Sizing service based on historical demand

[mbrooke]

When does the NEC allow this? And how is it done? I keep seeing cases where the maximum historical demand is very well below the service disconnect. But at the same time I can't see a name brand car dealership or a McDonald's with a 200amp service.

 

[david luchini]

When does the NEC allow this? And how is it done? I keep seeing cases where the maximum historical demand is very well below the service disconnect. But at the same time I can't see a name brand car dealership or a McDonald's with a 200amp service.

See 220.87.

 

[mbrooke]

See 220.87.

Thank you!


What was the section that permits a backup generator to be smaller then the service?

 

[kwired]

Thank you!


What was the section that permits a backup generator to be smaller then the service?

Not certain off top of my head, but depends on what it is connected to and whether it is manual or ATS and if there is any load shedding abilities for ATS.

 

[mbrooke]

Not certain off top of my head, but depends on what it is connected to and whether it is manual or ATS and if there is any load shedding abilities for ATS.

Can I be honest? I don't like how large my services are.

 

[packersparky]

Thank you!


What was the section that permits a backup generator to be smaller then the service?

702.4(B) for optional standby systems.

 

[Chamuit]

Curious as to what the actual demand is. I remember the instructor saying that the actual usage was always lower than the calculated in the class I took that covered load calcs.

 

[mbrooke]

Curious as to what the actual demand is. I remember the instructor saying that the actual usage was always lower than the calculated in the class I took that covered load calcs.

800amp service, history is saying it does not go above 100. With the new loads I doubt it will go over 125.


The usage is always lower, often by magnitudes.


I wish there was a way you could get smaller services even for new builds. The reduced cost, space and labor are highly attractive.

 

[kwired]

Curious as to what the actual demand is. I remember the instructor saying that the actual usage was always lower than the calculated in the class I took that covered load calcs.

Not always though. Limited load applications, say a pumping station or other limited load application, the service is often same or not much larger than the branch circuit for the primary load.

 

[mbrooke]

Not always though. Limited load applications, say a pumping station or other limited load application, the service is often same or not much larger than the branch circuit for the primary load.

Very true. But for things like municipal buildings, schools, stores, ect the service is way oversized.

 

[kwired]

Very true. But for things like municipal buildings, schools, stores, ect the service is way oversized.

I can agree with that most cases.

Sometimes you still run into needing to upgrade when you add load though. Had a school building we were adding HVAC load to. Started out with a 600 amp switchboard with six service disconnects. Plenty of power available, but with six service disconnects already there is no good place to tie the new load to. Ended up with I line panel with a 600 amp main breaker, six original feeders and two HVAC units supplied from it. Never checked load data since then, but I bet if it had a 400 amp main breaker would still not have ever tripped since it was installed.

 

[mbrooke]

I can agree with that most cases.

Sometimes you still run into needing to upgrade when you add load though. Had a school building we were adding HVAC load to. Started out with a 600 amp switchboard with six service disconnects. Plenty of power available, but with six service disconnects already there is no good place to tie the new load to. Ended up with I line panel with a 600 amp main breaker, six original feeders and two HVAC units supplied from it. Never checked load data since then, but I bet if it had a 400 amp main breaker would still not have ever tripped since it was installed.

I remember back in the day elementary schools were fed with a single 50kva pole pig. 400amp single phase fused service. Only the nurse's office had a through the wall AC. Maybe the main office. Central oil heat. That is until whole classroom AC came in. Now you have something like 750-1500kva pad-mounts for the same square footage. Perfect example of how energy consumption in the US is only going up. And I always have to ask myself if the gymnasium needs to be at 68* :blink:

 

[kwired]

I remember back in the day elementary schools were fed with a single 50kva pole pig. 400amp single phase fused service. Only the nurse's office had a through the wall AC. Maybe the main office. Central oil heat. That is until whole classroom AC came in. Now you have something like 750-1500kva pad-mounts for the same square footage. Perfect example of how energy consumption in the US is only going up. And I always have to ask myself if the gymnasium needs to be at 68* :blink:

kind of what the school I mentioned before was like. Not sure what was originally there, (1920's building) Did have 400 amp single phase breaker panel that was installed late 60's or early 70's. A second building with it's own service I upgraded to 2-200 amp mains (still single phase) because they were adding individual room AC's. A few years later they upgraded boiler system for both those buildings and mechanical contractor used three phase pumps. Was surprised when I told them there was no three phase on the premises. Then the school board had to make a decision. The future plans included potential chiller to be added to this new HVAC system - may as well put in necessary three phase service that can handle that chiller now.

The 600 amp service I mentioned before was another newer building with a gymnasium - the heat(gas) was in bad need of replacement in that gym, but they installed new units with cooling also.

I can't figure out why these schools can't start class about Labor day like we used to when I was still in school and get out a little later in May like we used to. Anymore they are starting early August when it is still pretty hot at times, but has been good for business for me at a couple of them.

 

[mbrooke]

kind of what the school I mentioned before was like. Not sure what was originally there, (1920's building) Did have 400 amp single phase breaker panel that was installed late 60's or early 70's. A second building with it's own service I upgraded to 2-200 amp mains (still single phase) because they were adding individual room AC's. A few years later they upgraded boiler system for both those buildings and mechanical contractor used three phase pumps. Was surprised when I told them there was no three phase on the premises. Then the school board had to make a decision. The future plans included potential chiller to be added to this new HVAC system - may as well put in necessary three phase service that can handle that chiller now.

The 600 amp service I mentioned before was another newer building with a gymnasium - the heat(gas) was in bad need of replacement in that gym, but they installed new units with cooling also.

I can't figure out why these schools can't start class about Labor day like we used to when I was still in school and get out a little later in May like we used to. Anymore they are starting early August when it is still pretty hot at times, but has been good for business for me at a couple of them.

Yup- how it typically goes. Kind of dumb IMO to be spending tax money like that. I must admit I survived without AC in school.

 

[Chamuit]

Not always though. Limited load applications, say a pumping station or other limited load application, the service is often same or not much larger than the branch circuit for the primary load.

Very true. But for things like municipal buildings, schools, stores, etc the service is way oversized.

Kwired, you are correct. I was thinking along the lines of mbrooke, though.

 

[electrofelon]

I wish there was a way you could get smaller services even for new builds. The reduced cost, space and labor are highly attractive.

Me too. I don't get to the obsession with all this extra capacity and load calcs. It should be design issue. Seens like when jurisdictions have plan review requirements, it's mostly about load calcs. Honestly I don't see overloads as that big a deal from a safety standpoint.

 

[mbrooke]

Me too. I don't get to the obsession with all this extra capacity and load calcs. It should be design issue. Seens like when jurisdictions have plan review requirements, it's mostly about load calcs. Honestly I don't see overloads as that big a deal from a safety standpoint.

Neither do I, as long as the service conductors are protected via 240.4 there is no hazard.

Does the inspector or county care if the service is not sized to load calcs?

 

[electrofelon]

Neither do I, as long as the service conductors are protected via 240.4 there is no hazard.

Does the inspector or county care if the service is not sized to load calcs?

I have never been asked for calcs for resi. Larger commercial services usually. Here in Seattle basically need plan review for 400 Amps and over and they want panel schedules with service and feeder calcs. They also look at AIC ratings of all equipment.

 

[mbrooke]

I have never been asked for calcs for resi. Larger commercial services usually. Here in Seattle basically need plan review for 400 Amps and over and they want panel schedules with service and feeder calcs. They also look at AIC ratings of all equipment.

Thats it, I'm putting in a 350 amp service on everything now!