# Step up transformer



## MotoGP1199 (Aug 11, 2014)

Ground H0 like you would any.other transformer secondary(usually X0 on a step down).

This transformer is huge. Your primary breaker might trip on initial start up if too small. Sometimes it will only do it on the first start up when using smaller breakers other times your not so lucky.


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## Forge Boyz (Nov 7, 2014)

Do you really need 480v? Most motors are dual voltage. Unless you have alot of motor starters and controls to replace it might be cheaper to run them at 208V.

Sent from my SM-G970U using Tapatalk


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## Morg12345 (Jan 22, 2016)

Forge Boyz said:


> Do you really need 480v? Most motors are dual voltage. Unless you have alot of motor starters and controls to replace it might be cheaper to run them at 208V.
> 
> Sent from my SM-G970U using Tapatalk


Good thought...I'll check motors for duel voltage and control transformer ..for 208


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## CMP (Oct 30, 2019)

Not to beat you up, but to give you a basic lesson.

First of all you should state your loads type and what their requirements are, not just that they are minimal. Details matter. There are other ways to power them depending on what they are. Do they require a wye supply, such as a VFD, switch mode power supply, or are they just plain motor or heater loads? Knowing the load data and doing the math also allows you to size the transformer correctly, and allows you to cut it close to size or give extra allowances for high inrush loads and how many of these high inrush loads must start at the same time.

At first glance one may think that the unit you procured is a step down unit, your planning to use in reverse to instead use it for a step up, by how the label is laid out. If that were the case, today the transformer is required to be listed for reverse connection by the NEC. Older units, before the labeling requirement, wont be labeled with this listing, but that don't necessarily mean that they won't work that way. If your job is being inspected, you might get hit on that detail. Looking up your unit, turns out it's classed as a low efficiency unit designed for step up operation. 
 Drive Isolation Transformers - Low Efficiency HPS Tribune™ take note of the installation manual on this page.

Model Number DM145BK Detail Page 

You may think that an oversize unit, will more than cover your needs and it may well, but that causes other problems, inrush current and excess wasted energy during the entire time it is energized, loaded or not, especially with a low efficiency model. Let me add in here, that using a model in reverse operation, compounds the inrush problem. The primary coils, the ones that are designed to energize the transformer, are wound right on the core iron, then the secondary is wound over the top of them. When using a transformer in reverse, energizing the outside set of coils instead causes the initial inrush current to become much higher and lower efficiencies as well. This can cause nuisance tripping of the supply over-current device, when sized according to the NEC or smaller. The bigger the transformer the worse this problem becomes.

You said that you wanted to use a 70A circuit to feed this setup, due to your minimal load requirements. But that is not going to fly very well. A 145KVA unit has a current rating of 402.5A @ 208V input, and that is before you add the factors allowed in the NEC for inrush current. On a 70A fuse or breaker, its likely to pop every time you try to energize it. That gets expensive in a hurry. Also makes you look unqualified, after it's installed and wired. The only other choice is to wire it for it's rating and the additional reserve margin the NEC allows for inrush current. something like 402.5A x 1.5 = 603.75A

I don't think that's something you want to do for 30A @ 480V, even if you could.

Lets stop here and go back to discussing the particulars of you loads, and in the mean time, return that monster before too much time elapses. And make some time to review the NEC transformer article. We can discuss the finer connection details once you arrive at a practical solution. First you need to determine the actual required load size and if the equipment can be powered by a delta or wye system.


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## Morg12345 (Jan 22, 2016)

Very good im


CMP said:


> Not to beat you up, but to give you a basic lesson.
> 
> First of all you should state your loads type and what their requirements are, not just that they are minimal. Details matter. There are other ways to power them depending on what they are. Do they require a wye supply, such as a VFD, switch mode power supply, or are they just plain motor or heater loads? Knowing the load data and doing the math also allows you to size the transformer correctly, and allows you to cut it close to size or give extra allowances for high inrush loads and how many of these high inrush loads must start at the same time.
> 
> ...





CMP said:


> Not to beat you up, but to give you a basic lesson.
> 
> First of all you should state your loads type and what their requirements are, not just that they are minimal. Details matter. There are other ways to power them depending on what they are. Do they require a wye supply, such as a VFD, switch mode power supply, or are they just plain motor or heater loads? Knowing the load data and doing the math also allows you to size the transformer correctly, and allows you to cut it close to size or give extra allowances for high inrush loads and how many of these high inrush loads must start at the same time.
> 
> ...


Thanks..I have home work to do... 1st thing is to see if it's listed For using in reverse...then checkthe vfd if any on the machines.....ill get motor load imfo...I can do the math on that...


