Generator Disconnect

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dema

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I have searched and read - there was a previous thread about the generator disconnects, but I see no conclusive continuous logically trail.

700.12.B.6) Outdoor Generator Sets. Where an outdoor housed generator set is equipped with a readily accessible disconnecting means located within sight of the building or structure supplied, an additional disconnecting means shall not be required where ungrounded conductors serve or pass through the building or structure.

Here is the exception. What is the rule it is excepting?

I have a client who is sighing at my insisting on putting in disconnects.

I have a colleague who says it isn't a service, so he isn't putting in disconnects where the generator conductors enter the building under any circumstance.

So please supply me with a logical thread.

Also, if you use the 225.31, 225.36 argument - then service entrance rated means a jumper between the neutral and the ground in the disconnect. I definitely don't want this. Either I am not switching the neutral and there is a solid neutral which will be bonded in the MDP, or I am switching the neutral and will bond between the neutral and the ground at the generator. I would never want to bond at the disconnect. Please comment.
 
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dema said:
Here is the exception. What is the rule it is excepting?
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What exception, 700.12(B)(6) stands as it is worded.


dema said:
I would never want to bond at the disconnect. Please comment.
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Why?

Roger
 
It is an exception to 225.31 and there is nothing is 225.36 that requires you to install the neutral bond. Disconnects that are listed "suitable for use as service equipment" have a main bonding jumper that is shipped loose and is installed in the field if required. The only service equipment that has a permanent bonding connection is equipment that is listed "suitable only for use as service equipment".
Don
 
roger said:
What exception, 700.12(B)(6) stands as it is worded.




Why?

Roger
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700.12.B.6 tells you when a disconnect is NOT required. It doesn't tell you when one is. The logic for saying one is would not pass a geometry test.

The neutral should be bonded to ground in one and only one place. If it is bonded at the disconnect and there is a solid neutral, then it is bonded two places and there is a ground loop. Likewise for bonding at the generatorwith a switched neutral.
 
dema said:
700.12.B.6 tells you when a disconnect is NOT required. It doesn't tell you when one is. The logic for saying one is would not pass a geometry test.
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700.12(B)(6) does infact address the disconnect,

6) Outdoor Generator Sets
Where an outdoor housed generator set is equipped with a readily accessible disconnecting means located within sight of the building or structure supplied, an additional disconnecting means shall not be required where ungrounded conductors serve or pass through the building or structure.
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why would you want to install another one?

dema said:
The neutral should be bonded to ground in one and only one place.
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Absolutely, this bond can take place at the generator if 700.12(B)(6) is applicable, the second disconnect (if you choose to install one) or at the MDP if it is the Main, hence my question "Why" to your
I would never want to bond at the disconnect.
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statement.

Roger
 
Chapters 1, 2, 3, and 4 apply generally; Chapters 5, 6, and 7 apply to special occupancies, special equipment, or other special conditions. These latter chapters supplement or modify the general rules. Chapters 1 through 4 apply except as amended by Chapters 5, 6, and 7 for the particular conditions.

1st I read 225.31

225.31 Disconnecting Means
Means shall be provided for disconnecting all ungrounded conductors that supply or pass through the building or structure.

2nd I read 225.36

225.36 Suitable for Service Equipment
The disconnecting means specified in 225.31 shall be suitable for use as service equipment.

OK. those are the rules unless chapter 5,6 or 7 amend them.

700.12(B)(6) Outdoor Generator Sets Where an outdoor housed generator set is equipped with a readily accessible disconnecting means located within sight of the building or structure supplied, an additional disconnecting means shall not be required where ungrounded conductors serve or pass through the building or structure.

701.11(B)(5) and 702.11 for what it matters... Does not modify the service rating requirment. If the disconnect is not service rated on the generator, these code articles do not apply.

Jim
 
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For what it is worth, Here is common installed deficiency in the state of NH. The State Inspectors write a list for each code cycle. Mike Holt had it in three of his newsletters. The link is

http://www.state.nh.us/safety/divisions/firesafety/electrician/deficiencies/index.html

Check out the last statement


#11 The location of the disconnecting means for Emergency Systems.

225.31 Disconnecting Means, 225.32 Location and 700.12 (B) (6) Outdoor Generator Sets.

It is not uncommon to find a disconnecting means that has been improperly located for an Emergency System (Article 700) feeder which has been supplied from an outdoor housed generator. By the definition in Article 100 the conductors supplying an emergency system from a "separately derived system," in this case a generator, are considered as "feeder" conductors. Where the generator is located outdoors, the conductors would be considered as "outdoor feeder conductors" which are subject to the requirements of Article 225, Outdoor Feeders and Branch Circuits.

The scope of Article 225 (225.1) 225.31 states that a means shall be provided for disconnecting all ungrounded conductors that supply or pass through the building or structure. The first sentence of 225.32 requires the disconnecting means to be located either inside or outside of the building or structure served or where the conductors pass through the building or structure. The second sentence in this section notes that the disconnecting means must be at a readily accessible location nearest the point of entrance of the conductors.

The confusion typically comes in when the language in 700.12(B)(6) is applied improperly. This section, by the format of Code in 90.3, can supplement or amend Chapters One though Four. At first glance, one gets the impression that a disconnecting means that is located under or within the housing of an outdoor generator set can be used as the disconnecting means required by 225.31.

700.12(A) - (F) provide the general requirements for the acceptable sources of power supplying Emergency Systems. 700.12(B)(6) is titled "Outdoor generator sets" and states that "where an outdoor housed generator set is equipped with a readily accessible disconnecting means located within sight of the building or structure supplied, an additional disconnecting means shall not be required where ungrounded conductors serve or pass through the building or structure. One must further recognize that Article 100 defines the term "within sight of" and means that the specified equipment is visible and not more than 50' away. In the case of 700.12(B)(6), the "specified equipment" is the disconnecting means and it must be visible and not more than 50' away from the building served. The definition of "within sight of" in Article 100 does not preclude the use of a window in a panel of the generator housing. However, the disconnecting must be completely visible through the panel window from the building. On one final important note, 225.36 requires the disconnecting means to be suitable for use as service equipment and this requirement in not amended by Article 700.
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Yes, you can bond in more than one place in this carefully described case which still amounts to there being only one path between the neutral network and the ground. I picture the neutral system as being a tree, with only one trunk connecting into the ground. In this case, you basically have two separated trees - connected by hots, but with no neutral connection. Basically a separately derived system.
 
Dema, of course the disconnecting means at the generator would have to be service rated if this disconnecting means is the Main, Jim mentions this in his post and I just took for granted it was a given. This is why I said "or at the MDP if it is the Main".

Roger
 
"I have a colleague who says it isn't a service, so he isn't putting in disconnects where the generator conductors enter the building under any circumstance."
In the either the 1999 or 1996 NEC a generator supply was defined such that it was considered a service. Its now a feeder.
 
On one final important note, 225.36 requires the disconnecting means to be suitable for use as service equipment and this requirement in not amended by Article 700.
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I don't agree with this statement. If the disconnect at the building is not installed per 700.12(B)(6), then the requirement in 225.36 does not apply. 225.36 only applies to the disconnect specifed in 225.31. 700.12(B)(6) deletes the requirement in 225.31. If there is no disconnect installed under the rule in 225.31, there is no disconnect to apply 225.36 to.
Don
 
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