Parallel feeder run? 400A 208V

[fastline]

So as I examine one of a complex of industrial buildings, I realized the power misspoke and what I thought was a 150kva 480/277 Xfmr, is a 208/120. Power comes in as parallel conductors into a trough where it goes into a distribution block, then broken off of that immediately into 3 main disconnects, so there is not a single main disconnect that carries all the load. Why they would bring in 208/120 into a large industrial space is beyond me! I might have to consider a higher voltage upgrade at some point but for now, I need to move about 400A of 208 about 50ft. I would either repurpose one of the main disconnects, or replace. Either way, the legs between the service distribution lug and the first disconnect would have to be either upgraded or paralleled to allow the higher ampacity. I was really trying to avoid a utility service disconnection for this work but the only other option is working it hot...... Work has to get done on that distribution lug, possibly even replacing it for the expansion.

Once I can get enough power to a disconnect, I need to run power about 50ft and I have priced either 750mil or a parallel 4/0 triplex. I was hoping to move 400A but appears due to derates (20% for 3-6 connductors), I land at just under 350A in which I had hoped it would be higher so I could use the 'next size up rule' to set it at 400A. for instance, 4/0Al is 205A at 90c, and with 20% derate, 164A*2 = 328. I think 750 was 348A.

Since I don't remember the last time I had to do a parallel run, I was wondering if there are other complicating factors other than 2 having to run 2 conduit runs? The conduit fill for 1.5" hits 40.16%!! So I get to bump to 2" over .16%?

At this point, i am probably not too concerned about running A neutral in this and would do that another way. 120V loads are not too important right now.

I was trying to stick with 4/0 mainly due to the price as a common triplex cable size.

 

[fastline]

LMAO.... I really should not try to design circuits with a beer in my hand! If Mods want to delete the above, that would be super! I don't know how I got to '3-6 conductors for derate'. If I don't throw in a neutral, this is a straight 75c calc right out of the bible!

So just to narrow down my question, which is really just the decision of a single 750mil run, or a parallel 4/0 run of conductors.

The parallel 4/0 run would be 180A*2 = 360A, size up rule, 400A OCPD
750mil single is 385A, still 400A OCPD.

I don't recall ever doing a parallel for a feeder, only a main service. However, I tend to believe it will dissipate heat better than a single run, not to mention training 750. Hate it!

 

[hillbilly1]

Not wanting to permit it, eh? LOL! 4/0 would probably be cheaper.

 

[augie47]

Parallel 4/0s in one conduit could not be placed on a 400 amp breaker (as you note--derated value is 328)
750s would take a 3" conduit whereas 4/0s in separate conduits could be in a 1-1/2
All factors considered I would likely do 2-conduits with 4/0

 

[fastline]

Parallel 4/0s in one conduit could not be placed on a 400 amp breaker (as you note--derated value is 328)
750s would take a 3" conduit whereas 4/0s in separate conduits could be in a 1-1/2
All factors considered I would likely do 2-conduits with 4/0

Ha, yeah, I forgot to mention 2 conduits but I am not aware you can even do a parallel in the same pipe? Inductance concerns? I seem to recall code disallows it?

Anywho, curious how you fly 1 1/2 EMT? I ran it through a calc and had 40.16% fill. ?? I mean this is literally a straight down the wall shot, I am not concerned, just wanting to create any code violations.

 

[fastline]

Not wanting to permit it, eh? LOL! 4/0 would probably be cheaper.

LMAO. However, this facility was recently acquired in which bandits went to chopping and destroying to recover $300 in scrap copper. It is a MESS right now, not to mention some of the previous shoddy work. I am scared to get brass involved yet. They would need to understand we are trying to fix this mess! There are bare wires that are LIVE, chopped off, found switches on going to nothing, just wow.

My intent is to start mapping the mess and probably removing most of it.

 

[augie47]

Ha, yeah, I forgot to mention 2 conduits but I am not aware you can even do a parallel in the same pipe? Inductance concerns? I seem to recall code disallows it?

Anywho, curious how you fly 1 1/2 EMT? I ran it through a calc and had 40.16% fill. ?? I mean this is literally a straight down the wall shot, I am not concerned, just wanting to create any code violations.

You are using AL and almost all AL is now compact conductors...I did assume EMT, Table 1A.. 3-4/0 XHHW Compact I believe is 1-12/" unless I misread

 

[hillbilly1]

LMAO. However, this facility was recently acquired in which bandits went to chopping and destroying to recover $300 in scrap copper. It is a MESS right now, not to mention some of the previous shoddy work. I am scared to get brass involved yet. They would need to understand we are trying to fix this mess! There are bare wires that are LIVE, chopped off, found switches on going to nothing, just wow.

My intent is to start mapping the mess and probably removing most of it.

I had an old Sam’s club they did that too. They apparently spent weeks there, all of the roof top units were nothing but a metal shell, all of the circuits feeding them, they built scaffolding out of pallets to reach the j boxes. They started to cut out the service, but halfway through the first cut, they figured out it was still live 480! Between the time I quoted it, and the job started, they broke in again and stole the panel feeders.

 

[fastline]

I had an old Sam’s club they did that too. They apparently spent weeks there, all of the roof top units were nothing but a metal shell, all of the circuits feeding them, they built scaffolding out of pallets to reach the j boxes. They started to cut out the service, but halfway through the first cut, they figured out it was still live 480! Between the time I quoted it, and the job started, they broke in again and stole the panel feeders.

What I've got is a combo between chopped off EMTs with live conductors in them, and some extremely poor electrical planning that looks like a blind guy designed this mess. Took me an hour just to get some grasp on what was even there and that was after moving the plastic tubs of crap off the 225 KVA transformer that is running but powering nothing! Not kidding!

You could not have reached a single disconnect if you wanted to. I don't yet know how to have that convo with the owner. Right now I am trying to figure out what is legit and safe, vs what is a DIY disaster. Every piece of wire needs checked for size and compared to the OCPDs.

It is not just the electric. Everything about this place smells of DIY bandit BS. Buildings are not even built right. We have load panels that are open, hanging, and live AF! I told people to NOT touch a thing until we tame this monster. It will take time but I need to get safe power moved to get some things spinning in the mean time.