DC GFCI [RE-wrenches]

[Jason Fisher, Aurora Energy]

Bill Brooks wrote: > Can you think of a fault that isn't covered?

I worked for some time on a large (>2000 modules) ground mounted
project. The inverter had GF protection even though it wasn't required.
Because of many factors that I shouldn't elaborate on, there turned out
to be multiple faults in the wiring in the field. Most of the faults
were ungrounded conductors to module frames and racks. The interesting
thing for me through troubleshooting this was to realize how multiple
faults in a single array can create current loops that flow through
metallic enclosures or conduits from fault to fault, but not back to the
inverter or other GFPI device. Most of these current paths did not even
flow through the series fuse. Because of this, several repairs had to be
made to wires and connectors that burned through.

I know, all of you are saying "well if they had installed them correctly
in the first place, they wouldn't have had this problem!" and you're
right, sort-of. Many of these faults could have been prevented during
the initial installation through the use of more qualified and
experienced electricians ("not economically feasible" I was told), but
many faults in this project could also be blamed on poorly engineered
wiring components, enclosures and mounts. No matter, no one was hurt and
there were no noticeable fires!

What it does illustrate for sure is, that when the situation presents
itself where interconnect wiring in an array contains more than one
fault to ground (i.e. one + pinched to a module frame and one - pinched
to another), the potential exists for these fault paths to flow without
tripping the GFPI or blowing fuses. If the array was of significant
size, and there were no blocking diodes to prevent reverse current flow,
this fault current could arguably be significant enough to cause a fire.

Though I'm not against the use of GFPIs, I'm afraid that most qualified
and experienced installers don't need them, and that these units are no
guarantee that unqualified installations will be safe. That said, this
example may not be too applicable to most residential installations
anyway (lower voltage and less #'s of modules in parallel) and I don't
have a better solution to sell "in a box".

Keep up the good work friends!

Jason Fisher
Aurora Energy

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://www.topica.com/lists/RE-wrenches/

List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com

==^================================================================
This email was sent to: michael.welch at homepower.com

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9
Or send an email to: RE-wrenches-unsubscribe at topica.com

T O P I C A -- Register now to manage your mail!
http://www.topica.com/partner/tag02/register
==^================================================================