Transformers Delta / Wye

[Buck Parrish]

I am installing two 225K and three 150K. 480 Delta to 120/208 Wye

There is no building steel to bond to. Water lines are plastic. Some one was telling me to install a ground rod at each one. To me that didn't seem correct.
I thought all I need at my primary is the three phases and the equipment ground. Then some body else is saying well pull a neutral and an equipment ground on the primary?.

Since each location is a newly derived electrical system. Must we isolate the grounds on the secondary disconnect / 200 amp 3 phase panel

Which is correct? Or maybe both ways are correct, or neither?
.

I've also been told I can adjust the 208 volts on my secondary. To a higher voltage. What are your thoughts on that?

Thanks for the help in understanding the inner windings of the transformers

Thanks

 

[iwire]

I've also been told I can adjust the 208 volts on my secondary. To a higher voltage. What are your thoughts on that?

Not without raising the 120 as well.

I will post the code sections for the other questions shortly.

 

[iwire]

You said the interior water pipeing is plastic but does the building have a metal water service?

250.30(A)(4) Grounding Electrode. The grounding electrode shall
be as near as practicable to, and preferably in the same area
as, the grounding electrode conductor connection to the
system. The grounding electrode shall be the nearest of one
of the fol1owing:

(1) Metal water pipe grounding electrode as specified in
250.52(A)(1 )

(2) Structural metal grounding electrode as specified in
250.52(A)(2)

Exception No.1: Any of the other electrodes identified in
250.52(A) shall be used if the electrodes specified by
250.30(A)(4) are not available.

 

[Buck Parrish]

The fire sprinkler is water when it first comes in the building. I'm pretty sure it goes back to plastic under the slab, too.

 

[__dan]

You need the primary delta lines, the primary side EGC from the source equipment grounding busbar, and a GEC grounding electrode conductor to an earth ground electrode. If you have multiple grounding electrodes, they all have to be interconnected, bonded together.

The EGC and GEC will have different paths and purposes. It happens but it is rare that they run in the same conduit. The GEC run in conduit has conduit bonding bushing requirements.

Standard transformers have taps every 2.5% on the secondary. I do not think I would use those to adjust for voltage drop, if that's what you're asking. If VD is an issue, I would look at the entire picture first before moving the taps.

 

[Buck Parrish]

Yes, thanks. .. The only metal is the main at the fire pump attachment. It's metal coming out of the slab. But right below it is plastic. It's not 10 ft of metal.

So the only ground I'll have to my transformers will be the equipment ground via ground rods at the main service outside.
Is that compliant? ?

 

[infinity]

Yes, thanks. .. The only metal is the main at the fire pump attachment. It's metal coming out of the slab. But right below it is plastic. It's not 10 ft of metal.

So the only ground I'll have to my transformers will be the equipment ground via ground rods at the main service outside.
Is that compliant? ?

Look at 250.30(A)(6), you should run a #3/0 common ground riser.

 

[texie]

Look at 250.30(A)(6), you should run a #3/0 common ground riser.

I would agree. FYI for the OP, underground fire sprinkler metallic piping is not allowed to be used as a grounding electrode per NFPA 13.

 

[Buck Parrish]

Okay, thanks.
So no Neutral to my primary. Just run the #3 as my equipment grounding conductor and it will serve as my grounding electrode, too. It will land on the frame of the transformer. Not the secondaries neutral bar
I've never installed this many transformers on a slab with no building steel any where near by.

 

[__dan]

3/0 is the minimum size for a GEC that is tapped multiple times. That may be what he was suggesting. Splices must be irreversible type.

A ground rod will not do anything performance wise. It may be possible to install the individual earth ground electrodes at each location if it allows a smaller and less restricted bonding jumper between earth electrodes. Just floating the thought, myself I would have to look through the code to see if I wanted to justify this view. If it complies, the electrode bonding jumper to the common facility earth grounding system would be a lot smaller than the GEC required per table.

The EGC can be expected to be noisy. I would look at the scenario with an eye towards arranging the GEC system in a way that may be independent of, or complementary to, noise and fault currents on the EGC. There can be an agreement between the code and the circuit behavior that anticipates future conditions.

 

[iwire]

3/0 is the minimum size for a GEC that is tapped multiple times. That may be what he was suggesting. Splices must be irreversible type.

The 3/0 has to be continuous or irreversible slices, the taps from the 3/0 to the individual transformer GECs can be made with any listed wire connector that does not break the 3/0 such as a split bolt etc.

The EGC can be expected to be noisy. I would look at the scenario with an eye towards arranging the GEC system in a way that may be independent of, or complementary to, noise and fault currents on the EGC. There can be an agreement between the code and the circuit behavior that anticipates future conditions.

Would wrapping the EGC with sound insulation quiet it down?

Kidding aside what is this noise and what harm am I trying to avoid?

 

[__dan]

There are two big ones that can be expected. First one is easy, fault current on the EGC.

Second one can be large depending on where you are. Consider a data center size UPS, could be megawatt load. Delta fed primary but internally the filter network is Y connected and grounded. It will have shelves and rows of caps. In a multi module system, there is no way the reactive power component will be perfectly balanced, or balanced instantaneously. There will be a reactive power imbalance that will flow between modules as it tries to equalize. The flow could be several hundred amps in a megawatt system.

