Should I install a second Main Breaker?

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11Haze29

Member
Location
Rhode Island
Occupation
Electrical Engineer
I have a large residential install which will utilize a pad mount transformer, and a Milbanks 400A meter socket enclosure with a 400A disconnect. Transformer and Meter enclosure will be about 70 feet away from the house. Milbanks tells me the 400A disconnect is actually a circuit breaker with Instantaneous and Long Time. A 400A Square D NQ panelboard will go in the basement of the house. My question to all is this: Since overcurrent protection for the 400A service feeders is provided in the Milbanks meter enclosure - should I install an additional 400A MCB in the NQ panelboard. I'm thinking it is not a mandatory requirement, but it does provide some convenience if you need to 'open' the service MCB. Its a New England location so could be snow on the ground if you need to isolate the service during winter. But a MCB in the panelboard adds cost and increases the height of the panelboard, and how often do you really need to disconnect the whole panelboard from the service. Even with a panelboard MCB, you would still have hot lugs in the panelboard.

What are you thoughts on the subject?
 
You need a disconnect at the house per 225.30. It must either be outside or inside nearest the point of entrance of the feeder conductors. If you are on the 2023 code, 225.41 will require the disconnect to be outside either on or within sight of the house. Per 110.29, 70' is not within sight.
 
don_resqcapt19 said:
You need a disconnect at the house per 225.30. It must either be outside or inside nearest the point of entrance of the feeder conductors. If you are on the 2023 code, 225.41 will require the disconnect to be outside either on or within sight of the house. Per 110.29, 70' is not within sight.
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I generally do not like to have a service disconnect on a remote pedestal, and I'm not sure why it seems like the majority of people install one. It ends up just being extra unnecessary equipment because you will typically need another one at the house regardless. Another disadvantage is then you need to run four wire to the house.
 
electrofelon said:
I generally do not like to have a service disconnect on a remote pedestal, and I'm not sure why it seems like the majority of people install one. It ends up just being extra unnecessary equipment because you will typically need another one at the house regardless. Another disadvantage is then you need to run four wire to the house.
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Required by the rural utility in our area. Probably the case for other utilities too.
 
electrofelon said:
I generally do not like to have a service disconnect on a remote pedestal
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If you were a utility you would not want too much customer owned infrastructure between the NEC service point and the customer demarcation point. Every foot of wire between a sealed meter and a service disconnect increases the likely hood you'll need to send a linemen to unseal the meter for some troubleshooting reason
 
I would always install over-current protection at the pedestal required or not. Would much rather the customer owned conductors be able to shut off if damaged.
 
OP. You should perform short circuit calculation at the end of the conductors. With a 400 amp service there is a good chance it may be over 10K.
If you have a Square D main it will be series rated and allow 10K branch/feeder breakers.
 
tortuga said:
If you were a utility you would not want too much customer owned infrastructure between the NEC service point and the customer demarcation point. Every foot of wire between a sealed meter and a service disconnect increases the likely hood you'll need to send a linemen to unseal the meter for some troubleshooting reason
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curt swartz said:
I would always install over-current protection at the pedestal required or not. Would much rather the customer owned conductors be able to shut off if damaged.
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Life is full of what ifs. In my opinion, the disconnect and all those connections is just another place you can have problems, failures etc.
 
The Milbanks 400A meter enclosure is rated 22KAIC. I have to check with the utility, but my initial guess is that Milbanks designs to meet utility requirements. The Square D NQ panelboad can be had with all 22KAIC breakers. So I don't think fault current will be a limiting factor.
 
11Haze29 said:
The Milbanks 400A meter enclosure is rated 22KAIC. I have to check with the utility, but my initial guess is that Milbanks designs to meet utility requirements. The Square D NQ panelboad can be had with all 22KAIC breakers. So I don't think fault current will be a limiting factor.
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There is a good chance you can use standard 10kaic breakers either because they will have a series rating with an upstream device or the fault current will drop enough by the time it gets there.
 
As this is the exact setup on one I am still dealing with and sort of in limbo, I personally would just want a disconnect at the ped, and NOT an OCPD! Customer keeps popping their 200A Milbanks on a demanding motor start.

I firmly agree with having that disconnect there.
 
11Haze29 said:
The Milbanks 400A meter enclosure is rated 22KAIC. I have to check with the utility, but my initial guess is that Milbanks designs to meet utility requirements. The Square D NQ panelboad can be had with all 22KAIC breakers. So I don't think fault current will be a limiting factor.
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electrofelon said:
There is a good chance you can use standard 10kaic breakers either because they will have a series rating with an upstream device or the fault current will drop enough by the time it gets there.
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My point was the series rating will only work if there is a 400 amp Square D breaker between the meter and the branch breakers.

For out project. Since Square D has not been willing to offer a 2020 NEC compliant (1 service disconnect per compartment) Class 320 combination service entrance device my supplier has been selling Milbank class 320 service panel. Typically for class 320 services the utility specs around 18KA. Milbank uses their own main breakers (Zinsco) but does not offer branch breakers. They list Siemens, Eaton & GE/ABB as listed branch breakers. Since they is not series rating we are required to use 22K branch breakers in the service panel. For feeders we install square D main braker apnles which have the series rating.
 
curt swartz said:
My point was the series rating will only work if there is a 400 amp Square D breaker between the meter and the branch breakers.

For out project. Since Square D has not been willing to offer a 2020 NEC compliant (1 service disconnect per compartment) Class 320 combination service entrance device my supplier has been selling Milbank class 320 service panel. Typically for class 320 services the utility specs around 18KA. Milbank uses their own main breakers (Zinsco) but does not offer branch breakers. They list Siemens, Eaton & GE/ABB as listed branch breakers. Since they is not series rating we are required to use 22K branch breakers in the service panel. For feeders we install square D main braker apnles which have the series rating.
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Yeah i was a little vague in my last post, thanks for being more clear. I was aware the mill bank would not series rate with the square d, but it sounds like he's going to need another disconnect either on the outside of the house or inside, depending on code cycle, so could use a square D and get the series rating.

I would try to avoid 22k Branch breakers just for convenience, but actually they may be cheaper than adding a 400 amp main breaker (if that was the only thing it was used for). If I remember right, I priced this out for Siemens panel boards and it was like a $6 per pole premium for 22k.
 
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