switching of inductive or capacitive loads

4 High inrush currents

4.2 High leakage currents can occur with electronic equipment which may have capacitors connected to earth for example computers,photocopiers and switch mode power supplies.

4.3 Max leakage current should not exceed 30% of the rated RCD current. An RCD must trip between 50% and 100% of the rated RCD current in mA.

[elkangorito]

RCD Fault finding

RCD trips intermittently or will not reset.

Possible faults.

1.1 Faulty equipment or appliance

1.2 RCD faulty- disconnect circuit conductors and test the RCD.

1.3 Low insulation resistance to earth, check using a 500VDC insulation tester,test the active and neutral to earth.

RCD test button inoperative.

2.1 Check that there is an A to N voltage on the line input terminals and the load terminals.

2.2 If supply voltage present disconnect active and neutral load conductors from RCD, if the RCD now trips on the test button check the insulation resistance between neutral and earth, it will be low.

2.3 A low resistance connection between the neutral and earth may occur in the wiring,or in appliances even those plugged in but not switched on. This type of fault can inhibit operation from the test button and lead to failure of the RCD to trip on test.

Neutral to earth connection.

3.1 The MEN connection must always be at the main neutral link on the line side of the RCD.

3.2 Faulty insulation between a protected circuit neutral conductor and earth is the major cause of problems in installations protected by RCDs.

3.3 Spurious tripping in the case of neutral to earth faults are caused by two different reasons.The RCD will trip when the load current drawn because the neutral conductor will divide between two parallel paths, one through the neutral pole of the RCD and one through the earth connection. The percentage which returns through the earth connection will appear in the RCD as an imbalance and cause the device to trip. Even in the case of a comparatively high resistance, tripping of the RCD may still occur during periods of high inrush current demand such as the starting of an airconditioning unit.

3.4 If there is a small neutral potential at the installation due to out of balance on the Supply Authority system, there may be sufficient current flowing in the earth connection where there is good conductivity to ground to trip the RCD.This will occur with all active circuits disconnected.

3.5 It should also be noted that, in the case of a neutral to earth fault where only a small neutral potential exists it is possible for a current less than the devices tripping current to flow in the earth connection .This current will oppose that introduced by the test circuit and can cause failure to trip on test.

3.6 A neutral to earth fault also constitutes a short ciruited turn around the RCD toroidal transformer which will have the effect of the RCD toroidal transformer which will have the effect of desensitising the device, causing it to fail on test.

4. Nuisance tripping of RCDs can be caused by the following,

1 Moisture

2 High leakage currents

3 Switching of inductive or capacitive loads

4 High inrush currents

4.2 High leakage currents can occur with electronic equipment which may have capacitors connected to earth for example computers,photocopiers and switch mode power supplies.

4.3 Max leakage current should not exceed 30% of the rated RCD current. An RCD must trip between 50% and 100% of the rated RCD current in mA.

I think you may find that most TPS cables sold in Thailand are 300v & so a 500v insulation test could give false results as well as damage the cable. In this case, a 250v insulation test is indicated. See pdf file attached.

[Spacer]

So start it in bypass. I believe that is why there is a bypass in the first place. All motors will draw more amps at start-up. Especially with a load attached.

[elkangorito]

Crossy...where are you? This is your baby

[Crossy]

Crossy...where are you? This is your baby

555. I didn't think the previous post was worth replying to Actually when I saw you'd posted I was looking forward to the sparks

Anyway, until Greg comes back having checked his installation, not sure how we can proceed.

[gregb]

Thanks for all the suggestions everyone.

I'm going to spend the weekend trying to troubleshoot this. If I can't find the answer I may host a free beer party at my place for anyone with a multimeter and the ability to explain the Biot-Savart law using phasors. (I hated phasors and transmission lines. Never could understand the lectures.)

I'll let you all know how it turns out.

[elkangorito]

Actually Greg, I think the device you have is an air blower & not an air compressor.

An air blower uses two solenoids opposite each other with a gap between them. A flat rectangular armature is placed within this gap. The armature is connected to a rod, which is then connected to two diaphragms. Each diaphragm has a reed valve to allow air to be sucked into the air reservoir connected to the diaphragm.

The armature vibrates at double the supply frequency. These blowers are very common.

When I worked in the sewage treatment industry, these were used in home sewerage treatment plants to stimulate aerobic activity within the treatment system.

Due to the type of device this blower is, I would expect it to be a bit 'leaky', which may be causing your RCD to trip. Keep in mind that you may already have leaky devices (frig etc), which will add to the overall leakage current.

Also, you mentioned that you have an adjustable RCD. I advise you to set it at 30mA trip current. This will not decrease the safety factor that the RCD provides.

One last question - is it a combination RCD/CB or is it only an RCD?

I don't like adjustable RCD's.

Look at these sites -

http://www.crossy.co.uk/wiring/Consumer.html

http://www.crossy.co.uk/wiring/protection.html

[Crossy]

I'm going to spend the weekend trying to troubleshoot this. If I can't find the answer I may host a free beer party at my place for anyone with a multimeter and the ability to explain the Biot-Savart law using phasors. (I hated phasors and transmission lines. Never could understand the lectures.)

555. I wonder how many readers think we're talking about Star Trek (although IIRC they used Phasers not phasors)

I did my degree in Electrical and Electronic Engineering, Biot-Savart (along with Coulomb and other gripping, 'totally useless in the real world' stuff) was discussed in the twice weekly Physical Electronics sessions, never understood it either. Machines & Control and Electronics no problem (hated maths too).

Keep us informed what you find

Edited September 12, 2007 by Crossy