310.15 Revisted...But w/Pics

[360Youth]

I think this is a single dwelling we are talking about.
I have never had a problem with installing a 40kw or even a 20kw generator on a 400 amp service for a dwelling, I could see a problem if it was all electric and no gas, but around here its almost all gas heat and cooking.

I did have a 15Kw Generac balk at two AC units trying to fire up at the same time of transfer on a 200 amp service, even with the built in time delays in the thermostat they would still both try to fire up at the same time, a couple of time delays set to fire up the 5 ton first then the 3 ton work great, but when we did 10 Kw ones we would always do load shedding by installing a separate 100 amp panel and just placing the needed loads in it and no AC's.

I would say if you use a 20kW on a 400 amp service and there are multiple AC units, just have time delays installed on the unit so they each fire up one minute apart.

I think his point is that the generators now have to be sized based on Art. 220. Gone are the days that you can install on gen on probable use. Load shedding does give you more options and we have had to do so on several of them.

 

[iwire]

I think his point is that the generators now have to be sized based on Art. 220. Gone are the days that you can install on gen on probable use. Load shedding does give you more options and we have had to do so on several of them.

Only generators used with automatic transfer means.

 

[iwire]

I will try again to explain a different way. Where in T. 310.15(B)(6) does it allow us to use parallel conductors? The Table does not address parallel setup so it cannot be used.

It pains me to bring this up as I see it exactly the same way, T310.15(B)(6) does not allow parallels but there is a CMP statement that says otherwise.

 

[360Youth]

Only generators used with automatic transfer means.

True, but we were talking in the context of an ATS install, so I went with it.:smile:

 

[weressl]

I think this is a single dwelling we are talking about.
I have never had a problem with installing a 40kw or even a 20kw generator on a 400 amp service for a dwelling, I could see a problem if it was all electric and no gas, but around here its almost all gas heat and cooking.

I did have a 15Kw Generac balk at two AC units trying to fire up at the same time of transfer on a 200 amp service, even with the built in time delays in the thermostat they would still both try to fire up at the same time, a couple of time delays set to fire up the 5 ton first then the 3 ton work great, but when we did 10 Kw ones we would always do load shedding by installing a separate 100 amp panel and just placing the needed loads in it and no AC's.

I would say if you use a 20kW on a 400 amp service and there are multiple AC units, just have time delays installed on the unit so they each fire up one minute apart.

Now you have provided a bunch of additional information and a bunch of hypotheticals that chages the entire picture.

The point is that the connected feeders on the load side are capable of carying twice the current than the standby source.

If the utility side cables are the same as the load side cables AND the utility cable is protected to the wire size, the utility protection will open up before the mains on each of the panel, eg. one tenant can pop the other by overloading his side.

Where is the utility metering?

It is just does not look right.

 

[360Youth]

Now you have provided a bunch of additional information and a bunch of hypotheticals that chages the entire picture.

The point is that the connected feeders on the load side are capable of carying twice the current than the standby source.

If the utility side cables are the same as the load side cables AND the utility cable is protected to the wire size, the utility protection will open up before the mains on each of the panel, eg. one tenant can pop the other by overloading his side.

Where is the utility metering?

It is just does not look right.

If you look at the first pic youwill the 320 amp meter for the house. Meter feeds ATS. ATS feeds two 200 amp house panels. I get what you are saying that the gen feeder does not equal that of the utility service. The gen is sized for the current load on the house, not for potential of the service. If everything was sized to potential they would probably need at least one more panel to handle the number of circuits it would take and I would have a 90kw genset for a 3000 sqft home.

 

[benaround]

Laszlo, Be informed, there are no tenents, this is a single family home.

 

[Twoskinsoneman]

then they can come screaming to the Owner that their load was interrupted, while they are paying for uninterrupted supply.
.

Just MO but I don't think this should be a concern of the NEC

 

[weressl]

Now you have provided a bunch of additional information and a bunch of hypotheticals that chages the entire picture.

The point is that the connected feeders on the load side are capable of carying twice the current than the standby source.

If the utility side cables are the same as the load side cables AND the utility cable is protected to the wire size, the utility protection will open up before the mains on each of the panel, eg. one tenant can pop the other by overloading his side.

Where is the utility metering?

It is just does not look right.

I guess I wondered off the plantation and got lost......:roll:

Sorry about that......

 

[riggenbw]

I have to agree with Dennis. The use of 2/0 CU is only allowed if it serves the entire house.