# Grounding And Bonding



## anthonysolino (Dec 10, 2019)

Hello every one, am Anthony, new to the site, I was told by a co worker this would be a good place to have discussions with good people in the community,



I would like to jump right in to the question I have,

I am currently working on a system that contains a 240V to 120V single phase potted transformer, the customer is requesting the area to be "reworked" essentially correct all the faulty branch circuit wiring from the prior contractor, 


the situation is, existing there were two phase conductors brought to this transformer with no equipment ground, and no primary OCP, today I bought an EGC to it. and repaired the OCP issue, installed a fused disconnect before it hit the xfmer, there is a bonding stud in this unit, now if I am not mistaken these types of transformers need to be bonded per 250 and OCPD per 450? there has been some back and fourth at my shop about this, what I decided (and felt was the proper way to do this) was drive an electrode and come to the bonding stud with my GEC from that bonding stud came to the "Neutral tap" and also my raceway grounds were all bonded to my GEC which was bonded to my EGC I brought to the disconnect from earlier, this seemed to stabilize my voltage and to me these transformers are treated as a separately derived system in the eyes of the NEC?

I feel as if though I installed this correctly, I would like the communities thoughts on this, I do have an IAEI meeting I will bring this up at the chapter meeting this month as well,

-Also I do not believe the intent was to have this used as an isolation transformer,
although I would like to have a topic on those as well, if any one has any knowledge of them, I know old TV repair guys used to use them, I would like to know the bonding process.


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## Awg-Dawg (Jan 23, 2007)

anthonysolino said:


> I would like to jump right in to the question I haveif I am not mistaken these types of transformers need to be bonded per 250 and OCPD per 450? there has been some back and fourth at my shop about this, what I decided (and felt was the proper way to do this) was drive an electrode and come to the bonding stud with my GEC from that bonding stud came to the "Neutral tap" and also my raceway grounds were all bonded to my GEC which was bonded to my EGC I brought to the disconnect from earlier, this seemed to stabilize my voltage and to me these transformers are treated as a separately derived system in the eyes of the NEC?
> 
> .


The GEC from your transformer needs to be tied to the grounding electrode system.


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## anthonysolino (Dec 10, 2019)

I took the GEC and tied it in to my EGC from my supply side, also installed a jumper from the bonding stud to the neutral taps the branch circuit is being fed some 1200 feet away from where this is installed, if that helps?


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## anthonysolino (Dec 10, 2019)

Did I possibly post this in the wrong thread?


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## Awg-Dawg (Jan 23, 2007)

anthonysolino said:


> I took the GEC and tied it in to my EGC from my supply side, also installed a jumper from the bonding stud to the neutral taps the branch circuit is being fed some 1200 feet away from where this is installed, if that helps?


 It needs to tie to the GEC system.

Is the building steel, if it qualifies as an electrode You can tie it in to the steel.


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## anthonysolino (Dec 10, 2019)

it is in the middle of a island off a road way, the branch circuits feed a receptacles and lighting in there, the primary side is being taped off the 240v street lighting circuit that continues on down the road for 1200 more feet or so, I guess what I am triying to ask if any one agrees with how I decided to install it and if these type of transformers are to be installed per 250 ? I didn't see any thing in 250 related to these type of transformers, thats where the head scratching came in, I treated it like a separately derived system, would you consider it as such?


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## Awg-Dawg (Jan 23, 2007)

anthonysolino said:


> it is in the middle of a island off a road way, the branch circuits feed a receptacles and lighting in there, the primary side is being taped off the 240v street lighting circuit that continues on down the road for 1200 more feet or so, I guess what I am triying to ask if any one agrees with how I decided to install it and if these type of transformers are to be installed per 250 ? I didn't see any thing in 250 related to these type of transformers, thats where the head scratching came in, I treated it like a separately derived system, would you consider it as such?


I see now.

I agree with how you’re doing it.

They are to be installed per 250 and other codes.

It is a separately derived system.


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## anthonysolino (Dec 10, 2019)

is there a thread on here that happens to be about transformers ?


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## CoolWill (Jan 5, 2019)

Sounds about right to me. Equipment ground to grounding electrode, to case, to white wire of 120 volt output.


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## anthonysolino (Dec 10, 2019)

CoolWill said:


> Sounds about right to me. Equipment ground to grounding electrode, to case, to white wire of 120 volt output.




what are your thoughts on if no electrode was installed? there would be no reference to ground, I would image the voltage would bounce all over just like a failed neutral might ?


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## CoolWill (Jan 5, 2019)

anthonysolino said:


> what are your thoughts on if no electrode was installed? there would be no reference to ground, I would image the voltage would bounce all over just like a failed neutral might ?


The voltage to the local earth might bounce around, but the voltage between the secondary poles would be fine. A failed neutral causes voltage fluctuations due to the resistances of different loads being unequal on opposite phases, so that's a different phenomenon.


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## anthonysolino (Dec 10, 2019)

CoolWill said:


> The voltage to the local earth might bounce around, but the voltage between the secondary poles would be fine. A failed neutral causes voltage fluctuations due to the resistances of different loads being unequal on opposite phases, so that's a different phenomenon.


voltage from L1 to earth I would imagine jump around, but from my L1 to the neutral WITHOUT the grounding electrode hooked up in the transformer would also give me that same phenomenon? theres no reference to earth for the neutral to stabilize, if I am thinking about this correctly the grounding electrode in this case provides a way to 'regulate" the voltage in the circuit


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## CoolWill (Jan 5, 2019)

anthonysolino said:


> voltage from L1 to earth I would imagine jump around, but from my L1 to the neutral WITHOUT the grounding electrode hooked up in the transformer would also give me that same phenomenon? theres no reference to earth for the neutral to stabilize, if I am thinking about this correctly the grounding electrode in this case provides a way to 'regulate" the voltage in the circuit


The voltage between terminals of the transformer is not dependent on grounding to Earth. Voltage to ground will be all over the place if there is no GEC. The circuit will not know the difference and will function normally.


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## anthonysolino (Dec 10, 2019)

CoolWill said:


> The voltage between terminals of the transformer is not dependent on grounding to Earth. Voltage to ground will be all over the place if there is no GEC. The circuit will not know the difference and will function normally.


thats a good point, what would happen to the branch circuit voltage if no GEC is connected to the transformer,? horrible voltage fluctuations on the secondary ties?


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## CoolWill (Jan 5, 2019)

anthonysolino said:


> thats a good point, what would happen to the branch circuit voltage if no GEC is connected to the transformer,? horrible voltage fluctuations on the secondary ties?


Nothing would happen. That's what I said in the earlier post. The GEC has NO effect on the voltage between the circuit conductors. If the transformer output is 120 volts, then the circuit will see 120 volts no matter if there's a GEC or not. 

The GEC only works to stabilize the voltage between the circuit conductors and the local earth. It has no effect on the normal operation of the circuit.


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