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## CMP (Oct 30, 2019)

Morg12345 said:


> Very good im
> 
> 
> Thanks..I have home work to do... 1st thing is to see if it's listed For using in reverse...then checkthe vfd if any on the machines.....ill get motor load imfo...I can do the math on that...


Read the post again, and the transformer detail page. The transformer you have, IS A STEP UP UNIT, no need for reverse connecting. Equipment pictures can be helpful.


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## Morg12345 (Jan 22, 2016)

CMP said:


> Read the post again, and the transformer detail page. The transformer you have, IS A STEP UP UNIT, no need for reverse connecting. Equipment pictures can be helpful.


Yes I looked again...noticed high side is 208 taps...I didn't buy these...the electrican that baled..bought them...I'm helping a freind out


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## Morg12345 (Jan 22, 2016)

Looks like the 


Morg12345 said:


> Yes I looked again...noticed high side is 208 taps...I didn't buy these...the electrican that baled..bought them...I'm helping a freind out


Loos like the few 480 machines has variable speed...and there is some resistive heat load


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## micromind (Aug 11, 2007)

If there are VFDs, then you absolutely must ground H0. If you don't, there's a good chance the surge protection on the VFDs will blow up. 

Grounding H0 will give you a basic 277/480 system, exactly the same as you'd get from the PUCO. 

If this is fed from a 208 panel, use the largest breaker you can get (usually 100 amp). It might trip and it might hold...........If it does trip the first time, go ahead and close it in again, the first brief surge may very well have magnetized the core to the point that the second time will hold.


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## Morg12345 (Jan 22, 2016)

micromind said:


> If there are VFDs, then you absolutely must ground H0. If you don't, there's a good chance the surge protection on the VFDs will blow up.
> 
> Grounding H0 will give you a basic 277/480 system, exactly the same as you'd get from the PUCO.
> 
> If this is fed from a 208 panel, use the largest breaker you can get (usually 100 amp). It might trip and it might hold...........If it does trip the first time, go ahead and close it in again, the first brief surge may very well have magnetized the core to the point that the second time will hold.


Ill for sure check that center tap next time I'm over there...the 480 panel they ordered is main breakerless...I'm thinking of a fused disconnect for the panel main any ideas on the fuse type?


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## Morg12345 (Jan 22, 2016)

CMP said:


> Read the post again, and the transformer detail page. The transformer you have, IS A STEP UP UNIT, no need for reverse connecting. Equipment pictures can be helpful.


CMP your saying that the transformer I have is a true step up transformer?...Just verifying 
Morg


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## MotoGP1199 (Aug 11, 2014)

Morg12345 said:


> CMP your saying that the transformer I have is a true step up transformer?...Just verifying
> Morg


I would think so. Generally a step down will have an X0 terminal and no H0 terminal. A step up would have an H0 and no X0. There's no reason and you should not bring a neutral to a 3 phase transformer on the primary side.


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## CMP (Oct 30, 2019)

Morg12345 said:


> CMP your saying that the transformer I have is a true step up transformer?...Just verifying
> Morg


Yes it is. Look at the 2nd link given above to the mfg site, then look under the details tab on the right side of the page.


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## micromind (Aug 11, 2007)

Morg12345 said:


> Ill for sure check that center tap next time I'm over there...the 480 panel they ordered is main breakerless...I'm thinking of a fused disconnect for the panel main any ideas on the fuse type?


Just basic class RK-1 (FRS) fuses will be fine. 

If you'd like, you can bolt the fused disconnect to the side of the transformer but keep the knockouts down low or hot air will get into the disconnect switch.


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## Morg12345 (Jan 22, 2016)

CMP said:


> Yes it is. Look at the 2nd link given above to the mfg site, then look under the details tab on the right side of the page.


Hello
Trying to figure what size grounding conductor to use for the center tap of the secondary Y..


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## micromind (Aug 11, 2007)

The 277/480 current is 174 amps. I don't have a codebook handy but it takes less than a minute to look it up.


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## CMP (Oct 30, 2019)

What size wire are you using on the input and output?


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## Morg12345 (Jan 22, 2016)

CMP said:


> What size wire are you using on the input and output?


4/0...#2


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## CMP (Oct 30, 2019)

I want to teach you how to fish, instead of feeding you a fish. You read the rules below and tell us what size you think you need. And what size grounding conductor do you need from the 208V feeder and what size do you need for the building grounding electrode?

