# Bonding X0 in Delta-Wye xformers



## Bob Badger

Mike in Canada said:


> Do you do it?


Yes, the NEC requires it in most cases.

Not a good idea to leave it floating.



> I don't like the idea because it feels like grounding the common, which is supposed to only happen at the service entrance.


It is a new 'common' and it has not been bonded until you bond it.


----------



## lectricboy

Mike in Canada said:


> Do you do it? I had a call-back on a transformer that I had wired. The voltage was balanced within 1.5% phase-to-phase, but they needed it balanced phase-to-ground for the machine they were powering. Since the source was delta it wasn't balanced that way. I had to bond X0 on the secondary side to make it work for their purposes. I've heard that some guys bond X0 as standard procedure... I don't like the idea because it feels like grounding the common, which is supposed to only happen at the service entrance.
> 
> Comments?
> 
> Mike


The same rules basically apply to a seperately derived system, as the main service entrance!


----------



## Navyguy

Agreed. Each transformer is considered a new "supply" however you still can only have one grounding system.

Often the mistake is made that there is a separate grounding system installed as well as a bonding of the XO and ground.

Treat the XO as a new supply but use the existing grounding system.

Cheers


----------



## Toronto Sparky

XO secondarys are always bonded as far as I know.. Never seen one that wasn't unless I was there to bond it because is was missed by someone..

Why would they be using a delta/wye transformer if they didn't intend to use the neutral?


----------



## nitro71

If you don't bond X0 on the secondary side you have a ungrounded system which isn't NEC compliant in most cases. Which means if you get a fault to ground on the secondary side your breaker won't trip.


----------



## Toronto Sparky

Added to that if you do get a fault to ground on one of the phases the others will have at full potential to ground.. Not a good idea..

Fairly sure the voltage between each phase and neutral would not be normal.. (not real sure about that.. )


----------



## brian john

Toronto Sparky said:


> Added to that if you do get a fault to ground on one of the phases the others will have at full potential to ground.. Not a good idea..
> 
> Fairly sure the voltage between each phase and neutral would not be normal.. (not real sure about that.. )


The first fault is the often touted "FREE FAULT", nothing happens except you now have a grounded system. One of the phase's is now grounded, not compliant but not a real problem from an equipment operational standpoint. What's different 208 VAC to ground or 277 VAV to ground.

As for the unground phase to neutral voltage is what it should be 120 nominal. The phase to ground voltages vary with load, load conductor length and any thing else that affects the system impedance.


----------



## Mike in Canada

In the case in question I had a voltage to ground of 115V, 125V and 135V. The phases were pretty much dead-nuts relative to one another, but despite the fact that the machine was running happily the CNC guy who came in to check it out after the move wanted the phases balanced relative to ground, so I bonded X0. It should be noted that the case of the transformer was bonded already... I just added a jumper from X0 to the case, so there was a grounding path beforehand. I was just treating the transformer as a straight delta.

Mike


----------



## Bob Badger

Mike in Canada said:


> It should be noted that the case of the transformer was bonded already... I just added a jumper from X0 to the case, so there was a grounding path beforehand.


Mike, *there was no ground-fault path* for anything down stream of that transformer until you added the connection from XO to ground.

The XO to ground connection will never effect the line to line voltage but will always effect the line to ground voltages.

The CNC guy was absolutely correct in expecting the system to be bonded and has been said the code (at least the NEC) requires that bonding.


----------



## brian john

Mike in Canada said:


> In the case in question I had a voltage to ground of 115V, 125V and 135V. The phases were pretty much dead-nuts relative to one another, but despite the fact that the machine was running happily the CNC guy who came in to check it out after the move wanted the phases balanced relative to ground, so I bonded X0. It should be noted that the case of the transformer was bonded already... I just added a jumper from X0 to the case, so there was a grounding path beforehand. I was just treating the transformer as a straight delta.
> 
> Mike


As Bob said...

The machine will run "HAPPY" ungrounded but with the setup as you originally installed it the UNGROUNDED system does not meet code. 
YOU HAD NO FAULT PATH PERVIOUSLY.

YOU WERE NOT treating the transformer as a DELTA secondary, because you can't it is not a Delta secondary, it is wye. 

I am not getting in your case, but you seriously need to get a few books on grounding before you kill someone.


----------



## Bob Badger

I modified some drawings I got from an NEC instructor.

Here is the ground-fault path when wired correctly.










Here it is with the bond removed











There is no ground-fault path, the potential between XO and the enclosures will be there but the fault current cannot get back to the source which in this case is the secondary windings of the transformer.


----------



## RePhase277

Here again we are faced with the myth that electricity "goes to ground". Mike is clearly of the belief that fault current seeks a path to the actual soil of the planet Earth, instead of its source. A few definitions:

*Ground #1: *An intentional electrical connection with the Earth (used in the GEC)
*Ground #2:* A common connection point in a circuit (as in, the chassis of your car is grounded)
*Ground #3:* A point used as a reference in a circuit to establish a standard measuring point (as in electronics, where you have +5 V, 0 V, and -5 V)
*Ground #4:* A connection used to carry fault current back to the source and complete a circuit

Electricians usually use defs. #1 and #4, but the problem is there is no distinguishing between them: "Ground the neutral at the meter", and "Make sure that receptacle has a ground". They are two different things serving different purposes, yet named the same.


