84 November/December IAEI NEWS

Transfer

Equipment for

Installation in

Accordance with

NEC Article 702 –

Optional Standby Systems

by Alan MancheSquare D Company

A HistoricPerspective onTransfer Equipment

Our society depends on

electricity, which drives the

purchase, installation, and use of

generators and other electrical

equipment that provides us with

convenient alternate sources of

power. Transfer equipment has

long been a part of the NEC

Article 700 � Emergency Systems

and Article 701 � Legally Required

Standby Systems.

84 November/December IAEI NEWS

IAEI NEWS 1999 November/December 85

The double throw switch is an example of transferequipment that spans the history of connecting elec-trical systems to alternate power sources from presentto back into the 1930�s. In 1981, the NEC Article 701(Legally Required Standby Systems) clearly definedthat transfer equipment must operate automaticallywhen installed for legally required standby systems.The 1981 NEC also introduced Article 702 � OptionalStandby Systems. Article 702 provides for the contin-ued use of manual transfer equipment for:

��industrial and commercial buildings, farms, andresidences, and to serve loads such as heating andrefrigeration systems, data processing and communi-cations systems, and industrial processes that, whenstopped during any power outage, could cause dis-comfort, serious interruption of the process, damageto the product or process��

Transfer Equipment, TransferSwitch – Is There a Difference?The 1999 NEC clearly distinguishes that transfer

equipment includes transfer switches and automatictransfer switches; it does not limit transfer equipmentto just automatic transfer switches.

701-7. Transfer Equipment(a) Transfer equipment, including automatic trans-fer switches, �

702-6. Transfer EquipmentTransfer equipment shall be suitable for the in-tended use and designed and installed so as toprevent the inadvertent interconnection of nor-mal and alternate sources of supply in any opera-tion of the transfer equipment.

Section 702-6 addresses a fundamental safety con-cern about transfer equipment installations. Thetransfer equipment must keep two electrical sourcesfrom connecting to the load at the same time. If si-multaneous connection of the two electrical sourcesto the load is ignored, the generator may backfeedthe utility system and create a hazard for utility andother personnel.

Listing agencies evaluate transfer equipment using anumber of different standards, such as UL 67, UL 98, orUL 1008. UL 1008 is a comprehensive standard thatmeets the NEC requirements in Articles 700, 701, and702 and is commonly used to evaluate automatictransfer switches. Transfer equipment such as doublethrow switches are evaluated in accordance with UL98 and panelboards with interlocked breakers areevaluated in accordance with UL 67 for compliancewith NEC Article 702.

According to NEC Section 702-4, transfer equipmentfor optional standby systems must be �approved for theintended use.� A number of other equipment arrange-ments may also qualify for application in accordance

with Article 702 and not be specifically Listed as �Trans-fer Equipment.� Examples include a substation tie or akeyed interlock arrangement.

Installation of an Article 702 SystemArticle 702 provides guidance for installation of Op-

tional Standby Systems. The scope of Article 702 requiresa permanently installed generator or �prime mover.�

702-1. ScopeThe provisions of this article apply to the installa-tion and operation of optional standby systems.The systems covered by this article consist only ofthose that are permanently installed in their en-tirety, including prime movers. [italics added]

For the thousands of portable generator systems be-ing installed, the scope of Article 702 technically leavesthe installer and inspector without an enforceable ar-ticle in the NEC. However, this is the only reasonableplace for us to reference when evaluating the installedsystem for safety. Removing the permanently installedprime mover restriction in the scope of Article 702 wouldbe a reasonable resolution for the 2002 NEC or adding asection on portable units.

Transfer equipment that is the service entrance equip-ment must be marked in accordance with NEC Section230-66 to indicate its suitability for use as service equip-ment. However, transfer equipment in a residential ap-plication is often installed near the service entranceequipment. A second panel allows the separation of �nec-essary� loads, such as heating, from convenience loads.

