125 amp 208 3 phase panel fed from 100 amp fuses.

S

steve61

licensed Electrical Contractor
Location
Nebraska
Occupation
Electrician
I am planning to install a 125 amp 208 3 phase panel for several 120 vac loads. I want to feed it with 100 amp fuses so that I can run 3 # 1 thhn, a # 6 thhn neutral and a # 8 EGC. This way I can use # 1 thhn and 1 1/4 EMT all of which I have in stock. The 120 vac loads will not get any where close to 100 amps so I think I will be ok with this installation.
Also, This panel does not come with a grounding terminal bar. Can I just purchase and install a grounding bar to allow connection for all of the EGC's ?
 
If you feed it with a 100 amp supply you can use #3 THWN unless there are some mitigating factors.
Unless you can justify reducing the neutral, it would need to be full size for that feeder.
 
Is it an Eaton panel?

I will never understand why they do this, but they ship their MLO panels with a bonded neutral bar and no ground bar.

The situations where this might work are so infinitesimally small that it’s not worth noting. So you must purchase a separate ground bar and unbond the neutral bar.

Even their panels with an MCB ship without a ground bar.
 
I forgot to mention. I will be feeding this panel from a 100 amp buss duct disconnect in the ceiling of our plant where we have a bus duct system in place. I am using the 60 degree C column in 310.16 since I want to feed it with less than the 125 amp rating and also since the wire feeding it will be smaller than # 1 wire. # 3 is only good for 85 amps according to 310.16.
Since this is a stand alone panel, do I still need to run a full size neutral ?
 
One more thing. The main lugs are marked for 2/0 through # 14. Does this mean that I can use the 75 degree C column ?
 
I'm curious, what is the voltage in the buss duct?

The reason I ask is it seems you're thinking about installing a Single Phase 120/240v Panel.

Is the buss duct actually 208/120v 3ph 4w? 208v Delta? 120/240v 3ph Delta? 120/240v 3ph 4w with a wild leg? 480/277v 3ph 4w? 480v 3ph delta?

JAP>
 
steve61 said:
One more thing. The main lugs are marked for 2/0 through # 14. Does this mean that I can use the 75 degree C column ?
Click to expand...
The allowable conductor size is mostly irrelevant as far as termination temperatures.
In all probability the 75° rating is allowed at both terminations.
 
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