Shorepower agony. Any ideas

[jfkal]

I have got a strange problem. My aircon system (don't ask, I am in the tropics) is tripping the RCB. I have a low amp slow blow automatic fuse as well as the high amp RCB plus an extra RCB on the dockside shore outlet.
Funny enough only the boat RCB trips randomly. If I just run the fan of the aircon everything seems fine. Starting the compressor the system takes the high starting current, current fall soff to normal running level and the aircon runs for awhile and then the RCB trips. I suspected a leak to ground somewhere and detached the grounding wire hoping the verify my suspicion. (NB The RCB measures live and neutral amps, if there is a mismatch i.e. current leaking to ground it trips). Now even with the ground wire off it still trips. That got me puzzled. The system is not overloaded and by right the RCB should not detect a ground fault since the wire is off. Have I overlooked something?

 

[Davolas]

Just because you have removed the earth wire, doesn't stop current escaping to earth and the distribution system will be earthed at the supply point, so any faulty insulation will lead to current to earth which is seen as imbalalnce between L & N.

I would expect the trip on the boat to operate before the shore side as it is closer to the load and possibly a lower trip setting. Do not confuse operating currents with earth leakage. A typical earth leakage trip is 30mA and in the marine environment (damp, good earth conductivity) is easily reached with only a slight defect, the fact that it doesn't occur straightaway probably means there is some minor crack in insulation of a motor winding or similar which opens up under temperature or on AirCon condensation could be building up on the cold side when it starts operating, which will find any poor insulation.

Hope this helps.

Steve

 

[halcyon]

Is it tripping on the RCD function ?, normally they are combined with an MCB function, yours may be tripping on over current and needs a larger rating fitted.

Brian

 

[Alex_Blackwood]

Without seeing the set up diagnosis is difficult, but one possibility is the capacitor associated with the compressor motor. They do have a tendency to "Leak". You would really have to change it for a new one and eliminate it that way.
Sorry can't be more specific.

 

[jfkal]

Its the RCD for sure. The MCB is additional and much lower rated. Besides it stays on during the 25A starting surge and trips during the 7 Amps normal run.

 

[jfkal]

Good point. Will try that. Just thought of something else. Since the aircon is filled with seawater for cooling, could it be that it leaks to via the housing to water and therefor creating the imbalance to trip the RCD?

 

[towzer240]

shore power consumer unit should be main incomer & or rcd, mcbs rated to protectc the size of the wire not the apliance, the appliance should be wired through a fused connection.if the rcd keeps tripping try swapping type b for a type c rcd of the same size, type b might not be suitable for the motor load .

 

[TrueBlue]

Interesting topic; just my two-currency's worth -

Peeps don't realise that a 30mA current is not a lot of juice - many times I've been the earth leakage conductor and have not felt more than a "whoops" of a jolt when touching the live conductor. A 100mA trip gives me a **expletive** jolt, and it's been many years since I've cooked my goolies without a ELCB...
(In a previous existence I've suffered a 2KV jolt and several 415V belts; doesn't half raise the curly bits, etc,etc).

What I'm trying to say - and from experience with dodgy connections to my outbuildings, is that a little damp causes problems which are usually cured (for me ) when the sun shines.

Have a look at the motor start capacitor and any possible damp bits - especially if salt is involved in the path. It's often the unlikeliest part which causes the glitch.

You didn't really expect a definitive answer did you???

 

[philip_stevens]

Jorge,
has your aircon been tripping since you put it in, or in high humidity season. I've spent a lot of time in Singers, and know that at some times of the year, there is a very high humidity. At other times the humidity is more bearable.

I ask this, as when you start to cool down, there is a lot of condensation removed from warm parts, and if the A/C cools down and then cycles, some condensation will settle on the coldest components - resulting in tracking and hence tripping the RCD.

We used to get this when I was on containerships if the A/C of tbe control room failed. The first thing that I would shut down (I was a lecky) was the data-logger, that was in the decline of its years - a very old NPN transistor Serck datalogger, with wrapped connections on the PCB cards. So I know what condensation can do when it was my job to keep this thing working - for the freezer cargo and engine monitoring.

The complete system was dust covered, and impossible to clean. When the A/C failed, condensation settled on the dust and tracked. Your aircon could be getting the same or similar problems.

 

[jfkal]

It worked fine for years. Will have a closer look and clean the whole unit plus change the capacitor.

 

[jfkal]

Hmm. That is what puzzles me. Since the whole unit is (now) no longer connected to earth how can I get an earth leakage? Only Hot and Neutral are connected right now and it still trips.

 

[halcyon]

If you have a ELCB, it measures the current in the earth wire, if you have a RCD, it measures the current in the L and N, and if the differance is more than 30ma it trips. Earth has no part in the life of a RCD trip.

Brian

 

[jfkal]

If there is nowhere else to go for the current (i.e. earth) then current on live and neutral should be identical, hence no trip. Since the earthwire is off, it is not going there but my question is where is it going then or is the RCD perhaps faulty.

 

[philip_stevens]

Jorge,
have a read of this, http://www.tlc-direct.co.uk/Technical/Distribution/How%20RCD%20Works.htm as it explains how an RCD works.

 

[VicMallows]

Halcyon,

I do recognise the sort of earth-trip which measured the current in the ground wire (often used in the past on overhead 2-wire distribution, where a good earth by bonding could not be achieved).

However, the term ELCB (earth leakage circuit breaker) was in use for many years for what we now call an RCD (residual current device) and indeed is still in common use and sometimes found on packaging/instructions.

I agree it can cause confusion.

Vic

 

[Alex_Blackwood]

The earth bonding wire may be disconnected but you can, as you previously thought, be getting an earth return through the system pipe work and cooling system. The earth wire is there to provide positve bonding and ensure that you do indeed have an earth.
Also agree completely with Vic Mallows. Don't worry if it is called an ELCB or RCD.

Alex.