Upgrading service on a 3 family house

[mtnelectrical]

I am upgrading the 100 amp service on a 3 family house. The existing service is 100 amps for the 3 apartments. It will be upgraded to 200 amps. Is there a minimun amps for the apartments main? they are protected by 30 amps fuses now.

 

[kwired]

I am upgrading the 100 amp service on a 3 family house. The existing service is 100 amps for the 3 apartments. It will be upgraded to 200 amps. Is there a minimun amps for the apartments main? they are protected by 30 amps fuses now.

There is no minimum required size for the feeder(s), just has to be enough to supply whatever the calculated load is.

 

[GoldDigger]

There is no minimum required size for the feeder(s), just has to be enough to supply whatever the calculated load is.

If there are common-area loads like outside lighting or laundry, will you be adding an additional house sub-panel to use some of the extra power that the 200A service will give? Or will you be running larger feeders to new or existing sub-panels?

 

[Strummed]

Why is the customer upgrading the service?

 

[mtnelectrical]

We will be adding a House meter, but no more loads, that is being served by one apartment right now. And the reason for upgrading is all these panels are fused and the owner wants to relocate the service from basement to outside wall.

 

[infinity]

The asnwer might be in here:

230.79 Rating of Service Disconnecting Means. The ser-
vice disconnecting means shall have a rating not less than
the calculated load to be carried, determined in accordance
with Part III, IV, or V of Article 220, as applicable. In no
case shall the rating be lower than specified in 230.79(A),
(B), (C), or (D).
(A) One-Circuit Installations. For installations to supply
only limited loads of a single branch circuit, the service
disconnecting means shall have a rating of not less than
15 amperes.
(B) Two-Circuit Installations. For installations consisting
of not more than two 2-wire branch circuits, the service
disconnecting means shall have a rating of not less than
30 amperes.
(C) One-Family Dwellings. For a one-family dwelling,
the service disconnecting means shall have a rating of not
less than 100 amperes, 3-wire.
(D) All Others. For all other installations, the service dis-
connecting means shall have a rating of not less than
60 amperes.

 

[GoldDigger]

The asnwer might be in here:

OK, the disconnecting means has to be rated for 60A minimum, but if that disconnecting means is not also the OCPD, the fuse or breaker does not have to be 60A or larger?
And the service disconnecting means would be applicable because the meter for each of the four MAIN panels would be on the POCO side, and there would not be a master disconnecting means upstream of the four meters?

 

[kwired]

The asnwer might be in here:

We need to know if the disconnect in question is the service disconnect. Once beyond the service disconnect there is no minimum feeder size to a dwelling unit, other than you must have at least 2 1500VA small appliance branch circuits and 3VA per sq ft. If you had a 200sq ft dwelling that would mean you need at least a 3600VA feeder, which would be 15A @ 240 volts. Since the SABC's are required to be 20 amp circuits I would like to think that maybe the feeder shouldn't be any less than 20A but don't see anything specifically saying this either.

 

[grasfulls]

60 amp minimum

60 amp minimum

The asnwer might be in here:

This is just what we had recently, only three meters, two units and one house meter in Palo Alto CA. Service ended up being 200 amps (they made us perform calcs for the entire building, segregated into units and common areas. The only disconnects were immediately after each meter, one at 125 amps, one at 100 amps for the units and one at what was originally going to be 50 amps (per calcs) but they made us do 60 per the referenced code section. There is no individual 200 amp main disconnect for the drop AND we were over 200 amps on our calcs AND the combined disconnect values.

I hope you can see the attachment, started in CAD, was 500 kb as a PDF, zoomed in, saved as a jpg....sheesh, tough to get under 146kb

 

[kwired]

This is just what we had recently, only three meters, two units and one house meter in Palo Alto CA. Service ended up being 200 amps (they made us perform calcs for the entire building, segregated into units and common areas. The only disconnects were immediately after each meter, one at 125 amps, one at 100 amps for the units and one at what was originally going to be 50 amps (per calcs) but they made us do 60 per the referenced code section. There is no individual 200 amp main disconnect for the drop AND we were over 200 amps on our calcs AND the combined disconnect values.

