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#78845 10/28/01 12:32 PM
Joined: May 2001
Posts: 129
F
frodo Offline OP
Member
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 12:47 PM
Joined: Mar 2001
Posts: 2,056
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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.

#78847 10/28/01 12:59 PM
Joined: May 2001
Posts: 129
F
frodo Offline OP
Member
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?

#78848 10/28/01 04:06 PM
Joined: Jan 2001
Posts: 75
G
Member
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).]

#78849 10/28/01 04:30 PM
Joined: May 2001
Posts: 129
F
frodo Offline OP
Member
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).]

#78850 10/28/01 04:39 PM
Joined: May 2001
Posts: 129
F
frodo Offline OP
Member
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).]

#78851 10/28/01 05:06 PM
Joined: May 2001
Posts: 129
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frodo Offline OP
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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.

#78852 10/28/01 05:16 PM
Joined: Oct 2000
Posts: 4,081
Likes: 3
Member
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


Bill
#78853 10/28/01 06:31 PM
Joined: Oct 2000
Posts: 5,392
S
Member
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.

#78854 10/28/01 08:48 PM
Joined: May 2001
Posts: 129
F
frodo Offline OP
Member
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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