L6-30R Floating ground when ground lug shows connection to earth ground.

[jim dungar]

Agreed.
All L#-L# are 240 plus/minus <5%
From Xfmr to panel only L1, L2, L3, and GND
any L# to GND changes based on what is connected or turned on.
No load all are in range of 105VAC to 138VAC
with loads random range is 11VAC to 198VAC

Thanks for your reply. I am just having problems convincing my coworkers and management that this is not correct.

If your transformer is a 3 wire delta output, you do not have the ability to feed L-N loads. Ungrounded delta configurations will show some amount of L-N voltage, but it is based on coupling capacitance and will vary based on several factors including unbalanced L-L loading.

 

[AAP]

Rare to have a true no earth ground system today. That said if you have a true ungrounded system you should have a fault monitoring alarm system installed to warn of a L-G fault as there is no way to trip the breaker on a fault to G. At bare minimum it should have one of there installed if not already there.

Most today are either corner grounded delta (giving 240 or 480 L-L with 120 or 240 L-G on 2 of the phase and 0V on the one L-G) or mid phase (center) grounded delta giving a high leg Delta (120/240/208)
Are you sure (tested) that these panels are still ungrounded? Seen many time the system over time had been changed and old labels never removed or modified.
If the facility had any general use receptacles (120V 15-20A) you must have somewhere along the system created a grounded (neutral) system.

Yes, this is a very old 240VAC 3Phase installation that someone later added the L6-30 to it without obviously realizing it was a floating ground.
But, thanks for the heads up on corner grounding. I believe this will resolve out problem in the most cost effective manor.

 

[AAP]

Agreeing with the above.

It sounds like the receptacles have a good connection to the supply EGC and to earth ground, but that the transformer source is not properly connected to ground. Because the source is not ground referenced, any test between the receptacle powered terminals and receptacle ground pin would show 'floating ground', even though the real problem is 'floating source'.

A good solution would be to replace the transformer with one that could have a grounded terminal. If your equipment only requires straight 240V, then either a secondary 240V delta with grounded center tap, or a secondary 240/139V wye would be fine.

I believe we will go with corner grounding for this panel. And move anything that requires 240/120 to another panel. I hope to convince the decision makers.

 

[AAP]

Why is any solution needed?
Maybe the system was installed with ground detection or it wasn't need at that time.
Maybe this is a labeling or training issue.

Yes, old installation was ungrounded delta.
later added L6-30 that works with most equipment.
New fault detection safety will not allow the new equipment to work.
Will make changes to improve safety.
Thanks

 

[jim dungar]

Yes, old installation was ungrounded delta.
later added L6-30 that works with most equipment.
New fault detection safety will not allow the new equipment to work.
Will make changes to improve safety.
Thanks

Any L-N(G) load on this system will be injecting objectionable current on the ground violating the NEC.

 

[AAP]

Another related question. It appears that and L5 or L6 installed in a residential panel would have 240V L-L and 120V L-G.
However in a commercial installation it would have 240V L-L and 240V L-G (sometimes 120V L-G). I don't necessarily see a problem, but was wondering if this is the norm?

 

[AAP]

Any L-N(G) load on this system will be injecting objectionable current on the ground violating the NEC.

Yes, Understood. I will be sure that the solution worked out with the electrician meets this requirement. My problem is not working with the electrician, but the ones paying the bills who prefer to do nothing.

 

[kwired]

I believe we will go with corner grounding for this panel. And move anything that requires 240/120 to another panel. I hope to convince the decision makers.

If you have any 120 volt loads in that panel you should have had some rather obvious problems for long time, unless they happened to be perfectly balanced across the non existent neutral at all times.

 

[kwired]

Yes, Understood. I will be sure that the solution worked out with the electrician meets this requirement. My problem is not working with the electrician, but the ones paying the bills who prefer to do nothing.

They need to be convinced how much the bills could potentially be if the problem isn't resolved, including potential wrongful death lawsuits.