# clamp on meters to read wire current in trucks trailers questions



## burntside bob (Sep 27, 2010)

Any one have or used one of the clamp on electric meters.
I am thinkng of purchasing one to use instead of poking holes into the electric wires to find out if there is current to the light that is not lighted, say a marker light on a trailer.
What model, make do you have?
Does it work,?
What do you think of them?
Would you recommend the clamp on meter to other contractors?


----------



## GettingBy (Aug 19, 2010)

burntside bob said:


> say a marker light on a trailer.


This light may only pull a half amp, and much less if it's an LED. Make sure your meter can read that low.


----------



## mehtwo (Nov 14, 2010)

Make sure that the meter can read DC amps, very important!


----------



## GettingBy (Aug 19, 2010)

"Typical hand-held Hall effect units can read currents as low as 200 mA, and units that can read down to 1 mA are available."
from
http://en.wikipedia.org/wiki/Current_clamp
Probably it's more money for meters that have lower full scale readings.

If you just want go/no-go readings try holding a compass next to a wire that is carrying normal current and then one that is not carrying any current and then compare readings. If it works at all, you'll get better readings if the point of measurement on the wire is far away from iron or steel.

http://electricuniverse.com/acommon/content_teacher/exper-galv.pdf


----------



## tgeb (Feb 9, 2006)

burntside bob said:


> Any one have or used one of the clamp on electric meters.
> I am thinkng of purchasing one to use instead of poking holes into the electric wires *to find out if there is current to the light that is not lighted, say a marker light on a trailer.*
> What model, make do you have?
> Does it work,?
> ...


Why not pull the bulb and test the socket?

I would imagine that the first thing you would do if a light was out would be to check the bulb. If the bulb appears to be OK, then check for power to the bulb at the socket.
If no power to the socket, then check the next connection, usually at the tongue of the trailer. Then on to the pulling vehicle, fuses, etc.

It is easy to check connections without "sticking the wires", it just takes more time.

I commend you on not wanting to break the insulation. Sticking a wire will most certainly lead to failure down the road, but as Getting By stated a meter that would work in this instance would probably be quite costly. 

How bad/often do you have to work on the trailer wiring?


----------



## Tinstaafl (Jan 6, 2008)

burntside bob said:


> I am thinkng of purchasing one to use instead of poking holes into the electric wires to find out *if there is current to the light* that is not lighted, say a marker light on a trailer.


Duh. Been blowing past this thread, but that just struck me. If the bulb is bad (or if the wire is broken), there won't be any current, and your clampmeter won't do you a bit of good. It only measures current, not voltage.

If you put a known good lamp in and it doesn't light, use normal meter probes to see if the socket has voltage. If it does, most likely your lamp isn't making contact. If it doesn't, you either have an open wire or a bad connector.

Troubleshooting shortcuts are great--if the theory behind them is sound. :thumbsup:


----------



## Seven-Delta-FortyOne (Mar 5, 2011)

Clamp meters don't read DC. A clamp meter works like a transformer, and only AC will activate it.


----------



## GettingBy (Aug 19, 2010)

With all due respect, that's where the Hall Effect comes in. Otherwise it's just a transformer with a movable split core.
My B&K Precision current probe measures 400 ADC or AAC, full scale, and gives you 400 mV, but for DC measurements there is a zero control to null out any nearby steel/iron or magnets.

The smallest current change I can measure with a 4-1/2 digit DVM on the 200 mVDC range is 10 mADC. Percent accuracy is worse and is kind of hard to calculate because you've got the current probe accuracy on top of the DVM accuracy.

Since you mention it, 
word is, it's not a choice.
http://en.wikipedia.org/wiki/Alcoholism
The research I did for a family member told me that it only cuts 10 years off your lifespan; I guess it's what all happens before you die that counts.


----------



## dayexco (Mar 4, 2006)

you pansies...hook the wiring up to 220....you'll trace it out real quick.


----------



## Seven-Delta-FortyOne (Mar 5, 2011)

GettingBy said:


> With all due respect, that's where the Hall Effect comes in. Otherwise it's just a transformer with a movable split core.
> My B&K Precision current probe measures 400 ADC or AAC, full scale, and gives you 400 mV, but for DC measurements there is a zero control to null out any nearby steel/iron or magnets.
> 
> The smallest current change I can measure with a 4-1/2 digit DVM on the 200 mVDC range is 10 mADC. Percent accuracy is worse and is kind of hard to calculate because you've got the current probe accuracy on top of the DVM accuracy.


I stand corrected.


----------

