Table 310.15(B)(6) and generators

[ceb58]

My point is that the conductors between the gen. and the load should be large enough to carry the entire capacity of the generator's output, load diversity has nothing to do with that at all. Example, if you have a maximum load of 50 amps connected to a gen. that can supply a maximum of 80 amps what size conductor would you install? The answer should be conductors that can carry 80 amps.

Back up and read post 37. Those 20 Kw units come with a 100 amp breaker. It doesn't matter if it is only capable of 83 continuous amps, the conductors that WE install must be sized to the OCP. If it is a factory whip then that is something different.

 

[elohr46]

Back up and read post 37. Those 20 Kw units come with a 100 amp breaker. It doesn't matter if it is only capable of 83 continuous amps, the conductors that WE install must be sized to the OCP. If it is a factory whip then that is something different.

I completely agree with you, the OP wants to use table 310.15(B)(6) to size the conductors. That table does not apply to optional standby generators IMO. There's no reference from art. 445 or art.702 back to T310.15(B)(6).

 

[kwired]

I completely agree with you, the OP wants to use table 310.15(B)(6) to size the conductors. That table does not apply to optional standby generators IMO. There's no reference from art. 445 or art.702 back to T310.15(B)(6).

That table applies to any conductor that supplies a "dwelling unit" that is supplied by single phase 120/240 volts, regardless of the source. The catch is it must supply all of the load associated with the dwelling. If the supply happens to be a generator all that matters is that all of the dwelling load be supplied by the conductor. If load shedding methods are used, or you are only supplying specific loads, you are no longer supplying all of the dwelling unit load.

 

[Smart $]

... If load shedding methods are used, ..., you are no longer supplying all of the dwelling unit load.

But with load shedding you are supplying all of the dwelling unit load, at that time, with the generator feeder (to a service-generator ATS with load shedding utilized). As I noted earlier, 220.60 confirms this.

220.60 Noncoincident Loads. Where it is unlikely that
two or more noncoincident loads will be in use simultaneously,
it shall be permissible to use only the largest
load(s) that will be used at one time for calculating the total
load of a feeder or service.

 

[Smart $]

But with load shedding you are supplying all of the dwelling unit load, at that time, with the generator feeder (to a service-generator ATS with load shedding utilized). As I noted earlier, 220.60 confirms this.

Forgot to mention, 702.4(B)(2)(b) also confirms...

(b) Load Management. Where a system is employed that
will automatically manage the connected load, the standby
source shall have a capacity sufficient to supply the maximum
load that will be connected by the load management system.

 

[iwire]

But with load shedding you are supplying all of the dwelling unit load, at that time, with the generator feeder (to a service-generator ATS with load shedding utilized). As I noted earlier, 220.60 confirms this.

But you are not supplying all loads associated with the dwelling unit.

 

[Smart $]

But you are not supplying all loads associated with the dwelling unit.

But you are at the time the generator is in use. Load shedding, in effect, disconnects loads or makes them noncoincident. Granted, the standby power load calculation will be different than the service load calculation where load shedding is utilized. But that does not mean you are not powering all loads associated with the dwelling unit... because you not only are at the time the generator is in use, it is required.

702.4 says the standby system (which includes its feeder) must have the capacity to supply the maximum load (<-- determined by Article 220 load calculation) for a service-generator ATS system. The ATS alternately connects the generator to the same system that the service is connected. If the service supplies all the dwelling unit load, then so does the generator system, as load shedding effectively disconnects loads from that system.

So by y'alls logic, if the generator is sized to supply the entire "normal" dwelling unit load (i.e. no load shedding), we would be able to use 310.15(B)(7) for the generator feeder...?????

 

[kwired]

But you are not supplying all loads associated with the dwelling unit.

I'll go with what Bob said. I think I have said the same thing earlier in this thread, and maybe others did also.

In my earlier example with the AC and or other loads being supplied ahead of a feeder that supplies the remainder of the home, that feeder is not allowed to be sized per 310.15(B)(7), I think most will agree with that. Why is that any different than 'shedding' loads from the feeder in any other way?

To be consistent I think 310.15(B)(7) means if used the conductor will supply all of the associated dwelling load. Whatever art 220 calculated load ends up being is the associated dwelling load. Locking out certain loads makes the actual less than the calculated and changes the load diversity. If you want to feed with a 4 AWG then use a 90 amp breaker. If you want to use a 100 amp breaker then use 3 AWG.

 

[iwire]

But you are at the time the generator is in use. Load shedding, in effect, disconnects loads or makes them noncoincident.

I understand your position, I disagree with it.

It is my opinion they chose the words associated with the dwelling unit to make clear it did not mean only the electrically connected loads.

 

[iwire]

So by y'alls logic, if the generator is sized to supply the entire "normal" dwelling unit load (i.e. no load shedding), we would be able to use 310.15(B)(7) for the generator feeder...?????

