Where to bond

[sketchy]

Our company installs wind turbines that put put out 480 volts, some single phase some three. On the single phase units, I need to usually feed back to the home owner. To do this we use a single phase 480 - 120/240 transformer with a fused disconnect on either side.
I have been bonding the 240 volt disconnect with the supplied bonding screw and not bonding the case of the transformer or the 480 side. So I have 2 hots, a neutral and a ground from the 240 volt disconnect where it is bonded, terminate on the X side, then from the H side I have 2 hots and a ground going to the next disconnect. The grounds in the transformer terminate on a lug mounted to the case. This is acceptable isn't it? The turbine doesn't need a neutral.

 

[augie47]

Does this help:

 

[sketchy]

Don't I have the option to bond in the disconnect OR the transformer?

 

[augie47]

I was in hopes you didn't ask
I'm still trying to grasp the changes tp 250.30 in the '11 Code.
I may be wrong but you may still install the system bonding jumper at the source or 1st disconnecting means. Note that 250.30(2) does require a supply side bonding condcutor between the two.
This, I think, is still permissible:

 

[texie]

I think Augie is telling correctly for the 120/240 side, but I'm wondering about the 480 supply side. This needs to be a grounded system to be safe and compliant.

 

[sketchy]

I have the ground, just no neutral. There isn't one.

 

[don_resqcapt19]

Is there a grounded conductor on the 480 volt side? If not you will need a ground detector on the 480 volt side. 250.21(B)

 

[sketchy]

How is this any different than a 240 v circuit with two hots and a ground? No need for a ground detector then.

 

[texie]

How is this any different than a 240 v circuit with two hots and a ground? No need for a ground detector then.

A 240 volt circuit with 2 ungrounded conductors and a EGC are fed from a grounded system, that is the difference. I think what we are thinking here is that your 480 volt source is operating as an ungrounded source, and would not have a fault return path. Even with no neutral you can still create a grounded system.

 

[sketchy]

Well I would love to hear any ideas on how to create that without a neutral. Never heard of single phase 480 until I started working here and the more I find out the more I wish I never heard of it.

 

[don_resqcapt19]

How is this any different than a 240 v circuit with two hots and a ground? No need for a ground detector then.

Most 240 volt transformers that have a center tap and would be required to be a grounded system by 250.20(B)(1). If the 240 volt transformer has no provisions for a center tap, then it would need a ground detector.
You could ground one of the 480 volt legs, making that a grounded system and then a ground detector would not be required.

 

[sketchy]

I am bonding X2-X3 (neutral) to ground in the disconnect. We have only done 2 of these and they both passed inspection.

 

[don_resqcapt19]

I am bonding X2-X3 (neutral) to ground in the disconnect. We have only done 2 of these and they both passed inspection.

That makes the 240 side a grounded system and you would not need ground detectors. The 480 volt side is an ungrouned system and will require ground detectors.

 

[tom baker]

How is this any different than a 240 v circuit with two hots and a ground? No need for a ground detector then.

The difference is its 480V to ground. 240 is almost always 120 V to ground. A 480 volt ground fault is very dangerous and will not burn clear as will a 120 V ground fault
And if you have 480 volt and get a line to case ground, you have just created a grounded 480 V system. Your second line to case fault will be a line to line short circuit at 480 V.

What I suggest you do is start with 250.20 and determine what systems must be grounded, what systems are optionally grounded and what systems are never grounded.
And then look at the requirements for operating ungrounded sytems

 

[ptonsparky]

Can you just create one, neutral or grounded conductor, by tying H2 & H3 together and grounding the mid point on the primary side? IDK. Open ended question.

 

[sketchy]

Can you just create one, neutral or grounded conductor, by tying H2 & H3 together and grounding the mid point on the primary side? IDK. Open ended question.

I have thought of that as well, not sure it's leagal. The transformer nameplate lists only single voltages on the H side, where as the L side lists 120/240.

 

[ptonsparky]

I have thought of that as well, not sure it's leagal. The transformer nameplate lists only single voltages on the H side, where as the L side lists 120/240.

I would only be applying 480v.

 

[SG-1]

The transformer nameplate posted in post 1 shows a duel voltage primary, 240/480.