Power setup

[RAL]

Can you elaborate on this? I'm considering the eFlow102N8D (which has PTC's) to power several components. Some are part of my M1G system (remote expansion boards, Uplink 2500, wireless receiver, etc.) and others are not (a couple of LAN switches). It looks like most Elk PS's use PTC's, so is it safe to assume that those components are not too sensitive? Can you give some examples of sensitive electronics that shouldn't be connected? There is an eFow102N8 that uses fuses instead of PTC's, if necessary.
 
Thanks,
Ira

 
PTCs differ from fuses in several ways.  Fuses are available in slow-blow and fast-blow varieties.  PTCs are generally considered a slow-blow device.  So if you have something that can't withstand an overcurrent condition for more than a very brief time, a PTC is not the right protection.
 
When fuses blow, they open the circuit completely, and no current can flow until the fuse is replaced.   A PTC, even in the "blown" state, still allows some current to flow.  This is called leakage current, and can be in the range of 10s to 100s of mA, depending on the particular PTC.  If your device can't withstand any current flowing when there is a fault, a PTC is not a good choice.
 
Since PTCs self-reset, if the fault condition has not been fixed, the device will subjected to an over current condition again and again after each reset, until the problem is fixed.  If the device can't withstand repeated over-current conditions, a PTC is a not a good choice.
 
You really need to know the details of the electronics you are trying to protect in order to decide whether a PTC is acceptable or not.
 
In my opinion, most fuses and PTCs on power supplies are there to prevent a dangerous condition, such as a fire, from occurring rather than to protect the connected equipment from permanent damage.  Many electronic components, such as diodes, transistors, and ICs will blow faster than even a fast-blow fuse.  It all depends on the size (current capacity) of the component vs the rating of the fuse.

 

[Del91574]

Yes, in addition to above (a slight clarification)
 
Fuses and PTC's are not there to protect equipment or components....they're only there to prevent overcurrent events on the cabling that may damage it....not to prevent fire, because 12V (or 24V) isn't going to start a fire or smolder, the cabling getting hot from a short or partial short can.
 
The same goes with circuit breakers and the like on HV circuits.

 

[Ira]

I'm reading the installation guide for the Altronix eFlow102N16 and N16D (fuse-protected and PTC-protected outputs, respectively). It says that the outputs from the distribution board are non-power-limited for the N16 and power-limited for the N16D, and also goes into the requirements to keep power-limited wiring separated from non-power-limited wiring. Can someone explain why the N16 outputs (w/fuses) are non-power-limited and the N16D outputs (w/PTC's) are power-limited, i.e., exactly what does "[non-]power-limited" mean?
 
Does this imply that, for example, the supervision wires for the PS can be in the same conduit as the 12VDC output wires if using the N16D, but not if using the N16? I realize the diagram shows the supervision wires exiting via a different knockout than the 12VDC output wires, but the diagram is for both panels.
 
Thanks,
Ira

 

[Del91574]

Power limited means the circuits are divided equally to distribute, say 4A across 8 outputs...so each would be fused at 500 mA for the output (tossing hypothetical numbers around)...so the total wouldn't overdraw the supply and pop the supply's fuse on failure. The PTC's have a defined cutoff
 
In non-power limited, the outputs can draw up to the complete output of the supply and while fused, they draw up to their rated value...then blow. There is no defined cutoff besides the value listed.
 
It has zero to do with HV and LV cabling but only the nature of the circuits connected to the output of the supply, which by nature is considered a power limited source (LV).
 
The only reason I can see the diagram showing supervisiory circuits leaving in a different raceway would be simply for induced EMI....but it's trivial at best in this case and application, otherwise why would you not separate the circuits on a PIR or GBD?