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  1. #1
    Join Date
    Mar 2001
    Posts
    475


    We do primarily residential work, but we do deal with some commercial. I was installing a 3 phase condenser and notified my boss that there was no ground coming into the disconnect box. He told me 3phase units do not need a ground. This doesn't make any sense to me. This doesn't make any sense to me. I fired the unit up, but I am worried we may be held liable if someone get hurt. Have any of you heard of not grounding 3phase units. It would be a new one for me.

  2. #2
    Join Date
    Dec 2003
    Posts
    1,739
    If your boss said that, GO find another boss. He is dangerous. There are such things as three phase non-grounded services, but I doubt that you would ever encounter one unless you were in an industrial park, and they have special provisions such as ground fault detectors. Anyway, ALWAYS ground!!! if this is not,, maybe you better have the owner call an electricain, it may not be grounded at the disconnect. Improper grounding is as dangerous or worse than no ground at all. A high percentage of all electocutions are ground fault.
    there but for the grace of god, go all of us

  3. #3
    Join Date
    Dec 2003
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    1,739
    You are talking about the groundING conductor right not the groundED conductor??? The groundING conductor is the one that is the return path for ground faults and is normally the green wire or the bare wire. The groundED conductor is the one a lot of people call the neutral or white wire. This is part of the normal current flow. Normally your units are either 208/240 or 480 three phase and these do not have a groundED condcutor, but are required by law ( in all states that accept the NEC as law) to have a groundING conductor.
    there but for the grace of god, go all of us

  4. #4
    Join Date
    Jul 2000
    Location
    Dallas,Texas
    Posts
    4,956
    Your boss is a repository of copious quantities of fecal matter.

    Section 250 of the NEC specifies grounding and bonding requirements. 3 phase is not excluded.

    It may be that the equipment is grounded thru the conduit. That is legal...though not a top quality job.

  5. #5
    Join Date
    Sep 2002
    Location
    Hampton Roads, Virginia
    Posts
    1,604
    Many old buildings used the metal conduit has the groundING conductor.
    "Profit is not the legitimate purpose of business. The legitimate purpose of business is to provide a product or service that people need and do it so well that it's profitable."

    James Rouse

  6. #6
    Join Date
    Dec 2003
    Posts
    1,739
    I agree conduit is allowed, but you have to remember that every single screw or compresson fitting is absolutely tight. So you are relying on no vibration, or sloppy workmanship. I always run a grounding conductor in the conduit. Rigid is a different story. This is only my opinion though. IT is completely legal and code compliant.
    there but for the grace of god, go all of us

  7. #7
    Join Date
    Jul 2004
    Posts
    44
    I take care of several buildings 208 and 480 3ph that has no ground. It's grounded through the coduit. when I replace a unit and there is no ground I still run one from unit to ground lug in disconnect.

  8. #8
    Join Date
    Dec 2003
    Posts
    1,739
    That is worth the effort, I think anyway. Be sure to clean the paint off the disconnect if you are attaching the lug yourself, and make sure the lug is tight in the box. Loose connections are like arc welders if a ground fault should occur.
    there but for the grace of god, go all of us

  9. #9
    Join Date
    Dec 2002
    Posts
    603
    Dave, Here is more information: From the main central distributibution panel there goes 5 wires to the subpanels. 4 current carrying wires are 3 phase wires and neutral wires. Safety ground is a spearate wire which also goes to the central grounding bar like neutral wire. The difference of neutral and safety gound wires is that neutral wire does carry current in normal operation (the difference of currents taken from each phase) but safety ground does not carry any current in normal operations. This separation guarantees that in normal operation the whole safety ground wire is in building ground potential. This 5 wire wiring system is basically good and it is used in most buildings and places where ground loops are expected to be a problem.

    All distribution of 3 phase voltage inside of building should be done using 5 wire system to avoid grounding potential difference problems. Distribution of 1 phase power should be done using 3 wire system. The safety ground wires should be interconnected in star or tree like fashion.

  10. #10
    Join Date
    Dec 2003
    Posts
    1,739
    good description shogun, one clarification on the 5 wire. If you are running a 208v compressor you would only need 4 wires abc phase and the grounding conductor. Or if pipe is used as grounding conductor, then only three wires would be present. In most or our applications the grounded ( or neutral) is not needed because there are no 120v or 277v applications. If your unit is 277v then it has one ungrounded (hot) conductor and one grounded (neutral) conductor and one grounding (ground or safety ) conductor. Some may say that using these names is not a big deal and it is not. But what if we called the suction line, the cold line, the big line , the sweat line, the gas line? hey I guess we do!! but it is easier if we all use the same language right?
    there but for the grace of god, go all of us

  11. #11
    Join Date
    Dec 2002
    Posts
    603
    Our ability to speak the same language is essental for understanding, interpretation, and the communication between parties. You hit on a very important subject in this profession, that's why its imperative that we always stress a knowledge of technical terms. We have people in this profession who speak many languages but when we speak to each other about our problems; we should speak only one langage. I believe all HVACR shools should stress more comrehension in the understanding of technical terms.

  12. #12
    Join Date
    Mar 2001
    Posts
    475

    In my area, we are only suppose to do electrical work from the after the disconnect. However, it is very common for installer/technicians to replace the box. I think this unit is extremely dangerous now. I was told to replace the disconnect. The metal conduit that went under ground and back up to connect to the disconnect was eliminated. We didn't use the conduit because we had to move the condenser. Now there is a plastic whip going to the unit. This is why I wish he would just subcontract out electrical when called for....
    The metal conduit was buried about two feet down, and the conduit going into the disconnect was definitely not grouned. So, by burying the conduit, was this the way the grounded the unit?


    [Edited by dave r on 07-30-2004 at 10:23 PM]

  13. #13
    Join Date
    Dec 2003
    Posts
    1,739
    Well now the unit does not have a grounding conductor, so any fault in the unit will absoulutely NOT fault to ground, so the breaker and fuse will not fail in a ground fault ( where the HOT wire touches any metal part of the unit) If that happens and someone touches it they may get killed. This happens unfortunately a lot. Most don't get killed. We had a few in the last 5 years, one touched a lamp post at a restaurant in OC maryland, dead on the spot. Bad vacation. IF you can use a metal disconnect, bond the box to the conduit, and the run a grounding wire to the unit. Use the same size condutor that the (hot) wires are. We can hope that the conduit is grounded, but if not you have done all that you can do. good luck.
    there but for the grace of god, go all of us

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