240 Delta ungrounded

[Fordean]

Viewing a panel in a shop.
Looks like a welding type panel.
3 phase coming in from street with no neutral/ground
240 volt 3 phase. I tested lugs. A-B = 240, B-C= 240, A-C=240.

They have a grounded bus with a ground, I'm guessing to a water pipe, Dont see ground rod. But still no
neutral ground from street.

I tested A- Ground= O volts, B-Ground= 240 volts, C-Ground=240 volts. Why is A =0 volts.

I plan on hooking 2 - 2pole 1 phase battery chargers @ 240 volts
1 - 3 phase @ 240 volts.

Is their a problem here with hooking these chargers up to this system. ?

 

[zbang]

You probably have a corner-grounded delta system, where A is the grounded conductor (what color is it?). Is it using 2- or 3-pole breakers for 3-phase feeds? You can also look for a bond from the A phase to the grounding system. Or call the PoCo to verify the service type there.

The single phase chargers may be alright but the 3-phase may not- it depends on whether it needs a wye-connected feed with under 150v from phase leads to equipment ground. Check the chargers' instructions or call the manufacturer for that.

 

[augie47]

You need to double check the source (POCO can help) and see exactly how the transformer secondaries are connected.
As zbang notes, you likely have a corner grounded 240v system with one phase purposely grounded OR you a 240 system with one phase accidently grounded.
Unless the equipment requires a neutral it will likely be fine.\
(If its a ungrounded system, you should have grounde detection per 250.21(B)}

 

[don_resqcapt19]

Viewing a panel in a shop.
Looks like a welding type panel.
3 phase coming in from street with no neutral/ground
240 volt 3 phase. I tested lugs. A-B = 240, B-C= 240, A-C=240.

They have a grounded bus with a ground, I'm guessing to a water pipe, Dont see ground rod. But still no
neutral ground from street.

I tested A- Ground= O volts, B-Ground= 240 volts, C-Ground=240 volts. Why is A =0 volts.

I plan on hooking 2 - 2pole 1 phase battery chargers @ 240 volts
1 - 3 phase @ 240 volts.

Is their a problem here with hooking these chargers up to this system. ?

This appears to be a corner grounded system (as others have suggested), but the part I put in bold is confusing to me. While a corner grounded system can have a grounded conductor bus in the panel, that is typically only seen where 2 pole breakers are being used. It would be very unusual to have a grounded bus in a corner grounded system that uses 3 pole breakers.

Of did you mean an equipment grounding bus and not a grounded bus.

Note that corner grounded systems do require a connection to a grounding electrode and must have a main bonding jumper.

 

[wwhitney]

With a high impedance meter, can you distinguish between a conductively grounded conductor (intentionally or accidentally) and a conductor that happens to be more capacitively/inductively coupled to ground than the others?

Cheers, Wayne

 

[__dan]

You need to double check the source (POCO can help) and see exactly how the transformer secondaries are connected.
As zbang notes, you likely have a corner grounded 240v system with one phase purposely grounded OR you a 240 system with one phase accidently grounded.
Unless the equipment requires a neutral it will likely be fine.\
(If its a ungrounded system, you should have grounde detection per 250.21(B)}

This ^^^.

When there's any doubt I usually always want to physically see the main bonding jumper or system bonding jumper, is physically installed as intended. Found more than few few floating or haphazardly grounded systems when checking flaky meter readings. There is usually a factory bar in the main switch, insulated neutral bus to the can, which I've found remaining in the factory shipping condition which is to float the neutral. The main bonding jumper should be in the main switch.

240 delta was a rare but standard system. The utility would provide 240 delta three phase three wire, and the corner grounded delta would use two pole breakers and a solidly connected grounded conductor. Red leg 240 delta four wire was also a standard system and if that was floating (or maybe even grounded at the pole) you would get 120, 120, 183, *or* 0, 240, 240 if A was faulted without being noticed. Could be red leg delta at the pole but floating and corner grounded delta at the customer's equipment. Have to physically see the MBJ to be sure.

Deltas and floating systems are poorly understood, so it could be many years before something that needs to be found ... gets looked at.