Section 702-5 addresses capacity and ratings ofoptional standby system equipment.

86 November/December IAEI NEWS

702-5. Capacity and Rating�Optional standby systemequipment shall be suitablefor the maximum availablefault current at its terminals....

Make sure the rating of the device isadequate for the available fault cur-rent from the serving utility and thegenerator. This section also requiresthe switch to have suitable electricalratings for switching a load betweentwo sources of supply. TransferEquipment listed in accordance withUL 67, UL 98, or UL 1008 will fulfillthis requirement.

The available fault current fromthe generator must also be consid-ered in order to comply with NECSection 702-6.

702-6. Transfer Equipment�Transfer equipment, locatedon the load side of branch-cir-cuit protection, shall be permit-ted to contain supplementaryovercurrent protection havingan interrupting rating sufficientfor the available fault currentthat the generator can deliver.

Section 702-6 is often misunder-stood. Many have misread the per-mission in this section to allow theinstallation of supplementary protec-tion as a substitute for branch circuitprotection. Any supplementaryovercurrent protection must be in-stalled on the load side of a branchcircuit overcurrent protection device.NEC Section 240-10 states:

�supplementary overcurrentprotection�shall not be usedas a substitute for branch-circuitovercurrent devices or in placeof the branch-circuit protectionspecified in Article 210.

The transfer equipment cannotswitch the branch circuit protection(listed breakers or fuses) out of thecircuit as this will leave the branchcircuit conductors unprotected andmay even remove Ground Fault Cir-cuit Interrupter protection from thecircuit if GFCI breakers are employedin the service entrance panelboard.

Other Considerations for anNEC Compliant Installation

Transfer equipment installed in aresidence is often found in the ga-rage or in an unfinished basement.The installer may employ a conve-nience receptacle at the transferequipment for portable lighting. NECSection 210-8(a) requires receptacleslocated in garages and unfinishedbasements to be GFCI protected.

Finally, the installation of transferequipment next to the service panelalso creates a possibility that install-ers may place a single / common neu-tral in the raceway between the ser-vice panel and the transfer equip-

ment. This is clearly a violation ofNEC Section 300-3(b) as the neutralfor each branch circuit �shall be con-tained within the same raceway.�

SummaryFundamental elements have been

discussed to assist in a safe and NECcompliant installation of transferequipment in accordance with NECArticle 702. The following list providesa summary of common items that canbe overlooked when reviewing the in-stallation of the transfer equipment:

1) The transfer equipment islisted by a recognized certificationbody (this would include productslisted to UL 1008, UL 67, UL 98, etc.,as transfer equipment).

2) The transfer equipment has ashort circuit current rating suitablefor the available short circuit currentat the panel�s installation point inthe system (this is especially criti-cal for transfer equipment locatednext to the service equipment).NEC 702-5, 110-10.

3) Receptacles installed as part ofthe transfer equipment have appro-priate GFCI protection if installed inan area requiring GFCI protection(unfinished basements, garages, out-buildings, outside, etc.). NEC 210-8

4) If supplemental protectors areemployed, they are always located onthe load side of a branch circuitovercurrent device... even when thetransfer equipment is operating fromgenerator power. NEC 702-6.

5) Raceway interconnectionsbetween the main panel and thetransfer equipment includegrounded conductors for each cir-cuit being fed from the transferequipment. NEC 300-3(b).

ALAN MANCHEAlan Manche, a registered

professional engineer in thestate of Kentucky, is a sr. stan-dards engineer for Square DCompany. He represents

Square D across the country by participating at IAEI meet-ings. He also represents NEMA on CMP 8 of the NEC andthe NFPA 73 Technical Committee. Alan has held posi-tions within Square D in product design and certificationfor panelboards, switches, metering, busway and wiremanagement equipment.

Fig. 1.Common Code Violation of 240-10 and 702-6 using Supplementary Protection