2017 Code

*250.30 Grounding Separately Derived Alternating-Current Systems.*
In addition to complying with 250.30(A) for grounded systems, or as provided in 250.30(B) for ungrounded stems, separately derived systems shall comply with 250.20, 250.21, 250.22, or 250.26, as applicable. Multiple separately derived systems that are connected in parallel shall be installed in accordance with 250.30.

(A) Grounded Systems. A separately derived ac system that is rounded shall comply with 250.30(A)(1) through (A)(8).
Except as otherwise permitted in this article, a grounded conductor shall not be connected to normally non–currentcarrying metal parts of equipment, be connected to equipment grounding conductors, or be reconnected to ground on the load side of the system bonding jumper.

(1) System Bonding Jumper. An unspliced system bonding jumper shall comply with 250.28(A) through (D). This connection shall be made at any single point on the separately derived system from the source to the first system disconnecting mans or overcurrent device, or it shall be made at the source of a separately derived system that has no disconnecting means or overcurrent devices, in accordance with 250.30(A)(1)(a) or (b). The system bonding jumper shall remain within the enclosure where it originates. If the source is located outside the building or structure supplied, a system bonding jumper shall be installed at the grounding electrode connection in compliance with 250.30(C).

(a) Installed at the Source. The system bonding jumper shall connect the grounded conductor to the supply-side bonding jumper and the normally non–current-carrying metal enclosure.

(b) Installed at the First Disconnecting Means. The system bonding jumper shall connect the grounded conductor to the supply-side bonding jumper, the disconnecting means enclosure, and the equipment grounding conductor(s).

(2) Supply-Side Bonding Jumper. If the source of a separately derived system and the first disconnecting means are located in separate enclosures, a supply-side bonding jumper shall be installed with the circuit conductors from the source enclosure to the first disconnecting means. A supply-side bonding jumper shall not be required to be larger than the derived ungrounded conductors. The supply-side bonding jumper shall be permitted to be of nonflexible metal raceway type or of the wire or bus type as follows:
(a) A supply-side bonding jumper of the wire type shall comply with 250.102(C), based on the size of the derived ungrounded conductors.
(b) A supply-side bonding jumper of the bus type shall have a cross-sectional area not smaller than a supply-side bonding jumper of the wire type as determined in 250.102(C).

Exception: A supply-side bonding jumper shall not be required between enclosures for installations made in compliance with 250.30(A)(1), Exception No. 2.

(3) Grounded Conductor. If a grounded conductor is installed and the system bonding jumper connection is not located at the source, 250.30(A)(3)(a) through (A)(3)(d) shall apply. (a) Sizing for a Single Raceway. The grounded conductor shall not be smaller than specified in Table 250.102(C)(1). (b) Parallel Conductors in Two or More Raceways. If the ungrounded conductors are installed in parallel in two or more raceways, the grounded conductor shall also be installed in parallel. The size of the grounded conductor in each raceway shall be based on the total circular mil area of the parallel derived ungrounded conductors in the raceway as indicated in 250.30(A)(3)(a), but not smaller than 1/0 AWG.

(4) Grounding Electrode. The building or structure grounding electrode system shall be used as the grounding electrode for the separately derived system. If located outdoors, the grounding electrode shall be in accordance with 250.30(C) .

Exception: If a separately derived system originates in equipment that is listed and identified as suitable for use as service equipment, the grounding electrode used for the service or feeder equipment shall be permitted to be used as the grounding electrode for the separately derived system.

Informational Note No. 1: See 250.104(D) for bonding requirements for interior metal water piping in the area served by separately derived systems.

Informational Note No. 2: See 250.50 and 250.58 for requirements for bonding all electrodes together if located at the same building or structure.

(5) Grounding Electrode Conductor, Single Separately Derived System. A grounding electrode conductor for a single separately derived system shall be sized in accordance with 250.66 for the derived ungrounded conductors. It shall be used to connect the grounded conductor of the derived system to the grounding electrode in accordance with 250.30(A)(4) , or as permitted in 250.68(C)(1) and (2). This connection shall be made at the same point on the separately derived system where the system bonding jumper is connected.


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## LGLS (Nov 10, 2007)

MotoGP1199 said:


> Ground H0 like you would any.other transformer secondary(usually X0 on a step down).
> 
> This transformer is huge. Your primary breaker might trip on initial start up if too small. Sometimes it will only do it on the first start up when using smaller breakers other times your not so lucky.


Damn... maybe use FPE as the primary overcurrent protection???


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## Morg12345 (Jan 22, 2016)

CMP said:


> I want to teach you how to fish, instead of feeding you a fish. You read the rules below and tell us what size you think you need. And what size grounding conductor do you need from the 208V feeder and what size do you need for the building grounding electrode?
> 
> 2017 Code
> 
> ...


