fluke - branch circuit loop checks

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.

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.

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?

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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