125 service 200 disconnect?

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stew

Senior Member
On a service panel changeout on 125 amp service where a few more circuits a re needed than the standard panel has may a person use a small 200 amp panel instead to get the added circuits. Seems ok to me but does the main disconnect have to be changed ? swap out the 200 for a 125? . Legal with the 200 ro no?
 

tonyi

Senior Member
If you're asking could a 200A MLO be hung off a 125A main, sure. Just make sure the lugs are spec'd to accept the smaller wire or you'll have to stub them out heavy and splice or backfeed it with a breaker..
 

stew

Senior Member
125 amp wire 200 disconnect

125 amp wire 200 disconnect

Ryan I am asking wheter or not with 125 amp service conductors I can connect them to a service disconnect rated 200 amps. In this case a 200 amp breaker in the service panel .
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Re: 125 amp wire 200 disconnect

Re: 125 amp wire 200 disconnect

stew said:
Ryan I am asking wheter or not with 125 amp service conductors I can connect them to a service disconnect rated 200 amps. In this case a 200 amp breaker in the service panel .


No.
 

tbonse

Member
Location
South Carolina
RE: 125 service 200 disconnect?

There are two possible scenarios as read with two possible answers.

1) You have a 125A Service with conductors rated for up to 125A as installed wired to a 200A panel with 200A breaker. This would be a violation.

2) You have a 125A Service with conductors rated for up to 125 A as installed wired to a 200A panel with a 200A breaker in that panel, fed by a 125A or less breaker at the main panel (assuming there are no other breakers in the main panel to potentially overload the system), then this is permitted and the 200A breaker in the subpanel is now just a service disconnect and not an overcurrent protection device. The 125A breaker regulates the available current to the subpanel.

As a general rule all current carrying portions of an electrical installation may be rated for a higher voltage/amperage/temp than required as long as the current limiting device (fuse/circuit breaker) is rated for the lowest V/A/temp portion of said configuration. There is one notable exception, and that is a multi-outlet circuit where the outlets themselves are the only devices rated for 15A while all other portions are rated for 20A including the CB, this scenario is permitted as each outlet can only accept a device designed to draw less than 15A (technically 12.5A due to the 80% rule) and there could potentially be another device plugged in to another outlet which would raise the total load above 15A whereas the individual outlets are not carrying greater than their rated 15A b/c they will not accept a plug for a device requiring higher current.
 
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