Dwelling unit circuits from two feeders?

[iggy2]

We have a project where a generator will be installed. Selected circuits in two separate occupancies of this building will be fed by a standby panel. Each of the occupancies is fed by a separate meter. One of the occupancies is a dwelling unit. To avoid having a transfer switch for each occupancy, some of the dwelling unit circuits would be moved to the 'other' meter, so that there would not be interconnection of the load side of the two meters.

The question then is can a single dwelling unit be fed by circuits from two separate meters? There is one service feeding both meters. Can't think of a reason why not, but.....

Thanks.

 

[jap]

We have a project where a generator will be installed. Selected circuits in two separate occupancies of this building will be fed by a standby panel. Each of the occupancies is fed by a separate meter. One of the occupancies is a dwelling unit. To avoid having a transfer switch for each occupancy, some of the dwelling unit circuits would be moved to the 'other' meter, so that there would not be interconnection of the load side of the two meters.

The question then is can a single dwelling unit be fed by circuits from two separate meters? There is one service feeding both meters. Can't think of a reason why not, but.....

Thanks.

I would think that the service disconnect for the dwelling unit on the load side of the dwelling meter would not acutually be disconnecting all of the power to the unit since there are circuits being fed to the dwelling unit from the "Other" meter.

JAP>

 

[iggy2]

I would think that the service disconnect for the dwelling unit on the load side of the dwelling meter would not acutually be disconnecting all of the power to the unit since there are circuits being fed to the dwelling unit from the "Other" meter.

JAP>

That is partly correct. The disconnecting means for the feeder to the dwelling unit (not the service) is a CB at the meter stack. The service disconnecting means is (are) the circuit breakers at the meter stack. But after that, we are talking feeders - not services, so no 'main' is required for the individual dwelling unit that I can think of... While this makes me a bit uncomfortable, is it a code violation? There is no main CB in the dwelling unit loadcenter. I think there could be plenty of labeling at the two panels, both within the dwelling unit, and next to each other "this dwelling unit is fed from multiple sources" - that sort of thing. But so far I am not finding a code violation.

 

[augie47]

One building, one service. Two panels. I see no problem. The only thing you did not mention would be a problem with 240.24(B), access to overcurrent devices,.

 

[jap]

That is partly correct. The disconnecting means for the feeder to the dwelling unit (not the service) is a CB at the meter stack. The service disconnecting means is (are) the circuit breakers at the meter stack.

JAP>

 

[mopowr steve]

So, if you move those circuits to the other meter then will the billing be fair to the tenants. I could see a legal issue to this if this is true.
Or did I miss something.

 

[david]

We have a project where a generator will be installed. Selected circuits in two separate occupancies of this building will be fed by a standby panel. Each of the occupancies is fed by a separate meter. One of the occupancies is a dwelling unit. To avoid having a transfer switch for each occupancy, some of the dwelling unit circuits would be moved to the 'other' meter, so that there would not be interconnection of the load side of the two meters.

The question then is can a single dwelling unit be fed by circuits from two separate meters? There is one service feeding both meters. Can't think of a reason why not, but.....

Thanks.

Where are the branch circuits to areas common to both the dwelling occupancy and the second occupancy being supplied from?

 

[iggy2]

So, if you move those circuits to the other meter then will the billing be fair to the tenants. I could see a legal issue to this if this is true.
Or did I miss something.

No, you did not miss anything - I did not mention the revenue aspects of it. The property is under single management, and they (or the tax payers...) pay for both meters.

 

[iggy2]

Where are the branch circuits to areas common to both the dwelling occupancy and the second occupancy being supplied from?

Those circuits are fed from the non-dwelling unit meter. the 'other' meter handles the office areas, community use space, and 'house' loads.

 

[iggy2]

One building, one service. Two panels. I see no problem. The only thing you did not mention would be a problem with 240.24(B), access to overcurrent devices,.

Correct. The circuits in the dwelling unit that will be on the standby power system will be fed from a small loadcenter in the dwelling unit, so the residents have access to the panel. The loadcenter will be a sub-panel form the main standby panel in the basement electrical space. The loadcenter will be right next to the existing panel in the dwelling unit, so we can label the crap out of everything.

The only issue we (always) have on these projects is 312.8, since the circuits already go to the existing panel, and they have to be extended to the new standby panel. It's not always realistic to pull the circuits out of the existing panel....