With the primary delta, 3 ph 3 w, the path is over the grounding, actually over the entire conductive structure between the modules.

Knowing this or seeing it, the GEC can be arranged to avoid this flow, or knowing this a dedicated path, a separate 3/0 ringing the modules in circle can be provided to intercept the flow on a preferred path.

The secondary N-G-GEC point is expected to be, can be made, clean for sensitive or electrically fragile loads, electronics. The primary upstream EGC is for fault current and other nearby noise.

 

[infinity]

The 3/0 has to be continuous or irreversible slices, the taps from the 3/0 to the individual transformer GECs can be made with any listed wire connector that does not break the 3/0 such as a split bolt etc.

That's exactly what we do in poured concrete buildings, run a continuous or irreversibly spliced #3/0 GEC riser and tap off with split bolt or Ilsco insulation piecing Kupler taps.

 

[Buck Parrish]

Thanks,
Let me see if I'm understanding you correct.
So you would use the 3/0 in addition to my primary equipment ground ?
Then land the equipment.ground on the transformer frame. ? The 3/0 on the transformer neutral bar.
Thanks

 

[iwire]

There are two big ones that can be expected. First one is easy, fault current on the EGC.

Second one can be large depending on where you are. Consider a data center size UPS, could be megawatt load. Delta fed primary but internally the filter network is Y connected and grounded. It will have shelves and rows of caps. In a multi module system, there is no way the reactive power component will be perfectly balanced, or balanced instantaneously. There will be a reactive power imbalance that will flow between modules as it tries to equalize. The flow could be several hundred amps in a megawatt system.

With the primary delta, 3 ph 3 w, the path is over the grounding, actually over the entire conductive structure between the modules.

Knowing this or seeing it, the GEC can be arranged to avoid this flow, or knowing this a dedicated path, a separate 3/0 ringing the modules in circle can be provided to intercept the flow on a preferred path.

The secondary N-G-GEC point is expected to be, can be made, clean for sensitive or electrically fragile loads, electronics. The primary upstream EGC is for fault current and other nearby noise.

So really not an issue that the OP has to deal with or worry about.

 

[__dan]

If there is flow on the EGC it can be expected. If there is flow on the GEC it is a violation of 250.6.

If the customer is running lab equipment or anything than can be specially sensitive to noise on the ground, the secondary N-G-GEC point can be made less noisy.

I don't see it as an extra cost item. It is a compliance requirement. So the concern is implementing in a way that achieves the desired objectives, with an eye on what those objectives are.

 

[iwire]

If there is flow on the EGC it can be expected. If there is flow on the GEC it is a violation of 250.6.

That is an opinion, not a fact.

If the customer is running lab equipment or anything than can be specially sensitive to noise on the ground, the secondary N-G-GEC point can be made less noisy.

I don't see it as an extra cost item. It is a compliance requirement. So the concern is implementing in a way that achieves the desired objectives, with an eye on what those objectives are.

Correctly designed equipment should not be effected by 'noise' on the EGC.

 

[__dan]

That is an opinion, not a fact.

It becomes a fact either by the contract language, ie, whose discretionary judgement determines satisfactory work, or in the opinion of the enforcement official. Whose opinion it is may make it a fact.

Correctly designed equipment should not be effected by 'noise' on the EGC.

It happens all the time. Some sensors work by generating very subtle electrical effects that are amplified and read by instrumentation.

I have seen strain gauges on steel beams, a lab test setup, that would not work. I found neutral current mixing on the grounding path. An audio recording studio will have extensive requirements to avoid electrical noise on the grounds (to provide a clean ground system). There are many many control and communication systems that can pick up ambient EMI in a way that is bad for normal operation. There are many occurrences of regular or persistent flow on the EGC's and other ground paths. It is routine.

Correctly designed EGC and GEC paths can mitigate this. Incorrect implementations can compound this.

 

[__dan]

Let's say you go to a common GEC busbar and amp clamp the conductors terminating there. You see 5, 7, 9, 12, 23, ... amps each conductor terminating there. Is it objectionable? Is it a violation? This would assume the wiring itself is compliant.

In some instances size of the signal may not matter, if it interferes with normal operation.

Even if it does occur in some manner, there is a way to construct the GEC system in a way that would meet someone's opinion of best practice.

 

[iwire]

It becomes a fact either by the contract language, ie, whose discretionary judgement determines satisfactory work, or in the opinion of the enforcement official. Whose opinion it is may make it a fact.

That is a stretch and clearly beyond the NEC.

It happens all the time. Some sensors work by generating very subtle electrical effects that are amplified and read by instrumentation.

What 'happens all the time'?

People claim many things when they can not understand the results their equipment is putting out.

I have seen strain gauges on steel beams, a lab test setup, that would not work. I found neutral current mixing on the grounding path. An audio recording studio will have extensive requirements to avoid electrical noise on the grounds (to provide a clean ground system). There are many many control and communication systems that can pick up ambient EMI in a way that is bad for normal operation.

You are talking about specific, unusual installations to buttress your point.

None of that is typical.