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Subject: TWL: Re: major shore powercord issue
From: Arild Jensen (elnav@XXX.XXX)
Date: Wed Dec 05 2001 - 01:43:13 EST
At 06:28 PM 12/03/2001 -0800, Shaun Sweeney wrote:
> Does anyone have a good design for a breaker on the
>dock post that we plug into?
>
>Plan B would be a design for a switching device which will throw the main
>relay in the boat. I have found the relay but not the switching device.
>Any suggestions on this one?
REPLY
An essential ingredient for a successful shore cord setup is a drip loop
on the power cord so that rain will run down the cord and drip off
before it runs to the plug.
The twist lock connector should be inserted so the cord hangs down from
the socket before it turns and is lead anywhere else.
To understand what I mean look at the service entrance on a house where
the wire comes in overhead not under ground.
With regards to breakers and power plugs.
The breaker should be close to the outlet so you can shut off power while
connecting or disconnecting.
In many older marina installations you have a central breaker -
distribution panel but only an outlet at the power post.
This design encourages people to do "hot" connects and disconnects.
The traditional 20, 30 and 50 amp twist lock power connector used for
marine shore cords is not what is called "load breaking".
A load breaking disconnect has a design which supresses or quenches the
arc which forms as you break the circuit under load.
A circuit breaker is designed to do this but a plug does not.
Not only does this arc burn and pit the blade contacts, but if there is
any surface moisture who oknows where the leakage traces will end up.
There is a potential for shock since salt air will coat the cable and
connnector with a moisture absorbing coating.
Add sweat on the skin or rain and mist in damp weather and you can get a
tingle or worse when handling the plug.
Regarding Plan B
As far back as 4 years ago, Carver had a main disconnect breaker that
tripped when the power was interrupted.
You had to manually reset the breaker after plugging in the shore cord. I
was told this was a new safety feature then.
Check Airpax, Carlingswitch, Heinenmann and Blue seas to see who supplies
them.
Cheers
Arild Jensen
The Electronic Navigator
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