Any floating system I would automatically assume the first ground fault may already be present, which is why I want to physically see the MBJ.

The charger wants a solidly grounded system. Should be OK with one or two high legs 240 V to ground, but only the phone call to the factory can answer that. It has surge suppressors connected line to line (maybe) and line to EGC (always).

 

[Phil Timmons]

This equipment and site have be getting as old as we are. At least as old as I am. And I am not young anymore.

This stuff is likely from some prior Century? ;P Sort of joking, but this is from back in the 1960s, or at newest 1970s?

Folks sometimes forget that EVERYTHING on the Grid and including the customers service equipment has a Service Life. 25 to 50 years is what most equipment (transformers, insulators, cables) are rated to last. But sometimes things just hang around until they fail or break . . . because they are still working . . . and that fail is not good for anyone.

You may want to check with the local Utility and see if they would like to upgrade this museum piece of antiquity to something more of this century, so some clueless kid in the maintenance department does not have to try work or repair some of this mess at 2 AM on a Sunday Morning (time here now ) when it all finally breaks next month

 

[ptonsparky]

We still have these 240 systems for small irrigation wells in the area SE of me. Most about 20 HP +-. Slowly disappearing.
I have only worked on two corner ground 480 systems. One installed in the 50s and one in the late 80s of the last century. Both still in use AFAIK.

 

[zbang]

You may want to check with the local Utility and see if they would like to upgrade this museum piece of antiquity

What's in it for the PoCo? Sure, they may replace it, but very few will be willing to do it for nothing. Consider that a few parts of the country still have real two-phase service because the utility will charge the customer $$$$ for changing it.

 

[electrofelon]

What's in it for the PoCo? Sure, they may replace it, but very few will be willing to do it for nothing. Consider that a few parts of the country still have real two-phase service because the utility will charge the customer $$$$ for changing it.

I could see the POCO having an interest in getting rid of it. I once had an ungrounded 600 volt Delta system to upgrade. The utility wanted it gone and did their end for free, upgraded to 800 amp 208y/120. I think the utilities want standardization now, they don't want these oddball transformers and PT's that might need upgrade or servicing.

 

[Phil Timmons]

What's in it for the PoCo? Sure, they may replace it, but very few will be willing to do it for nothing. Consider that a few parts of the country still have real two-phase service because the utility will charge the customer $$$$ for changing it.

PoCo has a repair and replace budget, as well. Part of on-going operations. Consider that very real Service Life issue? If everything (other than the concrete) has a Service Life typically of 25 to 50 years -- that means they are already replacing to 2% to 4% EVERYTHING (poles, wires, transformers, switches) any given year, anyway. You follow the math? Means everything is constantly being re-newed everywhere every-year, anyway. Add some growth of say 1%, and a busy area may have 5% new every year.

Exceptions (and bad examples) might be California, where some morons got cheap, did not keep the Overhead High Voltage maintained and set Billion Dollar forest fires. Not only did they kill people, cause Billion of Dollars of damage -- they also have to do massive repairs now which cost FAR more just keeping things up and running.

Our (Texas) Grid operators tend to be very responsive and very favorable to local upgrades WHEN there is activity and growth in an area. They are motivated to sell MORE electricity, after all. Jumping back towards the OP scenario -- battery charger -- consider Tesla Chargers. Back when they were still allowing 100 Amp chargers to be installed in homes (I think they have dropped to 60 Amp max, now) -- we would call the local PoCo, and they would look up the local neighborhood transformer loads, and if was marginal, and the transformer was 10 or so years old -- they would just schedule a R&R on the Transformer. But this is easy for the Grid Operator to cost justify, as it was increasing growth, which means increasing Cash Flow, which gives higher O&M budgets.

I have worked areas where there is not any growth or even declining use -- those operators tend to have tighter budgets. Some older northern "Rust Belt" areas would tend towards that. But even down here we have some older stuff and hand-me-downs. Have put Solar (yeah, no joke) on Oil Fields with corner grounded 480V Deltas. We just use buffer - interface transformers (site owner-operator owned and budgeted) in between to match things up.

