UL Listed terminal strips (power blocks) for field installation in 50Vdc 20A
application (wire type transition). Is there such an thing? Every
manufacturer I look at has only UL Recognized blocks.
I think this is because terminal strips are components of finished products,
not finished products themselves. UL will only list complete
products/appliances, not the individual components used inside. UL
Recognized means the terminal block *could* be used to make a safe consumer
product, but since UL hasn't seen the whole product that the terminal block
is in, they cannot verify the complete appliance.
Even a product made up 100% of UL *recognized* components may not
necessarily qualify for UL *listing*. After all, a UL *recognized*
component, used in an application that is beyond it's design, can be
dangerous to the end consumer.
Yes, your are right. There are tons of "RU" blocks and strips out
there and sold to anyone who wants to buy them. What I find strange is that
fuse blocks and ground/neutral bus bars can be found UL Listed for field
installation. They could certainly be mis-used too.
Perhaps these types of fuse blocks and bars can be listed because they are
'options' for installation in a particular panel. That is, the panel has
been listed with certain equipment 'optionally' installed. So those
*particular* blocks/bars can be installed in *particular* panels for which
UL has tested the configuration. The manufacturer has submitted the basic
panel and all the various 'optional' blocks/bars as a configurable set to
It would *not* be UL Listed to install a neutral bus bar for a square D
panel model 'XXX' into an entirely different model line 'YYY' or into
another manufacturer's equipment.
UL can't list a 'generic' terminal block for use in just any old 'generic'
installation. The best they can do at that point is 'recognize' that a
particular terminal block can be part of a soundly constructed installation.
And of course, *anything* can be misused. But if the field installer
follows manufacturer's instructions to install a manufacturer's authorized
option, then at least there is some assurance of a safe installation.
They mislead, or the people that compose the web site info don't know
better. Actually all three have blocks that are UL component RECOGNIZED
(backward-R U). AB looked promising at first because they said LISTED on
the cover page but further inspection reveals otherwise. Thanks though!
Your welcome. Keep in mind, that even if you put together a product
composed of nothing but UL *listed* pieces, you cannot say that your product
is UL Listed. Similarly, if you build something of UL *recognized*
components, the finished product still isn't UL listed or recognized.
But using such UL Recognized components should go a long way towards
*getting* UL approval of a finished product.
Actually, my application is a field installed wiring transition in
photovoltaic installations. At the end of a series string of pv modules we
often like to switch from (exposed 10 AWG USE-2/RWH-2 behind the panels) to
(12 AWG THHN-2 in conduit) and bring that to a readily accessible fused
combiner box or the inverter. This transition takes place in a UL Listed
raintight box large enough for fill requirements. I don't like using
wire-nuts or butt connectors or split bolts for this so that leaves me with
bulky UL Listed insulated pressure connectors like [Polaris].
Ideally, a neat-clean wire transition would take place on a power block or
terminal strip. The real issue is: Will the AHJ inspecting the installation
approve it? Less likely if the components are not Listed, but just
Recognized, and least likely if not UL at all. But in the end it's the AHJ
that decides. While my junction box may not be UL Listed as finished
product, it would contain all UL Listed components - and yes, it is possible
to misuse UL Listed components, but the AHJ would determine that.