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.
 
The bus duct voltage is 208 three phase with a neutral and a ground bar also. Since I will feed this panel with 100 amp fuses, this tells me that I would use the 60 degree column. But, the line terminals are stamped for 2/0 through # 14. Does the 2/0 stamping allow me to use the 75 degree column for wire size ? (110.14 c 1 a).
 
steve61 said:
The bus duct voltage is 208 three phase with a neutral and a ground bar also. Since I will feed this panel with 100 amp fuses, this tells me that I would use the 60 degree column. But, the line terminals are stamped for 2/0 through # 14. Does the 2/0 stamping allow me to use the 75 degree column for wire size ? (110.14 c 1 a).
Click to expand...
See post 9
 
I guess I will run 3 # 1's and a # 8 egc in 1 1/4 since I have to use the 60 degree column for the 100 amp current. # 3's would work if I could use the 75 degree column.
 
Seven-Delta-FortyOne said:
I will never understand why they do this, but they ship their MLO panels with a bonded neutral bar and no ground bar.
Click to expand...
That appears to be outside of the requirements of the product listing standard. The only panels that can be shipped with the neutral bonded to the enclosure are those marked "suitable for use as service equipment." Even when listed as "suitable for use as service equipment" the bonding connection is to be shipped loose, not installed at the factory.

The code changes in the 2020 code pretty much prohibit the use of a MLO panel as service equipment. The product standard has been changed to reflect the requirements in the NEC.

An equipment grounding bar is optional equipment with most brands.
 
With 3ph available, I'd be opting for dropping a 100a 3ph Feeder with (4) #3's and a #8 EGC to a 3ph MLO panel but that's just me.

Jap>
 
The reason that I was going to use the 60 degree column is because of 110.14(c)(1)(a). The way I understand this article is that since the circuit is 100 amps or less I have to use the 60 degree column. I would like to use the 75 degree column so that I can use smaller conduit and smaller wire. If I am wrong about this please enlighten me. Thanks.
 
steve61 said:
The reason that I was going to use the 60 degree column is because of 110.14(c)(1)(a). The way I understand this article is that since the circuit is 100 amps or less I have to use the 60 degree column. I would like to use the 75 degree column so that I can use smaller conduit and smaller wire. If I am wrong about this please enlighten me. Thanks.
Click to expand...
As far as I know, there hasn't been any 60 deg terminals in years, everything is 75 deg. The rule for using the 60 deg for 100A was only if the terminals were not marked.
 
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