[add on edit -- You know of areas with still operating 2 Phase (Hot-N + Hot-N 90 Degree) systems? I was telling some of a crew about that last week. I usually do lunch time card-board and marker chats for lunch when they let me play in the field. Youngsters seem to like all that learning stuff. ]

 

[Jraef]

I think it depends a lot on what equipment they have available. For example around here they still offer straight 240V delta or 240/120V “high leg” delta services up to a certain size, because they simply use the same transformers that they would use for single phase 120/240 service drops and configure them for a 3 phase bank. If for some reason you want something bigger than they can accommodate at 240V, they simply tell you that you are going to get a 12kV drop and you can get whatever transformer you want (in which case you own the transformer, losses, maintenance etc., but you get a lower rate).

 

[zbang]

You know of areas with still operating 2 Phase (Hot-N + Hot-N 90 Degree) systems?

Center City Philadelphia and as I understand a small part of Hardford CT. You can find some threads around here talking about them.

Relevant to that- The utility doesn't generate 2-phase anymore, they make it with a Scott-T transformer and deliver that to the customer. Customers then often turn it right back into 3-phase with another Scott-T; the writers said that this was cheaper than paying the poco to change their service.

PoCo has a repair and replace budget, as well.

But they don't always, and why change something that's turning the meter unless they have to? Depends on the poco, the service type, and the customer, of course. An ungrounded 240v delta can be made with the bog-standard transformers that they would have anyway.

 

[Phil Timmons]

Center City Philadelphia and as I understand a small part of Hardford CT. You can find some threads around here talking about them.

Relevant to that- The utility doesn't generate 2-phase anymore, they make it with a Scott-T transformer and deliver that to the customer. Customers then often turn it right back into 3-phase with another Scott-T; the writers said that this was cheaper than paying the poco to change their service.


But they don't always, and why change something that's turning the meter unless they have to? Depends on the poco, the service type, and the customer, of course. An ungrounded 240v delta can be made with the bog-standard transformers that they would have anyway.

Thanks, that is interesting. Very different world, as we tend to have good budgets because everything is in "growth" mode -- rather than static survival, or even in reduction.

I suppose the cheapest system is a 240 Delta "High leg?" They tend to be an "open delta" in the olde areas around here. Only uses two transformers, and you can sell the single phase directly to other customers?

 

[zbang]

Thanks, that is interesting. Very different world, as we tend to have good budgets because everything is in "growth" mode -- rather than static survival, or even in reduction.

Not as much survival but installed-base, could call that static- when there isn't a reason to spend $$ changing things, they don't change. And regardless of "service life", lots of poco's will run things until they fail since that costs less than scheduling outages to make replacement.

There's a lot of "it depends" going on.

I suppose the cheapest system is a 240 Delta "High leg?" They tend to be an "open delta" in the olde areas around here. Only uses two transformers, and you can sell the single phase directly to other customers?

Some areas have a lot of high-leg delta, exactly for that reason- drop in a large single-phase xformer for everyone and a smaller one to get the high leg for the 3-phase customers. It's especially popular in dense mostly-residential areas with a smattering of commercial customers that need 3-phase (and those customers usually need 3-phase for motor loads).

 

[kwired]

This appears to be a corner grounded system (as others have suggested), but the part I put in bold is confusing to me. While a corner grounded system can have a grounded conductor bus in the panel, that is typically only seen where 2 pole breakers are being used. It would be very unusual to have a grounded bus in a corner grounded system that uses 3 pole breakers.

Of did you mean an equipment grounding bus and not a grounded bus.

Note that corner grounded systems do require a connection to a grounding electrode and must have a main bonding jumper.

You can still have three pole breakers and grounded conductor bus. The rule is the grounded conductor must be simultaneously switched with the ungrounded conductors. For 240 volt rated panels/breakers this might still be preferred as it is easier to acquire 3 pole breakers than it is to acquire 2 pole that are straight 240 rated.

There still somehow needs to be a system/main bonding jumper on the grounded conductor and separate EGC's run with feeders/branch circuits though.