Optional Standby Generators

[brianlelectric]

Ok so little back round story... at a costumer's house they have a 7kW portable generator that dose not have the grounded (neutral) conductor bonded to the frame. So i put a 2 pole 30 amp breaker in under the 100 amp main breaker, and put the Murray breaker interlock kit in place. Ran 10/3 romex from the panel about 40-50 feet to the back of the house through the outside wall and into the back of a generator inlet power box. I then made up a 20 foot SJO cord (costumer wanted it 20 feet from the house). Now i call the Inspector for that town and he asks me to give him a description of what i did and i told him the above. He then told me he would save me the re-inspection fee and told me to read the Massachusetts amendments (page 11 code article 702.11 (C) ) and said that because I'm not breaking the neutral that i have to have the generator inlet box no more then 10 feet from the panel (which would put the box right in the front of the house) and that the SJO cord can't be any longer then 15 feet. So I reread the article that he was talking about and i believe he is reading it wrong. So i was hoping I could get some input from someone a little more code savvy. Here is what the Massachusetts amendment says...

702.11 (C) Classification of Supply. A generator with a grounded circuit conductor connection as part of its output shall be wired as a separately derived source unless its grounded circuit conductor is not bonded to the frame, or where used to supply a premises wiring system it shall be permitted to be wired as a nonseparately derived source if all of the following conditions are met:

(1) The generator rating does not exceed 15kW.
(2) The generator is connected through a flexible cord and a cord connector to a flanged inlet.
(3) The flexible cord does not exceed 4.5 m (15 ft) in length.
(4) The flanged inlet connection point is not more then 3.0 m (10 ft) from the main bonding jumper or system bonding jumper for the supplied premises.
(5) The point of connection is marked "Disconnect cord when generator is not in service".
(6) Ground-fault protection of equipment has not been installed on any portion of the premises wiring system supplied by the generator.

So the way i read it because the generator's neutral is not bonded to the frame it falls under the "unless" category and doesn't need the neutral broken (transfer switch). But if it was bonded then it would fall under the "or where used" category and then I would have to do (1)-(6).

Any help on this matter would be greatly appreciated.

 

[eprice]

I read it the same as you do. The first paragraph has two parts separated by a comma and "or". The first part says you wire it as a separately derived system unless the neutral is not bonded to the frame. The second part of the paragraph, along with all of the conditions seems to be an allowance to wire a generator with the neutral bonded as a non separately derived system. In your case, I don't think you need to go to the second part of the paragraph since your neutral is not bonded to the frame.

 

[brianlelectric]

Ok so its not just me reading it that way. I asked 3 other electricians I've worked with and they all say the same thing... it seems this inspector is the only one (that I've ran into so far) that sees it the other way.

 

[ceb58]

Ok so little back round story... at a costumer's house they have a 7kW portable generator that dose not have the grounded (neutral) conductor bonded to the frame. So i put a 2 pole 30 amp breaker in under the 100 amp main breaker, and put the Murray breaker interlock kit in place. Ran 10/3 romex from the panel about 40-50 feet to the back of the house through the outside wall and into the back of a generator inlet power box. I then made up a 20 foot SJO cord (costumer wanted it 20 feet from the house). Now i call the Inspector for that town and he asks me to give him a description of what i did and i told him the above. He then told me he would save me the re-inspection fee and told me to read the Massachusetts amendments (page 11 code article 702.11 (C) ) and said that because I'm not breaking the neutral that i have to have the generator inlet box no more then 10 feet from the panel (which would put the box right in the front of the house) and that the SJO cord can't be any longer then 15 feet. So I reread the article that he was talking about and i believe he is reading it wrong. So i was hoping I could get some input from someone a little more code savvy. Here is what the Massachusetts amendment says...

702.11 (C) Classification of Supply. A generator with a grounded circuit conductor connection as part of its output shall be wired as a separately derived source unless its grounded circuit conductor is not bonded to the frame, or where used to supply a premises wiring system it shall be permitted to be wired as a nonseparately derived source if all of the following conditions are met:

(1) The generator rating does not exceed 15kW.
(2) The generator is connected through a flexible cord and a cord connector to a flanged inlet.
(3) The flexible cord does not exceed 4.5 m (15 ft) in length.
(4) The flanged inlet connection point is not more then 3.0 m (10 ft) from the main bonding jumper or system bonding jumper for the supplied premises.
(5) The point of connection is marked "Disconnect cord when generator is not in service".
(6) Ground-fault protection of equipment has not been installed on any portion of the premises wiring system supplied by the generator.

