SunnyBoys and quick connects - A long explanation [RE-wrenches]

Fri Aug 17 19:55:21 PDT 2001

Wrenches:

First - The multi-contact connector is fine for use in PV systems at up
to 600 Vdc at this time.
The multi-contact connector is a good connector and we use tons of them
in Europe.
It is the defactor standard PV connector in Germany and all of the
European SB's come with MC connectors on them.

Second - The topic is very timely as I have been asked to form an ad-hoc
industry working group to address the issue and see what solutions we
can come up with.
The group will consist of module people, inverter people, Sandia folks,
UL folks, and installers.
If any of you want to participate please let me know off list and I will
add you to the email distribution list.
If you have not participated in Standards development before this is a
good way to contribute and see how the process works.

Wiring and connectors are discussed in Section 690-31 through 690-34.
I wont quote all of those sections here but a careful read is valuable.
Remember, every word is important and has meaning that can be
interpreted in different ways.

690-31 says that we can use any of the code approved wiring methods
allowed by code plus a couple of special ones as long as they are
specifically intended and identified for use in PV systems.
The people that determine if they are intended and identified for use in
PV systems is UL, ETL, etc.
UL is looking at connectors and starting to realize that some of the UL
Listed connectors may have some issues when used with PV.
As a result we (the industry) are starting to discuss the idea of UL
Listed wiring >>systems<< for PV.
Before everyone goes crazy remember that if the wiring system is Listed
then 690-31 says that is good enough.
With a Listed wiring we may be able to get around some of the other code
requirements Like the DC disconnect for example.
The goal is all of this is to make it safer, easier, and cheaper to
install PV.

Ok, now here are some of the "concerns" UL has voiced to me.

690-33 describes the requirements for connectors.
The MC connector meets all of them except (e)Interruption of Circuit
"The connectors shall be capable of interrupting the circuit without
hazard to the operator."

The MC is not UL Listed for load break (at any voltage).
Ok fine, so normally you can just stick a label on it and you are good
to go.
I call this the don't be stupid label and in this case it would say "do
not disconnect under load".
That is all fine and good if we can make sure the connector is operated
(opened) only by qualified people who know what they are doing.

But.... what if a 3 year old kid (pretend it is your kid) comes up to
the PV system and hangs on the wire and yanks the MC connector loose.
Today there is nothing that says you can only use MC connectors on roof
mounted arrays and I can see this happening in a ground mounted or pole
mounted array.
The MC connector is a latching type connector (as opposed to locking)
and you can pull it loose if you try.
You have to wiggle it back and forth but it will come loose - especially
with a kid swinging on it.

Now the connector is loose but it is touch safe right ?
Yes, but PV systems are outside so is it still touch safe if the
connector is wet when this happens?
Unfortunately, in the strictest sense the answer is no.
When you pull the connector under load (normal operation) there is a
little arcing and the little black plastic tip gets some carbon on it.
If the carbon gets wet, e.g. after a rain, it can become conductive and
>> could << represent a shock hazard to the operator.
So in the normal operation case there might be some hazard but, IMHO, it
is a little bit of a stretch.
For UL and the Code we have to design for both normal operation AND all
possible single fault failures.

Here is one scenario - Please don't shoot the messenger ...

We have a system with a couple sub array's  and one of the sub-arrays
(A) has a short in the wiring.
Sub-array B feeds this fault and goes to Isc and 0 Volts.
Since the fuses are rated at a minimum of 1.56 Isc none of the fuses
blow.

Ok, so now someone comes up and opens the MC connector.
The connector arcs like crazy since the Array B goes instantly from Isc
to Voc.
It happens so fast that, to the connector, it looks like it is breaking
Isc at Voc.
In this case the little plastic tip is badly eroded and in some of the
tests the metal electrode is exposed.
Interestingly enough, this happened at both 48 Vdc systems and 600 Vdc
systems.
There is enough energy is either case to create a problem.

So, if it is your 3 year old outside, after the rain, and he or she is
the one yanking on the wet connector do you think it is safe enough ?

What to do about it

UL and NEC have a rule of thumb that defines qualified personnel and
that is:

If it takes a tool to open the connector, Jbox, disconnect, inverter,
etc. then the use of tool means you have to be somewhat deliberate about
what you are doing.  In many cases the "use-of-tool" defines the
operator as qualified personnel.
If the MC connector was a locking (as opposed to latching) connector
then you would need a tool to open it.
This could be as simple a little plastic tab that snapped into a slot.
In order to open it you would have to use a screwdriver to push down the
tab before you opened it.
There are lots of other design ideas this one is just for illustration.

One of the other solutions we discussed with UL was pointed out here on
the List.
If you heat shrink the connector after you make the connection it takes
a knife to cut away the heat shrink.
The knife is a tool and so this means you are "qualified personnel" not
a 3 year old in the rain.

UL says this sounds pretty good and might be a good solution. (if you
use UL listed heat shrink, or course!)
Before they say it is ok they want to run a pull test to make sure this
great idea actually works.
They also want to run some additional thermal tests to see if the
connector over heats with the extra insulation of the heat shrink.
I think both of these are reasonable tests to run but who should pay for
it ?
That is the big question a the moment.

In the longer term we (the PV industry) need to come up with some really
cool connectors and wiring systems that eliminate Jboxes and disconnects
and make PV systems truly plug-and-play.
This approach should be much safer, more reliable, and if we do it
right, it should help to reduce installed system costs.
UL wants to do it, Sandia wants to do it, the module guys want to do it,
and the inverter guys want to do it.

If anyone on the List wants to help, let me know, and we'll get started.

Thanks for reading this long winded explanation.

Best regards,

John Berdner

SMA-America, Inc.
20830 Red Dog Road
Grass Valley, CA  95945
Tel: 530.273.4895
Fax: 530.274.7271

-----Original Message-----
From: jay peltz [mailto:jay at asis.com]
Sent: Tuesday, August 14, 2001 8:52 PM
To: RE-wrenches at topica.com
Subject: Re: SunnyBoys and quick connects[RE-wrenches]

Hi Jerry,

What code section would that be?  I have talked with many people on this
so
I guess the person would be John Berdner to answer this,  John??

jay

Peltz Power

Jerry Caldwell wrote:

> Kurt,
>
> Since SunnyBoys utilize a high voltage array, I
> believe you need to use a connector that requires a
> tool to be separated, and can't just be pulled apart
> by hand.  We use a piece of 600v rated heat shrink and
> totally encapsulate both plugs in the connection.
> This way you need to use a knife or some kind of
> cutting tool to separtate them.
>
> Jerry Caldwell
> Light Energy Systems
>
> --- Kurtj12 at aol.com wrote:
> > does anyone have any feedback on whether quick
> > connect solar modules are
> > acceptable for use with a sunnyboy inverter and if
> > the answer is that they
> > are not, is there a solution to make the two work
> > together?
> > thanks,
> > kurt
> >
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