Floating Neutral 1

[SomeYahoo]

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!

 

[Senselessticker]

If I understand you correctly....I believe the wiring is correct. There is no neutral needed to achieve 208 single phase. Two phases and ground is all that is needed.

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.

 

[SomeYahoo]

I guess my concern with the wiring to ground was the potential for 120V loads within the laundry unit (controllers, lights, etc.) which would cause the ground to be a current-carrying conductor. I don't believe that is allowed/acceptable.

I'll take a look at the NEC section mentioned. I didn't realize there was ever a reason not to bond the two.

 

[Senselessticker]

Verify the neutral upstream of the panel is bonded somewhere (perhaps at the secondary of a transformer or in another panel). Use your neutral to achieve 120V single phase....phase, neutral, ground as apposed to phase, phase, ground with 208. In either case...the equipment ground wire is not a current carrying conductor if installed correctly.

 

[rbulsara]

Gensetguy:

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.

 

[davidbeach]

For many years (it started as a way to save Cu. during WWII and finally came out of the code about 1999) it was permissible to dryers and ovens/stoves to derive their 120V control by connecting between one phase and ground, saving the need for a neutral (but putting normal load current on the ground that isn't supposed to have any current except during faults). In the appliance, the neutral would connect to the ground, and only the ground brought out. Since the change, all new installations are supposed to include a neutral in the circuit and all four conductors be included in the cord.

 

[itsmoked]

GensetGuy; Reading all the responses "I" understand it all just fine, but I think some people could be confused.

Are you clear on this?

 

[SomeYahoo]

Thanks for all the responses folks. I think I understand now, but will summarize to clarify what I am thinking.

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?

 

[itsmoked]

Yes! With just a wee bit more clarification.

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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!)

 

[resqcapt19]

To get to code on similar (new) installations, a four wire connection should be used.

Only if the equipment is designed for line to netrual loads. If the equipment is designed only for line to line loads there is no reason to bring the neutral to the equipment.
Don

 

[DanEE]

"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)

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..

 

[itsmoked]

Hey DanEE, Why did you find that problem? What was it doing/causing? I'm curious.

 

[DanEE]

Actually wasn't causing an operational problem, but the concern was a code and potential safety issue.

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.

 

[itsmoked]

Thanks DanEE.. Was just curious to know if it was discovered thru malfunction. But I see it was not. Thanks.

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.

 

[ITSTOAST]

The NEC prohibits any connection between the ground and neutral anywhere but the service entrance...with some exceptions. As DavidBeach mentioned NEC (Sec. 250.140) makes an exception for existing laundry equipment, otherwise the homeowners would have to rewire their homes when they got a new appliance if it only came with a 4 wire plug.
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.

 

[abcd3286]

OK here is how it SHOULD be done in modern era.

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.

 

[ITSTOAST]

Or pull a neutral to all the units from the panel. I think there is a good chance the motors are 120 volt and a tranformer isn't feasible. It appears you meet the requirements of the NEC as tens of thousands of old laundries are in this situation but I would recommend getting a reputable electrical contractor to advise you of your options.

 

[itsmoked]

You guys are thrashing a month old post... Probably a done deal by now.[flush]

 

[ITSTOAST]

Sorry, I got caught up in the moment.