Shore Power Rack Installation Design

[Vinny B]

Hello,

First time posting and I hope you can help!

While excavating we encountered, "BOOM" an existing conduit feeding an existing exterior Shore Power Rack at the edge of the parking lot. Thank God nobody was hurt. The conduit was not indicated on the contract drawings and not properly identified by Dig Safe.

Upon further investigation we discover a rack containing six 100 A fused disconnect switches. Each switch fed a 480 volt Arktite Heavy duty Receptacle for portable trailers. The Rack was fed from an existing pad mount transformer. The transformer also feeds a building with (3) sets of 500 MCM conductors to an MDP in the building .
At some point someone installed an undocumented 3" underground conduit with (6) sets of # 2 CU to a Hand Hole about 50' away from the transformer. They installed (6) 1-1/2 inch conduits underground to the (6) disconnects from the hand hole. The rack is about 15' from the handhole. They pulled a 3 phase circuit to each disconnect switch ( 18 ) conductors Total length of conductors is about 65-70' from the transformer.

When the excavator hit the conduit it damaged the bucket and the conductors were still energized. The transformer was de energized and rack feeders removed. We discovered the fuses at the pole were fine and turned the transformer back on to re feed the Building.

The following discussion started. Was the installation legal ? The Inspector indicated it wasn't because the conductors are un protected and longer than the tap rule allows. Is it a tap ? Did the original installer use the six throws of the hand rule and believe his installation was ok ?

We as the prime electrical contractor are caught in the middle. The Inspector is indicating its not legal. The owners on site electrician says it is. We can not fix and reconnect the feeders because we believe the original installation was not to code.

We site the following :

1) Multiple conductors (6) under one lug is a violation
2) The secondary conductors are not properly protected. The transformer and cut outs were designed for the original building and not the added tapped conductors
3) Parallel conductors are # 2 Minimum would be 1/0
4) Too many current carrying conductors in a conduit. 21-30 conductors would be an ampacity of 58.5 Amps feeding a 100 Amp disconnect switch


We believe the owner must install a Fused disconnect within 10' of the transformer to feed the rack. The feeders to the new fused disconnect/ Shore rack should be increased in size.

Are we correct in holding firm and not re-connecting the existing installation the way it was ? The Inspector is starting to have doubts that he is correct and is indicating he may allow the system to be re - connected as is.

Any help is appreciated.
Vin

 

[don_resqcapt19]

Hello,

First time posting and I hope you can help!

While excavating we encountered, "BOOM" an existing conduit feeding an existing exterior Shore Power Rack at the edge of the parking lot. Thank God nobody was hurt. The conduit was not indicated on the contract drawings and not properly identified by Dig Safe.

It sounds like these are privately owned conductors and they are not typically located by the one call service that locates underground utility facilities.

Upon further investigation we discover a rack containing six 100 A fused disconnect switches. Each switch fed a 480 volt Arktite Heavy duty Receptacle for portable trailers. The Rack was fed from an existing pad mount transformer. The transformer also feeds a building with (3) sets of 500 MCM conductors to an MDP in the building .
At some point someone installed an undocumented 3" underground conduit with (6) sets of # 2 CU to a Hand Hole about 50' away from the transformer. They installed (6) 1-1/2 inch conduits underground to the (6) disconnects from the hand hole. The rack is about 15' from the handhole. They pulled a 3 phase circuit to each disconnect switch ( 18 ) conductors Total length of conductors is about 65-70' from the transformer.

When the excavator hit the conduit it damaged the bucket and the conductors were still energized. The transformer was de energized and rack feeders removed. We discovered the fuses at the pole were fine and turned the transformer back on to re feed the Building.

The following discussion started. Was the installation legal ? The Inspector indicated it wasn't because the conductors are un protected and longer than the tap rule allows. Is it a tap ? Did the original installer use the six throws of the hand rule and believe his installation was ok ?

We as the prime electrical contractor are caught in the middle. The Inspector is indicating its not legal. The owners on site electrician says it is. We can not fix and reconnect the feeders because we believe the original installation was not to code.

We site the following :

1) Multiple conductors (6) under one lug is a violation

Yes, that would be a violation as I am not aware of any lug that would be listed for 6 conductors.

2) The secondary conductors are not properly protected. The transformer and cut outs were designed for the original building and not the added tapped conductors

This is not likely a violation. See the rule in 240.21(C)(4) that permits outside transformer secondary conductors of any length.

3) Parallel conductors are # 2 Minimum would be 1/0

Your description does not sound like a parallel installation as the conductors terminate at separate disconnects.

4) Too many current carrying conductors in a conduit. 21-30 conductors would be an ampacity of 58.5 Amps feeding a 100 Amp disconnect switch

That is an issue. If the loads are small enough, you could put smaller fuses in the disconnect to make it compliant.

