As most of you I receive via email newsletters from the Holt site. One tilted; Electrical Safety What you should know about backup power systems
I made a comment to the newsletter and Mike posted a response that had a link to a very old thread on the discussion forum as well as making a statement that Honda had worked this out with UL 30 years ago.
Looking for more clarification I sent an email to the Holt offices to wit I made the statement that 30 years ago in the 1982 code cycle the scope of 250 also said on page 84 that;“Systems and circuit conductors are solidly grounded to facilitate overcurrent device operation in case of ground faults.” I made this statement to show that a lot of things change over a 30 year period.
I also pointed out that NEC Plus has a link to UL FTCN in 702.10 of the 2008 and 702.11 of the 2011 code cycles and ask for clarification to just what role UL FTCN has to play in the installation of stand-alone generators. The reply I got from Sean Hutchings was;
"I am sorry, but there isn't anyone qualified to answer a technical question in our office. However, we do offer a free resource via our website, www.MikeHolt.com . Our Code Forum is 100% free and is a wonderful way to resolve any technical questions you may need answered. Not only do we have 1000’s of members that share information on the site, we also have several moderators that help out. Our Code Forum Moderators are experts in the electrical field and industry leaders that have been involved with the electrical industry for many years. You can register for free at the link included below. Please let me know if there is anything else I can help you with. Have a wonderful day."
On the advice I received from the Holt office I now ask these expert moderators what role does 110.3(B) and UL FTCN have to play in the connection of a stand-alone generator to premises wiring system. Why does NFPA have a link to UL FTCN in NEC Plus concerning Optional Standby Systems in 702?
702.11 Portable Generator Grounding. (A) Separately Derived System. Where a portable optional standby source is used as a separately derived system, it shall be grounded to a grounding electrode in accordance with 250.30. See related UL
(B) Nonseparately Derived System. Where a portable optional standby source is used as a nonseparately derived system, the equipment grounding conductor shall be bonded to the system grounding electrode. See related UL
I can’t find anywhere in the installation instructions outlined by UL where it is permissible to disconnect the neutral from the generator frame in order to connect it as a non-SDS. I do see where they make the statement in “1” that the generator is considered a SDS by both ANSI and NFPA.
From UL FTCN
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 or structure 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.
3. The frame of a Listed generator is connected to the equipment-grounding conductor and the grounded (neutral) conductor of the generator. When properly connected to a premises or structure wiring system, the portable generator will be connected to the premises or structure grounding electrode for its ground reference.
4. Portable generators used other than to power building or structure wiring systems are intended to be connected to ground if required by the NEC.
I am of the opinion that these stand-alone generators (the ones which have receptacles) are designed as temp power as outlined in 590.6(A)(3) and when used as a 702 installation must be connected as a SDS as outlined in UL FTCN.