|
| Ek's Home | Forum | Chat | Electrical Links | |
| Subject - Dedicated Circuits | |
| ravengotu | Do dedicated circuits have to have a dedicated neutral also. or can it share the the 1,3,5 neutral etc... |
| lctrc789 | Ravengotu, Unless is is marked as a circuit with a dedicated neutral you can have three phases 1,3,5 on one neutral, which is still a dedicated circuit. With three phase balancing it is better to have three circuits one neutral IMO> |
| ravengotu | Thanks , this is a topic that we have had a few heated lunch box discussions about and even with some of the foreman.....and then throw in mc cable and now it gets even better....anyway thanks that was my answer as well.. |
| RS377 | quote: One thing to consider though, is that the customer may not be using the term the same way that you are. I work in the Silicon Valley, where a lot of customers want to have a dedicated hot and nuetral, so there will not be a voltage spike if the nuetral is lost. They may want a dedicated nuetral for every circuit for their servers, but think that they are telling you this by saying a "dedicated circuit". |
| lctrc789 | RS377, I agree, that is why I stated unless it is marked that way in specs or by engineer. When you do have the same 3 phases on one neutral you do take a chance of a spike if a neutral is loose. I have seen that happen if some one is working on a panel or J Box and lose a neutral. But rarely does it happen, with proper competent employees. Many specs do say one neutral per circuit many do not. I have bid a lot of jobs with the specs marked as such: All circuits (3 Phase) will have one neutral per three 3 such circuits that balance out, and a # ten wire to be pulled for all 20 amp circuits replacing the #12 wire for such circuits. Ungrounded conductors can be #12, Grounded conductors (neutral) shall be a minimum 0f # 10 wire. Engineers like us have different views to I guess. |
| RS377 | quote: I totally agree on an engineered job, that the plans will tell you exactly what to do. I should have made it more clear that I was speaking form more of a service work point of veiw where you may be adding only one circuit without an engineers support and guidance. |
| zapped208 | IMO, a dedicated circuit means totally separate from other wiring, no sharing neutrals, single or 3 phase. |
| lctrc789 | Zapped, it can go either way I guess. However i think it depends on the estimator on how you have to do this in a lot of jobs. If I can pull a 12-3 in a residential dedicated circuit and use both ungrounded conductors as a circuit and share the neutral I will because of the cost. The same as in a large job if I can run 6 cicuits in one 3/4 pipe and share the neutral(s) why not. Actually the 3 phase is more balanced if you do it this way.I know we all have different opinions and we are entitled to them. LOL |
| SteveMc | IMO customers usually want dedicated circuits to handle a new piece of equipment, like a copier, and therefore need the circuit to be able to carry the load. Since the neutral has little to do with the load carrying capability of the circuit, sharing a neutral shouldn't be a problem. |
| zapped208 | I guess what it really boils down to,is what type of circuit it ends up being,like type of equipment or electronics. I was thinking more of commerial/industrial rather residential. |
| lctrc789 | Zapped, I work in a pharmecuetical company everyday, all industrial and a lot of explosion proof type atmospheres as well. We almost always run dedicated circuits and very seldom use a dedicated neutral for them. Unless the engineer specifies it otherwise we don't. The cost and the money is what we look at, not the fact that a neutral could come loose and the get a surge. Many localities are different I know that and again it is all in what you beleive or want. |
| RS377 | quote: I usually do commercial, but, the residential work that I have done have amazing home theatres in them. Things like projectors and flat screen tlevisions that cost over ten grand demand the same respect as a server or other sensitive equipment. |
| zapped208 | RS377,- Yes I do install some dedicated circuits in residential too! 789,- Like i am trying to say , it all depends on what you are doing! |
| Ryan_J | If you guys are discussing an individual branch circuit, and I think you are, it is a defined term in the NEC.quote: In my opinion, it has nothing to do with the neutral. |
| Russell120 | It is not the semantics that matter but the physics. If you share a neutral with another circuit the hot wire of that other circuit will likely carry some of the load of that circuit. If you have two receptacles on a three phase system sharing a neutral. Each receptacle is on a different phase. Each receptacle has a 10 amp load with no harmonics. The neutral will only show a 2amp current, the rest of the circuit is on the hot wires. On a single phase system of course the neutral would have no current what-so-ever as the load is balanced at 180 degrees and the entire load would be carried by the hot wires. Therefore the fact that your receptacle has its own wire all by itself going to it, has nothing to do with it being dedicated from an electrical point of view. That engineers don't pay attention to this is because most of them don't think these things through, and simply use the specs and plans of the engineer they learned their profession from: with occasional updates from some continuing education program they took to keep there license active. If you do not give electronic gear its own ungrounded conductor back to the source (your panel), the gear is very much subject to what ever waveform distortions, etc. that the other equipment on their circuit impart to it. On office and home equipment this is usually OK. But in scientific or medical settings it can be a recipe for a disaster. Of course it would help if the engineers paid more attention to it, and gave clearer directions. |
| iwire | Russel I read your post and the thought that comes to mind is your own words.quote: I respectfully suggest you think this through. quote: A panel is not the source, a transformer can be called a source. All the circuits that are in the panel share the same neutral back to the source, this is not semantics. All the issues you raise about one load affecting the other are true, however that is also true if you run a separate grounded conductor or not. The panel does not magically clean up the power. The only way to provide absolutely clean power to a circuit would be with isolating equipment right at the load. If the specs simply call for a dedicated circuit, one leg of a multiwire branch circuit fits that description as defined by the NEC. If the person wanted a separate grounded conductor for the circuit they wrote the specs wrong.  If the person writing the specs wants a separate neutrals for the circuit they need to say that in the specs. A couple of ways I have seen it writen are the following 1) Multiwire Branch circuits shall not be used. 2) Each circuit shall have it's own neutral conductor. When you write specs they have to be cyrstal clear if you want to get what was in your mind. Bob |
| cs409 | good post iwire......boils down to just how u word it. be careful how u write something down, u may end up with what u do not want! now, if your a good installer/electrician etc, and u read what they ask for and you know what they ask for isnt what they want, then your real good LOL. |