Electrical systems can be a bit like a puzzle – one that requires all the pieces to fit just right. If you’re gearing up for the Oklahoma Electrical Exam, understanding the specifications for copper grounding wire is a crucial part of the overall picture. Let’s break down the details around the smallest size copper grounding wire allowed for a 480/277V feeder running at 400A—because knowing your stuff helps keep both people and property safe!
So, what’s the answer? It’s #3 AWG. Yes, that’s correct! According to the National Electrical Code (NEC), when it comes to grounding conductors associated with service conductors over a certain amperage, specifically those above 200A, there are set minimum sizes you need to adhere to. And guess what? For our scenario here, a 400A feeder requires a copper grounding conductor that measures in at no less than #3 AWG.
Now, why is this #3 AWG grounding wire so important? Well, think of it this way: In the world of electrical systems, grounding wires are like the safety nets. They provide a crucial path for fault currents, allowing them to get back to the ground safely. This is particularly vital in high-amperage setups like our 400A feeder. If something goes wrong—say, a fault occurs—having the right size grounding wire can help prevent shock hazards and damage to equipment. That's a relief, isn’t it?
But wait, don’t just take my word for it! Look at NEC Table 250.122; it’s literally a blueprint for safety. This table outlines what size grounding conductor is needed based on the feeder's rating and usage. And for a 400A feeder system like ours, that #3 AWG copper wire comes through once again as the minimum size. This won’t just meet the requirements; it ensures that the electrical system functions smoothly—no surprises lurking around the corner.
Now, you might be wondering, “What would happen if I used a smaller gauge?” That’s where things get a bit dicey. A smaller grounding wire may not be able to safely handle the fault currents, which could lead to a host of problems. We’re talking potential electric shock hazards or even equipment damage. And let’s be honest; nobody wants to deal with that!
As you prepare for the exam, keep this grounding wire size close to your heart. It’s not just random trivia; it's critical knowledge that reflects real-world scenarios. So, as you study the NEC requirements, take a moment here and there to visualize how these rules apply on-site. Imagine the wires, think about their role in keeping everything running smoothly, and remember how essential they are in the big picture of electrical safety and reliability.
In summary, you know the drill: for a 480/277V feeder operating at 400A, the smallest size of copper grounding wire required is #3 AWG. This choice not only complies with safety regulations set forth by the NEC, but it also plays a pivotal role in protecting lives and equipment. So brush up on those details, and go into that exam confident, because you’ll have grounding wires covered!