Automatic generator installation

[crtemp]

With a manual transfer switch you can use any size generator with any size load. But for an automatic standby system, the generator has to be able to handle the load placed on it by the ATS.

First, you need to go by the generator's output, not the breaker's rating.

That generator is either 17kw on propane or 16kw on NG. That's 70a or 66A.

You need to do a load calc on that panel to make sure that it isn't above the rating of the generator. If it is, then you can either move loads to the other panel or load shed.

BTW, I am surprised that the generator only has a 65A breaker.

I'm sorry...what is "load shedding"?

I have also been tagged before for not having the two 200 amp panels evenly loaded. Is this a legitimate tag? The house is all electric stuff (furnace, water heater, cooktop, etc) and he only wants minimal lighting, freezers, well, water heater, microwave on the generator. Is this okay? I know the stuff he wants to be on the generator will calc out at less than 70 amps but I'm afraid that the other panel will be much more loaded and the inspector will not like it?

Thoughts?

Thanks again for all the info. Much appreciated.

BTW... generator is propane

 

[GoldDigger]

I'm sorry...what is "load shedding"?

I have also been tagged before for not having the two 200 amp panels evenly loaded. Is this a legitimate tag? The house is all electric stuff (furnace, water heater, cooktop, etc) and he only wants minimal lighting, freezers, well, water heater, microwave on the generator. Is this okay? I know the stuff he wants to be on the generator will calc out at less than 70 amps but I'm afraid that the other panel will be much more loaded and the inspector will not like it?

Thoughts?

Thanks again for all the info. Much appreciated.

BTW... generator is propane

Not having the two panels evenly loaded is not an overriding concern if the separation of circuits between the two panels is required by design, as where only one panel will be fed by the generator. Balancing normal load between two panels, as long as neither is overloaded, is a design goal, not an NEC requirement.

Load shedding refers to the use of relays to automatically cut some heavy loads (like A/C or electric resistance heat) out of the circuit if the measured load is greater than the capacity of the generator.
The goal is to make sure that when the generator auto-starts and the transfer switch throws it cannot, based on calculated load, overload the generator and trip its breaker or shut it down.

Imagine the results if nobody is home when the power goes out and the generator fails to take up the load because the A/C was running full blast and somebody put clothes in the dryer before they left. Now the refrigerator, freezer and sump pump have no power. Worse yet the DVR will not record any programs!

With a manual transfer switch, you know that there will be somebody there to turn off loads if necessary, so the NEC does not have any sizing or load shedding requirement.

 

[crtemp]

Not having the two panels evenly loaded is not an overriding concern if the separation of circuits between the two panels is required by design, as where only one panel will be fed by the generator. Balancing normal load between two panels, as long as neither is overloaded, is a design goal, not an NEC requirement.

Load shedding refers to the use of relays to automatically cut some heavy loads (like A/C or electric resistance heat) out of the circuit if the measured load is greater than the capacity of the generator.
The goal is to make sure that when the generator auto-starts and the transfer switch throws it cannot, based on calculated load, overload the generator and trip its breaker or shut it down.

Imagine the results if nobody is home when the power goes out and the generator fails to take up the load because the A/C was running full blast and somebody put clothes in the dryer before they left. Now the refrigerator, freezer and sump pump have no power. Worse yet the DVR will not record any programs!

With a manual transfer switch, you know that there will be somebody there to turn off loads if necessary, so the NEC does not have any sizing or load shedding requirement.

Worse yet the DVR will not record any programs!
LMFAS!

Thank you for the explanation. Makes perfect sense. I will only put in circuits in the generator panel that are crucial and will be sure to keep it under 60 amps to be safe. Should be easy to do with the stuff he requested to work.

 

[ceb58]

Structure - that which is built or constructed.

That's pretty vague. That could mean virtually anything.

If the breakers on the generator aren't accepted as the disconnect and I have to install one, does it have to be within site of the generator? I don't think it says one way or the other.

You need to sit down and read Article 225 II paying attention to 225.31 thru 225.37 and all of Article 702.

The disconnect requirements in Article 225 are for branch circuits or feeders supplying a structure. The conductors running from the generator to the transfer switch are not supplying the generator. No, but the generator is supplying the structure. There is no logical reason to install a service disconnect switch at a generator since it will not serve any useful purpose. The disconnect is not for the generator but the structure 225.31 The power is coming from the generator not to the generator so the generator will still be energized with the switch off. Then explain the need for 225.37. It is to disconnect the feeders to the structure in case of an emergency.

 

[curt swartz]

You need to sit down and read Article 225 II paying attention to 225.31 thru 225.37 and all of Article 702.

I understand it just fine. The discussion was about the generator being a structure and needing a service disconnect. The generator doesn't need a disconnect as it would serve no purpose. What needs a disconnect is the structure the generator is supplying. This disconnect needs to be located at the structure being supplied not at the generator.

