Testing emergency-lighting generator batteries

Q
Our two-story, 60,000-sq-ft office building has two diesel generators to back up the utility power to the building. The generators are fed from an on-site 20,000-gallon storage tank. The total building electrical load is powered by the generators in the event of a power failure, with a transfer time of 18 seconds. The capacity of each generator is roughly twice the present building load.

My question concerns the testing of the emergency lighting and exit light batteries. Is it necessary to test the batteries for these units yearly for 90 minutes or is the monthly 90-second test enough? Can the generators be considered the emergency power source as described in 700-12 (b) of the Code and battery backup light be the auxiliary back up for the time it takes the generators to start?

A
Section 700-4(b) requires testing of the emergency system. The schedule for such testing is not specified by Section 700-4(b). The authority having jurisdiction should be contacted to determine local testing requirements. Section 110-3(b) will also apply. The instructions for the unit equipment must be followed. If the manufacturer provided testing instructions you must follow those instructions. The requirements in Section 700-12(e) are not testing requirements. This section gives performance requirements only.

Section 700-12 requires a maximum start time of 10 seconds for your emergency generator. Section 700-12(b) allows longer than 10 seconds provided you have auxiliary power during the delay in excess of 10 seconds. Your generator can be used as the emergency power source. The unit equipment provided the auxiliary power required during the 8-second delay.

Because you power the entire building with the generator, you must also comply with Section 700-6 as well as Article 702. Section 700-6(d) does not allow emergency loads and other loads to be supplied through the same transfer switch. You will need a separate transfer switch for the Article 700 emergency loads. The rest of the building load is classified as optional stand-by load. Transfer of the optional loads is done in accordance with Article 702.
Dann Strube

Re-feeding an existing house panel

Q
I recently installed a meter stack on a multi-family dwelling, 200A single-phase, each position. To re-feed an existing house panel, I ran 2½-in. Sch. 40 PVC underground, then sleeved 200A type SE subfeed cable through conduit. This cable was also to run about 20-ft inside the dwelling. This is why I chose type SE — because it is moisture-resistant and flame retardant. Is this installation acceptable?

A
According to the UL Marking Guide for Wire and Cable, Type SE cable is for above-ground installations only. Type USE is intended for underground installations, but it may not be installed inside of buildings. Section 110.3(B) in the 2002 NEC (which is 110-3(b) in 1999) requires all instructions included in the listing or labeling to be followed. This is enough to cause your installation to be in violation of the NEC.

If your Type SE cable is aluminum, other references that are sometimes cited are Section 250-120(b) and 250-64(a), which restrict the use of aluminum equipment grounding conductors within 18 in. of the earth. This rule has been modified in 2002 and the new Section 250.120(B) restricts only the terminations of insulated aluminum equipment grounding conductors from being within 18 in. of the earth.
Noel Williams

Ceiling-grid hangers for low-voltage cable

Q
My boss loves the new Code requirement for hangers on limited energy cabling. We have about 100 miles of the stuff sitting above our ceilings waiting to pull down the tee-bar. Now he has a Code-related basis for telling the telecom folks to get with it and budget for some hangers on future installations (as well as get rid of the previous several generations of abandoned runs up there — even if they don't seem to be in anyone's way right now).

A
Because some people objected to even the limited amounts of cables that the Code panel intended to allow on ceiling grids, the rules are a bit watered down in their final form.

In deleting the allowance to put a few cables on the grid, which was an exception, the generally restrictive rule I referred to in the “Top 10” article was also deleted, so the primary restriction now goes back to workmanship and not interfering with access.

The general references to Section 300.11 have been deleted so the final rules only apply to support of surface-mounted cables. In this case, some of the good work got thrown out with some of the not so good.
Noel Williams

Arc-fault circuit interrupters

Q
What is an AFCI circuit breaker?

I've been an operating engineer for 15 years and an electrical journeyman for 20 before that, but this is a new one. I couldn't find it anywhere on your site or several others.

A
AFCIs (Arc-Fault Circuit Interrupters) have been around in portable form for a few years. Proposals to include them in the Code have been made for the last few Code cycles. They were introduced in the 1999 NEC. See Section 210-12 in 1999. They are microprocessor-based devices that examine the form of the sine wave and look for disturbances that are characteristic of arcing faults. You can download some technical reports on Square D's Web site at www.squared.com. I'm sure other information is available elsewhere too.
Noel Williams

Transfer switch

Q
I am looking for some preliminary information on the installation of a Cutler-Hammer 200A transfer switch. I don't know the specific model number, but it is a non-fused knife-blade type mechanical device, which has three positions, on-off-on, that stipulate a neutral or non-current carrying position and two other positions.

Does this switch, which will interrupt the normal current flow from the power company's load side of the meter, take the place of the load-center panel existing as the main/principal? Will I treat the existing load center as a sub-panel after installation? The transfer switch has a definite bonding terminal along with the neutral terminal feed-through connection.

A
Section 250-24(a)(1) requires that the grounded conductor (probably your neutral) be connected to the grounding electrode at or ahead of the service disconnecting means. Section 250-24(a)(5) prohibits any more such connections on the load side. Therefore, if you use the transfer switch as the service disconnecting means, the existing panel must have the grounded conductor and the equipment grounding conductors separated and connected to separate terminals. I assume this is what you mean by treating it as a sub-panel. Remember that the service overcurrent device must be located immediately adjacent to the transfer switch if the transfer switch does not include overcurrent protection.
Noel Williams

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