Wire Size?

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Red Forman

Red Forman

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Longview,Texas
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Electrical Designer
I have an old Industrial facility, It has a 250 Cu feed (3phase) to a weatherhead that splits to feed two separate 200A fused disconnects in separate warehouses. Is this correct or should the wire be upgraded to accommodate 400 amps worth of power? This type of situation has always been a little confusing.
 
With multiple disconnects, the size of the service conductors can be based on the calculated load so the 250Cu might be large enough.
Feeding two disconnect that are not grouped at one location is questionable. There are many variables involved such as conduit routing (interior vs exterior0, occupancy, fire walls, etc.
more info is needed to address that.
 
augie47 said:
With multiple disconnects, the size of the service conductors can be based on the calculated load so the 250Cu might be large enough.
Feeding two disconnect that are not grouped at one location is questionable. There are many variables involved such as conduit routing (interior vs exterior0, occupancy, fire walls, etc.
more info is needed to address that.
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The disconnects in question are actually side by side. I misstated my question a little bit. The feed comes from a main 400a disconnect to the disconnects in question (which are mounted side by side approx. 50' away from main.) Then those disconnects run to the weatherhead and then overhead to their respective warehouses with each warehouse having a 200a fused disconnect inside. It was originally ran with the 250 directly to the weatherhead and then split via splice blocks into two separate 3/0 feeds to their respective warehouse disconnect.
 
The wire on the load side of the 400 amp disconnect must have an ampacity of at least 400 amps unless one of the tap rules apply.
 
jap said:
Wouldn't the "next size up" rule still be allowed until you got to 800 amps?

JAP>
Click to expand...
Yes, but the next size up for 250 kcmil is 300 amps, not 400.
In addition, since the 250 is not being protected at its ampacity, then it must be a tap conductor, and if it is a tap, then you are not permitted to connect the 200 amp tap conductors to the 250.
 
don_resqcapt19 said:
Yes, but the next size up for 250 kcmil is 300 amps, not 400.
In addition, since the 250 is not being protected at its ampacity, then it must be a tap conductor, and if it is a tap, then you are not permitted to connect the 200 amp tap conductors to the 250.
Click to expand...

Just saying, you wouldn't have to use a conductor rated for the full 400 amps.

One could use 500mcm copper for a 400 amp feeder.

JAP>
 
don_resqcapt19 said:
The wire on the load side of the 400 amp disconnect must have an ampacity of at least 400 amps unless one of the tap rules apply.
Click to expand...
Actually the wire needs to have an ampacity equal to any overcurrent protection which may be in the 400A disconnect.

The OP needs to look inside the 400A disconnect as well as the (2) disconnects.
Also, how much of these conductor runs are outside of the building? Are the overhead conductors separate or in a cable?
 
Just install 2- 200 amp disconnects under the 400 amp disconnect or replace the 400 amp disconnect with 2-200 amp units.
 
don_resqcapt19 said:
Yes, but the next size up for 250 kcmil is 300 amps, not 400.
In addition, since the 250 is not being protected at its ampacity, then it must be a tap conductor, and if it is a tap, then you are not permitted to connect the 200 amp tap conductors to the 250.
Click to expand...

Actually the 250 kcmil may be protected at it's ampacity.

We don't know.

The 400 amp disconnect could have any fuse size installed in it from 201 to 400 amps.

JAP>
 
I feel like we are discussing a feeder, not service conductors.

If there are fuses in the 400 amp disconnect sized to protect the 250 kcmil feeding the (2) 200a fused disconnects, and, your not having any issues with it like it is, leave it alone, it's fine just the way it is.

If the 400a disconnect is actually a non fused service disconnect for the 250 kcmil, and, the load side service conductors are all outside until they reach the (2) 200a fused disconnects, and, your not having any issues as it is, leave it alone, it's fine just the way it is.


JAP>
 
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