 I'm going to work on this today and I'll get back to you with all the wire sizes and code references
Morg


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## Morg12345 (Jan 22, 2016)

CMP said:


> I want to teach you how to fish, instead of feeding you a fish. You read the rules below and tell us what size you think you need. And what size grounding conductor do you need from the 208V feeder and what size do you need for the building grounding electrode?
> 
> 2017 Code
> 
> ...





CMP said:


> I want to teach you how to fish, instead of feeding you a fish. You read the rules below and tell us what size you think you need. And what size grounding conductor do you need from the 208V feeder and what size do you need for the building grounding electrode?
> 
> 2017 Code
> 
> ...



So here's the transformer I'm using instead of 145 kva above.......
Primary OCP
75000/208x1.73=208
450.3(b)..max protection 125%208×1.25=260
240.6(a)next breaker 300
But unfortunately I only have a 225 amp breaker available so I have to underused the transformer and protect it with a 225 breaker
Non grounded conductors will be 4/0 cu
310.16..75c.230 amps
Secondary
75000/480×1.73=90.36×1.25=112
#2cu=115 amps

Main bonding jumper 250.102(c)(1)(4/0)=#2cu
Grounding electrode conductor 250.66
4/0=#2cu
I went fishing alone today instead of going to the seafood buffet
Please correct..iff needed please 
Morg


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## Morg12345 (Jan 22, 2016)

Morg12345 said:


> So here's the transformer I'm using instead of 145 kva above.......
> Primary OCP
> 75000/208x1.73=208
> 450.3(b)..max protection 125%208×1.25=260
> ...


Forgot to add using a 75 kva


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## CMP (Oct 30, 2019)

Smart move to downsize the transformer to something your situation can handle.

Your numbers look good along with your circuit sizes and overcurrent sizes. This unit has a bit higher impedance, wich will help with your inrush current surges on energizing. It is also listed as higher efficiency which is another bonus.

If it doesn’t have a ground block, in the enclosure get one. It should have the ground from the 208 source, the ground to the XO 480 winding, a ground from the transformer core and encloure and also a grounding electrode conductor to the building steel or existing service grounding electrode system. And also a water pipe if you have one within the area of the building that the transformer serves. Thats why you need a block you can bolt to the encloure, and connect all the required wires to.

Myself, I would also run a neutral to your panelboard now, even if you don’t require one now, in the future you might have a need for it. Easier to do it now than add one later.


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## Morg12345 (Jan 22, 2016)

CMP said:


> Smart move to downsize the transformer to something your situation can handle.
> 
> Your numbers look good along with your circuit sizes and overcurrent sizes. This unit has a bit higher impedance, wich will help with your inrush current surges on energizing. It is also listed as higher efficiency which is another bonus.
> 
> ...


Thanks for making me think...I'm sure
Ill have a few questions...have a good night
Morg


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## Morg12345 (Jan 22, 2016)

CMP said:


> Smart move to downsize the transformer to something your situation can handle.
> 
> Your numbers look good along with your circuit sizes and overcurrent sizes. This unit has a bit higher impedance, wich will help with your inrush current surges on energizing. It is also listed as higher efficiency which is another bonus.
> 
> ...


Would I have to debate running a neutral?


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## CMP (Oct 30, 2019)

Debate? You mean derate? No with no load on it there is no need, just to cover yourself in the future. But just do one bond between the neutral and ground, preferably in the transformer, not on both ends.


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## Morg12345 (Jan 22, 2016)

Morg12345 said:


> Thanks for making me think...I'm sure
> Ill have a few questions...have a good night
> Morg


So your mentioned grounding the core...how and where?
Morg


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## CMP (Oct 30, 2019)

There may be a lug on it alraedy, look near the core anchor bolts to the case. Should be rubber vibration isolators between the core mounts and the case. Som units have a copper bonding strap between the two, others need separate bonding wires. If you can’t figure it out, show a photo.

The core needs bonding , as thats where the windings are, where the windings are wound, and is not reliably connected to the case ground, because of the vibration isolation pads.


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## Morg12345 (Jan 22, 2016)

Morg12345 said:


> So your mentioned grounding the core...how and where?
> Morg
> 
> 
> ...


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## CMP (Oct 30, 2019)




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## just the cowboy (Sep 4, 2013)

micromind said:


> If there are VFDs, then you absolutely must ground H0. If you don't, there's a good chance the surge protection on the VFDs will blow up.
> 
> Grounding H0 will give you a basic 277/480 system, exactly the same as you'd get from the PUCO.
> 
> If this is fed from a 208 panel, use the largest breaker you can get (usually 100 amp). It might trip and it might hold...........If it does trip the first time, go ahead and close it in again, the first brief surge may very well have magnetized the core to the point that the second time will hold.


