Author Topic: Question about BNC test leads versus regular test leads  (Read 1098 times)

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Offline kleblanc

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Question about BNC test leads versus regular test leads
« on: February 01, 2016, 01:04:38 am »
I am looking for some general information about BNC vs regular single wire test leads. What I have found is BNC is generally rated for up to 500V and has dielectric shielding for frequency up to 4 GHz.  I am more or less looking at the BNC/banana/mini-grabbers used with DMM test equipment.  I like the BNC setup since it keeps multiple leads from becoming a rats nest.

My questions are

The pros and if any cons of BNC test leads.

Are there specific reasons not to use BNC?

Thank you.
 

Offline Ranger14

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Re: Question about BNC test leads versus regular test leads
« Reply #1 on: February 01, 2016, 01:25:40 am »
How much current can a bnc handle ??
 

Offline uncle_bob

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Re: Question about BNC test leads versus regular test leads
« Reply #2 on: February 01, 2016, 03:32:07 am »
Hi

If you are talking about a volt meter, the BNC / coax setup will add a bit more stray C to your measurement. That's not much of a deal at low frequencies. It can be an issue in some cases.

The bigger question is - what are you doing? If you have a multimeter and are checking a circuit, the ground may well clip on way over there and you are probing quite a ways away. That works fine with normal test leads, not so well with BNC stuff. If you have an RF circuit and want to get accurate numbers, some sort of probe will be a better way to go than any sort of test leads. Essentially a probe is a special case of a BNC / coax test lead. They have worked a bit on the stray C issues and improved it's performance a bit.

The other question seems to be - is there a magic way to avoid a rat's nest on my bench? The simple answer to that one is - no. You will have wires and cables all over the place.

Bob
 

Offline uncle_bob

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Re: Question about BNC test leads versus regular test leads
« Reply #3 on: February 01, 2016, 03:38:48 am »
How much current can a bnc handle ??

Hi

BNC's depend on the spring contact in the middle to keep a low dc resistance. Depending on how long you use them, that contact gets pretty worn out. They start out with a 2A rating and go down from there. They are not intended as a power connector. They are a test signal connector.

Surprisingly, banana plugs are very similar. They get rated all over the place (some say 3A max, others 5A, others 30A). In the real world after some use, they may get pretty warm at 3A. Tweak the springs a bit and they cool back down.

Crazy stuff.

Bob
 

Offline kleblanc

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Re: Question about BNC test leads versus regular test leads
« Reply #4 on: February 01, 2016, 03:46:00 am »
Thank you for the info. I typically work on controls measuring/supplying 24VDC 4-20 ma loops along with resistance measurements. So everything is within lead reach most of the time.  I was wondering if this is ok or not recommended.

Sorry for the ignorance, what is stray C and how would this affect my measurements if at all.

Thanks!
 

Offline uncle_bob

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Re: Question about BNC test leads versus regular test leads
« Reply #5 on: February 01, 2016, 04:51:23 am »
Hi

Stray C = stray capacitance. If you have an AC signal at high frequencies it can be an issue.

Bob
 


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