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	Subject - Upsizing nuetrals RS377 Just wondering, how many of you guys up size the nuetrals on things such as cubicles being fed with three circuits sharing a common nuetral? I've always been taught thats the way you do it, but I'm working with a new company who seems to be on the ball and they don't. Ryan_J I agree with you...I think it is a good practice. lctrc789 We just had a office meeting on this last year. Should we up the neutral size to # 10 wire if we are using #12 for hots. We even asked some of the engineers and they said, WHY? Some of the neutral in a large office building had been done that way, They had discussed this and came to the conclusion if you have three ungrounded circuits using # 12 and no voltage drop and common circuits, why would you increase the neutral it is balanced and pulls a lot less amperage then the hot wires but never more then 20 amps on a breaker. I have seen this done and unless you are derating IMO I don't think it matters unless it is in specs and they pay for it that way. Any body else have a suggestion for RS377. Ryan_J Pat: The issue here is harmonics. Think of the amount of 3rd and 9th order harmonic loads in an office. Computers, fax machines, copiers, printers, monitors, etc... lctrc789 Thanks Ryan, but I did state that in a common circuit. I guess I should have been more clear, A dirty circuit. LOL If we have fax machines, copiers, Computers and electronic things we generally use a # 10 wire, for that reason. I don't know if you read the post I had in the Mitigating transformers section, but we did a large Compaq tech office a few years ago. In that office all the 120/208 loads were stepped down from 277/480 Harmonic balancing transformers with neutral readings on them. No matter how much, how little, or what we installed on these transformers we got a completely balanced neutral. The specs for this job was for #12 wires only and we questioned this, but these transformers were very new to all of us. We had all the elctrocnic ballast on these as well on different transformers in the main area. That is why I said common circuits should have been more clear. Sorry iwire Personally I think a lot of times up sizing the Neutral is a waste of time and is done because an engineer is just covering his butt. I was told by an engineer that I have great faith in that harmonic neutral current is limited to 1.73 times the phase current. Given that the circuits that feed harmonic loads are generally lightly loaded you could not overload the neutral. In the office buildings I work we end up with only 3 or 4 PCs on each circuit which means about 3 to 6 amps on each circuit. PCs never draw the load stamped on them. You would have to use all the power supplies outputs at the same time see the nameplate amps. If the specs ask for 10 AWG neutrals we will of course comply and make money doing so.....even if it makes little difference. All that aside we often run 10 AWG for all conductors of 20 amp circuits due to derating for raceway fill and to combat voltage drop due to length. Bob JerryB52 I've worked on quit a few school board projects here in South Florida. In many of the new schools we pull separate neutrals for all the circuits dedicated for computer loads. All of the lighting is 277v. This being the case, how can there be harmonics on the load side of the 120/208 transformer, that supplies the 120v computer circuits? Scott Vickrey I worked at a research facility that had #8 neutrals pulled in for multiwire 20 amp #12 circuits. The wiring had to be pulled in before the 60's. When I first saw the wiring it had me rethinking my beliefs. I would love to have heard their reason for that but, since the place was packed full of EEs I decided to let it go. Pierre Belarge Upsizing the grounded (neutral) conductor does not eliminate the harmonics, if harmonics are present, it helps for the neutral conductor to carry the larger neutral current that will be present. Pierre lctrc789 Pierre, I agree with you on tis one. It may help the current back, but does not stop any harmonic imbalance. I am still researching those mitigating transformers and to date I cannot get answers on them. We just recently bid on a job again at Hewlett - Packard which was Compaq at the time. I want to get back in there and see what the name of these transformers was. iwire The easiest way to avoid harmonic currents is to feed the non-linear loads form single phase transformers. A 480 - 240/120 transformer used to supply non-linear loads will not see any harmonic currents as the phases are 180 degrees apart so they cancel each other out. lctrc789 Bob, good point but many times the job has been already bid and they almost always call for three phase transformers. I think it is a matter of engineering and design, and sometimes they should let some of the guys in the field to do their own.... LOL