Sizing service entrance conductors for equipment with multiple meters / services.

[Gary Alzaga]

Seems like this should be an easy code section to find but I'm having trouble finding it.

Heres the scenario. A 4 gang meter section at a multifamily dwelling property. The meter section will feed 3 units and the property lighting and gate motor. 3 + 1 = 4. Each service disconnect will be 100 amps. FYI the units are 900 sq ft with only the basic alliances. The load calcs are way below 400.

My my question is. What code article might tell me how to size the service entrance conductors. Specifically that they can be sized below 400 amps because the odds of the tenants ever pulling 400 amps from the service is are very unlikely or that it must be sized based on the sum of all the disconnects in that service.

Any advice helps. Thanks.

 

[iwire]

You are looking for 230.90(A) exception 3

 

[Gary Alzaga]

Thank you. 230.90(a) exception 3 is for the service conductors. Now my question is what about the service equipment. Can that be sized under the sum of the rating of circuit breakers or fuses. Is there a code article for that.

Just writing this question it sounds like an unsafe idea or at least like an idea that lacks any room for future provisions. At first my objective was to be able to offer a customer the lowest price possible but now I'm just curious.

 

[jaggedben]

While I have zero experience installing such equipment, I believe every one of this type that I have ever surveyed (quite a few) was rated for 100A times the number of meters. As such, I think the time you could waste searching for something different may be worth more than any money you might save.

The common areas breaker, BTW, does not need to be rated 100A if the load doesn't call for it.

 

[Cow]

While I have zero experience installing such equipment, I believe every one of this type that I have ever surveyed (quite a few) was rated for 100A times the number of meters. As such, I think the time you could waste searching for something different may be worth more than any money you might save.

I agree, the best price on gear is the stuff that moves on a regular basis. Trying to find gear with lower ampacity bussing will most likely be a snipe hunt. I save those for our shop guy...

 

[Smart $]

Thank you. 230.90(a) exception 3 is for the service conductors. Now my question is what about the service equipment. Can that be sized under the sum of the rating of circuit breakers or fuses. Is there a code article for that.

Just writing this question it sounds like an unsafe idea or at least like an idea that lacks any room for future provisions. At first my objective was to be able to offer a customer the lowest price possible but now I'm just curious.

Prior to the 4-gang meter, the service entrance conductors must have an ampacity equal to or exceeding the calculated load for the building(s).

After the 4-gang meter, each set of service entrance conductors must have an ampacity not less than the respective unit or "house" calculated load and comply with 240.4(B) with respect to the OCPD rating at each service disconnecting means, which must be rated not less than 60A or the calculated load, whichever is greater.

 

[jaggedben]

Prior to the 4-gang meter, the service entrance conductors must have an ampacity equal to or exceeding the calculated load for the building(s).

After the 4-gang meter, each set of service entrance conductors must have an ampacity not less than the respective unit or "house" calculated load and comply with 240.4(B) with respect to the OCPD rating at each service disconnecting means, which must be rated not less than 60A or the calculated load, whichever is greater.

Pretty sure that if it's an apartment in a multi-unit building that is a 'one family dwelling' and must be 100A. I guess it's open to interpretation.

As far as busbars I've always considered that they are service conductors or service entrance conductors or whatever, based on their location and configuration. But I wonder if there's a code section that makes this explicit.

 

[Smart $]

Pretty sure that if it's an apartment in a multi-unit building that is a 'one family dwelling' and must be 100A. I guess it's open to interpretation.

The definition sorts it out.

Dwelling, One-Family. A building that consists solely of one dwelling unit.

Therefore, an apartment cannot be a one-family dwelling.

As far as busbars I've always considered that they are service conductors or service entrance conductors or whatever, based on their location and configuration. But I wonder if there's a code section that makes this explicit.

None that I'm aware of.

 

[Gary Alzaga]

Thanks guys. That really helps clear things up For me.

 

[electrofelon]

Pretty sure that if it's an apartment in a multi-unit building that is a 'one family dwelling' and must be 100A. I guess it's open to interpretation.

As far as busbars I've always considered that they are service conductors or service entrance conductors or whatever, based on their location and configuration. But I wonder if there's a code section that makes this explicit.

