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#78845 - 10/28/01 09:32 AM Sub-Panels
frodo Offline
Member

Registered: 05/16/01
Posts: 129
Loc: louisville, ky usa
I was wondering what is the maximum limit of sub-panels that can be installed from a sub-panel that is fed from a main panelboard?

the sub-panel has a main as well as the main panelboard. the first sub-panel is protected on the supply side by a 100A two pole.

the voltage is 120/208.

i want to install a 100 amp sub panel from a 200A sub-panel that is fed from a 200A main panelboard, that also has a 200A main.

i want to use 3 #4 in a 1" emt, using the emt as the egc.

i will place a 100A main in my subpanel.

is this legal? what about 408.16 (A)?

thanks for any replies.

[This message has been edited by frodo (edited 10-28-2001).]

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#78846 - 10/28/01 09:47 AM Re: Sub-Panels
Redsy Offline
Member

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
frodo,
If you really need the second 100 amp panel due to load requirements, you might end up shutting down the first 100 amp panel due to overload.
It sounds like a co-ordination issue. Can you feed the second 100 amp panel from the main panel.
Also, do you mean 4 #3s?
And, as has been seen before, using the EMT as EGC is hotly debatable.

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#78847 - 10/28/01 09:59 AM Re: Sub-Panels
frodo Offline
Member

Registered: 05/16/01
Posts: 129
Loc: louisville, ky usa
there is not much load on the first sub-panel. the main panel is a different story.

i located the subpanel in the building while searching for a route from the main panel.

it would be very difficult to get from the main panel to where the circuit terminates at a 125 subpanel with a 100A main. i decided it would be legal to feed my new subpanel from the 1st subpanel.

as far as the number of conductors i plan to use, i want to use the 1" conduit for the ground, so as to only have to pull in 3 #4's...EMT is permitted as the EGC isnt it?

if not do i have to pull in a foruth conductor?

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#78848 - 10/28/01 01:06 PM Re: Sub-Panels
Glenn Offline
Member

Registered: 01/17/01
Posts: 78
How are you , without violating 310-16, going to protect #4 with 100 A OCP?

[This message has been edited by Glenn (edited 10-28-2001).]

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#78849 - 10/28/01 01:30 PM Re: Sub-Panels
frodo Offline
Member

Registered: 05/16/01
Posts: 129
Loc: louisville, ky usa
short time overload calculation....

also see 240-3 & 240-3(b)&
110-14(c) and 210-19(a)
"#4 is routinely used for 100A services here" western, ky...i am assuming i can apply the same rule to the #4 with a 100A OCPD? if not i would have to reduce to a 90A OCPD?

the panel is rated 125A

[This message has been edited by frodo (edited 10-28-2001).]

[This message has been edited by frodo (edited 10-28-2001).]

[This message has been edited by frodo (edited 10-28-2001).]

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#78850 - 10/28/01 01:39 PM Re: Sub-Panels
frodo Offline
Member

Registered: 05/16/01
Posts: 129
Loc: louisville, ky usa
the load is "non-continuos" conductors are 90 degree celcius THHN 120/240 vac

[This message has been edited by frodo (edited 10-28-2001).]

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#78851 - 10/28/01 02:06 PM Re: Sub-Panels
frodo Offline
Member

Registered: 05/16/01
Posts: 129
Loc: louisville, ky usa
i guess i cant get away with using a 100A OCPD on #4 THHN. the best thing to do would be to reduce the OCPD to 90A at both ends.

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#78852 - 10/28/01 02:16 PM Re: Sub-Panels
Bill Addiss Offline
Member

Registered: 10/07/00
Posts: 4196
Loc: NY, USA
Frodo,

The #4 is only allowed for a service to a Dwelling. Anywhere else you have to go according to the tables for ampacity.

Bill

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#78853 - 10/28/01 03:31 PM Re: Sub-Panels
sparky Offline
Member

Registered: 10/18/00
Posts: 5545
Frodo,
Read 310.15B6 and table, per Bill's post

Also, the code does not limit how many subpanels are in any given premisis, we could do a 'frankenstien home' with OCPD's in every room ( ok, not the bath..) and as long as 220 was met it would be compliant.

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#78854 - 10/28/01 05:48 PM Re: Sub-Panels
frodo Offline
Member

Registered: 05/16/01
Posts: 129
Loc: louisville, ky usa
hi,
thanks for all the input. i appreciate it...i am going to try and find a 90A main to limit the load to 90A...

as always you can count on solid info from ECN

-regards

frodo

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