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	Subject - How to ground a 120V separately derived circuit. unsaint34 I need to hook up a 208v motor. The control panel will contain 120V control circuit and a 208/120V transformer. I looked through the code book to find what I should do as far as grounding the 120V control circuit. Should I just jumper one leg of the secondary to the control box enclosure? Before you say yes, let me tell you two reasons why I think that might not be legal. 1) The system is 120V, therefore it has be grounded, meaning, one of the legs (either X1 or X2) shall be connected to a grounding electrode. 2) Now, about the grounding electrode... The code 250.30 (A) (4) states that the electrode of a separately derived system has to be as near as practicable to the same area as the grounding electrode conductor conenction to the system. So, I was thinking I might have to run a wire (grounding electrode conductor) through the control panel enclosure, then run it to a nearest metal structure. Am I right? Am I wrong? Ryan_J What about the exception to 250.30(A)(2)? unsaint34 250.30 A (2) exception applies to class 1,2 or 3 circuit. I thought those classes were power-limited circuits, and do not include a 120V control circuit. (I believe the rating of the transformer that I am using is below 1000VA, but that doesn't matter because the same exception limits the circuits applied to the 1,2,3 classes, "AND" not over 1000VA.) Ryan_J I don't beleive a class 1 circuit is power limited, generally speaking. unsaint34 that's the part I am not sure of and it sounds like you are not 200% sure. Here is what found from http://www.electrician.com/eltrain/lpage103.html "Class 1 circuits are divided into two types (1) power-limited, or (2) remote-control and signaling circuits. Power limited circuits are limited to 30 volts and 1000 volt-amperes. Class 1 remote-control and signaling circuits are limited to 600 volts, but there aren't any limitations on the power output of the source. Class 2 and Class 3 circuits are defined by two tables, one for alternating current and one for direct current. In general, a class 2 circuit using 24 volts with a power supply durably marked 'Class 2" and not exceeding 100 volt-amperes is the one most commonly used." Doesn't it sound like the max voltage of a class I is 30V? rabbitgun You might want to take a look at NEC article 725 The information you posted is correct. Class 1 circuits can be both power limited or a remote controle / signal circuit. In your case you are not under the power limited requirements. Think of a fire alarm system initiation and notification circuit as a power limited type of circuit. Those circuits are limited to the 30v requirement. Ryan_J You're right, I'm not 200% sure. Hell, I'm not even half sure, but I'm looking at 725.23, and I think that is why the rules for a class 1 circuit are drastically different than class 2 or 3. For example, with a class 1 circuit, you must use a chapter 3 wiring method, not a cheesy low voltage cable. Another thing to notice is that class 1 circuits are not in table 11 in chapter 9. I'll be honest, I'm not a big low voltage guy, so take my responses with a grain of salt. lctrc789 unsaint, you either ground this at the steel or the nearest water pipe because your voltage coming in is above 150 volts to ground... 208 v lucky1122 firstly,the installation which you describe is not a separately derived system according to the NEC. A separately derived system is a premise wiring system not derived from the service,which also has no direct electrical connection to its source ,and supplies wiring or conductors which supply another system .The system also has a solidly grounded circuit conductor. The key here is in the definition of premise wiring. premise wiring provides wiring for power,lighting,signal and control ;however, it goes on to say that" ...such wiring does not include wiring internal to appliances,luminaires,motors,controllers motor control centers and similar equipment." This installation does not require a grounding electrode conductor connection to the nearest electrode according to the NEC. unsaint34 Lucky, After I read the definition of a separately derived system, I now understand that a separately derived system only refers to a premise wiring. Any control circuit out of a transformer, whether isolation or auto, that control circuit is NOT a separately derived system. And if I have some equipments running only by generators, that circuit is not a separately derived system. That makes things lot easier. Thanks for the input. unsaint34 Disregard my last post. According to the code definition, my 120V control circuit out of a isolation transformer is a premise wiring, therefore a separately derived system. Therefore, I need to ground it separately. I will run a wire from X2 to nearest suitable electrode. rabbitgun May I ask what size your control transformer is? I still don't think your answer is per NEC. I would like to clear this up before the thread dies with the correct answer. lucky1122 unsaint ,firstly go ahead and do what you think is best. secondly from what you wrote in your posting you seemed to be describing a control transformer that is in a control panel which provides a reduced voltage to operate the controls in that enclosure. According to the code text which is directly out of the NFPA 70 handbook ,2005 it clearly excludes those scenarios from bonding to building electrodes. Notice I did not suggest that you did not need a bonding system jumper to clear fault current .Moreover, an auto transformer is never a separately derived system and I didnt say that a generator could not be a separately derived system . The code criteria for a generator not being separately derived is based on the neutral conductors being solidly connected and not switched through the autotransfer switch.I suggest you give the article another read maybe out the handbook. If The transformer was outside the enclosure feeding motors and control circuits I would definitely ground it as it would meet the requirements of a separately derived system in that case.I read your posting again carefully to see if I missed something.In it you said ,"I need to hook up a 208V motor.The control circuit will contain 208/120V transformer."According to the code that does not meet the requirements for a separately derived system because,..." such wiring does not include wiring internal to appliance,luminaires,motors,controllers,motor control centers."If that were the case could you imagine the grounding electrode conductors that would be needed in an industrial setting. one more thing unless your facility meets the requirements of a supervised location and the water pipe electrode system is visible throughout its entire length you would have to go to within 5 feet of the water pipe electrode. Hope you have effectively grounded building steel thats available