I hope you can see the attachment, started in CAD, was 500 kb as a PDF, zoomed in, saved as a jpg....sheesh, tough to get under 146kb

The service disconnecting means needs rated at least 60 amps. The feeder and overcurrent protection only needs to be according to the load. So in your installation a 60 amp disconnect with 50 amp fuses is fine. A single breaker enclosure rated for at least 60 amps with a 50 amp breaker installed would be fine.

If there would have been a 200 amp service disconnect ahead of the meters all those disconnects become feeder equipment instead of service disconnects and 230.79 doesn't apply at all.

ETA the more I think about this the more I think 230.79 possibly doesn't apply to individual disconnects where multiple disconnects are allowed. Any one else have any thoughts on this?

 

[grasfulls]

230.79

230.79

The service disconnecting means needs rated at least 60 amps. The feeder and overcurrent protection only needs to be according to the load. So in your installation a 60 amp disconnect with 50 amp fuses is fine. A single breaker enclosure rated for at least 60 amps with a 50 amp breaker installed would be fine.

If there would have been a 200 amp service disconnect ahead of the meters all those disconnects become feeder equipment instead of service disconnects and 230.79 doesn't apply at all.

ETA the more I think about this the more I think 230.79 possibly doesn't apply to individual disconnects where multiple disconnects are allowed. Any one else have any thoughts on this?

I had to review the load calcs, they only came out to a combined 171 amps, it was with a 25% allowance for growth that pushed the number over 200. Section 230.8 (Combined Rating of Disconnects) merely states that the combined rating shall not be less than the rating required by 230.79, so I think it does still apply. However, this also only requires a disconnect means not less than the calculated load. The AHJ enforced 230.79D and required a minimum of 60 amps to each loadcenter.

The combined rating of the three disconnects is 285 amps. Though perhaps unlikely, this does mean there is the ability to exceed the service drop rating of 200 amps. One would think that since the "weakest link" is the service drop and bussing for the meters, that the primary means of disconnect should not be allowed to exceed that. I do understand that disconnects are not installed to protect upstream equipment.... so is it just a reliance that the service will never see current beyond its rating?

Have we gone well beyond "Business Management / Estimating"?

 

[kwired]

I had to review the load calcs, they only came out to a combined 171 amps, it was with a 25% allowance for growth that pushed the number over 200. Section 230.8 (Combined Rating of Disconnects) merely states that the combined rating shall not be less than the rating required by 230.79, so I think it does still apply. However, this also only requires a disconnect means not less than the calculated load. The AHJ enforced 230.79D and required a minimum of 60 amps to each loadcenter.

The combined rating of the three disconnects is 285 amps. Though perhaps unlikely, this does mean there is the ability to exceed the service drop rating of 200 amps. One would think that since the "weakest link" is the service drop and bussing for the meters, that the primary means of disconnect should not be allowed to exceed that. I do understand that disconnects are not installed to protect upstream equipment.... so is it just a reliance that the service will never see current beyond its rating?

Single service disconnect - the upstream conductors must meet or exceed the overcurrent protection. Multiple service disconnects - the upstream conductors only need to meet or exceed the calculated load. It is done this way a lot with multiple disconnecting means. You might see 400 amps of disconnecting means but load calculations only have 200 or 300 amps of load - you do not need full 400 amp supply conductors in this case.

 

[Strummed]

Single service disconnect - the upstream conductors must meet or exceed the overcurrent protection. Multiple service disconnects - the upstream conductors only need to meet or exceed the calculated load. It is done this way a lot with multiple disconnecting means. You might see 400 amps of disconnecting means but load calculations only have 200 or 300 amps of load - you do not need full 400 amp supply conductors in this case.

I always found this odd.

For example, typically I would feed a 2-family house that had 2 X 100a panels with normal 200A service conductors. But if I did a load calc and it was under 100A I could feed it with a 100A service.

People could fudge on the load calcs or add a lot of stuff later and really push those conductors.

 

[kwired]

I always found this odd.

For example, typically I would feed a 2-family house that had 2 X 100a panels with normal 200A service conductors. But if I did a load calc and it was under 100A I could feed it with a 100A service.

People could fudge on the load calcs or add a lot of stuff later and really push those conductors.

People can fudge on any calculation, not just multiple service disconnecting means situations.

Adding load later means new load calculations to determine if sufficient capacity is available.

As long as NEC is met, everything else is design decisions.