Meter base transfer switch

[aptwes]

Our company is a small start-up manufacturing a meter socket/ meter adapter based whole house transfer switch. WE are wrapping up design/prototype development and are working with UL to secure a listing. I am not an electrician nor an electrical engineer, but do have a technical background.

There are clearly some code issues to be resolved around this product. In trying to draft some code proposals to address this product and related issues, I find I am a bit stumped. So I thought I would describe the key points of the device and some of the issues I see, and see what the members of this forum have to say.

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• <font size="2" face="Verdana, Helvetica, sans-serif">Unit is designed to be used with 120/240v service and a 240v generator input in a non-separately derived system configuration.</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">United is intended to be used in "Optional Standby Systems" as described in Article 702.</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">Basic design is based on interlocking breakers - typically 200 amp service inlet, 30 amp generator inlet.</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">Generator is cord connected to the switch.</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">Service input is routed from the lower meter stabs to the service inlet breaker.</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">Depending on breaker positions, the service or generator input is connected to the lower meter jaws in the existing meter base.</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">Neutral (grounded conductor) is not switched.</font>
• <font size="2" face="Verdana, Helvetica, sans-serif">Unit enclosure ground, generator neutral, and generator ground are bonded in the unit.(The generator neutral and generator ground should already be tied together in the generator via a floating connection - I believe). A single connection is then made from this point to the Grounded service conductor in the meter base.</font>

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Obviously, we would like to be able to avoid moving the main bonding jumper point.

Does the device fulfill the requirements of a service disconnect?

VI. Service Equipment - Disconnecting Means
230.70 General. Means shall be provided to disconnect all conductors in a building or other structure from the service entrance conductors.

230.75 Disconnection of Grounded Conductor. Where the service disconnecting means does not disconnect the grounded conductor from the premises wiring, other means shall be provided for this purpose in the service equipment. A terminal of bus to which all grounded conductors can be attached by means of pressure connectors shall be permitted for this purpose.


Our device switches the ungrounded service conductors, but does not switch the grounded conductor nor does it provide any other means for disconnecting the grounded conductor. The meter and device would have to be removed to get at the existing connections in the meter base.

IF our device is not a service disconnect then an amendment to 230.82 might be the place to address it. Perhaps it could be construed as "other current limiting devices" under (1).
UL has not yet determined if it will treat it as a meter socket or a meter socket adaptor, so item (2) may not work. Item (3) concerns meter disconnect switches, which are not defined. I suspect our device is not considered a meter disconnect since the connection is severed at the meter outlet rather than inlet, but I do not know for sure. I am also unsure if a case can be made that this would fall under the scope of item (5), but tend to think it does not.

Also, I am thinking that an amendment to 230.82 may necessitate a related change to:
230.94 Relative Location of Overcurrent Device and Other Service Equipment.


IF the device is deemed to be a service disconnect, then perhaps the language of:
230.72 Grouping of Disconnects. (B) Additional Service Disconnecting Means.

May come into play.

Thanks for your thoughts.

 

[pierre]

Re: Meter base transfer switch

Does your device have overcurrent protection - as in the service disconnect has to have overcurrent protection in/or adjacent to it?

 

[aptwes]

Re: Meter base transfer switch

Yes.

The circuit connecting the service to the lower meter jaws is a 2 pole 200 amp breaker, the circuit connecting the generator to the lower meter jaws is a 2 pole 30 amp breaker.

 

[mdshunk]

Re: Meter base transfer switch

I have seen such a device advertised, as a customer pointed me to it. Parhaps someone beat you to the idea? It plugged into the meter socket, and the meter plugged into it. It had a 30 amp flanged inlet in the bottom. While my inspector was perfectly willing, I couldn't get the serving utility (Allegheny Energy)to give permission for me to use it.

 

[aptwes]

Re: Meter base transfer switch

Other devices do exist but the ones I am familiar with use significantly different technology internally - our particular design is protected by a patent.

True enough serving utility blessings will need to be secured, much as they bless meter cans, and the issue of meter removal and reinstallation will need to be addressed. Our plate will be full enough "selling" utilities so we would like to deal with any NEC issues to try and keep it all manageable. Given where it lives in the system, its a challenge.

 

[petersonra]

Re: Meter base transfer switch

I don't think I would want such a contraption on my service. It would also seem to be a nuisance in retrofit work, and most generator installs are retrofit.

I don't see how this is any improvement over a standard transfer switch. It almost seems like it is going backwards.