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#82645 - 12/05/02 11:51 AM Question for the Council of Elders  
Joe Tedesco  Offline
Joined: Oct 2000
Posts: 2,749
Boston, Massachusetts USA
Field question sent to me needs qualified answers ......

My concern: the electrical system checks out o.k., except for a 15 amp branch circuit which feeds three outlets ... one in the front, one in the rear, and one in the garage where the GFCI protection for this circuit is also located (GFCI outlet).

The problem that I have found, using a SureTest ST-1D, is excessive voltage drop.

This circuit runs from the panel to the garage (about 30 feet), then to the remaining two outlets (total of about 50 feet of cable).

The garage outlet shows an 8% voltage drop under a 15 amp load. The front outside outlet shows an 8.2% drop, and the rear outlet shows a 12% drop under the same load (15 amp).

I advised the local code inspector of this, and he was not interested in hearing about it, replying that nothing in the rules address voltage drop.

A state inspector did, however, give me the specifics on enforcement to deal with this problem, and indicated that there must certainly be a problem with this circuit if the voltage drop is that high.

A retired code inspector friend of mine agreed, and gave me a scenario that he would use to find problems:

plug in a 15 amp load and turn it on. He said the problem will become readily recognized when the sparking and smoking begins.

There is a desire to know whether or not there really is a problem, and I am considering meeting with my clients, and powering an 1800 watt appliance (hair dryer) off this circuit.

This will allow me to test available voltage while the appliance is on, and should also confirm my initial and repeat test results of the excessive voltage drop.

Any advice or comments? Thanks

Joe Tedesco, NEC Consultant

2017 / 2014 NEC & Related Books and Study Guides

#82646 - 12/05/02 01:00 PM Re: Question for the Council of Elders  
resqcapt19  Offline
Joined: Nov 2000
Posts: 2,148
You have to remember that these types of tests are giving you the voltage drop from the transformer to the spot where you are making the test. You sould first make the same test at the panel to find the drop on the service and then make the test at the remote location. The difference in the voltage drop between these two tests is the voltage drop on the branch circuit. If you have used the same tester on the other circuits, and didn't find an excessive drop, it is likely that there is a poor connection in the circuit that is showing the excessive drop. My voltage drop calculator showes that 80' of #14 NM should have about 6.2% drop with a 15 amp load and 7.75% at 100'.


#82647 - 12/05/02 01:08 PM Re: Question for the Council of Elders  
ayrton  Offline
Joined: Dec 2001
Posts: 201
It is very easy to over think problems like this. 9 times out of ten there is a bad connection. I would check the connections on the receptacles. Many times they are back stabbed which will give you problems every time. Think simple! If after wrapping the wire around the screws correctly, you still have significant voltage drop, there is more than likly a bad wire. Could be lightly chaffed somewhere. You probably won't find it.
Try running a fifty foot piece of romex from the same breaker and hook up a receptacle. See if you have the same problem. You probably won't
Remember sometimes over thinking will just give you a headache!

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