second class motor questions

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walker
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second class motor questions

Postby walker » Tue Mar 31, 2009 8:57 am

Hi,guys!
I have to pass my motor exam and I can't find the answers for some questions.Maybe somebody cold help me to find these answers?
Questions:
1.describe the following tests and indicate where or on what part of a ship these would be carried out:
hose test,head test,drop test,hammer test?
2.Name two methods of measuring electrical resistance and describe one of them in full.
3.Sketch the connections for ground lamps on a D.C. switchboard. How do these lamps indicate a ground and how would you proceed to locate a ground if one was indicated?

Thank's in advance.

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Madzng
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Re: second class motor questions

Postby Madzng » Tue Mar 31, 2009 2:09 pm

Hi Walker,

Question 3 I cant give you a drawing, but I think you should have no problem drawing your own from the description.

The most common method uses two lamps, both suitable for the full switchboard voltage. The lamps are connected together in series (through fuses) from both the positive and negitive busbars. The centre point, between the two lamps, is connected to the vessels hull (earth).
If the insulation is good, both lamps will glow with equal "half" brightness. If the insulation is bad the lamp on the effected side is short circuited (dark) and the other lamp will glow with full brightness, due to the current flowing through it. The bigger the difference in brightness between the two lamps the bigger the earth fault.
The trouble with this system is that a slight earth fault on both phases will not show up. To help avoid this problem a switch can be placed in each cable to the lamp. If a earth is present the bulb will glow brighter, when one switch is opened.
To find the earth, simply isolate the equipment piece by piece keeping an eye on the lamps. Remember the one that goes dimmer or dark is the effected phase.

Question 2 - sorry, not sure on this one.

Question 1 - There are probably many different answers to this but here are a few suggestions;
hose test - prove watertightness of watertight doors or flap, can also be used to prove a bulkhead repair has been done satisfactorily. Generally done with a fire hose.
head test - (not heard of this one) Possibly to prove water tight integrity of a tank, fill the tank to the top of the vent, this is the max head that the tank should take without leak or distortion.
drop test - I know of one test, carried out on a new anchor. The anchor is dropped from 12ft onto an iron slab. If it doesnt fracture the anchor passes.
hammer test - Can be used to check if nuts/bolts etc are tight and gives a clear ring for tight and a dull thud for loose. Can also be used to check for cracks in springs etc... again, a clear ring is good, and a dull thud is bad.

Hope that helps

walker
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Joined: Wed Oct 29, 2008 11:13 am

Re: second class motor questions

Postby walker » Wed Apr 01, 2009 8:30 am

Hi,Madzng!
Thanks a lot for the time spent for answers. I appreciate it. I hope I can draw the scheme following your description :)
Yes, really, I have found many various descriptions of the listed tests, but nothing approaches for sea application. Most closest I have found, its the drop test for containers and the hammer test for concrete. Therefore thanks for the second answer too.
What about the question of two methods of measuring electrical resistance ...no idea :idea: Probably somebody else knows the answer? :wink:
Anyway thank's again and good luck!
walker.

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JK
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Re: second class motor questions

Postby JK » Wed Apr 01, 2009 12:32 pm

Resistance is measured by an ohmmeter. You can google that because I am lazy ;).

So do you know how to find 2 grounds?

walker
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Re: second class motor questions

Postby walker » Thu Apr 02, 2009 8:16 am

Hi,JK!
I heard about an ohmmeter but the question is:Name T W O methods of measuring electrical resistance and describe one of them in full.
What abou another one? :wink:
How to find 2 grounds?(Sorry,I'm not electrician.) :oops:

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JK
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Re: second class motor questions

Postby JK » Thu Apr 02, 2009 1:46 pm

If you googled ohmmeter, it talks about kelvin sensing, which I assume is the 2nd method.

And I was taught testing for 2 grounds as part of studying for my certificate. Thought you might be interested, JIC :wink:

walker
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Re: second class motor questions

Postby walker » Fri Apr 03, 2009 10:03 am

Hi,JK!
Actually I googled ohmmeter and found kelvin sensing method of high-precision measuring of an electrical resistace.Thanks a lot.
What about testing for 2 grounds ?I'm interesting for. :o


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