 

[ceb58]

I understand it just fine. The discussion was about the generator being a structure and needing a service disconnect. The generator doesn't need a disconnect as it would serve no purpose. What needs a disconnect is the structure the generator is supplying. This disconnect needs to be located at the structure being supplied not at the generator.

The reading articles were pointed to the OP as it seems he is new to generator installs.
As far as the generator being a structure by the definitions, then yes it is a structure. But no one said that a disconnect was required at the generator but the rules of 225 would apply to the structure served.

 

[david]

The reading articles were pointed to the OP as it seems he is new to generator installs.
As far as the generator being a structure by the definitions, then yes it is a structure. But no one said that a disconnect was required at the generator but the rules of 225 would apply to the structure served.

not that I really care that strongly but is a motor also a structure. How are we applying the definition of a structure to equipment I do not think to many her would say that the lamp in the room is a structure.

 

[GoldDigger]

I think that if it is inside another structure it does not matter whether the lamp in room meets the definition. But if the lamp is outside it might.

Tapatalk!

 

[iwire]

not that I really care that strongly but is a motor also a structure. How are we applying the definition of a structure to equipment I do not think to many her would say that the lamp in the room is a structure.

Based on the NEC defintion unless it was put here by mother nature it is a structure.

 

[ceb58]

not that I really care that strongly but is a motor also a structure. How are we applying the definition of a structure to equipment I do not think to many her would say that the lamp in the room is a structure.

I and I think most are going on the fact of what the definitions are and how they have been enforced by the AHJ over the years. But there is another definition in article 225, which is what covers the feeders, that backs up the definitions.

225.2 Definition.Substation.

An enclosed assemblage of equipment (e.g.,
switches, circuit breakers, buses, and transformers) under
the control of qualified persons, through which electric energy
is passed for the purpose of switching or modifying its
characteristics.

Based on the NEC defintion unless it was put here by mother nature it is a structure.

Unless you plant magic generator beans.

 

[crtemp]

I have all my parts now and I'm using a Generac automatic transfer switch. It says in the instructions that the power leads and transfer switch leads must be run in conduit. It this true? Can I not just use some SER wire for the feeder and 18 gauge thermostat wire for the control wire?

 

[curt swartz]

I have all my parts now and I'm using a Generac automatic transfer switch. It says in the instructions that the power leads and transfer switch leads must be run in conduit. It this true? Can I not just use some SER wire for the feeder and 18 gauge thermostat wire for the control wire?

I don't know why you couldn't use SER if the transfer switch is located inside and the wiring is not exposed to physical damage. You definitely can NOT use thermostat wire for the control leads. Thermostat cable can only be used for low voltage class 2 circuits. Some of the control leads are actually 240 volts and none of them are considered class 2.

 

[crtemp]

I don't know why you couldn't use SER if the transfer switch is located inside and the wiring is not exposed to physical damage. You definitely can NOT use thermostat wire for the control leads. Thermostat cable can only be used for low voltage class 2 circuits. Some of the control leads are actually 240 volts and none of them are considered class 2.

Okay thanks for the heads up! Maybe just 1/2" PVC the entire way and some 14 gauge thhn?

 

[crtemp]

Better yet can I just run a 14-2 nm-b (romex)

 

[GoldDigger]

Better yet can I just run a 14-2 nm-b (romex)

Run in conduit?
I am not sure why the Generac instructions require conduit, unless they are sure in their hearts that the wiring will be exposed to damage, but you have to follow the instructions.

 

[curt swartz]

Better yet can I just run a 14-2 nm-b (romex)

I believe Generac requires 6 control wires. Isn't this generator being installed outside? If so you will need raceways for the feeders and control leads anyway. Might as well continue them to the the transfer switch.

 

[crtemp]

Run in conduit?
I am not sure why the Generac instructions require conduit, unless they are sure in their hearts that the wiring will be exposed to damage, but you have to follow the instructions.

It just says it must be run in a separate conduit from the power feeder

 

[GoldDigger]

It just says it must be run in a separate conduit from the power feeder

That makes it more interesting. Technically, you cannot run one in a separate conduit if you do not run both in conduit.
But you can not run them in the same conduit just by not running one or both in conduit at all.
Based on what they mean, you may be OK if NM is allowed in the first place; based on what they said, you are screwed. :happysad:

 

[crtemp]

That makes it more interesting. Technically, you cannot run one in a separate conduit if you do not run both in conduit.
But you can not run them in the same conduit just by not running one or both in conduit at all.
Based on what they mean, you may be OK if NM is allowed in the first place; based on what they said, you are screwed. :happysad:

Here is what came with the load center and transfer switch. The generator is different though. It is a Honeywell that the homeowner purchased from Costco

 

[GoldDigger]

Well, that certainly assumes that the wiring will be in conduit in the first place.
Depending on the overall environment you may not be able to use NM anyway.
If the panel is surface mounted in a place where NM is not allowed to be exposed, or the generator is outside, for example.

Tapatalk!