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| Subject - Grounding system | |
| short circuit |
I'm a beginner would like to know more about the following can any body help me out 1. system grounding and the equipment grounding their application,and should they be bonded together. 2. how do we calculate or design the number and size of grounding rod to be installed in an certain project. 3. do we also bond the lightning protection system to the overall grounding system. |
| JimmyDee | 1st question, yes the code requires it. 2nd question, article 250.66 is a chart that gives the correct grounding electrode wire size. The size is determined by the size of the service conductors. Some common sizes are #2 or smaller should be #8 (#6 if subject to physical damage); #1 or 1/0 is #6; 2/0 or 3/0 is #4; and 4/0 through 350 is #2. Code now requires 2-8' ground rods at least 6' apart. There is an exception to this but it is not worth considering. 3rd question, article 250.106 says that the lightning protection system shall be bonded to the building steel or the structure grounding electrode system. So yes it does. (keep in mind that it still requires its own grounding electrode but they need to be bonded together.) Jim |
| tony thrower | where is the code reference that requires (2) 8' ground rods? |
| JimmyDee | 250.56 says that if the grounging electrode is not 25 ohm or less to ground, an additional ground rod is necessary. You will pay tons of money for the equipment for testing, have to write a report, sooo, just put in the second one and be done with it. It is code by inference. Jim |
| jackleung | For the second question, the calculation or design the number and size of grounding rod could be related to the protective devices in the electrical system. Since the grounding resistances count as a part of earth fault loop impedance, it should be kept small enough to ensure fast operation time of the protective devices. (Use of RCD may ignore this point). That's why, sometimes a large earth mat should be needed in some project with poor site soil resistivity. Earth mat calculation could be referred to IEEE Std80/2000. |
| JimmyDee | What Jackelyn is saying is usually only done on a large commercial building or factory. You as an electrician will never have to calculate these grounding systems. An electrical engineer with the designing architectural firm will be responsible for this. As an electrician, you will install it under the supervision of that engineer. For a residence, 2 ground rods and the underground water feed if it is a metal service is all you have to worry about. Jim |
| AlberKSpartan | listen to this man he knows what hes talking about! |
| jackleung | quote: Who is 'this man'? |