IMO Technical Brochure
Leaders in Solar Safety
8
Many alternative solutions, particularly those based upon an AC isolator designs
which use bridge contacts, have been modied and rated for DC operation.
These types of product have a switching speed that is directly linked to operator
speed therefore, slow operation of the handle results in slow contact separation
of the contacts which can produce arcing times of 100ms or more. Also in these
switches the contact surface is also the surface upon which arcs tend to form;
therefore, any surface damage or sooting caused by the arcing is likely to have a
detrimental eect on the isolator’s contact resistance and its longevity.
The IMO Solar Isolator range is oered in a number of congurations all rated for
installation and use as switch-disconnects and all with options allowing for
“LOCKABLE OFF” operation. Although able to oer the industry standard two
position 90° handle operation from LOCKABLE OFF-ON, IMO have also introduced
a SAFE-LOCK patented handle that allows for three rotational positions relating
to ON-OFF-LOCK. The facility oered by this design gives a LOCK position that
is removed from the OFF setting ensuring the handle can be placed in its own
unique position when locked, which is fully compliant with IEC 60947-1 section
8.2.5.2.1 for classication as an isolator or switch disconnector. When this design
is used within the IMO enclosed Solar Isolators it ensures that engineering access
can only be attained to the enclosure when the handle is in the OFF position;
whilst the “LOCK” position ensures secure power isolation combined with non-
access to the enclosure (when the isolator block is secured with supplied screws)
and thereby signicantly reducing the risks of tampering when maintenance/
repair is carried out on equipment in-line after the isolator, SAFE-LOCK. Once any
work has been undertaken the locking mechanism can then be removed and the
isolator returned to its normal operational mode.
IMO Solar Isolators use a rotary “knife contact” mechanism so when the unit is operated the handle movement gives a double make/
break per contact set. As DC load switching creates arcing the design is such that this only occurs on the corners of the switching parts
meaning that the main contact is made on an area where no arcing has occurred. The rotary contact mechanism methodology used in
the IMO Solar Isolators means that, when the isolator is operated, a self-cleaning action occurs on the arcing points and contact surfaces
thereby producing good high vibration resistant contact integrity, with reduced contact resistance. This IMO contact system ensures
that power loss per pole is kept as low as possible and consistent over the life of the product unlike conventional style isolators where
entrapment of contaminants, and then subsequent compression on lateral operation, can lead to variable and increasing contact resistance and
hence per pole losses.
As indicated in the section about Utilisation Categories, the IMO product is satisfactory for use in installations classied as either DC-PV1,
DC-PV2, DC-21A, DC-21B or DC-22A, and so suitable for a high number of “o load” operations (without current) and also a high number of
operating cycles “on load” (with current).
Unlike a number of DC isolators on the market, the IMO solar isolator is also polarity independent,
which means that there is no requirement for specic directional wiring of the PV supply. A further
advantage of the IMO contact mechanism is that, in the event of the supply to earth failure, the
high short circuit current pulls the contacts together thereby giving a high short circuit withstand
current of up to 2400A (product dependent). PV residential installations are typically 1000VDC
however, IMO Solar Isolators already have the capability to operate up to 1500VDC.
In the move towards safer installations of PV systems, whether it be in a domestic or
industrial environment, consideration has to often be given to the materials and the risk of
re hazard that they pose. Ratings referred to under the UL 94 category are deemed generally
acceptable for compliance with this requirement as this cover tests for ammability of
polymeric materials used for parts in devices and appliances. Although there are 12 ame
classications specied in UL 94, there are 6 which relate to materials commonly used in
manufacturing enclosures, structural parts and insulators found in consumer electronic products.
These are 5VA, 5VB, V-0, V-1, V-2 and HB.
Country RoHS USA, UL508i US, CAN, UL60947-1 Europe CE CCC China IEC CB Europe ESV Australia
SI16/SIM16/SIME16
SI25/SIM25/SIME25
SI32/SIM32/SIME32
SI38/SIM38/SIME38
SI40/SI55/SI65
*
RoHS
IMO DC Isolator Approvals
* Please note that the SI65 does not have CCC approval for China