Mystery electrical symbol ???

I have inherited an existing project, about 8 years old, at a chemical plant (think, Class 1, Div 2 environment). I cannot identify this device. It is some sort of fused terminal block, from the fuse symbol. Could it be a disconnect term?

http://radar.net/see/2293822


9A - 24VDC from power supply
9HO - 24VDC to input device
9HI - 24VDC from input device
9B - 24VDC to PLC input

This same block is used for outputs also. The PLC I/O is always passed through the "mystery symbol".

My guess is that this is related to grounding, surge or spark suppression. However, I have not been able to locate this symbol anywhere on the net, and I can't get the part number for the block itself.

Thanks for your assistance!

Um,
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...it's a fused terminal block. +,-, and ground.

Possibly an electronic fuse or filter(surge supressor). How is it tied into the circuit? Possible intrinsic barrier?

The red symbol at the bottom (chevron shape, sergeants stripes) is a standard symbol in motor control centers for a quick disconnecting device, a "stab", a plug-in device that allows disconnection of power to plug-in motor starters in a motor control center.

It appears then that this might be someone's idea for a symbol of a fuse with a disconnecting switch or a fuse plug that can be removed to disconnect the circuits.

Wild guess

Could it be a galvanic Intrinsic Safety barrier? The 9A and 9B are the Safe side, and the 9HI and 9HO are the hazardous side? This would make sense for a Class I, Div. II area.

More info

Apparantly, this device contains a fuse, a "stab" as mentioned above, and a push-to-test switch. The push switch bypasses the PLC output to energize the device. I haven't physically seen the device yet, but a plant engineer tells me this is the case. who knew?

Thanks for the responses!
C

C,

This is another example where a symbol cannot be understood by anybody except by the person who made it up originally. There are so many different modern devices that will not easily fit into the old definitions.

Over the years I have concluded that symbols can be used to mean everything and anything. Standard they are not. At most, you hope to get somewhere close to the real meaning. The best bet (for an unfamilar symbol where the manufacturers' key is not available) is to examine the physical device and compare it to the symbol and see if it makes any sense then. Sometimes the symbol used is simply incorrect or a poor choice for what is being represented. I have been known to erase symbols (on record drawings) and make up new ones that better represents the real devices.