 

[kwired]

Who pays the bills is not an NEC concern. The only NEC question here is whether or not two feeders are allowed to supply the space in question, and possibly access to overcurrent devices.

If this is part of a legally required standby or emergency system there could be more then just the general rules that apply as well.

For the general rules there isn't really an issue with more then one feeder to the space that I am aware of.

If the space is a separate building it can only be supplied with one feeder though - with exceptions that would include standby and emergency systems.

 

[jap]

Each of the occupancies is fed by a separate meter. To avoid having a transfer switch for each occupancy, some of the dwelling unit circuits would be moved to the 'other' meter.

This is the part that's cloudy for me.

JAP>

 

[iggy2]

This is the part that's cloudy for me.

JAP>

Since there are 2 meters, and 2 feeders serving the separate occupancies, I did not want to do anything that would 'tie' the load side of both meters together, to prevent any weird metering effects. My first thought was I need 2 transfer switches, to maintain isolation of the feeders, and 2 standby panels, each fed by their own transfer switch. But since I have to pull circuits out the existing panels into new standby panels anyway, the new panels can be isolated from either meter anyway. I need to post a picture....

 

[david]

Where are the branch circuits to areas common to both the dwelling occupancy and the second occupancy being supplied from?

Those circuits are fed from the non-dwelling unit meter. the 'other' meter handles the office areas, community use space, and 'house' loads.

I would think that the office area would be defined as tenant space in a multi- occupancy building. 210.25 indicates that branch circuits serving areas common to both are to be supplied from what is commonly referred to as a (house panel). I would think you would want to transfer the generator to handle the house panel loads.

(B) Common Area Branch Circuits. 210.25 Branch Circuits in Buildings with More Than One Occupancy.
Branch circuits required for the purpose of lighting, central alarm, signal, communications, or other needs for public or common areas of a two-family dwelling, a multifamily dwelling, or a multi-occupancy building shall not be supplied from equipment that supplies an individual dwelling unit or tenant space.

 

[jap]

Since there are 2 meters, and 2 feeders serving the separate occupancies, I did not want to do anything that would 'tie' the load side of both meters together, to prevent any weird metering effects. My first thought was I need 2 transfer switches, to maintain isolation of the feeders, and 2 standby panels, each fed by their own transfer switch. But since I have to pull circuits out the existing panels into new standby panels anyway, the new panels can be isolated from either meter anyway. I need to post a picture....

That makes more sense to me now except for the fact that wouldnt the startup of the generator be dependent on whatever panel the transfer switch's utility side power was fed from unless the whole service went down ?

JAP>

 

[jap]

If the power goes off on the dwelling side and the Xfr switch is monitoring the business side power , what's going to tell the generator to start?

JAP>

 

[iggy2]

I would think that the office area would be defined as tenant space in a multi- occupancy building. 210.25 indicates that branch circuits serving areas common to both are to be supplied from what is commonly referred to as a (house panel). I would think you would want to transfer the generator to handle the house panel loads.

(B) Common Area Branch Circuits. 210.25 Branch Circuits in Buildings with More Than One Occupancy.
Branch circuits required for the purpose of lighting, central alarm, signal, communications, or other needs for public or common areas of a two-family dwelling, a multifamily dwelling, or a multi-occupancy building shall not be supplied from equipment that supplies an individual dwelling unit or tenant space.

Hmmm. 210.25 is a good point. But, we only have 2 occupancies - dwelling unit and office/community space. There are really no "public or common areas". All spaces are in one occupancy or the other.

 

[iggy2]

That makes more sense to me now except for the fact that wouldnt the startup of the generator be dependent on whatever panel the transfer switch's utility side power was fed from unless the whole service went down ?

JAP>

Yes, the standby system would only operate on loss of utility power to the whole building - not loss of power to one space or the other. I suppose we could do some zone failure relays or something, but that scenario is pretty unlikely.

 

[iggy2]

If the power goes off on the dwelling side and the Xfr switch is monitoring the business side power , what's going to tell the generator to start?

JAP>

Nothing, and that's OK.

 

[iggy2]

Who pays the bills is not an NEC concern. The only NEC question here is whether or not two feeders are allowed to supply the space in question, and possibly access to overcurrent devices.

If this is part of a legally required standby or emergency system there could be more then just the general rules that apply as well.

For the general rules there isn't really an issue with more then one feeder to the space that I am aware of.

If the space is a separate building it can only be supplied with one feeder though - with exceptions that would include standby and emergency systems.

This is strictly optional standby.