----------



## brian john

InPhase277 said:


> He
> 
> Electricians usually use defs. #1 and #4, but the problem is there is no distinguishing between them: "Ground the neutral at the meter", and "Make sure that receptacle has a ground". They are two different things serving different purposes, yet named the same.



Which is why I feel the term EARTHED for the connection to an electrode MIGHT minimize some of the confusion.


----------



## RIVETER

The GEC and the EGC actually are not called the same thing...or at least, shouldn't be. The GEC is what we know it to be. The EGC is a conductor that is at Neutral potential at the panel which happens to be grounded. I guess what I am trying to say is that it is most important that the egc be at Neutral potential.


----------



## Bob Badger

RIVETER said:


> I guess what I am trying to say is that it is most important that the egc be at Neutral potential.


The ground*ed* conductor will only be at the same potential as the ground*ing* conductor at the bonding point. The further you move away from the bonding point and the greater the load on the ground*ed* conductor the more the difference of potential will rise between the ground*ed* and ground*ing* conductors.


----------



## RIVETER

Bob Badger said:


> The ground*ed* conductor will only be at the same potential as the ground*ing* conductor at the bonding point. The further you move away from the bonding point and the greater the load on the ground*ed* conductor the more the difference of potential will rise between the ground*ed* and ground*ing* conductors.


I don't dissagree. The grounded conductor I am talking about is not the normal circuit conductor. It conducts only in the event of a hot to ground fault.


----------



## Bob Badger

RIVETER said:


> I don't dissagree. The grounded conductor I am talking about is not the normal circuit conductor. It conducts only in the event of a hot to ground fault.


The ground*ed* conductor, the one that should be white, is a circuit conductor and it normally carries current.

The ground*ing* conductor, the one that should be green or bare is not a circuit conductor and only carries current during faults.


----------



## RIVETER

Bob Badger said:


> The ground*ed* conductor, the one that should be white, is a circuit conductor and it normally carries current.
> 
> The ground*ing* conductor, the one that should be green or bare is not a circuit conductor and only carries current during faults.


 We are saying the same thing. I am only trying to differentiate the two for the poster who insinuated that they were basically the same, which they are not. The EGC is not a normal circuit conductor, as I've said. It IS at ground potential because of its connection, and it has no normal current on it unless someone has errently connected it to the neutral out in the field.


----------



## Toronto Sparky

Noticed that the #6 I ran from my main disco to the water main carries up to 40A according to my Hioki clamp on.. Some day I will have to shut the main off and see how much remains.. Personally I think I'm grounding the transformer on the pole..
Remember this house was built in the 50s when it was common practice to use 14/2 romex from the incoming neutral to the closest water pipe , than a jumper (also 14/2) around the water meter. I can't see any ground on the street..


----------



## RePhase277

Toronto Sparky said:


> Noticed that the #6 I ran from my main disco to the water main carries up to 40A according to my Hioki clamp on.. Some day I will have to shut the main off and see how much remains.. Personally I think I'm grounding the transformer on the pole..
> Remember this house was built in the 50s when it was common practice to use 14/2 romex from the incoming neutral to the closest water pipe , than a jumper (also 14/2) around the water meter. I can't see any ground on the street..


40 A!? Yikes!! It is likely you are carrying some of the neighbors' neutral currents back to the transformer from the metal water piping shared between the buildings.


----------



## Mike in Canada

Bob Badger said:


> I modified some drawings I got from an NEC instructor.
> 
> Here is the ground-fault path when wired correctly.


 Bob, I really appreciate you taking the time to try to sort this out for me. I see in your drawing how the bond to X0 allows fault current to reach the 'source' of the power. Now, if this was a delta-delta transformer wired as I had originally wired it then would it have no ground-fault path?

Mike


----------



## nitro71

Mike in Canada said:


> Bob, I really appreciate you taking the time to try to sort this out for me. I see in your drawing how the bond to X0 allows fault current to reach the 'source' of the power. Now, if this was a delta-delta transformer wired as I had originally wired it then would it have no ground-fault path?
> 
> Mike


 
That would not be a NEC compliant, safe or otherwise approved install in the US. If you read the NEC section on ungrounded transformers there are very few approved ungrounded applications. 

And you are correct if you wired a delta/delta and did not bond one of the secondary legs you would have a ILLEGAL ungrounded system.


----------



## sparky105

Bob Badger said:


> The ground*ed* conductor will only be at the same potential as the ground*ing* conductor at the bonding point. The further you move away from the bonding point and the greater the load on the ground*ed* conductor the more the difference of potential will rise between the ground*ed* and ground*ing* conductors.


