23 June 2006
Thank you for more details on your system and on the type of near fire
that you suffered. Your description has led me to do some additional
research on my watermaker.
Does your water maker have an electrical control box similar to the
one depicted in the photo section of this web site under Watermaker Service?
You access the box from the port cockpit lazarette. See the photos on this
web site. I would quess that it must have a similar box.
This box on my water maker (160 liter per hour 220 volt sytem)
contains two circuit breakers. They are Merlin Gerin multi 9 C60N D5A and
D25A ciruit breakers (see photo) The D before the 25A or 5A indicates
that these are D curve rated circuit breakers that are motor circuit breakers.
The circuit breaker (20 amp) on the 220 volt panel in the galley is not a
motor rated circuit breaker but does supply feed power to this control
box (see photo).
The 220 volt power to the motors (both low pressure "BP" feed pump
and high pressure "HP" pump), are controlled by stacked relays on the
control circuit board and in the control box and the pumps
are protected by the above circuit breakers.
Everything you have said about protecting the pumps is correct. They
must be protected by motor circuit breakers or dual type fuses. I was
initially confused by the 5 and 25 amp breakers in the electrical box.
However,on my system, and based on reading the complete data sheets
for the manufacturer of these circuit breakers they meet all US and EU
electrical codes for both overcurrent and overload motor protection.
The US codes require the fuse or motor circuit breaker be rated at
125% of the motors data plate current rating. These CBs are D curve
breakers which means that they are appropriate for external motor
protection per the following US electrical Code UL 489, and EU Code
I will have to check the data plates on my motors to verify their rated
current draw to be absolutely sure the breakers are appropriately
sized but my first impression is that Dessalator did provide proper
motor circuit breaker protection for the motors. The specifications
for these circuit breakers say that they are marinized and rated
for at least 10,000 operations, so they are well made. They are
also expensive (about $117 USD each).
Additional protection for the motor could indeed be provided (and
redundant) by appropriate slow blow dual type fuses located at
the motor but neither of the the above noted codes require that.
I am sorry to hear about your electrical failure. I believe your
experience should serve as a warning to us all that we should
shut the system down immediately if either pump does not start
in sequence in their usual fashion.
I am not sure yet which circuit breaker from the 24 volt panel
protects the 24 VDC feed to the Dessalator water maker. Some
day I will complete my schematics, parts list, and parts diagram
for our water maker and post those on the files section.