National Electrical Code Tips: Article 692 -- Fuel Cell Systems
Fuel cells rated for commercial and industrial use typically are purchased as
engineered systems, skids, or units. But there's also typically quite a bit of
design involved at the site. Not so much in accommodating the fuel cells (e.g.,
transfer switches and switchgear) but in figuring out the overall power strategy
for the site.
A great example of this is the First National Bank of Omaha's facility that
uses fuel cells as its primary power source and more fuel cells as its secondary
source. This particular example has been a frequently cited case study for
groups such as the 7x24 Exchange.
This is true in no small part because fuel cells are so initially expensive
relative to other types of power sources plus have ongoing costs for maintenance
and cell change. If you're going to add one, you need to make it worthwhile in
terms of cash flow (unless the financials are not determining factors).
Typically, the NEC requirements are not limiting factors in the design and
installation of a fuel cell system, because the typical owner commissions the
project to increase uptime and reliability. This means the typical owner is
asking, "What are the potential problems and how can I avoid them" rather than
looking at the NEC and asking, "What can I get by with."
Still, not all owners are typical and the NEC would be remiss if it didn't
provide some minimum requirements for these systems. Let's address some
highlights of those.
- As with any non-utility power source, fuel cells must be listed on a plaque
or directory (along with all other power sources) at each service equipment
- Exactly who is going to install the fuel cell system? The NEC says only a
qualified person can do this [692.4(C) but instead of specifying what that means
it refers you to the general definition in Article 100. If you read that
definition, you see several key concepts such as necessary skills and safety
training to work on the equipment. Note that this doesn't mean you hire an
installer with previous experience (experience doesn't mean you've had the
required training or have the knowledge; lots of people "wing it" and then claim
they have experience). Read this carefully, then think through the specifics.
Whether you are the installer or are hiring one, consult with manufacturers to
get their view on what's necessary.
- If it's a stand-alone system, that doesn't make it something isolated where
the NEC doesn't apply. Whether the NEC applies or not is irrelevant to whether
or not you have a utility connection. Regardless of the power source, the
premises wiring must meet Code and that rule applies to premises supplied by
fuel cells too [692.9].
- Normally, you size your service conductors based on your calculated load.
But with a fuel cell system, their counterparts (conductors between the fuel
cell system output and the building disconnect) must be sized based on the
output rating of the fuel cells [692.10(B)]
- You must provide a disconnect that can disconnect all current-carrying
conductors of a fuel cell system from all other conductors in a structure
[692.13]. That is, you must be able to isolate the fuel cell from the structure,
electrically. Among the reasons for doing this so that fire personnel can
de-energize before entering the structure.
- You can use any Chapter 3 wiring method. Also, you can use any wiring method
that is intended and designed for use with fuel cell systems (this applies to
fittings also) [692.31].
- The grounding requirements depend upon whether the system is AC (apply
250.20, 250.30), DC (apply 250.160), or both (apply 250.66 for the AC and
250.166 for the DC) [692.41].
- You must install a separate equipment "grounding" (bonding) conductor
[692.44] and it must be sized per 250.122 [692.45].
- You must provide signs and markings for the fuel cell power sources
[692.53], manual fuel shut-off valve [692.54], and (if present) stored energy
system (e.g., batteries) [692.55].
- If the system is interactive (e.g., premises wiring also connect with the
utility), you must follow the requirements laid out in Part VII. These include
using a transfer switch, using only fuel cell systems identified and marked for
interactive use, and following some requirements specified in Article 705.