480 corner grounded delta service and new cnc machines

[gar]

210718-2418 EDT

Mitchell:

Why don't you call HAAS?

We have 7 HAAS machines all operating from a 240 V wild leg delta. One has been running almost 30 years. Others 20 to 25 years. On our machines I do not believe there are any input MOVs.

We have had some wild voltage problems when the connections at the pole transformers were bad. Just a few fusses blew.

The HAAS machines can be fed from either wye or delta, and various voltages via different taps.

.

 

[jim dungar]

High resistance grounding is not complicated but it is different.

And because it is different it may be very expensive and time consuming to install versus adding transformers to the OP's existing corner grounded system.
For example.
The OP system may be employing 2 pole disconnects, panels, and breakers, which would all need to be replaced. It is also possible the corner grounded conductor has been identified as white, as required by the NEC, which would also need to be addressed.

 

[zbang]

We have 7 HAAS machines all operating from a 240 V wild leg delta. One has been running almost 30 years. Others 20 to 25 years.

That may be your answer- they're 20+ year old machines and doubtless the controls are different. (And the OP did call Haas, who said No.)

 

[gar]

210718-1150 EDT

zbang:

In the first post there was no mention of what the HAAS serviceman said. And we do have newer machines from HAAS. Input to HAAS is delta. I will have to look in the manual and see if there is any indication of MOVs, or voltage limits at the input.

.

 

[kwired]

I have seen a couple post from this forum about corner grounded delta. They have answered some of my question but not really give an answer or solution to the problem I am having.

Story:
We are a small prototyping and engineering firm that ust to be a general machine shop with welding, cnc and fabrication throughout our plant. We have found a great niche and have been growing for a couple years. The building is quit old and after calling and testing the incoming service this is what we have. After the past week of research have found out that Incoming from POCO is 480 3 Phase Delta. In the electrical room it is switched to 480 corner grounded delta where one leg is carrying the neutral and a load. This has never really been an issue in the past since most of the equipment was welders, pumps, motors, and manual lathes that really never had VFDs or servo amplifiers within the machine.

Over the past couple of months we have started purchasing new CNC lathes and mills. Brand new Haas VF5ss is being installed. Install tech from Haas is testing incoming before turning machine on. Phase to Phase is all great 480 479 478. Then leg to ground 480 479 0. This is coming from the corner grounded delta that is feeding the buss. Not sure if it is B or C phase that is corner grounded. This normally would not be to big of an issue however the Haas machine VFDs and servo amplifiers probably require the 277 for surge overload and if a storm hits or we get a fault in on leg it will have the potential to send 480 surge instead of the 277. Any ideas on how to solve this or who to call that might have knowledge of possible solutions. Every electrician I call tell me I am dealing with a unicorn and that they cannot help. Machine is running fine and we cut power during hot part of the day in case POCO starts increasing voltages or if potential for storms are present. I maybe freaking out for nothing but I dont want to fry my machine. This is a huge investment for my small company. Any advice would be greatly helpful.

They probably have surge protection designed for use on 277/480 - so they maybe start clamping voltage around 300 volts or so to ground. If you connected to 480 corner ground and have been using, two lines have already been continuously clamping 480 volts to ground and probably have already burned up leaving you with no surge protection.