So the way i read it because the generator's neutral is not bonded to the frame it falls under the "unless" category and doesn't need the neutral broken (transfer switch). But if it was bonded then it would fall under the "or where used" category and then I would have to do (1)-(6).

Any help on this matter would be greatly appreciated.

Ok so its not just me reading it that way. I asked 3 other electricians I've worked with and they all say the same thing... it seems this inspector is the only one (that I've ran into so far) that sees it the other way.

Looks as if I see as the inspector dose. The way I read it what it is saying is if it is bonded then it must be wired as a SDS (switching the neutrial) but if not bonded then it is a non-sds. This is where I think the wording could/should be a little clearer.

or

This is where they are giving lattitude to connect it to a premis wiring system as a non-SDS as long as you follow the 6 conditions.
The whole reason behind this is by UL a portable gen. that is connected to a premis wireing system must be installed as a SDS with the neutrial being switched.

 

[brianlelectric]

Ya I see what you are saying about it needed to be worded differently if in fact it is meaning the way you and the inspector are reading it then it should be worded more like this...

702.11 (C) Classificaton of Supply. A generator with a grounded circuit conductor connection as part of its output shall be wired as a separately derived source, unless its grounded circuit conductor is not bonded to the frame where used to supply a premises wiring system then it shall be permitted to be wired as a nonseparately derived source if all of the following conditions are met:

(1) The generator rating does not exceed 15kW.
(2) The generator is connected through a flexible cord and a cord connector to a flanged inlet.
(3) The flexible cord does not exceed 4.5 m (15 ft) in length.
(4) The flanged inlet connection point is not more then 3.0 m (10 ft) from the main bonding jumper or system bonding jumper for the supplied premises.
(5) The point of connection is marked "Disconnect cord when generator is not in service".
(6) Ground-fault protection of equipment has not been installed on any portion of the premises wiring system supplied by the generator.

Worded that way would definitely mean the inspector was right but it's not worded that way that is why I think he is wrong. I spoke to another inspector (my old high school shop teacher) and he thinks that I am right too but said he would look into it some more and let me know.

 

[shortcircuit2]

So what extra level of safety is Massachusetts achieving by use of this rule?

 

[brianlelectric]

So what extra level of safety is Massachusetts achieving by use of this rule?

I really don't know I wish i knew what they were thinking when they write some of these amendments... but from what I heard is the guy that writes some of them just likes to get him self published so he submits a lot of them... and presto chango we get a couple of pretty odd amendments.

 

[ceb58]

I really don't know I wish i knew what they were thinking when they write some of these amendments... but from what I heard is the guy that writes some of them just likes to get him self published so he submits a lot of them... and presto chango we get a couple of pretty odd amendments.

I think you are missing the point. Instead of just failing the install out right by UL's instructions they are giving you a set of conditions to follow that will allow a portable to be connected to a premise wiring system with out it being installed as a SDS.

GENERAL
This category covers internal-combustion-engine-driven generators rated
15 kW or less, 250 V or less, which are provided only with receptacle outlets
for the ac output circuits. The generators may incorporate alternating or
direct-current generator sections for supplying energy to battery charging
circuits.

When a portable generator is used to supply a building wiring system:
1. The generator is considered a separately derived system in accordance
with ANSI/NFPA 70, ??National Electrical Code?? (NEC).

2. The generator is intended to be connected through permanently
installed Listed transfer equipment that switches all conductors other
than the equipment grounding conductor.

 

[ramsy]

I think you are missing the point. Instead of just failing the install out right by UL's instructions they are giving you a set of conditions to follow that will allow a portable to be connected to a premise wiring system with out it being installed as a SDS.

Looking at this from an engineering perspective may be more revealing.

This Massachusetts amendment, condition #3, limits conductor length and impedance of generator supply cable. Condition #4 similarly limits electrode impedance during lighting strikes.

Calculating the impedance shows the voltage potential (shock hazard), between portable-generator frame and hose bibs, or other electrode bonding systems.

Assuming a generator-frame lifted or transfer-switched neutral, using a #10 30A generator supply cable, this Massachusetts "15 foot" rule #3, keeps potential voltage under 1-vac between the generator frame and Grounding Electrode Systems of the building supplied.

Potential voltages at receptacle neutral & grounding prongs (N-G) inside buildings, are also typically under 1-2 vac.

Not switching the neutral during power transfer and keeping the neutral bond to generator frame, means objectionable current energized at line voltages pass thru the generator frame, as measured between generator frame and Grounding Electrode Systems of the building supplied.

Correct me if needed, but can someone be killed by line-voltage potential when touching such a generator frame and wet grass, or generator frame to hose bibs, or other Grounding Electrode Systems of the building supplied?