PLEASE HELP!

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allmarc

Member
Location
Chicago
Commercial installation

Existing feeder into space is a 3? conduit with 4 # 350mcm

The total connected load for the tenant will be 265FLA

The Fuses at the Landlords MDP are 350amps

The main breaker within the tenant space is 400amps

All loads are at 120/208volt 3phase 4wire



Question is

Can the 350mcm conductors remain or do we have to up size to 500mcm?



Let us know as soon as possible, I am having a meeting with the inspector on Monday and would like to be equipped with the necessary feedback



Thanking you in advance for your input
 

infinity

Moderator
Staff member
Location
New Jersey
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Your connected load is 265 amps and 350kcmil Cu is rated for 310 amps using 75 degree terminations. Since 310 amps isn't a standard size you can go up to the next standard size OCPD which is 350 amps. Look at 240.4(B) and 240.6.
 

allmarc

Member
Location
Chicago
Trevor,
So i believe we are in agreement
The landlords fuse is 350amps and the cables are 350mcm which at 90o are rated at 350amps
The tenant panel is equiped with a 400amp main breaker, but this now will only act as a disconnect switch since the cables are protected by the 350amp fuses-do you agree?
The 400amp breaker in the tenant space has a 65k aic rating and the lugs should be rated at 90o
What do you think?

Thanks for Allmarc
 

pierre

Senior Member
Allmarc

"The 400amp breaker in the tenant space has a 65k aic rating and the lugs should be rated at 90o
What do you think? "

I highly doubt that the lugs will be rated for 90 C. Most likely 75 C or possibly even 60 C depending on how old the existing equipment is.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Allmarc,

There are no UL Listed ovecurrent devices with terminations rated above 75C.

The rating stamped on the lug itself, is not the determining factor.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I agree with Pierre and JIm, lugs for 350 kcmil conductors would be rated for 75 degrees not 90 degrees.
 

allmarc

Member
Location
Chicago
so can the 350mcm stay or do we bite the bullet and upsize all conductors for the 400amp tenant breaker and not the fuse size?
 

infinity

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Staff member
Location
New Jersey
Occupation
Journeyman Electrician
allmarc said:
so can the 350mcm stay or do we bite the bullet and upsize all conductors for the 400amp tenant breaker and not the fuse size?

In your present set up, the 350 kcmil conductors are protected at 350 amps. This is fine given your connected load and applying the provisions of 240.4(B).
 

A/A Fuel GTX

Senior Member
Location
WI & AZ
Occupation
Electrician
What about derating for the four current carrying conductors here?


350A * .80 = 280A

Shouldn't the OCPD be 300A here?
 

RUWired

Senior Member
Location
Pa.
Does'nt the neutral in a 120/208 3phase 4-wire count as a current carring conductor.The 350 cu in this case is only rated @ 280 amps(350x.8 ).The next higher allowed is a 300 amp breaker.5oo kcmil would be the proper wire size to use in this case.(430x.8=344amp.Next higher=350amp breaker).8)
Rick
 

don_resqcapt19

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Location
Illinois
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retired electrician
Why are you counting the grounded conductor as a current carrying conductor? I don't see anything to indicate that the majority of the load in nonlinear.
Don
 

A/A Fuel GTX

Senior Member
Location
WI & AZ
Occupation
Electrician
Well, since it isn't stated one way or the other, wouldn't we assume that most loads are non linear in average everyday situations?
 

infinity

Moderator
Staff member
Location
New Jersey
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I'm with Don. There is nothing that indicates that a major portion of the load is non-linear. Therefore the grounded conductor is not considered a CCC and no derating is required.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
m73214 said:
Well, since it isn't stated one way or the other, wouldn't we assume that most loads are non linear in average everyday situations?


I wouldn't. IMO most loads are linear in nature and do not produce harmonics.
 

RUWired

Senior Member
Location
Pa.
Allmarc, What is the major portion of this 265a calculated load and is any of this load going to be continuously operated?
Rick
 

Zifkwong

Member
Does 240.4 B apply? I never really used this section. After reading it though it seems like it wouldn't apply. Dont the tenant spaces have multi-oulet branch circuits being fed from these feeders?
 

iwire

Moderator
Staff member
Location
Massachusetts
240.4(B) applies to feeders, it may apply to some branch circuits.

It does not apply to a branch circuit with multi outlets.
 
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