Transfer switch question

[hillbilly1]

Where in this post was it ever said that the generator had a 100 amp output breaker?

Unless I missed something the size of the output breaker on the Gen set was never indicated.

Therefore, there's still not enough information given to clarify a code violation or not.

JAP>

Even if the generator breaker is larger than 100 amp, the load maximum is 100 amp anyway due to the main breaker in the existing panel.

 

[jap]

Even if the generator breaker is larger than 100 amp, the load maximum is 100 amp anyway due to the main breaker in the existing panel.

There are existing conductors associated with all of this to take into consideration, not just load and overcurrent protection.

JAP>

 

[kwired]

Well, let’s think about this…
A generac 26 kW has a 125A output breaker.
Doesn’t make much sense to put this generator on this house since he said the house had a 100A main.
Now sizing the generator the same as the house breaker would be a 24kW or a 22kW. These come with a 100A output breaker.
Saving some money and getting smaller, a 20kW has a 90A output breaker, and they keep getting smaller from there.

Still, you have a generator output breaker feeding the load. So if it’s a 60A, that could feed a 200A in the house panel..

the generator output will not go through the 200A OCPD on the ATS, so all is well with the generator end. Even if it did, so what..

the utility side coming from the Meterbase to the main in the panel never had any protection at all, and is probably a #2 AL going to the topside of the main breaker.
So we add an ATS for a generator, with a 200A OCPD where there NEVER WAS ONE BEFORE.

Use the #2 from the Meterbase that was going to the main, reroute it to the topside of the 200A in the ATS. Feed #2 out back to the panel main like it has been for many years.

Whats the harm?
Even with the #2 after the 200A in the ATS, it’s still better than it used to be.

And if the ATS happens to be after the main, we’ll then the size of the ATS breaker is a moot point.

In my opinion…

I agree in principle that those conductors will never be overloaded, but can not say it complies with NEC either.

As I said earlier if the original panel still has original main breaker and ATS is basically back to back on exterior wall from it, it likely complies with feeder tap rules from a 200 amp feeder breaker. It still doesn't comply with overcurrent protection requirements on the service conductors though.

 

[Another C10]

I may be way off here but there could be a manufacturing panel bussing tolerance issue, whereas when used as 100A utility fed , the bussing is tested for that ... but to add lets say a125A Generac source with its 200 amp transfer, then the once approved 100A bussing could see much more current potential than ever intended.

just a thought ..

 

[LarryFine]

... but to add lets say a125A Generac source with its 200 amp transfer, then the once approved 100A bussing could see much more current potential than ever intended.

Wouldn't the original 100a main breaker still protect the 100a bus?

 

[kwired]

Wouldn't the original 100a main breaker still protect the 100a bus?

It is all about overcurrent protection issues here. Yes the original panel bus is still protected by the 100 amp main breaker, and in theory yes the service and feeder conductors are still limited by that 100 amp main breaker in the original panel, The feeder likely complies as a feeder tap and is ok with code from that perspective, but overcurrent protection for the service conductors is not in compliance - even though as is will never be overloaded either.

 

[jap]

It is all about overcurrent protection issues here. Yes the original panel bus is still protected by the 100 amp main breaker, and in theory yes the service and feeder conductors are still limited by that 100 amp main breaker in the original panel, The feeder likely complies as a feeder tap and is ok with code from that perspective, but overcurrent protection for the service conductors is not in compliance - even though as is will never be overloaded either.

JAP>

 

[jap]

I may be way off here but there could be a manufacturing panel bussing tolerance issue, whereas when used as 100A utility fed , the bussing is tested for that ... but to add lets say a125A Generac source with its 200 amp transfer, then the once approved 100A bussing could see much more current potential than ever intended.

just a thought ..

The current potential is driven by the load,,, not the source.

JAP>

 

[kwired]

The current potential is driven by the load,,, not the source.

JAP>

And most overcurrent protection rules driven by ampacity of the conductors being protected or by specific circumstances for feeder taps.

 

[Another C10]

The current potential is driven by the load,,, not the source.

very true but one might think I can add more while the generator is running, I know its a long shot but Inspectors don't usually need practicality, just a possibility. They tend to follow if it can go wrong it will.

 

[Another C10]

Wouldn't the original 100a main breaker still protect the 100a bus?

yes but if the generated power allows for a higher load demand then the utility main wouldn't care what's going on within the newly fed buss.

 

[Fred B]

IMHO, A Switch is a Switch.... A 200 amp Rated switch can switch a load rated up to 200 Amps.

Unfortunately the Generac ATS is not just a switch like some mfg use, their's is providing overcurrent/overload protection. My Generac rep indicated they do not have a "switch only" type of ATS. So a 200A breaker on a 100A wire would not be compliant. If however the ATS was one of the other types that do not include a breaker then I don't see an issue in putting a higher rated "switch" as protection of the lowest rated component (possibly the wire) is achieved by the appropriate original breaker. Also Generac has no offer (last speaking to the Generac Rep.) to accommodate the exception in the 2020 for use of 3 wire (120/240) from the outside disconnect (Emergency Disconnect Only).

