Floating Neutral
Floating Neutral
(OP)
Found some wiring that disturbs me and want to get the experts' opinion on it.
System is a laundry facility, input power is 120/208 3-ph Wye. Washers/Dryers are 208V, 1-ph.
The concerns are that the units are wired hot, hot, GROUND (as opposed to neutral) and the neutral and ground are not bonded together in the box.
What problems, if any, should I expect with this wiring. Any potential safety issues?
Thanks in advance for the replies!
System is a laundry facility, input power is 120/208 3-ph Wye. Washers/Dryers are 208V, 1-ph.
The concerns are that the units are wired hot, hot, GROUND (as opposed to neutral) and the neutral and ground are not bonded together in the box.
What problems, if any, should I expect with this wiring. Any potential safety issues?
Thanks in advance for the replies!






RE: Floating Neutral
Concerning the neutral and ground not being bonding in the box...there are a number of reasons why/why not to bond. Refer to NEC 205.32 for an example.
RE: Floating Neutral
I'll take a look at the NEC section mentioned. I didn't realize there was ever a reason not to bond the two.
RE: Floating Neutral
RE: Floating Neutral
If you are measuring 120V from Hot to Ground in normal condition, it is "normal" as the neutral is grounded at the service as it should be.
There should not be any load connected between Line and the Ground. If the unit is factory built, all lights, controls etc. therein would be arranged to work on 208V or would have internal trasnformer/circuitary to handle it correctly. As long as you or someone else do not tamper with the factory built unit, it should be fine.
As already mentioned by senselessticker, G is not supposed to carry current in "normal" condition, but is supposed to carry the "fault" current, should the live (hot) wire goes to ground (case of the equipment, for example) directly. This allows the breaker/fuse to open before someone comes and touches the "hot" enclosure.
RE: Floating Neutral
RE: Floating Neutral
Are you clear on this?
RE: Floating Neutral
Ground and neutral not being interconnected is NOT an issue AS LONG AS they are bonded at the power source.
The unit is designed to be a 208V single phase system and therefore should NOT have any 120V single phase loads in the system. This would NOT have the ground wire carrying any current (outside of fault current) and therefore this is not a safety issue.
To get to code on similar (new) installations, a four wire connection should be used.
Do I have it right?
RE: Floating Neutral
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"Ground and neutral not being interconnected is NOT an issue AS LONG AS they are bonded at the power source."
It would actually be an issue to have the ground and neutral connected together ANYWHERE EXCEPT at the one point of entry! One point and one point only. (shades of Red Oktober)
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I do not believe you need four wire installations anywhere you have no need for a single phase neutral. Another words your present example can be duplicated in a new facility.
(Someone please confirm this!)
RE: Floating Neutral
Don
RE: Floating Neutral
ditto... we just corrected a problem with a downstream wiring distribution panel from a UPS having an "extra" neutral to ground connection.
Had neutral current dividing to any and all parallel ground paths (green wire and metal conduit) from the panel with extra ground strap back to the the power source..
RE: Floating Neutral
RE: Floating Neutral
This is one of those situations we don't particularly care for, but run into where some customers hire us to do only the initial UPS installation, bypass switch and supply connections, and have their own electricians do the downstream wiring.
Turns out that when their electrician later installed the distribution panel down stream of the UPS, he put the neutral to ground strap in the panel and, that of course provided the path for neutral current to divide across the metal conduit and green wire paths back to the UPS.
This particular ferroresonant transformer based UPS provides the one (and should be only) neutral to ground XO connection on the secondary output side. The UPS documentation is quite clear on this.
We were called back to the site to replace the external UPS bypass switch that had failed (about 3 years after the original installation) and that is when the ground current was noticed.
By the way, the bypass switch failure had nothing to do with the wiring problem. This is the second bypass switch we've had fail (running considerably below max kva rating) from this particular manufacturer and believe there is an issue with insufficient torque on the screws (have found some far too loose) attaching the internal wiring at the bypass switch. The connections start heating up and ultimately cause the switch to fail.. or might be vice versa..
We have brought this to their attention and, also fully open up these bypass units, check and re-torque the internal connection screws.
RE: Floating Neutral
I bet loose connections are 50% of most switch, starter, fuse, breaker, and receptacle problems. Loose is soooo bad for things electrical. I always run away when my refrigeration buddy starts tightening lugs. I always expect high velocity plastic shrapnel. He sez he hates call backs for smoking/destroyed contactors. He never gets them, while his compatriots get them occasionally.
RE: Floating Neutral
The neutral and ground should be bonded at the service and at the dryers' junction blocks for existing systems. This can not be done on new installations as far as I am aware.
RE: Floating Neutral
At service
the GROUND (green) is bonded to the grounding system (stakes water pipe etc).
The GROUNDED (white) aka Neutral is bonded to the ground at the service ONLY.
THIS is the only place they are connected.
All subsequent panels (sub panels) have GROUND (green) going to a bus bar that is bonded to panel. The GROUNDED (white neutral) is connected to a bus bar NOT bnded to panel.
Your dryers (if they have no 120V components) do not need a neutral. Only two (or three if 3 phase unit) phase conductors and GROUND (green).
IF they have a 120 V load (motor control ckt etc) then you need a neutral. Technically you need you phase conductors plus GROUNDED (neutral white) and GROUND.
OK that is modern.
IS it dangerous to have the GROUNDED (neutral) tied to the dryer frame. Well yes and no. IF no one is messing with the wiring it is OK. Soon as someone lifts the neutral at the panel the neutral could be hot (if it is supplying a load ie carrying current)
Now for what you need to do.
Determine if dryers have any 120 loads. If so this will generallly be the motor. You can reconnect the motor (maybe check the label on it to see if dual voltage) to 208.
If it is control voltage then you can supply this with control transformer - ground the secondary. You can do this update as you go - especially as you upgrade or rebuild units.
USe green tape to remark the neut at BOTH ends - if fed from subpanel move neut to the ground bar.
RE: Floating Neutral
RE: Floating Neutral
RE: Floating Neutral