transformer connection

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papa

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Installed a 9 kva 480/240 delta/delta trans today, for a machine. In addition to h1,2,3 and x1,2,3 there is and unlabeled conducter. What is it for. Machine needs no neutral. Should it be bonded to grd and frame?
 
If it's H-0, let it float.

If it's X-0, you can ground it, ground a phase, or install ground-detection circuitry.
 
papa said:
Installed a 9 kva 480/240 delta/delta trans today, for a machine. In addition to h1,2,3 and x1,2,3 there is and unlabeled conducter. What is it for. Machine needs no neutral. Should it be bonded to grd and frame?
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Need more information.
Do you have a part number for the transformer?
What does the wiring diagram, on the nameplate, show?
Some companies (i.e. Acme) provided shielded transformers as standard, so this could be a shield connection.
 
jim dungar said:
Need more information.
Do you have a part number for the transformer?
What does the wiring diagram, on the nameplate, show?
Some companies (i.e. Acme) provided shielded transformers as standard, so this could be a shield connection.
Click to expand...

Dont have a part # with me , it is a bangor trans. not sure I am correct on spelling. The wiring diagram had a line between pri. and sec. drawn out to a grd symbol.
 
Shield

Shield

Its a shield, You have an isolation transformer. The shield keeps noise from going from one winding to the other.
 
Shield Connection

Shield Connection

The shield gets grounded.
For sure if the transformer is Delta-Delta there is no X-0 or H-0 terminals.
 
xo winding

xo winding

IF your transformer has an XO lead or terminal it's a WYE Secondary.
IF it has a HO lead or terminal it has a WYE primary.
I have seen a transformer with X1,X2,X3,X4,X5,X6,X7,X8,X9,X10,X11and x12 leads but it's been a while. They don't make economic sense. I think I have a reference book with it.
 
I do believe the extra terminal your seeing is a halfway point between 2 of the corners in the delta. This terminal provides 120 & 120 from those 2 corners to the terminal. it is NOT a neutral (XO). It acts kinda sorta like a neutral, but most D/D that I have seen the limit is 5% of the total load for these 120 V points.
 
Your transformer label should show if the lead is connected to a winding or a shiled. If not, as others have suggested, a check with a meter should tell you.
If it's a shield ground it.
If it is a tap to the secondary winding and not used you might cap it. If it is used then the application falls under 250.20(B).

If the secondary is delta 3 wire only then note that 250.21(B) applies and I would think if you chose to ignore a tap the same would apply.
 
augie47 said:
Your transformer label should show if the lead is connected to a winding or a shiled. If not, as others have suggested, a check with a meter should tell you.
If it's a shield ground it.
If it is a tap to the secondary winding and not used you might cap it. If it is used then the application falls under 250.20(B).

If the secondary is delta 3 wire only then note that 250.21(B) applies and I would think if you chose to ignore a tap the same would apply.
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Transformer label had a line between the winding to a grd symbol. I did ohm it out , and the conductor is open to frame and all other conductors. I capped it and checked sec. voltage , 242 v between all phases . I thought it is a shield and should be grd., but with no marking I did not have the confidence to grd it without further info . at the time of installation.
 
papa said:
Transformer label had a line between the winding to a grd symbol.
Click to expand...

I am curious, why did you question the nameplate drawing?
But, grounding the shield of a transformer is definitely optional, except when you need to reduce noise that may be coupled across the transformer.
 
jim dungar said:
I am curious, why did you question the nameplate drawing?
But, grounding the shield of a transformer is definitely optional, except when you need to reduce noise that may be coupled across the transformer.
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I questioned it because the conductor have not no marking indicating that it is the shield wire to be grd.
 
ActionDave.
if there is an XO it ain't a Wye wound transformer..
i would bet lunch you can not buy a 3 phase dry or a pad-mount oil filled transformer with a delta secondary and and one side of one winding center tapped. The corner oposite the center tapped is the "wild leg".

There are a few of those systems around here but they are being phased out. The local utilities will not provide a new service with a "wild leg".
The existing systems have three 120/240 single phase transformers (oil filled pole mounted distribution type) connected in a delta. One of the transformers is center tapped for 120volt.

http://en.wikipedia.org/wiki/High-leg_delta
 
You caught me.

In my case I was hooking up a 208 Delta/480Y step-up transformer so I had a HO not a XO and two leads that were labeled "SHIELD", which I capped.

This thread came up the same day I was hooking up my transformer. I was curious what others opinions were regarding shield leads, but I didn't want to thread jack so I asked what you would do if an XO was present rather than HO as XO would be more common.

On a side note- the power company where I live will provide a high leg delta if the customer requests it.
 
jim dungar said:
I am curious, why did you question the nameplate drawing?
But, grounding the shield of a transformer is definitely optional, except when you need to reduce noise that may be coupled across the transformer.
Click to expand...

Are we sure this shield is only for noise? when I did a delta to delta isolation of my dads marina many years ago, the state required me to use a isolating shielded transformer, to prevent any chance of a primary to secondary fault, I was told this shield was placed between the windings to prevent this from occurring, also in many requirements in the NEC for transformers for pool lighting the same reason is given for shielded transformers for line to LV lighting?
 
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I don't know what you have but you need to establish a EGC to the windings on the secondary side of your transformer ,unless you have a ungrounded system, so that faults will cause your breakers to trip. Whatever it takes to do that is what needs to happen.
 
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