Switchgear and panelboard section 408

augie47

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State Electrical Inspector (Retired)
230.71(B) allows the 6 disconnects in an enclosure for Service Disconnects
230.80 in combination with 230.79 and Art 110 provide that the calculated load not exceed the rating of the switchboard (buss)
Art 408 does not require switchboards to have a main.

What you are describing has been a common installation for years. Its up to the designer and the contractor to assure the S/B is not overloaded.
(I believe the requirements change in 2020)
 

hhsting

Senior Member
230.71(B) allows the 6 disconnects in an enclosure for Service Disconnects
230.80 in combination with 230.79 and Art 110 provide that the calculated load not exceed the rating of the switchboard (buss)
Art 408 does not require switchboards to have a main.

What you are describing has been a common installation for years. Its up to the designer and the contractor to assure the S/B is not overloaded.
(I believe the requirements change in 2020)

How? 230.80, 230.79 says nothing about switchboard bus its all about addition of service discos rating
 

augie47

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Tennessee
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State Electrical Inspector (Retired)
Fall back to 110.3(B) then 1000 amp switchboard is designed for 1000 amp load,.
 

don_resqcapt19

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Illinois
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retired electrician
I dont see how MLO Service Switchboard and their line side bus from 6 main service breakers inside the service switchboard considered service entrance conductor or service conductor? Those buses are not feeders either so where is it you are getting this from?


Also i dont see anything in Part II NEC 408 stating what you are saying for switchboard?
So the switchboard or switchgear uses non-conductive bus? Nothing in the code limits conductors to wire type conductors. The busing in switchgear or switchboards are conductors.
 

hhsting

Senior Member
So the switchboard or switchgear uses non-conductive bus? Nothing in the code limits conductors to wire type conductors. The busing in switchgear or switchboards are conductors.

I am not saying bus is conductor. I am saying bus inside the switchgear or switchboard is Not Service conductor. Keyword service its not from the utility
 

augie47

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Tennessee
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State Electrical Inspector (Retired)
I think we have beat this dead horse enough....
2 basics to keep in mind:
Your original questions:
1. Does this mean that switchgear that is NOT service equipment can be provided by breaker higher than its rating? For example MLO switchgear NOT service equipment is 1000A bus but up stream breaker can be 1200A trip? If no then I don’t see it in 408 part II? No, panleboards and switchboards other than service units must be protected at or below their rating

2. Does this mean that switchgear that IS service equipment is exempt or not like panelboard is for 408 part III 408.36? If it is then where is it in 408 part III or is it somewhere else in NEC 2017?
Service Switchboards & Panelboards are allowed to use "six disconnect rule"
 

don_resqcapt19

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Illinois
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retired electrician
I am not saying bus is conductor. I am saying bus inside the switchgear or switchboard is Not Service conductor. Keyword service its not from the utility
So the bus is a conductor and the rules in 240 for the protection of conductors apply as Jim said in post 10
 

don_resqcapt19

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Illinois
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retired electrician
For feeders maybe but not if switchgear is MLO service equipment
If the gear is MLO service equipment the bus is a service conductor and the only rule is that the ampacity of the bus must equal or exceed the calculated load. Of course there would also be the SSCR issue that would have to be looked at.
 
Conductors, including those in switchboards, need to be protected at there ampacity.
If you want code references look in110, 240, and 408.
It must still be protected by limiting it's loading.
I don't agree Jim. I actually agree with sting here. There is nothing in the NEC that requires a switchboard to be protected at it's rating by an OCPD. I don't know why there isn't a version of 408.36 for switch boards, you would have to ask the code writers that. I understand 110.3 addresses amperage and current ratings of equipment, but I see nothing in there that requires this by done with an OCPD. There are other ways equipment can be operated within their ratings, such as a load calculation.
 

jim dungar

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Wisconsin
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I don't agree Jim. I actually agree with sting here. There is nothing in the NEC that requires a switchboard to be protected at it's rating by an OCPD. I don't know why there isn't a version of 408.36 for switch boards, you would have to ask the code writers that. I understand 110.3 addresses amperage and current ratings of equipment, but I see nothing in there that requires this by done with an OCPD. There are other ways equipment can be operated within their ratings, such as a load calculation.
The rules in 230 prevent you from undersizing the service entrance gear based on your design loading, therefore no additional requirements are required in 408.
 
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