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Carling switch resistance for micro currents?

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fvalarm(at)rapidnet.net
Guest

Posted: Mon Aug 25, 2014 12:08 pm Post subject: Carling switch resistance for micro currents?

Hi Bob,



Last night I was metering a circuit (for total resistance) not including the

load at the end of the wire.  The circuit consists of about 10 feet of 18AWG

wire, an ATC fuse, fuse block and a carling SPST switch all obtained from

B&C, and two alligator test leads. I was surprised to find the meter (my

trusty Fluke) read several megohms when I closed the switch.  I was

expecting to see something less than 5 ohms (probably less than one).  It

would appear that there is quite a high resistance when only the very small

current of the metering circuit is passing through the switch.  Is this

normal?



Note:  The meter showed 0.2 ohms with the test leads shorted so the meter

seems to be functioning correctly.



Bevan

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Bob McC

Joined: 09 Jan 2006
Posts: 258
Location: Toronto, ON

Posted: Mon Aug 25, 2014 12:44 pm Post subject: Carling switch resistance for micro currents?

If you are actually measuring "several megohms" then  1; the switch is open, 2; the fuse is blown, or 3; one of the connections is not attached. Several megohms is what you would see holding the meter leads, one in each of your hands, with no metallic electrical circuit attached. You should be seeing less than an ohm or so with the circuit as you described it

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_________________
Bob McC
Falco #908
(just starting)

jluckey(at)pacbell.net
Guest

Posted: Mon Aug 25, 2014 12:54 pm Post subject: Carling switch resistance for micro currents?

Bevan,

what you are describing is not normal.  The resistance thru the closed switch should be the same as when you short the test leads together.

-Jeff

 

     On Monday, August 25, 2014 1:23 PM, B Tomm <fvalarm(at)rapidnet.net> wrote:

  

  



 --> AeroElectric-List message posted by: "B Tomm" <fvalarm(at)rapidnet.net (fvalarm(at)rapidnet.net)>



 

Hi Bob,



Last night I was  metering a circuit (for total resistance) not including the

load at the end of the wire.  The circuit consists of about 10 feet of 18AWG

wire, an ATC fuse, fuse block and a carling SPST switch all obtained from

B&C, and two alligator test leads. I was surprised to find the meter (my

trusty Fluke) read several megohms when I closed the switch.  I was

expecting to see something less than 5 ohms (probably less than one).  It

would appear that there is quite a high resistance when only the very small

current of the metering circuit is passing through the switch.  Is this

normal?



Note:  The meter showed 0.2 ohms with the test leads shorted so the meter

seems to be functioning correc= Use the Matronics List Features href="http://www.matronics.com/Navigator?AeroElectric-List" target="_bl-========================tp://forums.matronics.com/" target="_blank">http://forums.matronics.com</             t; http

  

 

  

 

 [quote][b]

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fvalarm(at)rapidnet.net
Guest

Posted: Mon Aug 25, 2014 1:28 pm Post subject: Carling switch resistance for micro currents?

Thanks for all the replies.  I have not been back to the  hangar to do anymore since posting my original question but I will add a little  more info here.

  

 This particular circuit has never operated any load yet.   It has been sitting for a couple years since originally crafted.   The  plane is in a heated/insulated space.  Nothing else rusts or corrodes in  this space.

  

 The fuse is 5amp.  I believe I also clipped the meter's  alligator directly to the screw terminal of the fuse block thereby eliminating  the block and fuse but will retry tonight.

  

 I don't have a battery in the plane yet.  I use a 30 amp  DC power supply that plugs into a piper style remote power  port.   It puts out 14VDC and has run all my other loads just  fine.  When the DC power supply is powered up, I get the full voltage at  the load end of the subject wire which is what I expected to see.  Since  there has never been any load driven by this circuit (no current flowing) there  has never been and arky sparky happening at the switch.  So, is some arky  sparky required to get the switch to indicate 0 ohms when in the on  position?

  

 I wouldn't think so but I seem to recall something about these  switches not being designed for extremely small currents.

  

 What I do see is open circuit with the switch off,   dropping to several megohms when on.  I may try powering a medium load  (5-10 amps) to see...

  

 A) If the load powers up as expected while metering current  through the circuit.

 B) Check the switch to see if it generates any noticeable heat  during this test

 C) Re measure the closed circuit resistance after the test to  see if it now appears more normal.

  

 Anything else?

  

 Bevan 

  

  



   From:  owner-aeroelectric-list-server(at)matronics.com  [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Bob  McCallum

Sent: Monday, August 25, 2014 1:43 PM

To:  aeroelectric-list(at)matronics.com

Subject: RE: AeroElectric-List:  Carling switch resistance for micro currents?

 

 If you are actually  measuring "several megohms" then  1; the switch is open, 2; the fuse is  blown, or 3; one of the connections is not attached. Several megohms is what you  would see holding the meter leads, one in each of your hands, with no metallic  electrical circuit attached. You should be seeing less than an ohm or so with  the circuit as you described it.



Bob McC



 > From: fvalarm(at)rapidnet.net

 	  Quote: 	
		   To:  aeroelectric-list(at)matronics.com

 Subject: Carling  switch resistance for micro currents?

 Date: Mon, 25 Aug 2014 13:05:51  -0700

 

 --> AeroElectric-List message posted by: "B Tomm"  <fvalarm(at)rapidnet.net>

 

 

 Hi Bob,

 

  Last night I was metering a circuit (for total resistance) not including  the

 load at the end of the wire. The circuit consists of about 10 feet  of 18AWG

 wire, an ATC fuse, fuse block and a carling SPST switch all  obtained from

 B&C, and two alligator test leads. I was surprised to  find the meter (my

 trusty Fluke) read several megohms when I closed the  switch. I was

 expecting to see something less than 5 ohms (probably less  than one). It

 would appear that there is quite a high resistance when  only the very small

 current of the metering circuit is passing through  the switch. Is this

 normal?

 

 Note: The meter showed 0.2  ohms with the test leads shorted so the meter

 seems to be functioning  correctly.

 

 Bevan

===================

 

  

 


	




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