 

[kwired]

Unfortunately the Generac ATS is not just a switch like some mfg use, their's is providing overcurrent/overload protection. My Generac rep indicated they do not have a "switch only" type of ATS. So a 200A breaker on a 100A wire would not be compliant. If however the ATS was one of the other types that do not include a breaker then I don't see an issue in putting a higher rated "switch" as protection of the lowest rated component (possibly the wire) is achieved by the appropriate original breaker. Also Generac has no offer (last speaking to the Generac Rep.) to accommodate the exception in the 2020 for use of 3 wire (120/240) from the outside disconnect (Emergency Disconnect Only).

I don't fully understand the three wire thing you mentioned. Ones I have been involved with I seem to recall would been easy to remove neutral to ground bond if needed and then can be used for other than service disconnecting means.

200 amp breaker on supply side of a lesser conductor can be acceptable if complies with feeder tap rules. A service conductor landing in an individual service disconnecting means however must be sized per the overcurrent device. A common service conductor ahead of the permitted 2-6 disconnects however only needs sized to the load calculation, the taps to each device must still be sized per the individual device.

 

[jap]

Unfortunately the Generac ATS is not just a switch like some mfg use, their's is providing overcurrent/overload protection. My Generac rep indicated they do not have a "switch only" type of ATS. So a 200A breaker on a 100A wire would not be compliant. If however the ATS was one of the other types that do not include a breaker then I don't see an issue in putting a higher rated "switch" as protection of the lowest rated component (possibly the wire) is achieved by the appropriate original breaker. Also Generac has no offer (last speaking to the Generac Rep.) to accommodate the exception in the 2020 for use of 3 wire (120/240) from the outside disconnect (Emergency Disconnect Only).

The only 200 amp overcurrent protection device mentioned in this scenario is incorporated into the 200 amp SE rated transfer switch.

As long as the conductors from the generator to the transfer switch are protected at or below the size of the output breaker on the generator, and, less than the 200 amp rating of the 200a SE rated transfer switch, and, the conductors from the load side of the 200a rated transfer switch to the line side of the existing 100 amp OCPD in the existing panel satisfy the Tap rule requirements, I would think all should be good to go.

JAP>

 

[xformer]

It is all about overcurrent protection issues here. Yes the original panel bus is still protected by the 100 amp main breaker, and in theory yes the service and feeder conductors are still limited by that 100 amp main breaker in the original panel, The feeder likely complies as a feeder tap and is ok with code from that perspective, but overcurrent protection for the service conductors is not in compliance - even though as is will never be overloaded either.

Its not a Feeder Tap since the conductors are protected by OCPD where they receive their supply.

 

[Another C10]

the conductors from the load side of the 200a rated transfer switch to the line side of the existing 100 amp OCPD in the existing panel satisfy the Tap rule requirements

Now I can see through the wiring tap connection point mentioned that there would be no excessive current potential to the panel bussing, I was thinking the load side of the transfer switch landed right on the panel buss. Pictures are so much better than words.

Hold on though, uh oh .. now I'm thinking again, ....So when power resumes from the utility side there is no over current protection from the conductors of the load side of the Transfer Switch. Although probably legal, that's a reasonably dangerous potential sitting in an enclosure almost anyone can open and tinker with.

One last curiosity for now ... If the generator is tapped upstream the consumers utility main, technically anyone on that same run of utility secondary could use the power too. Thanks neighbor. Or am I completely off.

 

[kwired]

Unfortunately the Generac ATS is not just a switch like some mfg use, their's is providing overcurrent/overload protection. My Generac rep indicated they do not have a "switch only" type of ATS.

They do have both service and non service rated. Transfer mechanism is same thing in both of them, the service rated one has a breaker to serve as the "service disconnect" and also has neutral to ground bonding jumper factory installed.

See page 23 & 24 of this document (pages 27 and 28 of the pdf file) it shows wiring diagram for both.

Your rep maybe doesn't stock any non service rated but they exist.

 

[hillbilly1]

Hold on though, uh oh .. now I'm thinking again, ....So when power resumes from the utility side there is no over current protection from the conductors of the load side of the Transfer Switch. Although probably legal, that's a reasonably dangerous potential sitting in an enclosure almost anyone can open and tinker with.

One last curiosity for now ... If the generator is tapped upstream the consumers utility main, technically anyone on that same run of utility secondary could use the power too. Thanks neighbor. Or am I completely off.

The ocp for the load side of the transferswitch is either the 200 amp main in the switch when on utility, or the 100 amp or whatever is on the generator, when on standby.
How would the generator be tapped “upstream” of the consumers utility? That’s what the transferswitch isolates.

 

[hillbilly1]

They do have both service and non service rated. Transfer mechanism is same thing in both of them, the service rated one has a breaker to serve as the "service disconnect" and also has neutral to ground bonding jumper factory installed.

See page 23 & 24 of this document (pages 27 and 28 of the pdf file) it shows wiring diagram for both.

Your rep maybe doesn't stock any non service rated but they exist.

I have a 100 amp Generac non-service rated transferswitch sitting in my shop right now.

 

[Another C10]

How would the generator be tapped “upstream” of the consumers utility? That’s what the transferswitch isolates.

I'm not an expert obviously regarding Transfer switch products, but I believe there are separate transfer switches and combination transfer switches.

Without looking it up, some units I believe are incorporated into the main panel, only allowing one position or the other to feed the panels breaker bussing whereas I've also seen others that are simply a secondary enclosure which separately connect into an existing main panel enclosure, many times a lug block is used or a secondary over current protection is used to regulate the potential from the generator onto the breaker buss.