dimmer linnier or non linier (not sure how to spell linnier)

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tajaj

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i am estimating a dimmer rack feed 800 amp wye 240/120 , two sets of 500mcm will work if non linier. three sets of 350 mcm if linier the factory cant say if it is linnier or not but they are kinda sure it is nonlinnier. who can tell me if it is or not it makes the difference on if you count four or three conductors for derating. just answers to the question dont tell me how wrong it is.
 
tajaj said:
two sets of 500mcm will work if non linier.
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No it won't. A set of 500 MCM is only good for 380 amps, and a pair of them is only good for 760 amps. So if the load is more than 760 amps, then you can't use a pair of 500's. That has nothing to do with whether or not the load is linear.
 
A typical SCR dimmer is the very definition of a non-linear load.

An 800 amp dimmer is probably in a theatrical or TV studio setting, and thus oversized neutrals would be needed there in any case.
 
tajaj said:
i am estimating a dimmer rack feed 800 amp wye 240/120 , two sets of 500mcm will work if non linier. three sets of 350 mcm if linier the factory cant say if it is linnier or not but they are kinda sure it is nonlinnier. who can tell me if it is or not it makes the difference on if you count four or three conductors for derating. just answers to the question dont tell me how wrong it is.
Click to expand...

OK, I won't tell how wrong it is but, I will tell you that there is no such thing as a "wye 240/120" so this along with other problems in your post basically suggest this is probably over your head.

Roger
 
sorry this is over my head but if i only did things i already knew then all i would get done is pointing out little faults of others. to learn you must do things that are new and challenging. yea 208/120 what ever just wanted to know if a 800 amp dimmer rack is a linear load the engineer and three unuoin contractors have done this job three times i questioned them and was told to prove they were wrong first contractor used 3/0 thhn three sets in two inch. second one used 500mcm in three inch two sets now the third is asking me why he cant use 300mcm in 3 2.5 inch conduits. the nmbers i get call for 350mcm x3 sets. the xfmr and disco are starting to look like swis cheese. and i get 840 amps for 500mcm in two three inch conduits if the load is linear.
 
tajaj said:
the nmbers i get call for 350mcm x3 sets. the xfmr and disco are starting to look like swis cheese. and i get 840 amps for 500mcm in two three inch conduits if the load is linear.
Click to expand...
So go with the biggest neutrals you can still fit in the conduits.
 
tajaj said:
first contractor used 3/0 thhn three sets in two inch. second one used 500mcm in three inch two sets now the third is asking me why he cant use 300mcm in 3 2.5 inch conduits. the nmbers i get call for 350mcm x3 sets. the xfmr and disco are starting to look like swis cheese. and i get 840 amps for 500mcm in two three inch conduits if the load is linear.
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You'll end up with this:

3 sets 3/0 = 600 amps Linear, 540 amps Non-linear
(3*200=600) or (3*225*.8=540)

2 sets 500 kcmil= 760 amps Linear, 688 amps Non-linear
(2*380=760) or (2*380*.8=688)

3 sets 300 kcmil = 855 amps Linear, 768 amps Non-linear
(3*285=855) or (3*320*.8=768)
 
tajaj said:
i am estimating a dimmer rack feed 800 amp wye 240/120 , two sets of 500mcm will work if non linier. three sets of 350 mcm if linier the factory cant say if it is linnier or not but they are kinda sure it is nonlinnier. who can tell me if it is or not it makes the difference on if you count four or three conductors for derating. just answers to the question dont tell me how wrong it is.
Click to expand...
just to confirm, the 800amp is the OCPD rating, and not the max the dimmer rack is rated for, correct?
 
My way
Ok I got off my butt and did some thinking on my own but only because you guys are so hard on people.
It is a phase control dimmer so that means non linear 520 def.
So the neutral counts in derating for conduit fill 80% more than three (4).310b
Ok 75 deg c per 110(something)c
400mcm thwn three sets in 3” conduit each with 1/0 ground and four 400’s. 800 amp fused disco. Emt conduit.
Don’t need to oversize neutral as this is fixed equipment.
Dimmer load is 276kva. 766 amp.
Their way
Ok now this is how it is two sets of 500 mcm in three inch four 500 each conduit with 1/0 ground.
In emt.
 
tajaj said:
why can't i use the 90c column for my conductors?
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you can find lugs rated at 90c from burndy ilsco ideal etc but the circuit breaker may only be rated 75c tops or if its not labeled with it its rated at 60c. you can use the 90c colum for derating if you want. article 110 explains this a little more so does article 310:smile: :smile:
 
tajaj said:
My way
Ok I got off my butt and did some thinking on my own but only because you guys are so hard on people.
It is a phase control dimmer so that means non linear 520 def.
So the neutral counts in derating for conduit fill 80% more than three (4).310b
Ok 75 deg c per 110(something)c
400mcm thwn three sets in 3? conduit each with 1/0 ground and four 400?s. 800 amp fused disco. Emt conduit.
Don?t need to oversize neutral as this is fixed equipment.
Dimmer load is 276kva. 766 amp.
Their way
Ok now this is how it is two sets of 500 mcm in three inch four 500 each conduit with 1/0 ground.
In emt.
Click to expand...

2 sets of 500 kcmil with non-linear loads will require derating, therefore the 688 amp adjusted ampacity is not large enough for a connected load of 766 amps.
 
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