This is the best way to keep it straight that I have come across


----------



## brian john

Mike in C.

Now for the $1,000,000.00 dollar (American Dollars) question, How many transformers have you hooked up ungrounded?:w00t:


----------



## RIVETER

How many premises is that transformer feeding? If you have that much current on your EGC, you potentially could have fatal current on your water piping system. This is to Toronto Sparky.


----------



## mattsilkwood

The first corner grounded delta you run into will through you for a loop. It did me at least.


----------



## Mike in Canada

brian john said:


> Mike in C.
> 
> Now for the $1,000,000.00 dollar (American Dollars) question, How many transformers have you hooked up ungrounded?:w00t:


 There is one, but I haven't put power to it yet. It's in the 'states, actually, and the customer has made it very plain that they do *not* want a corner-grounded transformer. They feel that it is a safety risk because a lazy maintenance guy could check the voltage on one random leg to ground, get zero volts, think that it's dead, and get zapped by one of the other legs. They've got a point. I've got a month or two to figure out what I'm going to do with it before it's needed.

Mike


----------



## nitro71

He will get zero volts to ground if it's not grounded. If it is grounded he will show voltage to ground on his meter. You have it exactly opposite of how it works.

And it doesn't matter what they want in this scenario. There is no way I would not bond the secondary even if a customer wanted it not done.


----------



## Mike in Canada

nitro71 said:


> He will get zero volts to ground if it's not grounded. If it is grounded he will show voltage to ground on his meter. You have it exactly opposite of how it works.


 Wait a minute... you're telling me that a corner-grounded delta transformer will *not* show zero volts to ground from any leg, but a delta transformer that is *not* corner-grounded then you *will* see zero volts to ground?

Mike


----------



## brian john

mattsilkwood said:


> The first corner grounded delta you run into will through you for a loop. It did me at least.


 
Which is why I feel backfed transformers wye/delta 208 to achieve 480 should be avoided if possible. 

I have fielded numerous frantic call ffrom contractors and customers freaking out about wierd voltages.

I know it is perfectly legal and I know a professional should be able to figure it out. But quite a few have no clue.


----------



## nitro71

Mike in Canada said:


> Wait a minute... you're telling me that a corner-grounded delta transformer will *not* show zero volts to ground from any leg, but a delta transformer that is *not* corner-grounded then you *will* see zero volts to ground?
> 
> Mike


Mike, 

I jumped the gun on that, on that one leg he wouldn't see voltage but the other two he will. I'd probably not corner ground it but ground it in between two of the legs if possible.


----------



## nitro71

After thinking about corner grounding for a minute here I can't see it being a legal NEC install because that one leg will have the same potential as your ground.


----------



## Mike in Canada

nitro71 said:


> Mike,
> 
> I jumped the gun on that, on that one leg he wouldn't see voltage but the other two he will. I'd probably not corner ground it but ground it in between two of the legs if possible.


 This is the problem... if a guy happens to pick the corner-grounded leg to test to ground to verify that the line is off, then there is the potential for mayhem. This can be avoided by simply checking more than one leg, but the plain fact is that the customer doesn't like corner-grounded delta, and doesn't want it used. I try to keep the customer happy, so I'm looking for options. I'm not sure what you're referring to by 'ground it in between two of the legs'.

Mike


----------



## nitro71

Ground in between = center ground. I'm not a transformer expert but I have the basics down. 

Think about what happens if you get a fault to ground on that one corner grounded leg. Now your grounding system is energized with a full line to line potential to the other two legs. Your breaker for that one leg won't trip if that leg is the only one with a fault. 

Here's a read at MH:
http://forums.mikeholt.com/showthread.php?t=79256&page=2

If you check out the ungrounded section of the NEC you could probably use ground fault detectors on your ungrounded system to make it compliant. You'll have to research that. 

Non-compliance of grounding and bonding gets people killed. Make it safe and NEC compliant.


----------



## Control Freak

I have to be honest...........can't help it at all......
the op has no business installing a transformer in the nec jurisdiction. You are just installing vioations. I would so get laid off for that. Bonding the x0 is standard practice where Im from.
are you licensed in the U.S? If not that must be some side job you picked up............


----------



## Control Freak

not safe man...not safe and thats scary!!!!!


----------



## Control Freak

Handy men and transformers thats even scarier.......lol


----------



## miller_elex

The OP is installing a high-impedance ground. :blink:

So what you do is: find a suitable impedance. I remove the heating element from a hair-dryer.

Now take the heating element, and bond one lead to the X0. Bond the other lead to your GEC's and gnd. 

To monitor for ground faults: Put the heating element under a fat woman's desk. When the fat lady stops complaining about her freezing feet, its time to go search for your fault. :thumbup:


----------



## brian john

miller_elex said:


> The OP is installing a high-impedance ground. :blink:
> 
> So what you do is: find a suitable impedance. I remove the heating element from a hair-dryer.
> 
> :thumbup:


Or contact Post Glover.

http://www.postglover.com/highresistance.html?high resistance grounding resistors


----------

