480 delta 3 wire disconnect

[williamervin77]

I ran into a unusual grounding application at work the other day and it just doesnt sit to well with me but hopefully someone can make light of it for me. 480v delta 3 wire system, B phase is being used as the egc? On the line side of the disconnect B phase is jumped over to what is supposed to be neutral terminal and then ran as ground to my MDP. Besides the box not being, grounded what am I misssing? To me it seems as if the whole system is ungrounded:huh: thank you ahead of time.

 

[Smart $]

Welcome to the forum :thumbsup::thumbsup:

Sounds like your dealing with a 480V 3? 3W grounded B-phase system (service?), more familiarly known as a corner-grounded delta system.

If so, you can wire wire it like a 240/480V 1? 3W system... but you will have to use equipment specifically made for 480V 3? 3W grounded B-phase... in most cases it is identical to 240/480 1? 3W equipment except for the labelling, which is why you have to get the equipment made specfically for the corner grounded system... or you can use standard 480V 3? 3W equipment and not wire the grounded corner to the normal respective ungrounded bus.

The grounded phase conductor must meet the requirements of such (white, gray, traced, etc.).

 

[williamervin77]

thank you.

thank you.

Thank you smart$. After doing some research it seems as though the Bphase is a grounded phase and its not supposed to be fused as it is now. I am still unclear about bonding it with the system I know I need to ground the can with ground rod but do I need to bond my earthed ground with my corner ground "B"?

 

[GoldDigger]

Thank you smart$. After doing some research it seems as though the Bphase is a grounded phase and its not supposed to be fused as it is now. I am still unclear about bonding it with the system I know I need to ground the can with ground rod but do I need to bond my earthed ground with my corner ground "B"?

Yes. When the service has a grounded conductor you must locally bond that conductor to your GES.
A properly sized jumper from the B phase wire to a ground/neutral bar in the service disconnect may satisfy this requirement as long as the GEC is landed there too.

 

[Smart $]

Thank you smart$. After doing some research it seems as though the Bphase is a grounded phase and its not supposed to be fused as it is now. I am still unclear about bonding it with the system I know I need to ground the can with ground rod but do I need to bond my earthed ground with my corner ground "B"?

Grounding and bonding is done the same as any other grounded system. The only difference is that in this case it's a grounded phase conductor, whereas in other cases it's a grounded neutral or center-tap conductor. In fact, after done, unless one examines it "closely", one might think it's a 240/480V 1? 3W system.

 

[augie47]

I think it is important to note, as mentioned above, that on a corner grounded system, one phase is grounded.. and NOT grounding. Bonding and grounding of items beyond the service would be accomplished just as in any other type system. A grounded to grounding connection would still be a violation of 250.24

 

[ceb58]

Thank you smart$. After doing some research it seems as though the Bphase is a grounded phase and its not supposed to be fused as it is now. I am still unclear about bonding it with the system I know I need to ground the can with ground rod but do I need to bond my earthed ground with my corner ground "B"?

You are correct the B phase should not be fused. They make a " no blow " fuse that should be used in the place of a standard fuse.

 

[Smart $]

You are correct the B phase should not be fused. They make a " no blow " fuse that should be used in the place of a standard fuse.

IMO, the grounded conductor shouldn't even be run through a fuse holder... even a no-blow is too easy to be replaced inadvertently.

 

[don_resqcapt19]

IMO, the grounded conductor shouldn't even be run through a fuse holder... even a no-blow is too easy to be replaced inadvertently.

On a corner grounded system, would that really be a big issue, other than a code violation? There would typically not be any line to grounded conductor loads or multi-wire branch circuits.

 

[Smart $]

On a corner grounded system, would that really be a big issue, other than a code violation? There would typically not be any line to grounded conductor loads or multi-wire branch circuits.

Other than inadvertent replacement of the no-blow with a standard fuse, no big issue that I'm aware of.

I haven't worked with any 480V grounded-B phase equipment. Just noted them in panelboard catalogs. Are 480V 1-pole breakers even available for 1? line-to-grounded-conductor circuits?

 

[kwired]

On a corner grounded system, would that really be a big issue, other than a code violation? There would typically not be any line to grounded conductor loads or multi-wire branch circuits.

As long as the bonding jumper at the service or first disconnecting means is ahead of the fuseholder and not after it probably isn't too much of a problem. If bonding jumper is after the fuseholder you lose your EGC if the fuse blows.

 

[don_resqcapt19]

As long as the bonding jumper at the service or first disconnecting means is ahead of the fuseholder and not after it probably isn't too much of a problem. If bonding jumper is after the fuseholder you lose your EGC if the fuse blows.

That is a good point. I had just assumed that the main bonding jumper would have to be on the line side of the disconenct, but not sure the code actaully says that.