Thanks
I always wondered why they held the second time, I have had VFD's do it many times on charge up but never thought of transformers magnetized holding so it could reset.


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## CMP (Oct 30, 2019)

just the cowboy said:


> Thanks
> I always wondered why they held the second time, I have had VFD's do it many times on charge up but never thought of transformers magnetized holding so it could reset.


The transformer core has a magnetic core memory, it holds that memory for a very long time in the steel lamination's.
When the transformer is shut off, the magnetic phase angle is set in that magnetic memory. When you re-energize the transformer, the phase angle of the supply timing compared to the magnetic memory matters. If the supply phase timing and the magnetic memory phase timing are opposed, near 180° opposed, you will get a very high inrush current, rearranging the magnetic polarity in the steel lamination's instantaneously. That surge current can briefly trip the over-current device, especially a magnetic trip element of a breaker.

Fuses, especially time delay variety, can hold up a bit better without blowing when sized to the high end, but will also blow if they are undersized or sized very close to the load size. Sometimes the phase angles align fairly close and there is no false tripping, it's best to size the input overcurrent protection to the high side of the allowed range to prevent this nuisance tripping. Especially where a larger transformer, with low impedance is switched regularly, and is close to a high capacity service or feeder.


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## paulengr (Oct 8, 2017)

just the cowboy said:


> Thanks
> I always wondered why they held the second time, I have had VFD's do it many times on charge up but never thought of transformers magnetized holding so it could reset.


If residual magnetism made a difference it would cause problems every cycle of AC power.

It’s a phase angle thing. If contacts close at the peak of the sine wave (90 degrees) you get “normal” magnetizing current. If it happens at zero degrees it doubles. Transformers can pull as high as 100 their rated current during startup.


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## Morg12345 (Jan 22, 2016)

CMP said:


> View attachment 169803


CMP...I found that copper strap... It goes from the top plate down to that bolt sticking through on the bottom it's a copper strip How do I size that conductor?
Morg


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## CMP (Oct 30, 2019)

The strap is factory sized and installed to bond the core and case together. So you need to connect your HO output terminal, to your input 208 grounding conductor, and your building grounding electrode conductor to the case. Then Provide a grounded conductor (neutral) lead from HO to your downstream load distribution point, panel or disconnect neutral bar.


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## Morg12345 (Jan 22, 2016)

CMP said:


> The strap is factory sized and installed to bond the core and case together. So you need to connect your HO output terminal, to your input 208 grounding conductor, and your building grounding electrode conductor to the case. Then Provide a grounded conductor (neutral) lead from HO to your downstream load distribution point, panel or disconnect neutral bar.


So I take it it should sized the same as my bonding conductor #2 copper 
Morg


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## CMP (Oct 30, 2019)

Yes, that's the minimum, you could use bigger if you have some scraps on hand.


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## Morg12345 (Jan 22, 2016)

CMP said:


> Yes, that's the minimum, you could use bigger if you have some scraps on hand.


Here's how turned out...thanks for all the help!


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## CMP (Oct 30, 2019)

Your install looks good. What I would like to see is an overall shot of the entire installation. Lets see that stand and your wiring methods.

One thing I don’t see is a grounding electrode conductor added to your grounding system. The NEC requires a GEC to the building steel , service grounding electrode system, or a local water line that is connected to the GEC.

The purpose of this connection is for a ground fault path back to that transformer common terminal for failt current in the event that somthing gets damaged and shorts to the building or its piping systems. This is needed to trip the overcurrent device and remove the faulted circuit fed from that transformer.

Take a look in that NEC sections that I sent you, the requirement is in there. It’s required for safety in the event that a circuit fed from that transformer or a piece of equipment gets damaged and energizes the building or it’s piping systems. Its very similar to the grounding electrode conductor required at the service, and does the same function.

Your isolation transformer is a separately derived system, and needs to be treated just like a service, bonded to the grounding electrode system.


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## Morg12345 (Jan 22, 2016)

CMP said:


> Your install looks good. What I would like to see is an overall shot of the entire installation. Lets see that stand and your wiring methods.
> 
> One thing I don’t see is a grounding electrode conductor added to your grounding system. The NEC requires a GEC to the building steel , service grounding electrode system, or a local water line that is connected to the GEC.
> 
> ...


The one on the terminal with tthe bonding jumper HO. Goes out to the steel frame of the building
Morg


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## CMP (Oct 30, 2019)

If you show us, then we can be assured. Just want to make sure you now know how to fish.


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