mcymabm@voila.fr <mcymabm@...>

Dear Gary

Sorry for answering late, but I am not so often near an internet

I confirm that I nearly had fire in my boat due to Dessalator 220 V. motor by end 2005.

My equipment is a Duo 220 V. / 24 V given for 60 L./h.
Equipment and electrical cabling are strictly original.(20A. 2 poles Diruptor, low breaking capacity C.B. )

The Facts: how it happened

One day, I started the water maker on 220 V. as usual, from the galley with gen set running.
I was waiting for the “good quality” green light to switch on, which, of course happened after 2/3 min.
When I turned the pressure up, it was not rising. I then understood that the 220 V. motor had not started and switched the CB on the panel board in the galley off.
This circuit breaker had not tripped ( see further why). I thought I would have a look at it later.

Then, I could smell a strong odour invading the boat. When I opened the engine compartment, I understood the odour was coming from there.

The Diagnosis : why it happened

Examining the motor, I discovered that the capacitor on the motor was damaged, leaking, probably having been mounted too close to the motor. Which I had not noticed before.

Since, without the capacity functioning, the motor didn’t start when I turned the water maker on.
But the Circuit breaker remained in ON position (didn’t trip), nevertheless the short circuit, and nothing told me that the motor had not started. A blocked rotor motor is exactly the same as a short circuit.
The motor was completely burned and I had to have it rewired at my next port of call (Panama). Should have it lasted longer,… you can imagine the possible disaster.

The electrical facts are as follow:
· in order to allow the motor to start and pass the starting peak of current, the breaker is calibrated much higher than the nominal current of the , motor ( 20 A for 5.4 A. nominal current of the motor).

· This setting makes that, in case of blocked rotor, the current, which is the same than the starting one (~16A. for this type of motor), is not high enough to trip the breaker….leaving the motor burn.

· A circuit breaker is designed to protect lines, and not appliances, with exception (see further).

· There is no fuse on the motor to back up the CB.

The professional installation could be in two ways (twofold):

· Use a “motor CB”. This is a special type of CB with special tripping curve to let the peak pass, although being calibrated for the motor nominal amp.
· Use CB + Fuse (a slow blow one) . This is called “line starter” in the US. The CB protects the line (which is the normal aim of a CB) and the fuse protects the motor, but being slow, let the peak pass as long as it last only a very short time (normal starting delay).
· Never protect a motor with a standard CB. A slow blow fuse should have been set on the Dessalator motor.

I made my utmost to be clear, but if not, don’t hesitate to come back.

As to the Watermaker, the responsibility problem is not easy ( see my recent post on this forum):
· I have in hand a letter from Dessalator stating that it was together with Amel that they had decided to do so; Wagner sent a copy of this letter, and others, to J.Y. Selo, at that time after sales director.
· On the other hand, I know other boats, non Amel, having the same problem.
· I am glad that, after having been very doubtful, Ian is now becoming very active on this big issue.

Take care,

Blue Marine
SM 311


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