I have pondered that question. In regards to a meter/meter stack, there is no equivalent to 408.36, so I think it would default to a 110.3(B) and the calculated load.

 

[Gary Alzaga]

408.36 is specifically about overcurrent protection of panel boards. It says "a panel boars shall be protected by an overcurrent protective device having a rating than that of the panel board". In exception 1. it says "individua protection shall not be required for a panel-board used as service equipment with multiple disconnecting means in accordance with 230.71. I don't get the text that follows in exception 1. but my interpretation is service equipment with multiple mains shall be protected by the accumulative vale of those mains. Just to be on the safe side.

 

[Smart $]

408.36 is specifically about overcurrent protection of panel boards. It says "a panel boars shall be protected by an overcurrent protective device having a rating than that of the panel board". In exception 1. it says "individua protection shall not be required for a panel-board used as service equipment with multiple disconnecting means in accordance with 230.71. I don't get the text that follows in exception 1. but my interpretation is service equipment with multiple mains shall be protected by the accumulative vale of those mains. Just to be on the safe side.

The text that follows...

In panelboards protected by three or more main circuit
breakers or sets of fuses, the circuit breakers or sets of
fuses shall not supply a second bus structure within the
same panelboard assembly.

...seems pretty straightforward to me.

To protect the "primary" bus Code simply requires that the panelboard be rated not less than the calculated load.

 

[kwired]

The 4 gang meter socket is not a panelboard. It's bus is just an extension of the service conductors. That bus needs to be rated at least to the level of the load calculation.

Can you find a 4 gang socket with only 100 amp main bussing? Probably not. Can you find a 4 gang socket with 200-225 amp main bussing? Seems more likely.

 

[iwire]

I agree with Kwired. The bus bars are just service conductors.

It is not odd to find a 1600 amp MLO panelboard with six breakers as the service disconnects. The panel only needs to be rated for the load not the total of the breakers.

 

[electrofelon]

408.36 is specifically about overcurrent protection of panel boards. It says "a panel boars shall be protected by an overcurrent protective device having a rating than that of the panel board". In exception 1. it says "individua protection shall not be required for a panel-board used as service equipment with multiple disconnecting means in accordance with 230.71. I don't get the text that follows in exception 1. but my interpretation is service equipment with multiple mains shall be protected by the accumulative vale of those mains. Just to be on the safe side.

Yes I know, my point was that there is no analogous statement in article 312. Thus I think all we have to go by is 110.3(B) and sizing the meter socket to meet or exceed the load. If there is one service disconnect on the load side of the meter, then one could take the stance that the bussing in the meter socket are service entrance conductors and need to be protected by the OCPD integral or adjacent to the service disconnect (Not sure I hold that philosophy though).

 

[JoeStillman]

Follow article 220, part III or IV to calculate multi-family loads. Then size the conductors accordingly. 220 has some nice diversity factors so you don't necessarily wind up with a 400A service to (4) 100A sockets. When you size the service cables, the house load is continuous and the dwelling units are non-continuous.

 

[kwired]

Follow article 220, part III or IV to calculate multi-family loads. Then size the conductors accordingly. 220 has some nice diversity factors so you don't necessarily wind up with a 400A service to (4) 100A sockets. When you size the service cables, the house load is continuous and the dwelling units are non-continuous.

Whether or not the house load is continuous depends on details of that load doesn't it? Most common items you may run into probably are continuous though.

 

[iwire]

When you size the service cables, the house load is continuous and the dwelling units are non-continuous.

Whether or not the house load is continuous depends on details of that load doesn't it?

I agree with kwired, you can certainly choose to call all the house load continuous but in my opinion only a percentage of it, if any really would be an NEC continuous load.

 

[kwired]

House panel may feed common areas lighting - likely a continuous load.

House panel feeding a common laundry area - not a continuous load. Multiple electric dryers in that area - demand factors can be applied and the result is not a continuous load needing further adjustment.

 

[JoeStillman]

House panel may feed common areas lighting - likely a continuous load.

House panel feeding a common laundry area - not a continuous load. Multiple electric dryers in that area - demand factors can be applied and the result is not a continuous load needing further adjustment.

That is all correct. I just don't see too many of those common laundry rooms anymore.