I need help understanding this applicaation

[shortckt70005]

This is at a Hospital..maybe I am just use to Hospital regualtions but here goes....

A new 3000 amp Switchboard is being installed in a new part of the hospital.

Existing Utility Transformer (13.8 to 480 volt 3 Phase) will be relocated and will feed this new 3000 amp Switchboard.
New 3000 amp Switchboard will have a 1600 amp breaker in it to feed the existing Switchboard by way of running new conduits to the old Utility Transformer Pad, installing a junction box and capturing the old conduits that fed existing Switchboard. These conduit only have 4 conductors in them... 3-500 mcm (A,B,C) and one 4/0 Neutral... No Ground Conductor.

I was under the impression that all conduits were going to be repulled with new wire and a Ground would be added. Electrical contractor wants to reuse the existing conductors from junction box to the existing Switchboard. Does this meet Code?

This existing Switchboard is now going to be a big Sub panel in my opinion and its Ground should originate from the new Switchboard. The existing Neutral to Ground Bar Bonding Jumper at existing Switchboard needs to be removed.

Am i missing an exception in the Code? Any input is appreciated.

Thanks
Shortckt

 

[Elect117]

215.6

Is this one structure?

 

[shortckt70005]

Physically not connected. A new Central Plant is being built and the new Switchboard is going in it. Existing Switchboard will remain in the Hospital. first floor.

 

[Elect117]

Then 250.32 can apply.

 

[shortckt70005]

There is a main boding jumper across the buss at existing switchboard... (Neutral bus to Gornd Bar)... I do not know if it is inside of utility transformer.

 

[hillbilly1]

Several problems there, the 3000 amp breaker will have ground fault protection, in which the 1600 amp feed neutral will be bonded to the GEC, which will cause possibly nusiance tripping. The 1600 amp feeder would also be ground fault protected, which the bond at the old gear would nullify or greatly reduce the ground fault protection.

 

[shortckt70005]

Thank you both for the imformation.
If I am reading 250-32 correctly, because its a separate building, and if in the existing Switchboard, the Bonding Jumper from the Neutral to Ground Bar is removed,then a separate Grounding Electrode needs to be driven and this application is OK by NEC Code.

Again, am I reading this correctly.... It just does not sound correct.

thanks for all the input
shortckt

 

[mtnelect]

If it's a separate building it needs to have a separate service.

 

[curt swartz]

Thank you both for the imformation.
If I am reading 250-32 correctly, because its a separate building, and if in the existing Switchboard, the Bonding Jumper from the Neutral to Ground Bar is removed,then a separate Grounding Electrode needs to be driven and this application is OK by NEC Code.

Again, am I reading this correctly.... It just does not sound correct.

thanks for all the input
shortckt

Each building requires a grounding electrode system. You need a 5th wire or qualifying metal raceway between the buildings. You can't use the grounding electrode system (earth) as the equipment ground.

 

[Jpflex]

There is a main boding jumper across the buss at existing switchboard... (Neutral bus to Gornd Bar)... I do not know if it is inside of utility transformer.

I have made several post about this. The confusion when to know if a main bonding jumper should be at your fist disconnect while assuming their isn’t a second one in your utility transformer?

If this is the case your supply side bonds jumper (ground bonding between the source transformer and first disconnect would be sized to 250.102c based on memory - (largest ungrounded conductor).

This supply side bonding jumper would be paralleled in each of the 3 feeder conduits I believe but I’m not sure about curing 4/0 nor am I familiar with mcc vs kcmil which I’m familiar with

 

[Jpflex]

Each building requires a grounding electrode system. You need a 5th wire or qualifying metal raceway between the buildings. You can't use the grounding electrode system (earth) as the equipment ground.

Each building or structure served requires a disconnect which would be required to be connected to the same grounding electrode system. I think you’re saying the same thing but it sounds like separate ground systems the way you put it? All grounds are bonded together as one system.

To my understanding even if you have several different sources or multiple services such as the exemption for a very large building, I believe all the derived grounded conductors from the secondary neutral windings from different service source transformers bond together as one large single grounding electrode conductor system?

If I’m correct it seems weird that the mid point from different transformer secondary’s interconnect because you would think the potential of both transformer secondary winding mid points would need to be exactly equal in voltage potential?

 

[roger]

Thank you both for the imformation.
If I am reading 250-32 correctly, because its a separate building, and if in the existing Switchboard, the Bonding Jumper from the Neutral to Ground Bar is removed,then a separate Grounding Electrode needs to be driven and this application is OK by NEC Code.

Again, am I reading this correctly.... It just does not sound correct.

thanks for all the input
shortckt

Correct, however it will be more than just a driven rod(s) all the qualified GE's in the second building will need to used, and this GES will only bond to the Equipment Grounding bar/equipment in the now sub panel. The new service equipment will be treated as normal to it's own GES.

 

[shortckt70005]

Thanks you all for sharing..... still a bit confusing though

so "IF" there is a metal raceway from existing Transformer Pad to original Switchboard then I don't need the 5th wire ? Remove the Bonding Jumper (Neutral to Ground Bar of Switchboard) in existing Switchboard. Bond all metal raceway feeders to the Ground Bar. There are two Ground Rods in existing Switchboard already.

Thanks again for information.... I will ask Chief Inspector of jurisdiction but want to be familiar with options before I talk with him because scenario is a bit confusing.

 

[david luchini]

Thanks you all for sharing..... still a bit confusing though

so "IF" there is a metal raceway from existing Transformer Pad to original Switchboard then I don't need the 5th wire ? Remove the Bonding Jumper (Neutral to Ground Bar of Switchboard) in existing Switchboard. Bond all metal raceway feeders to the Ground Bar. There are two Ground Rods in existing Switchboard already.

Thanks again for information.... I will ask Chief Inspector of jurisdiction but want to be familiar with options before I talk with him because scenario is a bit confusing.

Yes, IF the raceway can be used as an equipment grounding conductor then you don't need a wire type EGC.

 

[roger]

If there is a metallic raceway you won't need an EGC (5th wire) and you are correct about the rest. The one thing I question is the rest of the GE's. I would think there is building steel and maybe a metallic water entrance that would both qualify as GE's and those would need to be used as well as the rods.

 

[Strathead]

Thanks you all for sharing..... still a bit confusing though

so "IF" there is a metal raceway from existing Transformer Pad to original Switchboard then I don't need the 5th wire ? Remove the Bonding Jumper (Neutral to Ground Bar of Switchboard) in existing Switchboard. Bond all metal raceway feeders to the Ground Bar. There are two Ground Rods in existing Switchboard already.

Thanks again for information.... I will ask Chief Inspector of jurisdiction but want to be familiar with options before I talk with him because scenario is a bit confusing.

For clarity, if you also install a metal raceway or equipment grounding conductor front he new switchgear to the metal conduit.

 

[shortckt70005]

Thank you all !!