Over Current Protection

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killer76

Member
I have a question on over current protection for a main lug only load center

I have a QO112125 I have been told that I do not need a circuit breaker rated for the main buss

and may place a 20 amp circuit breaker for over current protection

the load center will have only (2) 10 amp breakers at the time of manufacturing

Please direct me to the location in the code were I can find this information

thanks
Robert
 

jbwhite

Senior Member
Re: Over Current Protection

Is your last name Kilkenny? I was in the navy with a guy named bob kilkenny.

Why are you using a MLO panel and field installing a main breaker?

Can you fill us in on more of the details of the install?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: Over Current Protection

There is no code minimum on the size of the OCPD that is used to protect the panel. The code only sets a maximum size and that is the rating of the panel itself.
Don
 

killer76

Member
Re: Over Current Protection

no not mr Kilkenny sorry


ok maybe not enough info, sorry

I needed to ask if it is to code to install a 20 amp main circuit breaker for protection to a load center rated for 125 amp

I do not see this as safe in the event that the panel can allow for a increased number of breakers
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Re: Over Current Protection

As Don said there is no minimum only a maximum, 408.36(A). Also be sure to follow 408.36(D).

Now, why do you think it is unsafe? Because the busbars are 125A and the protection is 20A?
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Re: Over Current Protection

Originally posted by killer76:
I do not see this as safe in the event that the panel can allow for a increased number of breakers
Killer check out your own panel. I'll bet the breakers total higher than the main, unless you have an unnecessarily-large service.

To add: an OCP device is supposed to be the weak link in a circuit or system; that's how it does its job: minimizing equipment and wiring damage.

[ January 12, 2006, 06:47 PM: Message edited by: LarryFine ]
 

paul32

Senior Member
Location
Minnesota
Re: Over Current Protection

Originally posted by killer76:

I do not see this as safe in the event that the panel can allow for a increased number of breakers
This makes me wonder if you really mean "main." If you reverse feed a 20A breaker to supply the panel, what they said is right, no problem. You can have as many load breakers as you want. Your comment above suggests to me you are feeding the panel through the main lugs and putting a 20A breaker in it, with room for more. In that case the feeder supplying the panel would have to limit it to the panel rating.

[ January 12, 2006, 06:45 PM: Message edited by: paul32 ]
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Re: Over Current Protection

Originally posted by paul32:
In that case the feeder supplying the panel would have to limit it to the panel rating.
Technically speaking, the OCP device protecting the feeder does that.
 

killer76

Member
Re: Over Current Protection

I see that 408.36 indicates a combined rating not greater than the panel board, and does not have a minimum

my application is a UPS MLO Load center with only (2) 10 amp breakers, with an EXP 20 amp Main outside only 120v feed

it now makes since just like a smaller main in the panel, don't know what I was thinking
sorry to have even asked now duh....

thanks jim dungar for the location in the code

thanks again for all your help,
 

triphase

Senior Member
Re: Over Current Protection

I have been around awhile and granted have not seen or have not done everything and maybe I just woke up after a long sleep, but I don't think I have ever seen a "10 Amp Breaker" Educate Me. Thanks.
 

bdarnell

Senior Member
Location
Indianapolis, IN
Occupation
Retired Engineer
Re: Over Current Protection

Triphase, I was just about to say, SquareD makes a QO110. But you found it.

The other issue I have with this is, it's a loadcenter, presumably with plug in breakers. Don't think you can use a plug in style breaker as a main without supplemental hardware to fasten it to the panel.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Re: Over Current Protection

If it is a QO112L125G loadcenter all that is needed is a #PK4MB2LA retaining kit
 
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