I can't speak for y'all but as far as I am concerned, yes if the generator supplies or has the ability to supply 100% of the loads associated with that dwelling unit you could use the reduced sized conductors.

You don't see the potential for zero load diversity when a generator is only set up to supply a cherry picked group of loads?

 

[Smart $]

I can't speak for y'all but as far as I am concerned, yes if the generator supplies or has the ability to supply 100% of the loads associated with that dwelling unit you could use the reduced sized conductors.

You don't see the potential for zero load diversity when a generator is only set up to supply a cherry picked group of loads?

On an ATS system, a load calculation would have to be performed using just the cherry picked group. Load diversity would apply only to those loads.

 

[Smart $]

I understand your position, I disagree with it.

It is my opinion they chose the words associated with the dwelling unit to make clear it did not mean only the electrically connected loads.

So a resident has some electrical gear in his basement which, is only powered by a permanently connected generator (not a standby power source). Can you use the reduced size for the service? It doesn't power all loads associated with the dwelling unit...!!!

 

[elohr46]

That table applies to any conductor that supplies a "dwelling unit" that is supplied by single phase 120/240 volts, regardless of the source. The catch is it must supply all of the load associated with the dwelling. If the supply happens to be a generator all that matters is that all of the dwelling load be supplied by the conductor. If load shedding methods are used, or you are only supplying specific loads, you are no longer supplying all of the dwelling unit load.

Let's put load shedding aside for now. Let me just say this; if your generator comes from the factory with a 100 amp cb and you wish to use the generator at it's maximum load capabilities then you should be using a conductor for your feeder rated 100 amps or higher.

 

[iwire]

Let's put load shedding aside for now. Let me just say this; if your generator comes from the factory with a 100 amp cb, you should be using a conductor for your feeder rated 100 amps or higher.

That is common but I can find NEC compliant work arounds to that.

Starting with outside feeder taps of unlimited length, however perhaps we should take this discussion to its own thread if we want to expand on this aspect of it.

 

[iwire]

So a resident has some electrical gear in his basement which, is only powered by a permanently connected generator (not a standby power source). Can you use the reduced size for the service? It doesn't power all loads associated with the dwelling unit...!!!

Damn dude, can we not try to make up unrealistic scenarios when talking about a code that is generally developed as the need arises?



Due to the fact that combination is so unusual I will say that one will have to be up to the AHJ.

 

[Smart $]

I'll go with what Bob said. I think I have said the same thing earlier in this thread, and maybe others did also.

I realize that... and for the record, I'm just playing the devil's advocate here.

In my earlier example with the AC and or other loads being supplied ahead of a feeder that supplies the remainder of the home, that feeder is not allowed to be sized per 310.15(B)(7), I think most will agree with that.

I agree.

Why is that any different than 'shedding' loads from the feeder in any other way?

Because it is what it is, and not what it's not... :happyyes:

To be consistent I think 310.15(B)(7) means if used the conductor will supply all of the associated dwelling load. Whatever art 220 calculated load ends up being is the associated dwelling load. Locking out certain loads makes the actual less than the calculated and changes the load diversity. ...

But with optional standby power with ATS and load shedding, you have to supply the maximum "unshedded" load per a separate Article 220 calculation, essentially shedded loads removed from service calculation. So load diversity is per Article 220. The load side feeder of the service-rated ATS is already sized for the calculated load of the service. This is just consideration of the ATS line side feeder from generator.

 

[Smart $]

Damn dude, can we not try to make up unrealistic scenarios when talking about a code that is generally developed as the need arises?



Due to fact that combination is so unusual I will say that one will have to be up to the AHJ.

:rotflmao:

 

[iwire]

:rotflmao:

I would like to be a fly on the wall at one of those IAEI gatherings where you could ask them that question. I think you might stump them.

 

[Smart $]

Damn dude, can we not try to make up unrealistic scenarios when talking about a code that is generally developed as the need arises?

...

I would like to be a fly on the wall at one of those IAEI gatherings where you could ask them that question. I think you might stump them.

Probably so. And FWIW, I could probably think up a more realistic scenario... perhaps something like a stand-alone photovoltaic lighting system.

 

[kwired]

So a resident has some electrical gear in his basement which, is only powered by a permanently connected generator (not a standby power source). Can you use the reduced size for the service? It doesn't power all loads associated with the dwelling unit...!!!

I say no.

Let's put load shedding aside for now. Let me just say this; if your generator comes from the factory with a 100 amp cb and you wish to use the generator at it's maximum load capabilities then you should be using a conductor for your feeder rated 100 amps or higher.

Generators maximum load capability is limited by the 100 amp circuit breaker, so 100 amps is the max load capability IMO, even if it has a label on the side that says 100kVA, you will never load it more than what it takes to trip the 100 amp breaker if that is what is installed.