disconnecting means for generator

[substation guy]

why must you install a disconnecting means ahead of main breaker ie disconnect at meter when installing a generator ive always done it only because i know it has to be done but what is the reason behind it?

 

[iwire]

Any electrical source entering a building or structure is required to have a disconnecting means at, on or in the building or structure.

 

[Mike01]

Ats??

Ats??

What if the generator has an OCPD at the generator and when you enter the bldg. you terminate in a transfer switch, in an OCPD still required??

 

[iwire]

What if the generator has an OCPD at the generator and when you enter the bldg. you terminate in a transfer switch, in an OCPD still required??

Overcurrent protection and required disconnecting means are different problems even though they are often solved with the same device.

Lets assume the generator has proper overcurrent protection for the conductors. (It should)

Unless the transfer switch is capable of locking off you will likely need a disconnecting means ahead of the transfer switch.

This disconnecting means has to meet the location specified in 225.32 which in a nutshell says 'inside or outside nearest the point of entrance of the conductors'

It also has to meet the requirements of 225.36 'suitable for use as service equipment' doubtful any generator breaker is suitable for use as service equipment.

 

[substation guy]

disconnecting means gen

disconnecting means gen

okay, if the disconnecting means is shut off though the gen is going to turn on so i guess i dont understand why you would need the disconnect

 

[substation guy]

ill check those codes out maybe itll help me understand

 

[iwire]

What part are you having trouble with?

The basic idea is that anyone service the building supplied by the generator can open the circuit and place a lock on it so that they can safely work on buildings wiring systems.

 

[substation guy]

the way ive done this in the past is the feed from meter goes to disconnect then load side of disconnect goes to xfer sw then distribution panel is fed from xfer sw. so if you were to shut off main disconnect, wouldnt that show as a power outage causing gen to start? so you also would need to turn off breaker at gen (power source)

 

[augie47]

What part are you having trouble with?

The basic idea is that anyone service the building supplied by the generator can open the circuit and place a lock on it so that they can safely work on buildings wiring systems.

Bob, On a typical residential install with a generator & automatic transfer switch, do you feel the circuit breaker on the generator (detached from the residence) can serve as the required disconnect (such as in 225.32) or must there be a disconnect on or withing the residential structure.

 

[ceb58]

Bob, On a typical residential install with a generator & automatic transfer switch, do you feel the circuit breaker on the generator (detached from the residence) can serve as the required disconnect (such as in 225.32) or must there be a disconnect on or withing the residential structure.

Let me throw my $0.02 worth in on that. This year I was in a cont. ed. class that dealt with generators and the new code changes. As it turned out I was the only non-inspector in the class of about 20 people.
This question was raised. There consensus on the install you described is they would not allow the breaker on the generator to act as the required disco.
Their reasoning was. The breaker on the generator was not service rated and it was not readily accessible due to having to remove a cover to access the breaker. The question was then ask "what if the cover had a window to access the breaker with out removing any thing"? Their answer still reverted back to the breaker not being service rated.
Also one thing they were very animate about was the transfer switch being marked with the location of the main service and generator disconnect if it was not readily apparent. Such as in a case where the TS was located in side and the disconnects were out side.

 

[Pierre C Belarge]

You also should be aware of 700.12(B)(5), 701.11(B)(5), and 700.11.
These all require an additional disconnecting means if the generator is not within-sight.

 

[augie47]

Thanks. I think I've missed that on a few inspections.

 

[roger]

Their reasoning was. The breaker on the generator was not service rated and it was not readily accessible due to having to remove a cover to access the breaker. The question was then ask "what if the cover had a window to access the breaker with out removing any thing"? Their answer still reverted back to the breaker not being service rated.

Curtis, I have purchased generators with service rated OCPD/disconnecting means, the most recent was a 250 kw Onan, this requirement was included in the job specs.

Roger

 

[LarryFine]

the way ive done this in the past is the feed from meter goes to disconnect then load side of disconnect goes to xfer sw then distribution panel is fed from xfer sw. so if you were to shut off main disconnect, wouldnt that show as a power outage causing gen to start? so you also would need to turn off breaker at gen (power source)

All of this is correct. Yes, the genny would start, which is why it also must have a means of disconnect. You now have two sources which need disconnectability.

By the way, if the transfer switch is rated for use as service equipment, it can be wired immediately after the meter, and act as the main service disconnect.

Added: Another advantage of using a service-rated transfer switch is that they include generator disconnects as well, reducing the quantity of enclosures.

 

[hurk27]

all of Generac's transfer switch's are now service rated, so there is no need for a second generator disconnect as far as the house panel goes, but if the generator is out of site of the transfer switch then one is required as Pierre mention in post #11

with the utility main ahead of the TS shut off, just by placing a service rated TS in utility will keep the generator from powering the house.

For ATS then the control switch and or the breaker at the generator must also be shut off, or the generator will try to start up and transfer.

 

[don_resqcapt19]

It is my opinion that the disconnect itself and not just the generator or generator enclosure must be within sight of the building if you want to eliminate the disconnect at the building. If the generator disconnect is inside the generator enclosure it is not within sight of the building. Even if the generator disconnect is installed outside of the generator enclosure, it must be on the side of the enclosure that faces the building.

 

[ceb58]

Curtis, I have purchased generators with service rated OCPD/disconnecting means, the most recent was a 250 kw Onan, this requirement was included in the job specs.

Roger

Hi,Roger
I was refering to this

On a typical residential install with a generator & automatic transfer switch,

With an install such as what you are refering to you have all the specs. to back up any question that may arise.
But, and I am sure that you are aware the smaller, lower $ gen. sets that home owners buy are not speced for much of any thing

 

[augie47]

A recent post on generator grounding brought this older post to mind and upon rereading I still find myself unsure. I'm leaning toward 225.32 requiring a disconnect where the conductors enter the building (either on the inside or outside). Am I overlooking something that would allow the breaker on the generator to serve this purpose ?

 

[augie47]

don_resqcapt19 answered thru another post. 702.11 covers it.