Top Document: Electrical Wiring FAQ (Part 1 of 2) Previous Document: Bonding requirements Next Document: Why is one prong wider than the other? Polarization See reader questions & answers on this topic! - Help others by sharing your knowledge Testing grounds is a tricky and somewhat dangerous process. Testing for continuity is not enough. Nor is simple resistance testing. We will outline some possible approaches, but if you're the slightest bit uncomfortable, don't even think of trying these procedures. For a ground conductor to be good, the resistance must be "low". It must also be robust enough to withstand an overload long enough to allow the fuse or breaker to trip. The electrical code states, as a general principle, that the resistance of the grounding conductor be such that 4-5 times the current of the breaker rating will flow. For example, if your breaker is 15A, the grounding conductor's resistance should be low enough to permit 60-75A to flow - around 2 ohms maximum at 120V. For comparative purposes, 1000' of 14ga wire is 2.5 ohms. The difficulty in older homes is that the grounding conductor's condition may be that even though the resistance is < 2 ohms, a ground connection may blow out before the fuse/breaker goes, leaving the case of the appliance that just shorted out live. Therefore, you have to measure both the resistance and it's ability to stand up to load. One simple way to perform a "real" test is dead short the hot to ground and see if the fuse or breaker trips. This is, unfortunately, _extremely_ dangerous. The fuse might explode. The breaker may malfunction. You may get sprayed with molten copper. You may start a fire. You may get electrocuted or blinded. So don't even think of trying this. One moderately safe approach is to connect a 100W lightbulb between hot and the ground you wish to test. The lamp should light fully. If you have a voltmeter, test the voltage between the ground and the neutral. You should see less than 2 volts. If the voltage is much higher, or the lamp dims, disconnect it quickly - the ground may be overheating somewhere. The ground should be checked for poor connections. Testing a grounding electrode is a somewhat different matter. The codes aim for a dirt-to-electrode resistance of 25 ohms or better. One moderately safe way is: - turn off the main panel - turn off all of the breakers - disconnect the grounding electrode from the rest of the system. (often just a bolt in the panel) - connect a 5A fuse between the output of one 15A breaker and the grounding electrode. (use a 5A automotive fuse in a pigtail holder) - turn on the main breaker and the single breaker connected to the 5A fuse. - if the 5A fuse blows, your ground is good. User Contributions:Comment about this article, ask questions, or add new information about this topic:Top Document: Electrical Wiring FAQ (Part 1 of 2) Previous Document: Bonding requirements Next Document: Why is one prong wider than the other? Polarization Part1 - Part2 - Single Page [ Usenet FAQs | Web FAQs | Documents | RFC Index ] Send corrections/additions to the FAQ Maintainer: clewis@ferret.ocunix.on.ca (Chris Lewis)
Last Update March 27 2014 @ 02:11 PM
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I bought a new receptacle and installed the same. I still have no power I suspect there could be a bigger problem,this is aluminum wiring.
I've killed the breaker and call an electrician but am curious as to what happened.P.s. there is a dimmer switch on the same circuit.
I have multiple switches to lights. Ran 12/2 and 14/3 into switch box and inspector wrote correction needed.
What should I have done instead?
thank you
dennis
Ex: 15 amp-14awg. 12awg-20amp only rule for thumb other factors such as continuous load,heating and others if you do not know the safe NEC rules then please call a qualified journeyman Electrician better be safe