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Branch circuit loop checksHow much time does it take you to find
an intermittent con-nection on one lug of a 120 Vreceptacle, if its
one of tenreceptacles on a circuit? Think ofthe steps involved for
checkingall those receptacles, and howlong it usually takes you to
iso-late the problem. Think of howmany hours that eventually addsup
to hours when you areunder pressure because some-thing isnt
working.
What if technology allowedyou to check every
receptacleconnection without even remov-ing a faceplate? And what
if youcould apply the same technologyto all branch circuit devices,
notjust receptacles? Would that beworth something to you? Wouldit
help you even more to knowthe exact impedance of a branchcircuit at
120 V, not the 9 V fromyour DMM?
Today, we can do this andmore with an instrumentdesigned for
power distributionbranch circuit loop testing. Sev-eral models are
on the market,and its worth taking a look atwhats out there.
The right stuffSimply put, a branch circuit looptest measures
circuits to look forhigh-impedance connections.And its a simple
test, if you havethe right equipment. If youvedone an insulation
resistancetest, youll have no problemdoing a branch circuit loop
test.As with an insulation resistancetest, you cant do this test
with aDMM. Connections that mayappear fine with no load canshow
high impedance when the
connection heats up with a 15 Aload. Thus, testers designed
forbranch circuit loop testing use atest voltage and current
thatmatches the circuit under test.With confirmation that the
instal-lation is safe and reliable for use,electricians can avoid
costly call-backs, save valuable troubleshoot-ing time and provide
proof ofworkmanship to customers.
What you can learn fromloop impedance testingon a branch
circuit
It works for youIf youve spent any time pullingout one
receptacle after another,tearing connections apart andredoing them
only to think youfound the problem, then you areprobably already
thinking thistest can save you money,improve your productivity,
andreduce your frustration. Andyoure thinking along the rightlines.
Here are some areas toconsider.
F r o m t h e F l u k e D i g i t a l L i b r a r y @ w w w . f
l u k e . c o m / l i b r a r y
Application Note
Some insulation testers make branch circuit loop test
measurements easier than others. TheFluke 1650 has ergonomic
dashboard-like controls, and a neck strap that frees you from
hav-ing to hold the instrument or have someone hold it for you-no
third hand required.
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2 Fluke Corporation Branch circuit loop checks
Troubleshooting. Lets sayJoe the electrician goes to thejob site
to fix a problem withoutlets not working right. Thecustomer
complains of intermit-tent equipment operation. So, Joestarts at
one end of the circuitand starts examining receptacles.On the third
receptacle, he findsa loose neutral wire. Joe repairsthe
connection. Now, do youwant Joe to remove and checkthe other seven
receptacles onthat circuit while hes there?Probably not, because if
he doesthat he might create other prob-lems and its likely those
recep-tacles are fine anyway. Given thecost and the potential for
furtherproblems, most of us would justassume the problem was in
theone receptacle and not in theothers.
The normal procedure, afterfixing a problem like this, is toplug
in equipment and show thatit runs right. Joe does this, andtheres
no problem. Until a weeklater when another connection one that
would have shown upon an impedance test Joe didntdo heats up and
begins tocause a repeat of the symptoms.
So, Joe pulls every receptacleand checks the screw
terminalconnections. They are all tight,but the problem persists.
Now,Joe has to go back through thereceptacle boxes and redo
everytwist-on connector, hoping hellchance upon the problem
thatway. On a standard 3-wire sys-tem, that would be three or
fourconnectors per box (assumingpigtails to each non-GFCI
recep-tacle). How long will it take Joeto take apart and remake all
30or more connections? Does hehave that kind of time? Do youhave
that kind of money? Doesthe end-user have that kind ofpatience? And
what if Joe inad-vertently creates another looseconnection easily
done whenpulling on wires while fixingthe original problem? And
heisnt aware of that?
Now, imagine the same jobagain. Joe goes to the end of
thecircuit, plugs in his tester andfinds high impedance. He
thenmoves down the circuit, plugginghis tester into each receptacle
inorder until he finds one that hasthe proper amount of
impedance.Now he knows where the prob-lem lies - somewhere
betweenthe last receptacle with highimpedance and the first
thatshowed normal impedance. Hetracks down the problem, fixes
it,then takes one last measurementat the end of the circuit. If
theimpedance there is normal, theproblem is solved and he knowshes
not going to have a callbackon it because he can see all ofthe
connections are sound.
Documenting. With the righttester, you can store test resultsfor
later download. Suppose Joegets called out three days laterabout a
receptacle problem onthat same circuit. Who picks upthe tab for
that callback? If thework has tested as being doneright, the
problem is not thework Joe did and probably notin the receptacle
circuit at all.You have the results documentedright there. Or,
suppose theres afire or other event that might beattributable to
bad wiring of abranch circuit. Your ability todocument the
condition of thework you completed can short-circuit an attempt to
sue you.And in todays lawsuit-crazyenvironment, thats a
definiteadvantage. Let your competitorsspend their time trying to
build adefense you already have yourproof.
Loss prevention. If youredoing preventive maintenance,you can
spot problems in branchcircuits as they begin to emerge.Excess
humidity, age, and vermincan all cause connections todeteriorate.
At first, theres noproblem with this just a littleenergy waste
through heat.Thats the ideal time to identifyand repair these
connectionproblems. Left to fester, theyresult in nuisance breaker
trips,low voltage at the point of use,outright failure,
mind-numbingintermittent problems, or evenfire.
Installation inspector. Elec-trical inspectors can save timewith
these tests and get moremeaningful information than theycan by
poking around in com-pleted work to visually checkconnections. So
can a contractor,thus preventing callbacks likethe one Joe dealt
with in ourexample.
Going to the next levelNow, heres an interesting twist. How
about trou-bleshooting the problems before the callback?Before the
drywall goes up and youre stuck withrefinishing costs? The
Europeans are doing exactlythat, by doing branch circuit tests in
the normalcourse of construction.
You can quickly see that consistently doingthese tests provides
compelling benefits. Becausethese tests are so quick and easy to do
at the timeof installation, the added labor cost is
inconse-quential. You can now eliminate problems beforeyou leave
the jobsite. This means your customer ishappy and your costs of
operation are lower.
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3 Fluke Corporation Branch circuit loop checks
Fluke CorporationPO Box 9090, Everett, WA USA 98206
Fluke Europe B.V.PO Box 1186, 5602 BD Eindhoven, The
Netherlands
For more information call:In the U.S.A. (800) 443-5853 or Fax
(425) 446-5116In Europe/M-East/Africa (31 40) 2 675 200 or Fax (31
40) 2 675 222In Canada (800) 36-FLUKE or Fax (905) 890-6866From
other countries +1 (425) 446-5500 or Fax +1 (425) 446-5116Web
access: http://www.fluke.com
2004 Fluke Corporation. All rights reserved.Printed in U.S.A.
3/2004 2140194 A-ENG-N Rev A
Fluke.Keeping your worldup and running.
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Tester
Junctionbox
Step 2Results: High
Step 3Results: Low
Step 4Repair
Step 5Test again
Results: LowFixed!
Badconnection
What is loop impedence?
Breakerpanel
Line
Tester
Neutral
i L
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iNEUTRAL
Loop impedence is anotheranother way of thinking aboutvoltage
drop. The loop being tested starts at the panel, passes through the
tester, and returnsto the panel. High loop impedenceis a strong
indicator of a problem;bad connections, or too long a runfor the
wire diameter.
Step 1Results: High