Paralleled Runs

[icanfixit]

Came across an unfinished project from another contractor that I was asked to check over. I was not asked to inspect, but to determin what was needed to finish the project. From a new generator with a 400amp main 2 parallel runs of #4/0 were run inside the building. 800 ft (estimated) away the runs were installed in a junction box and terminated together. From the termination 2 #6 wires were run to different 60amp fused disconnects. After telling the building owner of this installation I was asked to identify what was against code. The #6 on a 400amp breaker is easy. Can parallel runs terminate in a junction box and then feed different equipment? I can't find it in the book. I always practiced that parallel runs had to start and end at a device such as a breaker or disconnect.
Chris

 

[stickboy1375]

Is there a transfer switch?

 

[iwire]

There may be nothing wrong with this if the taps meet the requirements spelled out in 240.21(B)

The paralleled conductors do not have to terminate in a over current device.

Take a look at 310.4

 

[DesertRat]

What you describe, with the conductors terminated together at both ends, would seem to meet the criteria for a paralleled conductor.

What is the distance between the splice and the disconnects? It would appear that the previous EC has applied one of the tap rules here.

 

[iwire]

This is actually a common method of supplying motor loads in some occupancies.

You run a large feeder from point A to point B than apply the tap rules as you need.

 

[roger]

We do this quite often. We will run a large feeder (may or may not be parallel) to a gutter and install distribution blocks to accommodate the number of smaller conductors needed. The block below will take a parallel feeder and up to 12 smaller taps.

Roger

 

[Jim W in Tampa]

I would not even touch this job untill i talked to the first electrician.Most likely there is some bad blood.Perhaps no pay or perhaps owner looking for free info on how to finish.It smells like a rat

 

[icanfixit]

Update

Update

Tap rule-
From the junction box the two sets of #6 feed to two different 60amp fused disconnect switches that are located 6ft and 30ft apart. The tap rule could apply except for one is located 30ft away and both are located on the other side of the block wall in different room.

Past contractor-
The person who orderd the project over a year ago has retired. The project has been idle for about a year. The generator was not sized correctly for the main project and was not the contractor's fault, so I have been told. The correct generator was ordered and the first generator was repostioned to hook to a diffeent building. From what I get out of it there was a order for one generator and it turned into two.
I have been working at this complex for over 15 years. I usally end up years later going back over my own work as more renovations are done. In many ways I want things done right so that in the future when I have to work on it there will not be any problems. There is already a request to add another part of the building to the generator power. Once the system has been finished by the origional contrator I believe I will have to do the additional work.

 

[don_resqcapt19]

icanfixit,

he tap rule could apply except for one is located 30ft away and both are located on the other side of the block wall in different room.

The 30' is a problem but the fact that they are on the other side of the wall from the tap box is not.

 

[kingpb]

Wouldn't it be easier to put a 400A panelboard at the end of where the paralle conductors come together? That way addtional loads can be added without the worry of length to meet tap rules.

From what you explain, I think voltage drop is a possible issue. It would seem that the original (2) #4/0AWG per phase may have been for a smaller unit. To get the full 400A capacity you will need (4) #4/0AWG or (2) 500KCMIL per phase to have a 2% voltage drop @ 480V.

 

[iwire]

Wouldn't it be easier to put a 400A panelboard at the end of where the paralle conductors come together?

It is, and I know you will be surprised....a cost saving issue.

I can directly feed a number of disconnects or combination motor starters grouped together with out the need for a panel and breakers.

It really is a common method in buildings with lots of motors.

That way additional loads can be added without the worry of length to meet tap rules.

Yes, if the customer wants to spend the money today or when they add new equipment.

voltage drop is a possible issue. It would seem that the original (2) #4/0AWG per phase may have been for a smaller unit. To get the full 400A capacity you will need (4) #4/0AWG or (2) 500KCMIL per phase to have a 2% voltage drop @ 480V.

Now how can we possibly know what the voltage drop will be?

The installation has two 60 amp disconnects supplied with 400 amps of copper.

If that is all it is supplying than it seems someone already increased the copper in the run.

Code wise they could have run one set of 1 AWG CU with 125 amp OCP to these dual 60 amp disconnects.

Of course at 800' I doubt the customer would have liked the result.

 

[kingpb]

If that is all they are going to supply, somebody sure wasted their money on 400 amps worth of generator.

And, now, why would you think I would be surprised by cost cutting, (I mean savings) measures??

 

[iwire]

If that is all they are going to supply, somebody sure wasted their money on 400 amps worth of generator.

Did you spec that generator.

Seriously though, that is a interesting point even though I still would not figure the VD based on 400 amps.

A generator with a 400 amp breaker will not be rated 400 amps and good design suggests not using a generator at its max output.

So I wonder what amount of current should be used for the VD?

 

[icanfixit]

Thank you

Thank you

Thank you for all the replies. I know some of the work that was performed was according to the code and some was not. This is my first time posting an item for comment.
Chris