TWL: RE: Shore-Power Cords that "burn-through" rather quickly.....
Arild
Is there any way a boater can do crude tests of the waters in and around
his slip to see if he needs the expert help? For example, can I use a
digital voltmeter and copper wire probe to determine that something is
abnormal? Are the only alternatives to call the expert or wait for
visible damage?
Jim Fidler "Fiddlesticks"
---===========
Arild wrote:
My advice to Mr. Burke is to get an experienced stray current expert to
examine
his boat, dock and the immediate marina environment for sources of stray
current.
Regards
Arild
Jim Fidler asks:
Is there any way a boater can do crude tests of the waters in and around
his slip to see if he needs the expert help? For example, can I use a
digital voltmeter and copper wire probe to determine that something is
abnormal? Are the only alternatives to call the expert or wait for
visible damage?
REPLY
Fair question!
Yes there are several things you can do. The problem lies in how to interpret
the information you get.
I am often able to analyze and correctly diagnose problems which the experts
miss because they didn't put the facts together in the right sequence or
context.
To detect if you are seeing stray current migrating through the water from an
adjacent boat you need something with large surface.
A wire is not good enough.
A square foot of copper plate mounted on a PVC handle is a good probe.
Two such probes placed six to ten feet apart in the water can distinguish a
voltage differential of a few millivolt.
CAUTION!!!
Be very careful doing this. If a lethal voltage is being dumped into the water
the step voltage gradient may be sufficient to cause shock.
Therefore the probes MUST be mounted on good insulators , no broom handles,
and the leads going back to the meter should be treated as if they were plugged
directly into the power source 120/ 240 v for example.
Rubber gloves are recommended for doing this test.
The direction of the current flow can be roughly estimated by rotating the
plates and also by aligning the axis connecting the two probes.
My partner has even resorted to mounting the probes on the ends of a long plank
laid across the dinghy which he rowed around to see how the gradient changes.
Another way to detect if a boat has a problem is to meter the shore power cable
for leakage current.
In addition the resistance of the green wire back to the transformer ground
rod can be measured.
It should not exceed 3 ohms.
CAUTION!
This is another test requiring extreme caution. You are effectively plugging an
ohm meter into a plug which if miswired or defective will have lethal voltages
on pins you assume is grounded. Blown meters or worse may result. Wear rubber
gloves!
The above mentioned should only be undertaken by those who feel comfortable
with working on live circuits and who fully understand the procedures necessary
to protect themselves from shock. This is not recommended for occasional wire
pullers who work mainly on DC.
I worked for four years with a power utility and spent all my time working on
27,600 volt switch gear, We had weekly safety training sessions and it was an
ironclad rule that we always worked in pairs. The second person was there to
watch that the first guy didn't get careless and get too close to anything live
or at the worst pull him away if he did get shocked.
Despite such training and care I have been shocked a number of times. S**T
happens occasionally, despite all your best efforts.
Be careful!
And good luck
Arild
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Yes a great test and can be done with DC also, but exercise caution, use
rubber gloves, etc. If you don't understand what you are doing, then
don't do it.
I've checked my harbor waters and found AC in the water and mentioned it
to the harbor master; they got some electricians down to check it out
and somehow fixed it. I don't know what they did, but it was gone. As
part of my tests I noticed the 30 amp plugs were wired wrong too. They
were fixed too.
I loked the idea of rowing around the harbor to find stray currents,
either AC or DC. I wonder what has been found by others?
Depending on the situation the DC could cause electrolysis on the boat.
Another test I do on my boat when hauled out is to ensure low ohmage
(less than one ohm) between all metal fixtures on the outside of the
hull and the boat grounding (usually a thick green wire) wires. Once I
found a poor connection (had some electrolysis) on the boat grounding
wire connectors. By fixing this I at least saved some zincs and perhaps
other expensive parts. I have never heard of anyone else that does this
test.
Regards, Bob Rapasky
Arild Jensen wrote:
Fair question!
Yes there are several things you can do. The problem lies in how to interpret
the information you get.
I am often able to analyze and correctly diagnose problems which the experts
miss because they didn't put the facts together in the right sequence or
context.
To detect if you are seeing stray current migrating through the water from an
adjacent boat you need something with large surface.
A wire is not good enough.
CAUTION!!!
Be very careful doing this. If a lethal voltage is being dumped into the water
the step voltage gradient may be sufficient to cause shock.
Therefore the probes MUST be mounted on good insulators , no broom handles,
and the leads going back to the meter should be treated as if they were plugged
directly into the power source 120/ 240 v for example.
Rubber gloves are recommended for doing this test.
...........etc.........