We believe the owner must install a Fused disconnect within 10' of the transformer to feed the rack. The feeders to the new fused disconnect/ Shore rack should be increased in size.

Not required per 240.21(C)(4)

Are we correct in holding firm and not re-connecting the existing installation the way it was ? The Inspector is starting to have doubts that he is correct and is indicating he may allow the system to be re - connected as is.

The only real issues I see are six conductors in a single lug which should be easy to fix and the conductor ampacity because of the required ampacity adjustment. The ampacity would be hard to correct unless the loads permit the use of smaller fuses in the disconnects.

Any help is appreciated.
Vin

 

[xptpcrewx]

Interesting scenario.

Upon further investigation we discover a rack containing six 100 A fused disconnect switches. Each switch fed a 480 volt Arktite Heavy duty Receptacle for portable trailers. The Rack was fed from an existing pad mount transformer. The transformer also feeds a building with (3) sets of 500 MCM conductors to an MDP in the building.

At some point someone installed an undocumented 3" underground conduit with (6) sets of # 2 CU to a Hand Hole about 50' away from the transformer. They installed (6) 1-1/2 inch conduits underground to the (6) disconnects from the hand hole. The rack is about 15' from the handhole. They pulled a 3 phase circuit to each disconnect switch ( 18 ) conductors Total length of conductors is about 65-70' from the transformer.

Based on the picture, it appears those lugs can support up to 3 wires per lug, so really 2 conductors under one terminal is the violation here.

Also, you mention these are parallel conductors, but it's not a parallel installation if the conductors terminate individually to each disconnect.

Btw. I don't see a grounding electrode or GEC installed at the transformer, which is now a requirement for outdoor transformers.

The following discussion started. Was the installation legal ? The Inspector indicated it wasn't because the conductors are un protected and longer than the tap rule allows. Is it a tap ? Did the original installer use the six throws of the hand rule and believe his installation was ok ?

Check the local building code to determine if it is legal or not. Usually, not permitting or documenting an installation is illegal - which can fall back on the customer/owner and/or the contractor. There are of course exceptions based on the jurisdiction and scope.

Tap rules apply but the length of the conductors are not the violation. Protection of the conductors is limited to physical damage. Them being underground and in a raceway is reasonably sufficient.

We as the prime electrical contractor are caught in the middle. The Inspector is indicating its not legal. The owners on site electrician says it is. We can not fix and reconnect the feeders because we believe the original installation was not to code.

Don't take the inspectors word for granted. Tell him to provide the code reference.

We site the following :

1) Multiple conductors (6) under one lug is a violation

See comment 1 above.

2) The secondary conductors are not properly protected. The transformer and cut outs were designed for the original building and not the added tapped conductors

How do you know if allowable demand factors have already been considered? Primary cut-outs are sized based on the transformer rating and not the connected load. What constitutes proper protection?

3) Parallel conductors are # 2 Minimum would be 1/0

How is this a parallel installation if each conductor terminates individually to each disconnect?

4) Too many current carrying conductors in a conduit. 21-30 conductors would be an ampacity of 58.5 Amps feeding a 100 Amp disconnect switch

I thought you said, these were run in separate raceways? Why are you applying correction factors?

We believe the owner must install a Fused disconnect within 10' of the transformer to feed the rack. The feeders to the new fused disconnect/ Shore rack should be increased in size.

Why? See 240.21(B)(5).

Are we correct in holding firm and not re-connecting the existing installation the way it was ? The Inspector is starting to have doubts that he is correct and is indicating he may allow the system to be re - connected as is.

This depends on your contractual obligations, insurance and standard duty of care as a contractor. If you don't have a clause in your contract to protect against this kind of accident or clearly state it is the customers responsibility to produce accurate and up-to-date information, then just bite the bullet and own it.

 

[xptpcrewx]

4) Too many current carrying conductors in a conduit. 21-30 conductors would be an ampacity of 58.5 Amps feeding a 100 Amp disconnect switch

Sorry, re-reading this I now realize these conductors are bundled together in the 3" raceway, so I see your logic. Wouldn't the adjustment factor be 0.50 for 18 phase conductors (excluding unbalance from the neutral per 310.15.(B)(5))? Also, you could use a temperature correction factor greater than 1 for the cool temperature underground to get you additional ampacity.

 

[Vinny B]

Thank you for the responses. I will look into the Shore Power Ampacity. I believe it varies. It will depend on the mobile trailer they bring to the site. The are privately owned conductors. The Inspector works on base. I agree that the conductors are not parallel. I agree the fusing for the transformer is based on the transformer rating. So the recommended corrections will be. Increase the feeder ampacity to the Shore Power Rack. Add a Grounding conductor and change the lugs in the transformer.