[RE-wrenches] eternabond or epdm?

Mon Nov 15 07:42:33 PST 2010

Wrenches,

It has been a while since I have seen this subject and I was wondering if
there has been more experience in the field with using either EPDM or
products such as http://www.eternabond.com/DoubleStick-p/cr-ds.htm for
sealing L-feet or stand-offs directly to metal roofing. . .

Seems to make sense to directly seal off the one or two holes for that lags
rather than placing a boot over it and drilling 20 screws around the Otey.
The only weakness I could see would be the seal directly over the lags, but
I think this could be cured with a dollop of silicone or other EPDM safe
caulk in and on top of the hole.

My main worry is the compression of the material over time, which may
compromise the bond/seal.

Has anyone successfully used the Eternabond-looks like it could be a good
solution.

Best regards,

Mark Dickson,

NABCEP Certified Solar PV Installer T

Oasis Montana Inc.

  _____  

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of William
Miller
Sent: Sunday, November 14, 2010 10:36 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Head Spinning..(Con) fused.

Eric:

Thanks for the research.  I confess that I commented on an inverter system I
knew little about.  My thanks to Darryl for keeping me honest, and for the
kind words.  I had assumed that all modern inverters are certified to
prevent back feed, but this needs to be checked for each new inverter.

I'm not sure the language below is the same as an independent verification
that back feed will not occur.  You may need to ask your AHJ what they will
accept.

The limit on allowable back current is the fuse sizing specified by the
module manufacturer.  This relates to how much fault current the internal
module wiring can handle before it fails (and possibly catches fire).

Humbly,

William Miller

At 07:42 PM 11/14/2010, you wrote:

Thanks William and Daryl,

Here is Auroras backfeed stipulation from the installation manual:

"Installation and Operator's Manual Page 98 of 108

(PVI-3.0/3.6/4.2-OUTD-x-US Rev: 2.1)

8.5 Input Source Backfeed Current

PVI-4.2(3.6, 3.0)-OUTD-x-US Grid Tied Inverters are provided with two
separate and
consecutive power stages:

. Booster Stage (DC-DC converter) connected to DC Input Terminals.
. Inverter Stage (DC-AC converter) connected to AC Output Grid Terminals.

The Booster Stage is provided with forward diodes that allows the current
(power)
flow only from DC Input terminals towards Inverter (Output) Stage.
In case of any fault on Inverter Stage, these diodes avoid any back-feed
current
phenomena towards input terminals.

In case of fault of the forward diode, the corresponding booster MOSfet goes
immediately and permanently in short circuit state and it avoids any current
propagation form output to input terminals.

Abnormal Fault tests conducted during UL1741 qualification show also that
these type
of faults produce the opening of internal grid disconnect relays and cause
the external
AC CB protection devices to trip, preventing any power flow from the grid.

In conclusion for PVI-4.2(3.6, 3.0)-OUTD-x-US-y models it is not possible to
have
any single fault responsible of Input source back-feed current flow. For
these models
the Back-feed current into DC Source is negligible."

According to this, the inverter will not backfeed even under most fault
conditions. My biggest concern is the four independent strings shorting
together somehow. I guess technically 4 strings of 8A for a total of 32A
doesn't exceed the ampacity of 10AWG XHHW-2....until you derate it for roof
temps. 

So whats the consensus?

-- 
Eric Thomas
Solar Epiphany LLC
(206) 919-3014
www.solarepiphany.com

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Please note new e-mail address and domain:

William Miller 
Miller Solar
Voice :805-438-5600
email: william at millersolar.com
http://millersolar.com <http://millersolar.com/> 
License No. C-10-773985

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